Understanding Climate Change and Climate Smart Greenhouses

#### **Chapter 1**

## Introductory Chapter: Climate Change and Climate-Smart Greenhouses

*Ahmed A. Abdelhafez, Mohamed H.H. Abbas, Shawky M. Metwally, Hassan H. Abbas, Amera Sh. Metwally, Khaled M. Ibrahim, Aya Sh. Metwally, Rasha R.M. Mansour and Xu Zhang*

#### **1. Introduction**

World is, nowadays, facing one of its most pressing ecological challenges — climate change. This phenomenon is characterized by significant and enduring shifts in weather patterns. It is mainly attributed to anthropogenic activities that increase the emissions of greenhouse gases [1] such as CO2, CH4, N2O, O3, chlorofluorocarbons (CFCs), CCl4 [2], and H2O [3]. Probably, CO2 is the most important heat-trapping greenhouse gas (GHG) [4]. These gases absorb outgoing thermal (infrared) radiation, which is emitted by the surface of the Earth [5] and trap it within the atmosphere [6], thus increases the temperature of Earth's surface [7]. These gases also increase the temperature of troposphere while decreased stratosphere temperature [8]. In addition to GHGs, 5–15% of the organic carbon is found as aerosols that persist in the atmosphere for long time periods [9] and serve as cloud condensation nuclei (CCN) [10], which absorbs visible solar radiation (approximately 20% of total absorbed light) [11]. This is known by brown carbon, which are particulate matters containing chromophores that increase global warming threats [10]. The repercussions of climate change span a vast spectrum from altering weather patterns to impact human health and exacerbating disparities. This chapter delves into the intricate relationship between climate change and agriculture while spotlighting the innovative concept of climate-smart greenhouses as a promising solution.

#### **2. Climate change: causes, impacts, and effects on human health**

Climate change, a lasting alteration in weather patterns spanning decades to millions of years [6], results mainly from escalating greenhouse gas (GHG) emissions linked to activities such as fossil fuel combustion, deforestation, and industrial processes [12]. Carbon dioxide stands as the primary GHG from human activities [13], with methane and nitrous oxide trailing closely [14]. These gases trap heat in the Earth's atmosphere, elevating average global temperatures by 1–2% [15, 16].

These GHGs hasten the Earth's water cycle [8], leading to amplified evaporation from water surfaces [16], resulting in heightened drought frequency and intensity in various regions [17]. In contrast, other areas experience increased precipitation [16], leading to rising sea levels [12], expanding regional tides, and intensifying extreme events, such as hurricanes and floods [12]. Climate change exerts profound impacts on food and water supplies, human habitation, public health, and economic activities [18, 19]. The World Health Organization predicts that climate change may contribute to roughly 250,000 additional annual deaths by 2050, primarily due to malnutrition, malaria, diarrhea, and heat stress [20]. Vulnerable populations, including children, the elderly, low-income communities, and individuals with chronic illnesses, bear a disproportionate burden [19]. Heatwaves pose risks of heat exhaustion and heat stroke, exacerbating cardiovascular and respiratory diseases. Altered temperature and precipitation patterns also affect disease-carrying insects, increasing the transmission of illnesses, such as malaria and dengue fever [20]. Furthermore, climate change exerts adverse effects on mental health. The growing frequency and severity of extreme weather events and natural disasters contribute to post-traumatic stress disorder (PTSD), anxiety, depression, and other mental health issues [21]. Health disparities worsen with climate change, particularly impacting vulnerable populations with limited resources to adapt [22]. Addressing climate change necessitates a concerted global effort to reduce GHG emissions and adapt to ongoing changes [6].

#### **3. The impact of climate change on agriculture**

Climate change poses significant challenges to global agriculture and food security [12]. Rising temperatures, driven by the Industrial Revolution, have increased by 0.9°C since the nineteenth century and are projected to reach 2°C by 2100 [23, 24]. This warming can accelerate crop respiration and evapotranspiration [7], alter pest and disease distribution, and shorten the reproductive period in crops, such as wheat and rice [24, 25]. Wheat yields may decrease by 20–45%, and rice yields by 20–30% by 2100 [24]. Heat stress can cause post-heading carbon deficits in wheat [26]. Irregular precipitation patterns also impact agriculture [24], with some regions experiencing increased rainfall and others facing more frequent and severe droughts [7]. Both flooding and drought have adverse effects on crop yields, limiting growth, causing damage, and influencing the prevalence of pests and diseases [27, 28].

Climate change further challenges natural resource management in agriculture. Higher temperatures lead to increased evaporation rates, depleting water resources, and particularly affecting irrigation-dependent agriculture. Rising sea levels and increased salinity can degrade arable land, especially in coastal and delta regions [29]. To ensure agricultural sustainability in a changing climate, it is crucial to develop and implement adaptive strategies, including climate-resilient crop varieties, improved pest and disease management, and efficient water resource utilization [12].

#### **4. Adaptation and mitigation strategies for climate change**

Climate change presents significant challenges that require a comprehensive response. In 2015, an agreement was held in Paris to lessen the rise in global temperature by 2°C in 2100 [30]. Two primary strategies were adapted to attain this

aim, which are adaptation and mitigation [31]. While mitigation focuses on reducing the causes of climate change, adaptation involves adjusting to its impacts [12]. Adaptation, therefore, is essential to manage unavoidable impacts, while mitigation is needed to limit the long-term changes in climate. The optimal mix of adaptation and mitigation measures will depend on local and regional factors, including climate change impacts, economic structures, and societal values.

#### **5. Adaptation**

Adaptation strategies mitigate global warming impacts [32] for future food security [33]. They involve altering processes, practices, and structures to reduce potential damage and capitalize on climate change opportunities [34]. Adaptation spans individual actions to institutional policies and includes financial adjustments [35]. In agriculture, strategies encompass crop enhancements, food waste reduction [33], water conservation policies [36], adjusted planting schedules to avoid extreme weather, and adopting resilient crop varieties [37]. Biodiversity enhancement can also aid climate mitigation [38]. Organic extracts, such as humic and fulvic acids or compost tea, promote plant growth, sequestering more CO2 in plant tissues [39–41]. In the health sector, adaptation focuses on enhancing public health infrastructure to manage heatwaves and disease outbreaks, incorporating early warning systems, and improving air and water quality [42]. Urban areas should adapt by bolstering infrastructure resilience, implementing heat-wave action plans, creating cooling urban green spaces, and efficient water resource management [43].

Despite adaptation's importance in mitigating global warming's negative effects, maladaptation can occur [44]:


#### **6. Mitigation**

Mitigation involves strategies to lessen or even stabilize emission of greenhouse gases in the atmosphere *via* adopting three strategies mentioned by Fawzy et al. [30] which are:

1.Switch to clean energy (renewable energy and nuclear power) or low carbon fuel to generate electricity and get heat rather than the burning of fossil fuels (conventional mitigation efforts). According to this approach, emissions of GHGs should be reduced by 45% in 2030 versus their levels in 2010 levels then reach finally to net-zero emissions by 2050.


Probably, energy production is the major source of greenhouse gas emissions, so applying new technologies to improve energy efficiency in buildings, transportations, and industrial processes might reduce effectively GHGs emissions [45]. In the agricultural sector, mitigation strategies include improving crop and livestock management practices to reduce methane and nitrous oxide emissions, protecting and restoring forests to sequester carbon, and managing soils to increase their carbon storage capacity [46, 47].

#### **7. Climate-smart greenhouses: a sustainable approach to agriculture**

The global agricultural sector faces climate change challenges, impacting crop yields and food security [12]. Climate-smart greenhouses, part of controlled environment agriculture (CEA), use advanced technologies to optimize plant growth and reduce environmental impact. They prioritize increasing productivity, adapting to climate change, and minimizing emissions [48, 49]. These greenhouses employ precision irrigation to conserve water and ensure ideal moisture levels, automated climate control to optimize growth and energy use, and energy-efficient lighting, such as LED, with minimal energy and water consumption [50–52]. Integrated pest management reduces reliance on chemical pesticides, benefiting crop health and sustainability [48].

Renewable energy sources, such as solar and wind power, further reduce environmental impact, and water conservation practices are employed [48]. Climate-smart greenhouses offer a promising solution to climate-related agricultural challenges, integrating technology and sustainable practices for increased productivity and reduced environmental impact [49].

#### **8. Design and structure**

Climate-smart greenhouses are designed to optimize the use of natural resources and energy. Sensors and devices (Internet of Things, IOT) can be used to monitor precisely, and then efficiently control all indoor parameters [52]. Greenhouses are often constructed with materials that maximize light transmission while provide insulation to reduce energy use for heating or cooling. Their structure and orientation allow maximizing natural light and regulating temperature [48]. Roofs and/or sides may be covered by an impermeable transparent plastic film to allow natural ventilation [53]. Android mobile applications are sometimes used to monitor and send warning messages about the state of plants.

#### **9. Climate control systems**

One of the key features of climate-smart greenhouses is to lessen energy consumption while increasing plant productivity [54]. This may take place *via* applying

#### *Introductory Chapter: Climate Change and Climate-Smart Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113212*

automated climate control systems that use different sensors to collect data continuously [50] and then use mathematical models for calculating solar irradiation, photosynthesis, and evapotranspiration [55]. These schemes can, therefore, regulate temperature, humidity, and light levels to create optimal growing conditions needed for plants at each growth stage to get high-yield production [56]. Ventilation and shading can also be adjusted to control the internal climate and reduce the need for artificial heating or cooling. In tropical and subtropical climates, covering materials are used for shading and cooling in greenhouses [56]. Some systems even include CO2 enrichment to enhance plant growth [48].

#### **10. Water and nutrient management**

Climate-smart greenhouses often incorporate precision irrigation and fertigation (fertilizer + irrigation) systems [57] using a combination of sensors and nutrient delivery schemes [58]. These systems deliver water and nutrients directly to the plant roots, reducing wastes, and ensuring that plants receive the optimal amount of moisture and nutrients. Some greenhouses also capture and reuse water through rainwater harvesting or condensation capture systems, contributing to water conservation efforts [48]. The emission of N gases from high-tech greenhouses that follow efficient recirculation systems is thought to be very low [59].

#### **11. Energy efficiency and renewable energy**

Energy efficiency is the key aspect of climate-smart greenhouses. Many climate-smart greenhouses use renewable energy sources, such as solar or wind power [48]. Using photovoltaic-thermal collectors of solar energy can produce both heat and electricity, with less shading [60]. Also, using energy-efficient lighting, such as LED lights, provides specific light spectrum needed for photosynthesis while using less electricity (40%) than traditional lighting systems and also less heat (9–49%) [61]. In cold regions, minimizing heating cost is another challenge. Thus, isolating greenhouses and/or using geothermal energy may help to lessen these costs [62].

#### **12. Integrated pest management**

Climate-smart greenhouses often use integrated pest management strategies to reduce the need for chemical pesticides. These strategies include the use of beneficial insects to control pests, use of physical barriers or traps, and the careful monitoring of pest populations to determine when control measures are needed [63, 64]. Microbial pesticides can also be used if natural enemies are not sufficient for pest control [65]. Moreover, solar ultraviolet-B lamps can provide a physical control for spider mites [66]. Climate-smart greenhouses represent a promising solution to the challenges posed by climate change in the agricultural sector. By integrating advanced technologies and sustainable practices, these greenhouses increase agricultural productivity, adapt to changing climate conditions, and reduce environmental impacts.

#### **13. The role of greenhouse cultivation in climate change mitigation**

Greenhouse cultivation, particularly when implemented with climate-smart practices, can play significant roles in mitigating climate change. This can be achieved *via* applying more efficient techniques in resource management, reducing wastes, and carbon sequestration. Generally, there are two methods to control greenhouse conditions (i) a passive method that depends on a natural phenomenon "hot air rises and cold air sinks," so it requires minimum energy while (ii) the active method needs fans for and heaters to control the environment inside greenhouses [67]. By means of thermal energy storage (TES) systems, heat can be successfully stabilized within greenhouses for plants [68]. These systems analyze the complex thermal processes within this indoor microclimate area and contribute toward efficient usage of this energy [69]. On the other hand, CO2 enrichment environment inside greenhouses can boost plant growth by approximately 35% [69, 70] *via* sequestrating CO2 from ambient air rather than being emitted to the atmosphere to increase the emissions of GHGs [71].

#### **14. Efficient use of resources**

Managing agricultural resources to meet rising food demands due to population growth is crucial [69], but natural resource limitations challenge food production [72]. Agricultural activities also contribute significantly to greenhouse gas (GHG) emissions [68], emphasizing the need for ecological considerations. Controlled environment agriculture (CEA), such as greenhouses, offers year-round food production possibilities [67]. Utilizing intelligent shading systems, smart glass, sensors, IoT, and AI [68], greenhouses precisely control conditions such as temperature, light, and humidity [73], increasing yield per unit area compared to traditional methods and conserving water through precision irrigation [48]. Some greenhouses capture and reuse water, further reducing water use [48]. Bioagents in greenhouses enhance horticultural yields and environmentally friendly pest and disease control, reducing GHG emissions related to agrochemicals [64, 74]. Greenhouses, by growing crops near consumption points, reduce transportationrelated carbon emissions, especially in urban agriculture [75].

#### **15. Carbon sequestration**

Greenhouse gases can be reduced *via* a process known by phytosequestration [6]. In this method, plants absorb carbon dioxide gas from the atmosphere, change it to organic forms *via* Calvin cycle then sequester large amounts of C in their biomasses [76]. Herbaceous plants, which have relatively low planting-environment requirements, exhibit more capability to sequester C in their tissues than woody plants[77]. Surprisingly, sequestration of CO2 by microalgae is deemed as a net zero GHG emissions [78]. On the other hand, amounts of carbon sequestered *via* this process are relatively slow versus CO2 release due to anthropogenic activities [79]. Also, this process lasts for relatively short time periods because when plants decay and sequestered C returns back to air [6]. Weighing up pros and cons of phytosequestration, reforesting, and managing ecosystems are still effective ways to mitigate the global warming threat [79].

#### **16. Reduced waste and emissions**

The terrestrial carbon pool is four times larger than the atmospheric carbon pool [4]. Recycling agricultural waste can significantly reduce greenhouse gas emissions, with over 5.6 billion mega grams of carbon potentially sequestered from the 18 billion wasted annually worldwide [80]. This can be achieved by converting organic residues into biochar, produced under limited oxygen conditions [81–86]. Biochar reduces easily oxidized carbon content, decreasing microbial metabolic activity by 47% [87], leading to longer soil retention when used as a soil amendment [88–90] or organic fertilizer [91, 92]. Its porous structure enhances soil CO2 adsorption *via* physisorption and chemisorption [93], sequestering carbon instead of releasing it into the atmosphere [87]. Scientists have devised a method to capture smoke emissions during biochar pyrolysis, using them for soil injection to improve seed germination and potentially achieve net-zero greenhouse gas emissions [94, 95]. Using biochar as a soil amendment can reduce CO2 emissions by about 1/8 [95], while converting residues to charcoal may cut GHG emissions by 80% within 8.5 years [96]. The potential for carbon sequestration in greenhouses remains an ongoing research topic, with outcomes depending on various factors, including greenhouse type, crop varieties, and management practice.

In conclusion, climate-smart greenhouse can contribute to climate change mitigation through more efficient use of resources, reduced waste and emissions, and potentially through carbon sequestration. However, it is important to note that not all greenhouses are the same, and the climate impact will depend on the specific design and management practices used.

### **Author details**

Ahmed A. Abdelhafez1,2\*, Mohamed H.H. Abbas3 , Shawky M. Metwally4 , Hassan H. Abbas3 , Amera Sh. Metwally<sup>5</sup> , Khaled M. Ibrahim6 , Aya Sh. Metwally7 , Rasha R.M. Mansour8 and Xu Zhang<sup>9</sup>

1 Department of Soils and Water, Faculty of Agriculture, New Valley University, Egypt

2 National Committee of Soil Science, Academy of Scientific Research and Technology, Egypt

3 Department of Soils and Water, Faculty of Agriculture, Benha University, Egypt

4 Department of Soils and Water, Faculty of Technology and Development, Zagazig University, Egypt

5 Zagazig University Hospitals, Zagazig University, Zagazig, Egypt

6 Department of Agronomy, Faculty of Agriculture, New Valley University, Egypt

7 Department of Pharmacology, Faculty of Veterinary Medicine, Aswan University, Aswan, Egypt

8 Faculty of Specific Education, Benha University, Benha, Egypt

9 Eco-Environmental Protection Research Institute, Shanghai Academy of Agricultural Sciences, Shanghai, China

\*Address all correspondence to: ahmed.aziz@agr.nvu.edu.eg

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Introductory Chapter: Climate Change and Climate-Smart Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113212*

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#### **Chapter 2**

## Hydroponic Production Systems in Greenhouses

*Božidar Benko, Sanja Fabek Uher, Sanja Radman and Nevena Opačić*

#### **Abstract**

Hydroponic production means the growing of vegetables, herbs and ornamental plants and fruits in a nutrient solution (a solution of water and macro- and micronutrients) with or without the use of a substrate that gives the mechanical support to plant. The most important advantages of hydroponics are as follows: continuous cultivation of one crop, better control and supply of plants with water and plant nutrients, reduced occurrence of plant pests and minimized environmental impact and increased water use efficiency. The main hydroponic cultivation technique of fruit vegetables is cultivation on substrates, often called soilless system. Growing substrate (organic, inorganic or synthetic) provides an aseptic environment, good oxygenation and an adequate nutrient solution flow, so the most important substrate properties are biological and chemical inert, porosity and capillarity. Its choice depends on climatic conditions, the type of equipment in the greenhouse and the plant requirements. Hydroponics is also suitable for growing crops with a shorter growing period such as leafy vegetables and herbs. Plants are grown by different growing techniques in a nutrient solution without a substrate (nutrient film technique, floating hydroponics, ebb and flow and aeroponics). These are closed hydroponic systems, which means that drainage nutrient solution is collected, sterilized and reused.

**Keywords:** soilless culture, nutrient solution, inert substrates, water culture, open and closed systems, aeroponics, floating hydroponics fruit vegetables, leafy vegetables

#### **1. Introduction**

Human population increasing and market demands require major adjustments in the way food is produced, and turning from previous traditional forms of cultivation to new and sustainable ones. One way to increase the food production sustainability is to grow plants in different hydroponic production systems. Hydroponics represents a climate-smart production method, due to environmental concerns, resource sustainability and efficient use as well as climate changes [1, 2]. This mean, when compared to the open field production, which is often exposed to biotic and abiotic stress factors that hinder production, hydroponics use less resources such as land space, pesticide, and water. As in the most cases hydroponics are placed in the greenhouses, the control of production factors such as temperature, relative humidity, light and carbon dioxide, as well as extension of the growing season is possible. These production systems also make the supply and distribution of nutrients to crops easier and more uniform to enhance crop growth and yield [3].

Hydroponically grown plants in greenhouses are optimally supplied with water and nutrients and have optimal growth and development conditions due to climate control. Production mostly takes place in heated greenhouses, which allows the production and supply of the market throughout or most of the year, depending on the culture grown. Vegetables, herbs and ornamental plants and fruits are grown in a nutrient solution (solution of water and macro- and micronutrients) with or without the use of substrate that gives the mechanical support to plant. Plant nutrients are in optimal relation, and concentration determined by the electrical conductivity (EC-value) and the pH value.

Mentioned above results are with the advantages of hydroponics [2, 4]:


These advantages result in higher production of biomass in the time and area unit in hydroponic cultivation compared to the soil cultivation, and thus earlier harvesting (faster entry into technological maturity), more harvests in crops that multiple harvested and higher total yields. Besides that, hydroponics represents an appropriate and sustainable growing technology for urban and peri-urban areas, where higher yield could be achieved by using vertical space (vertical farming systems) to meet food demands in densely populated areas [5].

Disadvantages of hydroponic cultivation techniques are high initial investments, that is, higher costs of installing hydroponic systems in relation to conventional soil cultivation. Successful hydroponic production requires a high degree of knowledge and expertise in the field of agronomy and technical skills and knowledge to manage the equipment applied. If diseases and pests occur, the infection spreads rapidly due to optimal conditions for their development in a greenhouse. Due to significantly higher costs, the successful application of hydroponic technology is limited to species of high economic value, in some regions often to a certain part of the year. An additional problem of hydroponic cultivation techniques on

substrates is also a disposal and recycling of inorganic and synthetic substrates after use [2, 4].

Hydroponic production systems include both cultivation on different inert substrates or growing media (soilless culture) and water culture with nutrient solution as root environment (without substrate). Regarding drainage solution usage hydroponic systems could be divided to open or closed. In open systems, the drainage solution is discharged, while in closed systems the drainage solution is collected, sterilized and reused [6]. Velasquez-Gonzales et al. [2] stated that choose of hydroponic growing technique depends on the plant species, local climate and budget, among other factors.

Despite some disadvantages mentioned above, hydroponic production is a rapidly growing sector that has seen tremendous growth in recent years. According to various statistics, the global hydroponic system market is projected to reach 16.03 billion USD by 2028 and Europe represents the largest market for this industry, accounting for 41% of its share. The compound annual growth rate of the hydroponics between 2022 and 2028 is estimated at 11.3%. Hydroponic greenhouse vegetable production is growing at a rate of 5–10% annually worldwide, and tomato is the most popular crop in the commercial hydroponics, accounting for over 30% of hydroponic production. When using hydroponic production systems, producers could achieve up to 2–4 times higher yield with approximately 90% less water consumed than traditional soil-based agriculture. At the same time, environmental pollution is decreased by nearly 70% [7].

To reach positive financial results, hydroponic production systems should be placed in a well-equipped, high-tech greenhouses where soilless culture equipment represents only a small fraction of the total investment of about 200 €·m–2. However, low- or mid-tech greenhouses may sometimes be modernized and used for hydroponics, depending on the economic and technical conditions, such as region, farm characteristics, type of greenhouse, soil problems, water resources, market requirements, establishment costs and, last but not least, restrictions on environment pollution. Low-cost alternatives are suitable for growers with limited capital or in regions with a fluctuating demand. In low-tech hydroponics, the heart of the system is the growing medium or water, while a simple system controls and distributes the nutrient solution or a drip irrigation system can be used [8].

This chapter will discuss about growing technology and substrates used in soilless culture and about water culture growing techniques.

#### **2. Soilless culture**

#### **2.1 Growing substrate**

There is no material or mixture that would be universal for growing all crops in all growing conditions. Growing substrate properties should match the requirements of the crop and the growing technology. Substrate should provide an aseptic environment, good oxygenation and an adequate nutrient solution flow, so the most important substrate properties are biological and chemical inert, porosity and capillarity. Biologically inert substrate means the absence of pathogens of plant diseases, pests and weed seeds. The chemical inert substrate does not contain any nutrients and does not affect, and they do not change the composition of the applied nutrient solution. In last years, life cycle and substrate sustainability (economic, social and environmental viability) becomes more and more important properties. For sustainable production of vegetables in growing media, priority should be given to locally available and not very

**Figure 1.** *Inorganic growing substrates (A: rockwool; B: perlite; C: expanded clay).*

expensive or locally manufactured and standardized products. The choice of substrate as a growing medium depends on climatic conditions, the type of equipment in the greenhouse and the requirements of the plants that need to be met [2–6, 8].

*Hydroponic Production Systems in Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113056*


#### **Table 1.**

*Physical and chemical characteristics of some growing substrates [9, 10].*

Hydroponic growing substrates are divided into organic (peat, coconut fiber, sawdust, corn, straw), inorganic (rockwool, perlite, sand, expanded clay, pumice, vermiculite, zeolite) and synthetic derived from petroleum (polystyrene, polyurethane and urea-formaldehyde foam). Also, they are divided into fibrous and granular. Fibrous are characterized by a high fiber content of different dimensions giving the substrate high water capacity and low for air. Retained water is easily accessible to the plant, and the volume is significantly reduced and varies from 2 to 7 liters per plant. Granulated substrates (sand, perlite) as opposed to fibrous ones have increased air capacity and reduced water by 10 to 40%. Retained water is more difficult to access to the plant, and the volume of substrate for one plant must be much higher than the fibrous substrates and amounts to between 10 and 40 liters [9].

#### *2.1.1 Rockwool*

Rockwool is a natural material obtained by heat treatment of volcanic rocks (bazalt and diabaz), which, with the addition of coke and limestone, are talent and refined to the final product, which, under the influence of high temperatures, acquires a fibrous structure. These fibers are then pressed into blocks or cubes (**Figure 1**) of light volume weight (80–90 kg·m−3) [6]. It absorbs water very well and has good drainage properties. Total porosity is from 95 to 97%. Of these, 75 to 80% are water micropores and 10 to 15% are air macropores (**Table 1**). One of the most significant features of rockwool is its sterility, that is, the complete absence of pathogenic microorganisms and everything else that could contaminate soilless cultivation. It has mild alkaline reaction (pH value from 7 to 8.5). Because rockwool is an inert pH value can be easily reduced to optimal in hydroponic cultivation (from 6 to 6.5) using a slightly acidic nutrient solution. After use, it can be thermally sterilized and reused for one or 2 years, which reduces environmental pollution. However, after each use, the fiber structure worsens and reduces the proportion of air pores. In areas with colder climates, less density rockwool with vertical threads is most used, while for warmer appetizers, higher-density stone wool with horizontal threads is recommended to allow for better water retention [9, 10].

**Figure 2.** *Organic substrates: coconut fibers (a), and peat (b).*

#### *2.1.2 Perlite*

Perlite (**Figure 1**) is an aluminum silicate of volcanic origin containing 75% SiO2 and 13% Al2O3. It is a sterile material, neutral in pH (6.5–7.5) and no decay, with light volume weight (90–130 kg·m−3) [6]. Its porosity (50–75%) ensures good breathability important for the growth of the root system (**Table 1**). Several different perlite granulations are produced (<3 mm, <5 mm, etc.). It can be purchased on the market packed in bags of volume 10 to 15 L on which the plants are planted or in large bags of volume about 100 L when filled into breeding vessels. It can be used alone or in a mixture with other substrates. If it is represented in a higher ratio in the mixture, attention should be paid to the pH value, which should not be lower than 5. It is often mixed with organic materials (peat) that improve its elasticity, permeability and other physical characteristics [9, 10].

The main disadvantage of rockwool and perlite is high energy consumption during production and their high price [6].

#### *2.1.3 Expanded clay*

Expanded clay (**Figure 1**) is obtained by roasting natural clay at 1200°C over 3 hours, giving a porous medium in the form of balls with a diameter of 4 to 20 mm, depending on the purpose. It is an inert substrate without a nourishing, neutral pH reaction. Capillarity on the surface of the ball provides a nutrient solution near the roots of the system. The balls dry easily and do not contain excess water that provides enough oxygen near the roots The lack of expanded clay is a fairly large volume mass, making it difficult to manipulate and very low water porosity (**Table 1**), which requires frequent and short fertigation [9, 10].

#### *2.1.4 Coconut fiber*

Coconut fiber (**Figure 2**) is increasingly used in hydroponic cultivation, and can be found on the market under different names, most often in the form of pressed blocks (plate). This substrate combines high water capacity of vermiculite and air capacity of perlite. However, it is completely organic in origin obtained by peeling coconuts. By its physical properties (**Table 1**), it is most similar to rockwool. Coconut fiber has physical stability [6], light weight (65–110 kg·m−3), good air content, high total pore space between 94 and 96%, and water holding capacity, subacid-neutral pH (5–6.8). It is rich in hormones and sterilized by pressurized water vapor, which ensures ideal conditions for rooting and protects against the causes of plant diseases. Also, unlike peat, coconut fiber is a completely renewable resource. The lack of coconut fiber as a substrate can be the content of NaCl [6], which affects the ion concentration in the root zone and has a detrimental effect on its development. Pressed blocks require soaking in aqueous solution before use. During soaking, the substrate rehydration and swelling occur up to six times the initial size. It is very often mixed with perlite or vermiculite in equal proportions [9, 10].

#### *2.1.5 Peat*

Peat is the most important material of organic origin and is obtained from the remains of *Sphagnum* moss (**Figure 2**). It is characterized by good drainage and structure, that is, physical stability, good air and water holding capacity with total pore space ranging 85–97%, low microbial activity, light volume weight (60–200 kg m−3), low and easily to adjusted pH, and low nutrient content [6]. According to the degree of decay, the amount of hinges is divided into white, brown and black peat. White peat has great absorption power and high acidity, and pH values between 3.5 and 4.2 (**Table 1**). It contains very few nutrients so it improves the water regime and air capacity. Black peat contains larger amounts of minerals that are suitable for plant growth. The reaction varies from 6.5 to 7.2 so that it is suitable for growing plants to suit a neutral or weakly alkaline reaction [9, 10].

Disadvantages of peat are that it is finite resource, environmental concerns and contribution to CO2 release due to peatlands use, increasing cost due to energy crisis. It may be strongly acidic; shrinking may lead to substrate hydro-repellence [6].

**Figure 3.** *Tomato plants in rockwool plugs ready for pricking.*

#### **2.2 Soilless growing technology**

The main form of fruit vegetables production is cultivation on substrates. The substrate is a medium whose role is to strengthen the root system, maintain water in the form of accessible plants, runoff of excess nutrients, and ensure air exchange. Soilless culture of fruit vegetables on substrates is technologically similar to soil cultivation in the greenhouse.

#### *2.2.1 Greenhouse preparation*

Before planting, it is necessary to prepare a greenhouse. In the greenhouse, equipment for nutrient solution preparation and a drip irrigation system should be installed. Substrate plates are placed in rows or double-row strips. The substrate is placed on hanging gutters, which serve to runoff an excess nutrient solution. The distance between the rows is 120 to 150 cm. If planted in double-row strips, the distance between the rows in the strip is 70 to 80 cm, and between the strips 100 to 120 cm. If cubes with two prickled plants are planted, two rows of plants are obtained from one row of substrate. After the substrate is placed, the planting sites are cut at the polyethylene foil into which the substrate is packaged. The distance between the plants in the row is 33 to 50 cm. Capillary carriers are inserted vertically into the cut openings so the substrate could be soaked with a nutrient solution before planting.

#### *2.2.2 Sowing and planting*

The seed sowing is most often done in rockwool plugs and planting on a selected inert substrate. Another possibility is sowing in rockwool blocks, 2.5-cm brides and

*Hydroponic Production Systems in Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113056*

**Figure 4.** *Tomato seedlings in rockwool cubes.*

**Figure 5.** *Cucumber planted in peat bags.*

4 cm high. Fifty to sixty blocks are connected by an upper edge so that they form a larger sowing unit. The plugs are placed in polystyrene containers with 240 pots. Sowing is most often done in late November or early December. After sowing in

**Figure 6.** *Tomato plants at the beginning of harvest.*

rockwool plugs, seeds are covered with vermiculite, which keeps constant temperature and retains moisture needed for emergence.

Emerged plants are pricked at the phase of developed cotyledon leaves and the first true leaf (**Figure 3**) into the rockwool cubes. The cube size depends on the culture and the number of plants being prickled into one cube. If one plant is prickled per cube, 7.5-cm edge cubes and 6.5 cm high or 10-cm edge cubes and 7.5 cm high are used, and if two plants are pricked per cube, cubes with 10- or 12-cm edge are used. Since seedlings are produced during a short day, supplemental lighting should be used in order to shorten the growing period.

Seedlings are grown in rockwool cubes until planting. During cultivation, they are fertigated with a nutrient solution of reduced concentration every day or every other day. If necessary, after watering with the solution, the leaves are rinsed with tap water to wash out the remains of nutrient salts. When the plants begin to touch each other, the cubes need to be spaced apart to prevent the seedling elongation. The cube is separated once and twice during the cultivation of seedlings (**Figure 4**). The seedlings are ready for planting when the root grows through the volume of the cube, that is, in late January or in the first half of February. Tomatoes are planted in the developing phase of 7 to 8 leaves and with a visible the first bloom, peppers in the phase of 10 to 12 leaves and a visible branching and the first flower, and cucumbers with 3 to 4 leaves.

The volume of inert substrate per package is most often between 10 and 20 liters. These bags (plates) are 1 m long, 15 to 20 cm wide and 7.5 to 10 cm high. Granular substrates such as perlite and expanded clay can be filled into pots or bags (**Figure 5**). The volume of substrate per plant is most often between 2.5 and 5 liters. Due to the small volume of substrate per plant, frequent fertigation is required, and the number and duration of a single ration depend on the substrate capacity for water (nutrient solution), the development stage of plant microclimatic conditions in the greenhouse.

Planting is done by placing the cube with the seedling/s on the openings provided on the substrate plates. When planting, it is necessary to remove the capillary carrier from the plate and insert it into the cube. Due to favorable temperature and humidity conditions, the rooting lasts for 2 to 3 days and plants continue their growth. Because the substrate is soaked with a nutrient solution before planting, only a few rations of fertigation are needed daily after planting. A few days after planting, the substrate plate is cut into two places, about 2 cm from the bottom of the plate, to allow the runoff of the excess nutrient solution.

#### *2.2.3 Plant care measures and harvest*

After rooting, plants are wrapped to prevent the stem breaking. It is necessary to maintain the plants by training them up a vertical supporting twine, removing older leaves as the lower fruit clusters are harvested, and by lowering the main plant stem to keep the whole plant within easy reach of workers.

During vegetation, the daily number and duration of the fertigation rations gradually increases. It is needed to control pH and EC values of nutrient solution in root zone, and ant to perform periodic laboratory analysis of nutrient solution composition. At the same time, in a greenhouse it is necessary to maintain the microclimatic conditions as close as possible to the optimal ones. Harvesting of fruit vegetables in soilless culture is performed at technological maturity, and begins 70 to 90 days after planting for tomato (**Figure 6**) and pepper, and about 30 to 40 days for cucumber. Pepper fruits could be also harvested at physiological maturity. The frequency of harvest depends on the time of harvest and species grown: every 2 to 3 days in cucumbers, every 3 to 5 days in tomatoes and every 10 to 14 days in peppers.

Forty to fifty days before the planned end of the harvest, plants are topped to improve the maturation of formed fruits. A few days before the harvest end, fertigation is stopped.

After the harvest end, plant residues, substrate and parts of the drip irrigation system are moved out from the greenhouse, the greenhouse is cleaned and disinfected

**Figure 7.** *NFT channel with tomato plants.*

and preparations for the next season begin. If the substrate is planned to be reused, it should be stored in a greenhouse to prevent freezing and disrupting the structure.

#### **3. Water culture**

Hydroponic techniques for growing plants in a closed system in a nutrient solution without substrate (water culture) are appropriate for growing crops of shorter vegetation, such as leafy vegetables (lettuce, arugula, lamb's lettuce, spinach, Swiss chard, chicory, endive and cress salad) and herbs (parsley, basil, oregano, marjoram, thyme, sage and dill). As the most commonly used in growing leafy vegetables, nutrient film technique, floating hydroponics, ebb and flow and aeroponics could be pointed out.

#### **3.1 Nutrient film technique (NFT)**

The nutrient film technique is based on maintaining a thin layer (up to 1 cm) of aerated nutrient solution that continuously flows over the plants root in shallow channels laid under a slope from 0.3 to 2%, which allows the solution to be circulated with a free fall (**Figure 7**). As stated by Velasquez-Gonzales et al. [2], nutrient solution flow can be periodic also. The nutrient solution is supplied by the pump from the container to the channel with the plants, and the solution not used by the plants is collected in the storage tank, analyzed and returned to the system. It is precisely the recirculation of the nutrient solution that is the main advantage of this hydroponic technique. Depending on the culture grown, the channel width varies from 10 to 20 cm, while the maximum length is 20 m.

The channels can be located on the ground or gutters, and are most often made of polymer materials (polyethylene, polyvinyl chloride). The channels contain openings in which seedlings or pots with plants are placed and their root is continuously supplied with water and nutrients, with an ideal solution flow rate of 3 to 8 L/ m<sup>2</sup> per hour for crops such as chrysanthemums and salad. The disadvantages of

**Figure 8.** *A-frame aeroponics.*

*Hydroponic Production Systems in Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113056*

this technique are the risk of interrupting the flow of a nutrient solution that very quickly causes root drying, stress and excessive channel warming in the summer due to which young plants may suffer in the initial growth phase. Contrary to growing on substrates, the ion concentration in the root zone does not increase due to continuous solution flow [11].

#### **3.2 Aeroponics**

#### *3.2.1 System work out*

In aeroponics, the plant root is in the air of dark space, and the nutrient solution is supplied by spraying every 3 to 4 minutes for 15 to 20 seconds in the form of an aerosol, which ensures high humidity (> 95%) in the root zone [11]. The optimum EC and pH values of nutrient solution in aeroponics system lie between 1.5 to 2.5 dS/m and 5.5 to 7.0, sprayed in different intervals, depending on species grown. Nutrient-rich solution is used as a growing medium and provides essential nutrient for sustain plant growth [12]. Velasquez-Gonzales et al. [2] pointed that there is no need for aeration system as oxygen is delivered to root with the sprayed nutrient solution.

In aeroponics, Styrofoam plates with plants are attached to a structure that can be horizontal, or at an angle of 45 to 60 degrees (A-frames). The pump distributes a nutrient solution from the tank to the spray pipe, which is located inside the structure and supply the root of the plant. The nutrient solution is returned to the tank by free fall [11]. The nursery plants might be either raised as seedlings using specially designed lattice pots or cuttings could be placed directly into the system for rapid root formation. Lattice pots allow the root system to develop down into the growth chamber where it is regularly misted with nutrient under controlled conditions [12].

**Figure 9.** *Stinging nettle in ebb and flow system.*

#### *3.2.2 Advantages and disadvantages*

The aeroponics provides numerous advantages including a free extension of the root system, direct and sufficient oxygen uptake, and rapid and provision of uniform nutrient spray mist with best root growth environment. Aeroponics uses less water and nutrients because the plant roots are sprayed at intervals using a precise droplet size that could utilize most efficiently by osmosis to nourish the plant [12]. Using A-frames aeroponics (**Figure 8**) results in good utilization of the greenhouse volume because the number of plants has doubled, but due to the variation of light intensity, uneven plant growth may occur.

High initial investments and the application of complex electronic devices justify the application of this hydroponic technique only to high-income cultures [11]. Lakhiar et al. [12] stated that the main problem in aeroponics is related to water nutrient droplet size. The larger droplets permit the less supply of the oxygen availability in the root zone, while the smaller droplets produce too much root hair without developing a lateral root system for sustainable growth. The main potential challenge and drawback of the system is constant power supply throughout the plant growth. Any prolonged rupture of power energy shuts down the nutrient supply and contributes to permanent plant damage.

#### **3.3 Ebb and flow**

#### *3.3.1 System workout*

The ebb and flow technique is also called "flood and drain" because of its principle of time intervals between dry and wet periods. Nutrient solution is available periodically by soaking the benches filled with plants in containers (**Figure 9**), or with pot plants. After a certain time interval that is programed according to plant species and development stage, the nutrient solution is drained from the bench. The system is closed and the solution is recycled [11, 13].

Benches are covered with an impermeable rigid plastic profile that directs all water to the lowest point at one end of the bench where a siphon device (unpowered) drains nutrient water from the bench surface to a gutter below to return the water to the nutrient storage tank. The supply water is pumped from the water and nutrient management storage tank to each bench or group of benches, filling to a depth of 1–2 cm within 5 min and draining within 10 min for a total water cycle per bay of 15 min. Water and nutrient management system includes freshwater filter and disinfection, nutrient dosing device, storage tank with pump, sensors and controls to distribute irrigation water and nutrients. Mechanical filtering devices are required to remove particulates from the drainage water [14].

#### *3.3.2 Advantages and disadvantages*

Ebb and flow has many advantages such as root moisture optimization, water saving and fertilizer saving as compared to top sprinkler irrigation. The nutrient solution concentration may be reduced by up to 50% when compared to nutrient solutions for top sprinkle irrigation, with no detrimental effects on plant growth and quality. Subirrigation systems improve the uniformity and quality of bell pepper and tomato if grown with minimal nutrient and drought stress. When used for potted plants grown on concrete floor, some specific advantages of ebb and flow include:

*Hydroponic Production Systems in Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113056*

**Figure 10.** *Seed sown in Styrofoam plates filled with perlite.*

elimination of manual watering, flexibility in design of internal transport of potted plants, heating the root zone with low temperature water, and reducing bacterial and fungal diseases because of cultivation surfaces that were easy to clean and disinfect between cultivation cycles [14].

#### **3.4 Floating hydroponics**

The floating hydroponics was first applied in the production of tobacco seedlings, and today they are used efficiently in the production of vegetable seedlings and in the cultivation of leafy vegetables and herbs. It is important to emphasize that in

**Figure 11.** *Floating hydroponics.*

the cultivation of seedlings, the solution is not aerated to prevent the root growth of plants outside the container pot [4].

In floating hydroponics plants are grown in a nutrient solution. The basic advantage of this system is that plants provide access to water, and macro- and micronutrients in the form of ions and oxygen over 24 hours, which they can optimally use during all stages of growth. This results in faster growth and earlier harvesting, which provides more production cycles throughout the year and higher yields [11, 13].

This hydroponic system consists of shallow pools filled with a nutrient solution on which Styrofoam plates or containers with plants float. The nutrient solution is raised capillary through the openings of the pot of containers or the slit of the plates to the substrate in them, that is, to the root of the plant. Styrofoam containers can have a different number of pots, and the plates can be of different dimensions, depending on the type of vegetables and the purpose of cultivation, respectively, whether leafy vegetables are grown due to young leaves for cutting or due to rosette or head. Container pots or slots on plates are filled with perlite or some other substrate into which the seeds of vegetables or herbs are sown (**Figure 10**).

#### *3.4.1 Greenhouse preparation and pool construction*

The most demanding part of the work in floating hydroponics growing is preparing the terrain for pool construction, and includes precise straightening, with minimal drop along the greenhouse to keep the water level in all parts of the pool uniform. To allow a simpler pool emptying, it is sufficient to ensure a pool drop of 0.1%. If the surface of the terrain is rough, it is recommended to apply the sand in a layer of 2.5 to 5 cm before rolling and final straightening. Due to the good drainage under the pool, the level of terrain subjected for floating hydroponics construction should be raised 10 to 15 cm above the level of the surrounding terrain. The production surface of the

**Figure 12.** *Growing lettuce in floating hydroponics.*

#### *Hydroponic Production Systems in Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113056*

pool, that is, its width and length, depends on the dimensions of the greenhouse and floating Styrofoam plates or containers for growing leafy vegetables. It is very important that the surface of the entire pool is completely covered with Styrofoam plates to prevent the development of algae that cannot develop without light, and which pollute the nutrient solution and create unfavorable conditions for growing vegetables. The pool frame height should ensure a nutrient solution depth of 20–25 cm and the floating of Styrofoam plates with plants (**Figure 11**).

Agrotextile is first laid on the aligned soil, followed by PE-film of 0.5 mm thick, with complete frame coverage. At the pool bottom, a pipe system for occasional replenishment and daily circulation of the nutrient solution (to enrich the solution with oxygen) is placed. The nutrient solution is gradually added to the pool depending on its consumption, and the transpiration of the plants, respectively. For the entire production of leafy vegetables, it is also recommended to set up a pipe system to maintain the required nutrient temperature [4].

#### *3.4.2 Growing technology*

Leafy vegetables (**Figure 12**) harvested by cutting in the developed phase of 5 to 6 leaves (baby leaf) sown in Styrofoam plates (96 × 60 × 2.7 cm), with narrow conical slits filled with perlite of coarse granulation (0 to 6 mm). Sown plates are covered with finer perlite, moistened with water and stacked on each other until seed germination, when the plates are laid in pools filled with aerated nutrient solution. Optimal conditions for germination (temperature from 18 to 20°C and relative humidity around 95%) are provided in the germination chamber [4].

If leafy vegetables is grown for harvest of rosettes or heads, seeds are sown into rockwool plugs (cubes) 3 × 3 cm. Cubes with seedlings are placed in lattice pots, in holes (planting sites) distanced 20 × 20 cm in Styrofoam plates [11]. The plates with seedlings are laid in pools filled with a nutrient solution of a certain chemical composition and optimal temperature.

In this hydroponic technique, plants are constantly absorbing a nutrient solution, especially at higher air temperatures when transpiration is more intense, so the level of the solution decreases and it is necessary to ensure a pool supplement. The pH and EC values, the amount of dissolved oxygen and the nutrient solution temperature should be measured daily, and the nutrient solution composition by chemical analysis should be done every 2 weeks. The optimal pH value of the solution is from 5.8 to 6.2, while the EC value in leafy vegetable cultivation should be in the range between 2.5 (lettuce, lamb's lettuce) and 3.2 dS/m (arugula). The availability of nutrients for plant is affected by the pH value and temperature of the nutrient solution and the amount of dissolved oxygen in the solution. The recommended temperature of the leafy vegetable growing solution should be from 21 to 23°C, while the optimal amount of dissolved oxygen is 4 to 9 mg/L [13, 15]. If the solution temperature is higher, the ability of the solution to retain oxygen decreases and the breathing of the roots is more intense and oxygen consumption is higher. Lack of oxygen in the nutrient solution (below 3 mg/L) results in less root permeability to the water so the plant cannot adopt nutrients in the required amount, and toxin accumulation can occur. Plant growth is slower and plant damage and leaf chlorosis are possible. Lowering the solution temperatures too high will ensure that larger amounts of oxygen are retained and root respiratory is reduced [16].

The length of the vegetation from sowing to harvest depends on the type of leafy vegetables and growing conditions, and the equipment of the protected area (side and roof ventilation, heating and shading equipment and supplemental lighting, nutrient solution heating and cooling system). Lettuce, lamb's lettuce, endive and chicory are harvested once, while arugula and herbs can be harvested repeatedly. However, the vegetation tip should not be damaged during the first harvest, so the plants could grow again. The annual yield of arugula and lamb's lettuce in floating hydroponics may be 40 to 50% higher than the yield in the case of soil grown in greenhouse [17, 18].

After a year-round production period, the pools are cleaned from the rest of the nutrient solution, perlite particles and organic matter, than disinfected and prepared for a new year-round cycle with the preparation of a nutrient solution, filling the pool and continuous sowing and harvesting.

#### **4. Water and nutrient solution**

#### **4.1 Water quality**

Water is the basis of any nutrient solution and therefore, it is necessary to provide sufficient amounts of quality water. High water quality is determined by the low concentration of dissolved substances, especially salts. The higher the water quality, the easier it is for producers to formulate an optimal nutrient solution. If the water quality is lower, more water is needed to dissolve the nutrient salts in open systems, that is, to remove excess salt from closed systems. Low quality can be supplemented by more water [4].

The quality of water should be taken into account at each beginning of the production season in the greenhouse since low-quality water is not usable and is expensive to "process" by filtration and/or reverse osmosis. Quality primarily depends on the available water source (rainwater, surface water-treated waste water and ground water). Rainwater is one of the best sources regarding quality. Before water can be used, it must be analyzed to determine the basic level of all minerals and ions (Ca2+, Mg2+, SO4 2−, HCO3 − , Na<sup>+</sup> , Cl<sup>−</sup> ,) present and the pH and alkalinity. Without this information, it will be difficult to prepare the optimal nutrient solution [19, 20]. Water quality depends on the concentration of dissolved substances, and the presence of microorganisms such as algae, fungi and bacteria, and certain sediments. The overall analysis should show anions and cations, and special attention should be paid to salinity, alkalinity, and excessive concentrations of sodium, sulfate, and chloride. When using a drip irrigation system, high water quality is required to avoid possible interference by clogging the droppers with iron and manganese [20].

The required amount of water is mainly determined by microclimatic conditions and a leaf surface [4], which also affects the optimal composition of a nutrient solution [6] and EC value [19]. Under conditions of high humidity, low light and low temperature, water consumption can be very low. It is very important to know how to estimate the maximum amount of water used when the irrigation system is constructed and installed. The amount of water that plants consume is caused by the degree of growth of the plant, solar radiation, relative humidity and air movement.

Salinity is the amount of all dissolved salts quantified as water electrical conductivity (EC value), and is expressed in mS/cm or dS/m. An important assumption is that the EC value of the spring water should be below 1 dS/m. In some cases, the use of water with higher EC value is possible for so long while ions, which cause high

*Hydroponic Production Systems in Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113056*

**Figure 13.** *Fertigation unit.*

EC-value, are used as plant nutrients. Even then, the concentration of these ions should not be excessive. Water with EC value 0.75–2.25 dS/m has slight to moderate restriction in use, while with >2.25 it has severe restrictions. The use of salted water in hydroponic cultivation in arid areas results in a slightly lower yield of cultivated crops, but therefore of excellent quality. Harmful effects on plant growth are caused by water and salinity stress. The maximum acceptable level of Na+ in the nutrient solution varies between 1 and 8 mmol/l, while the maximum acceptable Cl− level in the root zone is 0.2–0.5 mmol/l higher than the maximum acceptable level for Na+ [19–21].

#### **4.2 Nutrient solution preparation and distribution**

In addition to water, nutrient salts or water-soluble complex fertilizers and acids are necessary to prepare a nutrient solution. The advantage of nutrient salts is that they represent high-purity chemical compounds composed of two to three nutrients. Complex water-soluble fertilizers most often contain nitrogen phosphorus, potassium and magnesium with the addition of microelements, which means that when correcting the composition of the nutrient solution, it is not possible to change the concentration of only one nutrient than to change all the concentrations of all nutrients found in the fertilizer [4]. Acid (nitric or phosphoric) needs to be added to the nutrient solution to lower the pH value of water (7.2 to 7.5) to optimal for hydroponic cultivation, which is between 5.5 and 6.8 [8, 17, 19, 21], although values between 5.0–5.5 and 6.5–7.0 may not cause problems in most crops [22, 23]. The EC value measured in fresh nutrient solution ranges from 1.5 to 3 dS/m [1, 8]. Lieth and Oki [24] stated that EC in soilless production may vary between 0 and 5 dS/m. It has been advised to maintain the EC below 3 dS/m to assure rapid plant growth, but this is impossible if the water is high in dissolved salts, and the addition of nutrients will raise EC to higher value than 3 dS/m.


#### **Table 2.**

*Nutrient solution composition in tank for greenhouse crops according to different authors [9, 19, 21–23].*

The preparation of fresh nutrient solution is performed using a dosatron, mixer or fertigation unit (**Figure 13**) depending on the greenhouse. Regardless of the hydroponic cultivation technique, the finished nutrient solution is prepared from 100-fold concentrated solutions in relation to the concentration of the solution that is brought to plants by the system. Therefore, in each hydroponic production there are at least three tanks for concentrated solution [11]. Two tanks are filled with different stock solutions to separate calcium from sulfate and phosphate fertilizers, thereby avoiding precipitation of low-soluble compounds. The third tank contains a solution of nitric or phosphoric acid, which serves to regulate the solution pH value, by neutralization of HCO3 − ion [19]. An equal volume of stock solutions used for fresh solution preparation is necessary in order to avoid nutrient misbalance. The volume of acid used depends on the water pH and the desired pH value of the nutrient solution [4].

In modern hydroponic growing systems, the nutrient solution parameters (oxygen concentration, temperature, pH and EC) are automatically controlled by a computer system that uses special sensors. The software sets the target values, and the fertigation unit measures water parameters and compares them with target values to add proper volumes of concentrated solutions and acid until the target values are reached. Additionally, probes are immersed in the growing substrate or in nutrient solution to collect data in root zone. The data is transmitted in real time to the cloud, from where it can be read at any time *via* a mobile app or computer. In this way, a faster response is possible when the parameters of the nutrient solution

#### *Hydroponic Production Systems in Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113056*

need to be corrected, which undoubtedly has a positive effect on the success of the cultivation [25].

Lieth and Oki [24] stated that nutrient solution in hydroponic growing systems could be delivered to plants by overhead, surface or subsurface irrigation. However, the dominant way of irrigation is surface, particularly drip irrigation in substrate grown crops. Nutrient solution is delivered by drippers, pinned or laid on the upper side of substrate. One of the most significant problems of drip irrigation is dripper clogging, mechanically or chemically, directly related to the quality of irrigation water and its physical, chemical and microbiological properties. Therefore, a water quality analysis should be performed before installing the drip irrigation system. The filtering site must certainly be an integral part of the drip irrigation system [4].

#### **4.3 Nutrient solution composition**

Although there are no significant differences in the nutrient solution composition among crops, crops can vary significantly in the absorption of individual nutrients, especially in certain parts of the vegetation. Nutrient absorption is affected by many abiotic (air and substrate temperature and humidity, light intensity and CO2 concentration) and biotic (growth and development phase, fruit load and pest presence) factors. However, for more or less standardized growing conditions on substrates, a strong correlation between fresh fruit yield and nutrient absorption has been established [4, 23]. Contrarily, Sonneveld and Voogt [19] and Savvas et al. [26] quote that specialized nutrient solution for each greenhouse crop or even for developmental stage is available. Use of this kind of solution is optimal when nutrient uptake ratios are similar with the relative proportions between the same nutrients in fresh solution. This principle should be strictly followed in closed hydroponic systems to avoid

**Figure 14.** *UV-sterilization unit.*

nutrient accumulation and/or depletion. Vox et al. [27] stated that the more concentrated nutrient solutions are used for fast-growing crops, such as vegetables, while for ornamental plants and strawberry lower nutrient concentrations are normally used. Plenty of different nutrient solution formulas have been published and some of them are summarized in **Table 2**.

#### **4.4 Nutrient solution sterilization and recirculation**

According to the use of a nutrient solution, hydroponic systems are divided into the following: open ones where once used nutrient solution is not used again in the system but is drained into evaporation channels or used to fertilize soil-produced crop; and closed ones where drained nutrient solution is passed through a sterilization system, supplemented with a fresh nutrient solution and reused [6]. If the hydroponic system is open, the irrigation system should ensure the amount of nutrient solution or water, which will maintain or reduce the salt concentration. Due to that, the part of supplied nutrient solution should be drained from the substrate. In practice, the drained solution volume varies between 10 and 30%, depending on the quality of the water and/or on the crop sensitivity to salinity [4, 6, 23, 27]. In closed systems, salt accumulation in the root zone is more common, resulting in reduced yields. To avoid this kind of problem, the nutrient concentrations and injection rates of fresh and recycled nutrient solution should be monitored and regulated. Also, irrigation with freshwater, which washes away excess nutrients, could be applied.

Root's zone in hydroponic systems needs to be pathogen free to efficiently produce good-quality products [2]. Due to hydration, there is a high potential for the rapid spread of root diseases [28], especially in closed hydroponic systems. Closed hydroponic systems reduce or limit the runoff of drained nutrient solution into the environment [3], so in closed systems the drained solution should be filtered and disinfected before it is recycled, to avoid spread of pathogens [29]. There are five main methods of pathogen control in these systems: heat, filtration, chemical, radiation and biological control. Sterilization (heat, oxidizing chemicals and UV-radiation) and membrane filtration methods are generally very effective, but may adversely affect beneficial microorganisms in the recirculated solution (**Figure 14**). Slow filtration and microbial inoculation methods are less disruptive of the microflora, but effectiveness may vary with the pathogen. Microbial inoculation is perspective in targeted disease suppression, but still just a few products are commercially available [28, 29].

From a sustainability perspective, it is important to recirculate the nutrient solution to minimize water consumption and residuals to dispose into environment. However, it is not always possible to implement systems that balance the consumption of natural resources, energy and financial costs [2]. Besides the environmental benefits, closed hydroponic systems can provide higher economic profits, since they reduce the quantity of water and fertilizers used during production, and they are more efficient in using water and nutrients than open systems, respectively [30]. In their research, De la Rosa-Rodríguez et al. [30] achieved 26.9% (13.5 kg) higher tomato yield per liter of water in closed than in the open system.

#### **5. Conclusions**

Hydroponic growing systems include plant growing techniques without soil, on inert substrate (soilless culture), or without substrate (water culture). Inert

#### *Hydroponic Production Systems in Greenhouses DOI: http://dx.doi.org/10.5772/intechopen.113056*

substrates used are mainly of inorganic or organic origin. The advantage of organic substrate use is their sustainability with no or minimal impact to the environment, so they could be recommended. Water culture techniques represent closed hydroponic systems, which are more efficient in water and fertilizer use compared to open systems (mostly on substrates), and especially compared to soil production. Due to high-quality yield regardless of grown crop, hydroponic systems could be a way to increase the food production sustainability in the future, characterized by population growth, climate changes and the reduction of natural resources.

Future development of hydroponics through research and particularly through application should be focused on vertical farming and plant factories, which will ensure continuous production increase with sustainable use of resources by controlled environment agriculture.

#### **Conflict of interest**

The authors declare no conflict of interest.

#### **Author details**

Božidar Benko\*, Sanja Fabek Uher, Sanja Radman and Nevena Opačić Faculty of Agriculture, University of Zagreb, Zagreb, Croatia

\*Address all correspondence to: bbenko@agr.hr

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 3**

## Agriculture's Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N2O) and Its Feasible Mitigation Strategies

*Raushan Kumar and Nirmali Bordoloi*

#### **Abstract**

Climate change and agriculture have a dual mode of relationship. Agriculture is an important sector of the country's economy and it significantly contributes to climate change by releasing greenhouse gases (GHGs) to the atmosphere. On the other hand, climate change is a global threat to food security and it can affect agriculture through variation of weather parameters. Reducing GHGs emission mainly methane (CH4) and nitrous oxide (N2O) from the agriculture could play a significant role in climate change mitigation. N2O is a potent greenhouse gas mainly emitted from rice-wheat cropping system. Agricultural lands are considered as one of the important anthropogenic sources of N2O emissions and it account almost 69% of the annual atmospheric N2O emission and application of commercial fertilizers is considered as a major contributor to the N2O emission. This book chapter focuses on the feasible soil and crop management practices to reduce the N2O emission from agriculture without compromising the productivity. Different environmental factors that have a major impact on N2O production are also discussed in this chapter. On urgent basis, the world needs to reduce the anthropogenic N2O emissions from agriculture and adapt its sustainable cropping system and food-production system to survive with climate change.

**Keywords:** climate change, food security, fertilizer, nitrous oxide, management practices

#### **1. Introduction**

Global climate change is caused by the increasing concentration of many climate pollutants like carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) etc. The agriculture and food production is connected with emissions of all these three gases but emissions of CH4 and N2O are directly dominated by agricultural activities [1] and 10–12% of the total GHGs produced globally by anthropogenic activities [2]. Among the non-CO2 greenhouse gases (GHGs), N2O is an important long lived GHG and agriculture represents its largest source worldwide. N2O is a major driver of climate change and considered as a very reactive gas and potent ozone-depleting substance

in the stratosphere [3]. Moreover, it exerts adverse impacts on crop production and human health [4]. The emission of N2O can lead to an indirect health impact, namely the depletion of the stratospheric ozone layer. This depletion results in higher levels of UV radiation reaching the earth's surface, leading to an increased incidence of skin cancers [5]. Additionally, regions with elevated N2O concentrations may experience air pollution due to its contribution. When N2O combines with other pollutants, it can form ground-level ozone and fine particulate matter, which can worsen respiratory issues, particularly in individuals who already have asthma and chronic obstructive pulmonary disease (COPD) [5]. The rising earth's temperature due to the increasing N2O concentration can have also detrimental effects on precipitation patterns and lead to more extreme temperatures, adversely impacting plant growth and productivity. Additionally, increased N2O levels in the atmosphere can cause higher nitrogen deposition in soils. While nitrogen is vital for plant growth but excessive amounts can disrupt the nutrient balance, depleting essential nutrients and compromising plant health [5]. Furthermore, the depletion of the ozone layer due to the emission of N2O allows harmful UV radiation to reach the earth's surface, potentially harming plants and hindering the process of photosynthesis.

Since 1750, concentrations of GHGs have been increasing due to anthropogenic activities. The anthropogenic N2O is increasing annually, which has risen from a preindustrial value of 270 ppb to a value of 324 ppb in 2011 and 332 ppb in 2019 [6].

Agriculture is the major primary anthropogenic source of N2O emission, globally contributing around 3.8 (2.5–5.8) Tg N yr−1 or 22% to the atmospheric N2O budget [7]. The use of synthetic fertilizer, manure and increase in agricultural lands are the main reason of N2O emissions from soil (**Figure 1**). When plant roots cannot uptake all the applied fertilizer due to their growth stages, some of it runs off or leached out and remaining amount is consumed by the soil microbes and convert the ammonia to nitrate and finally back to N2 gas (**Figure 2**).

N2O is emitted as a byproduct during the conversion of ammonia/ammonium to nitrate and nitrate to N2 by microbial process of nitrification and denitrification respectively [8]. The excess nitrogen in the soil also leads to lower nitrogen use efficiency (NUE) by plants. Although the global agricultural food system depends of application of synthetic fertilizers to increase the crop productivity however; the

*Agriculture's Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N2O) and Its… DOI: http://dx.doi.org/10.5772/intechopen.113021*

#### **Figure 2.**

*Use of excess nitrogen and N2O emission from the soil.*

abundance use of synthetic fertilizer is unsustainable due emission of N2O from soil and pollutes waterways through nitrate leaching. The global food system is responsible for ∼21–37% of annual emissions [9]. Further, N2O emissions are expected to increase over to coming decades due to projected increases in food demand for over increasing population, agricultural land and fertilizer use. However, active management of agroecosystems through managing soil and plants can offer a sustainable opportunity for N2O mitigation without jeopardizing crop growth and food production. In this chapter, we have tried to address all the factors associated with agricultural N2O emission and their feasible management practices to reduce the production and emission of N2O.

#### **2. Role of rice-wheat cultivation in N2O production and emission**

The primary sources of N2O in rice-wheat soil is the transformation of reactive N by soil microbes [10]. When N enters the soil in the form of NH4 + and NO3 − via organic or mineral fertilizers, various reactions might occur, resulting in N2O production. Three main processes, namely nitrification, denitrification and nitrifier denitrification, are considered the main contributors to N2O emissions [11]. Nitrification (NF) is regarded as the primary process involved in the global N cycle. The majority of N transformation during nitrification is mediated by autotrophic microorganisms. The initial stage in NF is NH3 oxidation to hydroxylamine. This mechanism is mediated by ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Denitrification (DNF) is a reduction process involving the conversion of NO3 to N2, mediated by facultative anaerobic bacteria [12]. This process can be completed up to N2 production, but if it is not completed, N is released as NO and N2O. 70% of worldwide N2O emissions are attributed to NF and DNF microbial activities [13]. Nitrifier denitrification is the reduction of NO2− to NO, then to N2O and finally to N2 [14]. The soil gets submerged or saturated with water during rice cultivation. This reduces the amount of oxygen available to nitrifying microorganisms, halting

the nitrification process. In such soils NH4-N is the major form of N. The drying of the soil at the harvest of rice crop and aerobic condition of soil in wheat cultivation favors nitrification and accumulation of NO3-N, which is prone to losses by denitrification and leaching during flooding in subsequent rice cultivation. Moreover, the fluctuating soil moisture conditions and the intermittent drying and flash flooding in rice cultivation, cause large N losses to occur. Therefore, though continuously flooded rice paddies are not considered to be an important source of atmospheric N2O because N2O, an intermediary product of denitrification, would be rapidly reduced to N2 under the intensive anaerobic conditions and rice-wheat systems may produce considerable amount of N2O. Each process's contribution to N2O emission is affected by soil texture, organic C, soil pH, microbial activity, and environmental factors such as precipitation and temperature [15], as discussed in next section.

### **3. Factor affecting N2O emission from rice wheat soil**

N2O production and emissions from rice wheat soil are regularly governed by different microbial-mediated activity and also depends on several pathways of gas transport, such as: plant-mediated transport (through the aerenchyma). N2O emission from the rice wheat soil are also mediated through biologically, therefore, its emission from the soil is affected by different climatic as well as agricultural management factor which are depicted in **Figure 3**.

#### **Figure 3.**

*Factors affecting N2O emission from rice wheat ecosystem.*

*Agriculture's Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N2O) and Its… DOI: http://dx.doi.org/10.5772/intechopen.113021*

#### **4. Sustainable mitigation strategies of N2O emissions**

There are a number of mitigation strategies that can be applied to rice and wheat grown soil that would increase productivity while lowering N2O emissions and strengthening agriculture's ability to withstand climate change. In this section, briefly we draw attention to some recent research advances in mitigation strategies and technology tools to expand our understanding about soil and crop management for enhanced nitrogen use efficiency (NUE) and N2O emission mitigation (**Figure 4**). All mitigation strategies focus on site-specific management practices and the use of technologies that will assist limit N losses via ammonia volatilization and nitrate runoff, leaching and drainage pathways. The importance of site-specific agricultural management practices to improve crop and soil recovery of applied N (efficiency), crop productivity per unit of N applied (efficacy), and N2O per unit of crop production has been stressed.

#### **4.1 Agricultural management practices**

#### *4.1.1 Irrigation pattern management*

Flood irrigation (FI) is the most widely used irrigation method in developing countries such as India, Pakistan, Bangladesh, and most part of Africa. High volumes of water are given to crops in FI, resulting in fertilizers dilution and easily absorbed [16]. Large irrigation volumes, on the other hand, influence the anaerobic conditions permissive to N2O generation and nitrate leaching [17]. To avoid this, a precise water application strategy, such as alternate wetting and drying (AWD), could save water while also lowering N2O emissions. This is because low water content requires more time for oxygen penetration into the soil, which leads to inhibition of microbial activity in the soil responsible for N2O formation [18]. Similarly, intermittent irrigation, which means the field is alternately watered and drained, has a high potential to reduce N2O production from soil because this irrigation method has the advantage of improving soil oxidative conditions by increasing root activity, soil bearing capacity, and ultimately minimizing water inputs that create anaerobic conditions. This

#### **Figure 4.**

*Key principles of climate smart agriculture and associated mitigation strategies of N2O emissions.*


#### **Table 1.**

*Different agricultural management practices and N2O mitigation potential from rice-wheat fields.*

promotes the penetration of oxygen into the paddy soils and, as a result, reduces N2O emissions. Another modified irrigation strategy is sprinkler-irrigated field (SI), the surface layer in a SI is comparatively loose than FI. As a result, in such soils, the NO3-N and NH4-N are less leached and remain more concentrated in the root zone, making them more easily absorbed by plant roots and hence less likely to be converted to N2O [19]. Different irrigation pattern and N2O mitigation potential from ricewheat fields are showed in **Table 1**.

#### *4.1.2 Tillage practices*

Soil tillage has a significant impact on N2O emissions during rice-wheat cultivation because it alters soil physiochemical and biological characteristics, stimulating microbial N2O generation [26]. Traditional plowing or rotational tillage, which is extensively employed today, exposes the surface, which increases soil depletion and lowers the quality of cultivated land as well as the soil's ability to continually feed fertilizer. The usage of conservation tillage (CT) techniques, such as no-tillage (NT) and reduced tillage (RT), is progressively increasing, owing to the reduction of greenhouse gases, improvement of soil and water quality and enhanced water efficiency. Six et al. [27] proposed that preserving NT throughout time could lower N2O emissions. These findings are also corroborated by van Kessel [28]. The researchers conducted a meta-analysis on 239 direct comparisons of CT, NT and RT and found that, on average, neither NT nor RT emit more N2O than CT. Long-term research (>10 years) using NT and RT procedures, primarily in dry regions, revealed a considerable reduction in N2O emissions. Different tillage practices and N2O mitigation potential from rice-wheat fields are showed in **Table 1**.

#### *4.1.3 Crop residue management*

Crop residue (CR) return regulates N2O emissions by regulating microbial activity and C/N availability and it is predicted that CR return produces 0.4 million metric tons of N2O-N yr−1 globally [29]. Several authors have noted that returning CR can increase N2O emissions by increasing C and N availability for microbial activities and modifying soil aeration by improving soil aggregation and microbial demand, which is thought to be a major factor mediating soil NF and DNF for N2O production [29]. Other authors, on the other hand, reported that adding CR had an inhibitory effect on N2O emission, depending on soil conditions and crop residue C/N ratio [30]. The

*Agriculture's Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N2O) and Its… DOI: http://dx.doi.org/10.5772/intechopen.113021*

return of CR can act as a carbon source for microbial development, promoting N uptake by microorganisms. This activity can result in a fierce competition for NH4+ between heterotrophic microorganisms and autotrophic nitrifiers, which results in N2O production [31]. However, in CR management, it is believed that no unambiguous behavior with regard to N2O emission can be detected. To improve smart CR management and its contribution to reduced N2O emissions, several factors must be considered, including CR properties and ambient circumstances.

#### **4.2 Inorganic fertilizer management**

Mitigating N2O emissions requires increased NUE through improved temporal synchrony between N supply and plant demand. This requires efficient N management strategies, such as selection of the right source (enhanced efficiency fertilizers), right quantity, right time and right application method.

#### *4.2.1 Altering fertilizer dose and matching N supply with crop demand*

Appropriate fertilizer management can significantly reduce N2O emissions from rice-wheat fields. It has been reported that the application of N fertilizers in soil is not totally consumed by the crop; consequently, it is more vital to enhance fertilizer usage efficiency, which can significantly reduce N2O emissions [8]. A potential technique for reducing N2O emissions is to reduce the amount of N input into the soil [32]. This is due to lesser N input in soil causing competition between plants and soil microorganisms, which favors soil N uptake by plants, resulting in lower N2O emission than with high N fertilizer application. Bordoloi et al. [24] observed that reducing fertilizer rates by 25% (from 60 to 45 kg N ha−1) significantly reduced N2O emissions from fertilized rice fields. The N application method can also have an impact on N2O production. In fact, placing N near the roots boosted NUE and lowered N2O emissions [33]. Furthermore, optimizing N fertilizer application to better match nutrient availability with crop demand considerably reduced soil residual N, lowering N2O emissions [34]. Split fertilizer applications at different crop stages ensure continuous N availability, which enhances NUE and decreases N2O emissions [35].

#### *4.2.2 Right time of fertilizer application*

The right time implies applying fertilizer when the plant will benefit the most and avoiding times when fertilizer will be lost to the environment. In terms of lowering N2O emissions, the time of fertilizer application is closely related to the amount of fertilizer used. Fertilizer application weeks after planting rather than before sowing enhances the likelihood that applied N will end up in crop tissues rather than being lost to the atmosphere and ground water.

#### *4.2.3 Improving N fertilizer placement*

Improved N placement strategies, such as urea deep placement (UDP) at a soil depth of 7 ± 10 cm, boost NUE and crop yields while lowering emissions when compared to broadcast application [36]. In flooded rice fields, UDP keeps N in the root zone as NH4 + -N for a longer period of time, ensuring a constant supply of N to plants throughout the growing season. It has been observed that UDP boosts rice yields by 20%, NUE by 30%, and decreases N2O emissions by 84% when compared to broadcast urea treatment [37]. Deep placement of N fertilizers in lowland rice resulted in an 80% reduced N2O emission than traditional surface spreading [37]. This is because a substantial part of N was maintained in the soil for a longer period of time. The positioning of N closer to the plants reduces N2O emissions significantly, as in the case of urea band application rather than broadcasting.

#### *4.2.4 Selection of suitable fertilizers*

Different fertilizers influence N2O emissions due to varying levels of NH4 + , NO3 − , and organic carbon. The higher the level of N application, the greater the increase in N2O emissions [38]. Higher quantities of N application significantly enhance the DNF, which increases N2O emissions. Furthermore, types of fertilizers also influence NF and DNF process which ultimately affect the production of N2O emissions. The use of anhydrous ammonia, for example, considerably enhanced N2O emissions [39]. Grave et al. [40] investigated how different N sources affected N2O emission in a maize-wheat rotation. They reported that, in comparison to the control plots, the application of urea and slurry increased N2O emission by 33% and 46%, respectively. Bordoloi et al. [41] investigated the effects of various urea concentrations on N2O emissions in a wheat cropping system and discovered that N2O emissions rose concurrently with urea concentration, reaching a maximum of +174% with 100 kg N ha−1 from urea. Furthermore, Lebender et al. [42] examined the effect of the N source calcium-ammonium-nitrate (200, 400 kg ha−1) on N2O emission from the wheat crop. They observed that 400 kg N ha−1 consistently produced considerably more N2O emissions than 200 kg N ha−1 over time. Higher N2O emissions result with the application of calcium ammonium nitrate, particularly in moist soils with high OM [43]. In another study, Nayak et al. [44] discovered that substituting ammonium sulphate for urea enhances N2O emissions. However, changes in N2O emission from N fertilizers can be attributed to soil parameters including as texture, bulk density, pH, organic carbon, N, and microbial population [45]. Overall, the most important domain of intervention to reduce N2O emissions is the selection and management of appropriate fertilizers.

#### *4.2.5 Use of nitrification inhibitors or slow-release fertilizers*

Enhanced-efficiency fertilizers including nitrification inhibitors (NIs), urease inhibitors (UIs), and control release fertilizers (CRF) have been developed to increased NUE. The use of NIs, such as dicyandiamide (DCD), in conjunction with urea or ammonium-based fertilizers (at the optimal N rate), could boost NUE while decreasing N2O emissions in a variety of agricultural systems [46]. The NI decreases N2O emissions directly by inhibiting NF, as well as indirectly by reducing NO3 − availability for DNF without compromising yield [47]. The chemical components in the NI inhibit the enzymes involved for the first step of NF (ammonia mono-oxygenase; AMO), allowing NH4 + to remain in soils for extended periods of time [48]. As a result, the NI reduces the rates of NF and the availability of substrates for denitrifiers, lowering N2O emissions from fertilizers [49]. Various authors observed a considerable reduction in N2O emission with the application of various NI, including dicyandiamide, hydroquinol, nitropyrimidine, and benzoic acid [50]. Plant-derived products, such as neem oil, neem cakes, and karanja seed extract, can also be used to inhibit NF. CRF should be used in places where the sensitivity to N losses is significant [51]. CRF treatment reduced N2O losses and N application rate in *Agriculture's Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N2O) and Its… DOI: http://dx.doi.org/10.5772/intechopen.113021*


**Table 2.**

*Different inorganic fertilizers management and N2O mitigation potential from rice-wheat fields.*

paddy rice by 26–50% without impacting yield [52]. However, CRF can be used as a sustainable strategy to minimize N losses in conjunction or as an alternative to urea [53]. Different inorganic fertilizers management and N2O mitigation potential from rice-wheat fields are showed in **Table 2**.

#### **4.3 Organic fertilizer management**

Organic fertilizers (OFs) such as biochar, manure, compost etc., offer soil bacteria with a variety of C compounds with diverse chemical compositions, ranging from labile to recalcitrant, that they can use to improve their growth rates and biomass during the mineralization process. OFs have dramatic, short- and long-term effects on the soil microbiome and are critical for soil health by increasing microbial activity, microbial interactions, and nutrient cycling [61]. Application and potential of different organic based fertilizers for mitigating N2O emission from rice wheat soil have been discussed below as well as shown in **Table 3**.

#### *4.3.1 Biochar application*

Recently, the use of biochar has been regarded as an effective method for improving soil fertility, agricultural productivity, and mitigating GHG emissions from soil [19]. Biochar contains unique properties such as a highly porous structure, C-rich fine grain and enhanced surface area [70], which can draw attention to an effective GHG mitigation technique [71]. Several research have been reported by various authors relating to the amendment of biochar and its impact on GHG generation [72]. Biochar has been shown to minimize N2O emissions by inhibiting NF and DNF processes or by promoting N2O reduction in soil. Recent meta-analyses have revealed that biochar reduces N2O emissions after application by an average of 20% [39]. Another study found that using biochar reduced N2O and NH3 emissions by 16.10% and 89.60%, respectively, as compared to a control treatment in rice crops [65]. Zhang et al. [69] reported that amendment of biochar at the rate of 10 t ha−1 and 40 t ha−1 significantly reduced the N2O emission by 58% and 74%, respectively when compared to field without biochar application. The use of biochar raises soil pH and causes N2O to be


**Table 3.**

*Different organic fertilizers management and N2O mitigation potential from rice-wheat fields.*

completely converted to N2, lowering N2O emissions [73]. However, the effect of biochar on N2O emissions varies depending on the amount of biochar used and soil parameters such as pH, C:N ratio, organic carbon, water status and microbial and enzymatic activity [74].

#### *4.3.2 Use of organic amendments*

Organic amendments (OA), which include compost, vermicompost, green manure, animal wastes (i.e., manures and slurries), etc., have been widely employed to reduce N fertilizer application, improve soil fertility and mitigate environmental deterioration [75]. Some studies have shown that OA increases N2O emissions through DNF by acting as an energy source for denitrifiers and promoting the establishment of anaerobic micro-sites within soil aggregates [76]. Other researchers, on the other hand, found that OA reduces N2O emissions by boosting N microbial absorption, reducing the availability of N substrates for N2O synthesis via NF and DNF [77]. A long-term study found that the amount of OA is crucial for organic carbon accumulation and the consequent impact on N2O emissions [78]. Furthermore, it is considered that the synthetic fertilizer substitution ratio by OA is a significant aspect in regulating N2O emissions [78]. Application of fermented manures a type of OA can minimize GHG emissions due to the rapid depletion of OM pools during fermentation [79]. Nayak et al. [44] exposed that using composted manure reduced N2O emissions considerably. In paddy soil, application of compost reduced N2O emissions by more than 50% when compared to urea [80]. When compared to fresh straw, the use of organic material produced by aerobic composting of rice straw significantly reduced N2O emissions [81], indicating that this strategy is environmentally favorable. Type of OA i.e., vermicomposting is a promising method that involves converting organic waste into compost in the presence of earthworms [82]. Because of the abundance of suitable resources, the material created as a result of their action has good structure and microbiological activity. In a rice study, the use of vermicompost reduced the transfer of NH4 + and NO3 − to water [83]. In contrast, the combined application of biochar and vermicompost impacted soil characteristics by increasing the abundance of nosZ genes and decreasing N2O emission [84]. As a result, combining biochar with vermicompost may be a potential way to reducing N2O emissions. Compost or manure *Agriculture's Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N2O) and Its… DOI: http://dx.doi.org/10.5772/intechopen.113021*

which is another type of OA, can help to enhance soil structure and nutrient availability to growing crops, reducing the demand for mineral fertilizer and thereby lowering GHG emissions [85]. Green manure crops such as Cowpea, Sesbania, Azzola, and Mungbean had a high ability to reduce N2O in rice fields [86]. Because of the gradual release of nitrogen from decaying green manure residue, plant uptake efficiency and crop production can be better aligned, while N leaching losses are decreased. Different organic fertilizers management and N2O mitigation potential from ricewheat fields are showed in **Table 3**.

#### **4.4 Crop management practices**

#### *4.4.1 Selection of plant cultivars*

The selection of suitable crop cultivars with improved resource use efficiency appears to be an auspicious and environmentally acceptable technique for minimizing N2O emissions from soil. Before selecting suitable crop cultivars, it is more important to investigate the mechanism of exudate and aerenchyma effects under field conditions, because variations among different types of crop cultivars have been linked to deviations in N2O emission production, oxidation, and transport capacities [87]. According to Baruah et al. [88], different rice cultivars have varying capacities for transporting N2O from paddy soil to the atmosphere, and these approaches are suitable for lowering GHG emissions. The physiological and anatomical properties of different rice cultivars may influence N2O emission. Rice plant shape and physiology regulate GHG emissions by giving energy sources to microorganisms via sloughed-off root cap [89]. Another study found that lower N2O emissions were associated with a plant strategy defined by more effectively N absorption [90]. Plant cultivars with higher N uptake were demonstrated to be able to reduce the N pool, particularly NO3 − , resulting in lesser substrate availability for denitrifiers and, as a result, lower N2O emission. Variation in N2O emission among cultivars has also been documented in grain and legume intercropping [91]. In another study, researchers observed that plants contribute significantly to N2O emissions and proposed that N2O emission is significantly controlled by plant characteristics in the soil-crop system [92].

#### *4.4.2 Modifying cropping schemes*

In paddy field, switching from conventional puddled transplanted rice (TPR) system to directly seeded rice (DSR) may contribute to reducing GHG emissions. Under the DSR method rice seeds are sown directly in the soil where they will grow instead of transplanting seedlings. DSR methods are classified as wet (pre-germinated seeds) or dry seeding. Wet sowing method involves broadcasting pre-germinated seeds into a puddled and leveled field that is free of standing water. However, standing water on the soil surface in conventional rice fields hinders the passage of oxygen from the atmosphere into the soil and microbial activities render the water-saturated soil practically devoid of oxygen, resulting in anaerobic conditions. Denitrification is the primary mechanism for N2O emission in TPR, because of the anaerobic conditions. In DSR, the main mechanism for N2O emission is nitrification, which takes place under aerobic condition. In fact, it was noticed that DSR increased N2O emission when the redox potential (RP) crossed 250 mV [93]. Therefore, in DSR water should be applied in such a way that RP be kept at a range of 100–200 mV to reduce N2O emissions. Furthermore, it was noted that the GWP of DSR can be further reduced by converting to no-tillage farming [94]. DSR's lower GWP and higher production rate imply that it would reduce N2O emissions. More extensive research involving GHG measurements under the concurrent effects of elements like as water, tillage, fertilizers, and biochar are, however, desperately needed to validate DSR as a feasible method that also minimizes the environmental impact.

#### **4.5 Integrated nutrient management**

Integrated nutrient management (INM) is the application of OA and inorganic fertilizers together to promote NUE and reduce N losses by coordinating crop demand with soil nutrient availability [36, 75]. Different components of INM are given in **Figure 5**. Some researchers compared the effects of NPK fertilizer, compost, and their combination on N2O emissions [36, 95]. They exposed that combining NPK and compost lowered N2O emissions when compared to using only compost or NPK. Furthermore, they proposed that applying composted material with a C:N ratio less than 20 considerably reduced N2O emissions due to the release of less N during soil decomposition. The longer breakdown of C and N, as well as the slower release of mineralized N, resulted in decreased N2O emissions when OA was used [96]. Huang et al. [97] observed a reduction in N2O emission with increasing C:N ratio plant amendments and observed that this relationship grows stronger with the addition of inorganic N. In line with the previous findings, study found that applying OA with a lower C:N ratio alone or OA with a higher C:N ratio in combination with

#### **Figure 5.**

*Different components of INM practices.*


#### **Table 4.**

*Different INM practices and N2O mitigation potential from rice-wheat fields.*

*Agriculture's Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N2O) and Its… DOI: http://dx.doi.org/10.5772/intechopen.113021*

inorganic fertilizers reduces N2O emissions without affecting crop productivity [98]. Application and potential of INM practices for mitigating N2O emission from rice wheat soil are shown in **Table 4**.

#### **5. Recent technological advancements and innovations in mitigation strategies of N2O emissions**

Several technological advancements and innovations have shown promise in further reducing N2O emissions in agriculture. While there might have been additional developments beyond that date, here are some of the notable advancements up to that point: (a) Precision agriculture technologies, such as GPS-guided equipment and sensor-based systems, enable farmers to apply fertilizers more efficiently and accurately. By precisely matching nutrient application to crop needs, these technologies can reduce nitrogen losses and subsequent N2O emissions. (b) Efficient irrigation systems, such as drip irrigation and sensor-based watering, can optimize water and nutrient application, reducing excess nitrogen leaching and subsequent N2O emissions. (c) Advancements in data analytics, remote sensing, and artificial intelligence can provide farmers with valuable insights into soil health, crop performance, and weather patterns. Access to real-time data can help optimize nitrogen management, leading to reduced N2O emissions. It is essential to note that while these technological advancements hold promise in mitigating N2O emissions, their effectiveness can vary depending on local conditions, farming practices, and the scale of implementation.

#### **6. Adoption of greenhouse technology for climate control**

The greenhouse cultivation for field crops comprises basis climate control parameters which depend on their design and complexity. It provides more or less climate control condition for plant growth and productivity [101]. This technology is beneficial in increasing crop production with limited resources and in harsh climate. Elimination of heat load is the main concern for greenhouse climate management basically in arid and semi-arid region and this can be done by reducing incoming solar radiation; removal of extra heat through air exchange; and increasing the fraction of energy partitioned into latent heat [102]. Considering shortage of resources, climate change, urbanization and population growth, the active smart greenhouse technology can support the countries food security while meeting the sustainability [103]. The current technology like fertigation, closed hydroponics, climate control systems (natural and forced ventilation, heating and fog systems and fan and pad systems) are used in greenhouses for sustainable production.

#### **7. N2O measurement techniques from soil**

N2O emissions from soil are largely affected by environmental variables such as substrate availability, redox potential and temperature etc., across various temporal and spatial scales. Therefore, it is necessary to understand the environmental variability of N2O emissions, to further quantify the scale of soil–atmosphere N2O exchange and create statistically viable measurement programmes to establish emission rates from plot to regional levels. The optimal method should be selected from the

viewpoint of cost, required accuracy, time consumption, and so on. Here we describe different N2O emission measurement techniques used by different researchers.

#### **7.1 Closed chamber technique**

The closed chamber technique is now the most extensively used measurement technique for estimating soil N2O emissions. This is simple to use, inexpensive and allows us to study treatment effects as well as to carry out specific process studies. The closed chamber is made of 6 mm thick acrylic transparent sheets (50 cm length, 30 cm width and 70/90/120 cm height) used for gas sampling [24]. In each sampling plot, U-shaped aluminum channels (50 cm × 30 cm) is inserted into soil to a depth of 15 cm well in advance to accommodate the chambers. The chamber is placed on the U-shaped channels at the time of sampling. During gas sampling the aluminum channel is filled with water, which acted as air seal when the chamber is placed on the channel. Air inside the chamber is thoroughly mixed or homogenized with a battery-operated fan before sampling. Air temperature inside the chamber and soil temperature at 5 cm depth is measured by using mercury thermometers while taking gas samples. Gas samples are collected from the chambers by airtight syringe (50 ml volume) fitted with a three-way stop cork at an interval of 15 min (0, 15, 30 and 45 min). Gas samples are brought to the laboratory immediately after sampling and analyzed for N2O concentrations using gas chromatograph (GC). However, there are several advantages to using a closed chamber technique, such as shortcomings related to environmental conditions (e.g., temperature effects, soil compaction, plant damage, disturbance of diffusion gradients [104], limited coverage of soil surfaces (usually less than 1 m2 ), which means that spatial heterogeneity is often not adequately addressed, collar insertion in the soil and root cutting, or temporal coverage of measurements [105].

#### **7.2 Fast-box method**

The fast-box approach is a new method that will be used to investigate spatial variability of trace gas fluxes [106]. An N2O analyzer (e.g. Tunable Diode Laser (TDL)) is coupled to a chamber in this setup. This allows for a large reduction in closure times, allowing chamber positions to be altered in minutes and spatial variability to be investigated. Closure durations of 30–60 min are usual with standard GC procedures.

#### **7.3 Micrometeorological measurements**

Micrometeorological measurement of N2O with TDL detection is based on the principle of diode laser absorption spectroscopy. It offers a non-intrusive, continuous spatially integrated measurement technique for detecting and quantifying baseline and episodic N2O emissions at the paddock scale. Pattey et al. [107], analyzed the wide variety of conceivable micrometeorolgical applications of TDL technology. The TDL measurements were made using the TGA-100A (Campbell Scientific Inc.). They were reported that dried air was sampled from the two heights at 3 s intervals, raw N2O measurements were taken at 10 Hz, and concentration data were averaged over 20 min. Micrometeorological approaches require homogeneous areas with a considerable fetch (>1 hectare) that are unaffected by structures, trees, hills, and other factors. For the straight fetch area, land use, land management, vegetation, and soil qualities should be uniform. These methods are most commonly used in flat terrain with vast, homogeneous land uses, such as pasture, grassland, maize, or wheat monocrops, woods, or tree plantations.

*Agriculture's Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N2O) and Its… DOI: http://dx.doi.org/10.5772/intechopen.113021*

#### **7.4 Modeling based approaches**

Over the last few decades, a wide variety of process models for modeling soil N2O emissions have been created, each of which is suitable to one or more specific ecosystem types (e.g., arable, grassland, forest) [108]. Models can be classified depending on their degree of complexity of the biogeochemical N cycle such as mineralization, nitrification, denitrification as well as trace gas production, consumption and emission processes.

#### **8. Role of policies and economic incentives in promoting N2O mitigation strategies**

Policy formulation should aim to encourage farmers to adopt mitigation methods that do not compromise their productivity and profitability. To promote the use of mitigation technology in agriculture, three main paths should be pursued: investments, incentives, and information. Agricultural output as a GHG source is unique due to its small-scale, dispersed nature, and often inadequate physical and institutional infrastructure. Policy initiatives should consider these variations and implement cost-effective payment schemes to incentivize and support agricultural mitigation efforts. Establish an extension system to assist farmers in adopting climate change mitigation practices. This support can include facilitating access to new markets, especially carbon markets, providing information on new regulatory systems, and informing farmers about government goals and policies related to climate change. Increase research funding to enhance our understanding of how climate change impacts agriculture. This includes studying the interactions between climate change and agricultural practices, which can lead to better forecasts and informed policies for long-term sustainable growth, particularly with a focus on pro-poor development. By implementing these policy approaches, the government can effectively encourage farmers to adopt mitigation methods that contribute to climate change mitigation while ensuring their agricultural productivity and economic well-being.

#### **9. Co-benefits and potential trade-offs associated with N2O mitigation strategies**

N2O mitigation strategies in agriculture can offer both co-benefits and potential trade-offs. These strategies aim to reduce nitrous oxide emissions from agricultural practices, thereby addressing its negative impact on climate change and the environment. However, the effectiveness of these strategies may vary, and they can have additional implications for agricultural productivity, soil health, and economic aspects. There are several co-benefits associated with N2O mitigation strategies. By implementing N2O mitigation strategies, such as better nitrogen management practices, farmers can help reduce greenhouse gas emissions and contribute to global efforts to combat climate change. Some N2O mitigation strategies, such as using cover crops, reduced tillage, and organic farming practices, can enhance soil health. These practices can increase soil organic matter, improve nutrient cycling, and enhance soil structure, leading to better water retention and reduced erosion. Implementing N2O mitigation measures often involves optimizing nitrogen use on farms. This can lead to better nitrogen use efficiency, which benefits farmers economically by reducing input costs and minimizing nitrogen losses to the environment. N2O is not the only nitrogen compound emitted from agricultural practices. Nitrogen runoff and leaching can lead to water pollution, affecting aquatic ecosystems and human water supplies. N2O mitigation strategies can also reduce other forms of nitrogen pollution, thereby improving water quality. Beside these co-benefits there are also some potential trade-offs associated with N2O mitigation strategies. Some N2O mitigation strategies, particularly those that involve reducing synthetic nitrogen fertilizers, can lead to decreased crop yields if not managed properly. Balancing nitrogen inputs to optimize both yield and environmental benefits can be challenging. Implementing certain N2O mitigation strategies may involve initial investments in new technologies or changes in farm management practices, which can impose additional costs on farmers. While some practices may have long-term economic benefits, short-term financial constraints can be a trade-off. Agricultural systems are complex, and the effectiveness of N2O mitigation strategies can vary depending on factors such as soil type, climate, and local management practices. The uncertainty associated with their outcomes can be a trade-off.

#### **10. Knowledge and capacity building in promoting N2O mitigation strategies**

The adoption of N2O mitigation strategies in agriculture requires more than just the availability of technologies and practices. Awareness campaigns, training programs, and knowledge-sharing platforms play a critical role in promoting the understanding and adoption of these strategies among farmers and stakeholders. These initiatives can address barriers to adoption, disseminate valuable information, and foster behavioral change toward sustainable agricultural practices. Many farmers might not be aware of the environmental impact of N2O emissions or the available mitigation strategies. Awareness campaigns can help disseminate knowledge about the link between agricultural practices, GHGs emissions, and climate change, thus creating a sense of urgency and responsibility among farmers. Training programs provide farmers and agricultural stakeholders with the necessary skills and knowledge to implement N2O mitigation strategies effectively. These programs can cover various topics, such as precision agriculture, improved fertilizer management, and soil health practices. Farmers might be hesitant to adopt new technologies due to unfamiliarity or uncertainty about their benefits. Knowledge-sharing platforms can showcase successful case studies, demonstrations, and testimonials from other farmers who have successfully implemented N2O mitigation practices. Different regions and farming systems have varying challenges and opportunities for N2O mitigation. Awareness campaigns and knowledge-sharing platforms can tailor information and strategies to suit specific contexts, making it more relevant and applicable for farmers. Overall, fostering awareness, providing relevant training, and establishing knowledge-sharing platforms are essential components of promoting the adoption of N2O mitigation strategies in agriculture.

#### **11. Conclusions**

It is becoming obvious that no single management strategies can result in increased crop yields and lower N2O emissions across the wide geographical areas. While site-tosite variability and climate influences on N2O emissions are significant, site-specific

*Agriculture's Contribution to the Emission of Greenhouse Gas Nitrous Oxide (N2O) and Its… DOI: http://dx.doi.org/10.5772/intechopen.113021*

adjustments in agricultural management strategies can provide remedies and should be given more attention. Understanding the mechanisms of N2O formation in ricewheat fields has led to the development of various mitigation techniques to reduce N2O emissions. Site-specific fertilizer management, modifying irrigation strategies such as AMD, intermittent irrigation and the use of DSR all help to reduce N2O emissions. N2O emissions can be reduced by using fermented manures, altering N fertilizer sources, timing, placement methods, applying NI, or using slow-release fertilizers. Similarly, biochar, compost, straw ash inclusion, and INM have the ability to significantly reduce N2O emissions while maintaining crop production. On the other hand, farmers will only accept mitigation techniques that do not reduce grain yield. More agricultural focus may be drawn to site-specific management adjustments and the use of technologies that will assist limit N losses via ammonia volatilization and nitrate runoff, leaching, and drainage pathways. The mitigation measures outlined above are scientific discoveries, but effective implementation of these options alone or in combination at the farmer level requires a deliberate policy and strong government backing. The policy to reduce or eliminate N2O emissions into the atmosphere will differ depending on the region or country and it will be heavily reliant on government financial assistance. However, in order for such techniques to be effective and fruitful in reducing GHG emissions and maintaining crop output in a changing environment, all social, economic, educational, and political barriers must be addressed. More research on climate-smart agriculture is needed to validate at the agricultural system level and to inform policymakers about the projected implications of climate change and the effectiveness of mitigation strategies.

#### **Acknowledgements**

Authors are grateful to SERB (File No. EEQ/2018/000125), GOI, New Delhi, India, for financial support and Central University of Jharkhand, Brambe, Ranchi, India, for facilitating and supporting the activities.

#### **Conflict of interest**

The authors declare no conflict of interest.

#### **Author details**

Raushan Kumar and Nirmali Bordoloi\* Department of Environmental Sciences, Central University of Jharkhand, Brambe, Ranchi, India

\*Address all correspondence to: nirmali.bordoloi@cuj.ac.in

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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### Section 2
