**1. Introduction**

As a result of anthropogenic activities, billions of tons of carbon dioxide deriving mainly from the burning of minerals fuels (oil, coal, and natural gas) as well as other gases, such as methane and nitrous oxide, are annually released into the atmosphere, thus changing the composition of the gases that have remained stable for tens of thousands of years [1, 2]. This overturning is expected to change drastically the climate in the next decades. Its dioxide coal is responsible for 50% of the atmosphere's overheating [3, 4].

Despite the environmental burden, the shifting to alternative forms of energy has begun from the oil crisis in the 1970s and the sudden rise in oil prices. This has led to the first boost for the development of renewable energy sources. In addition to food production, many governments supported the development of new cultivated plants for energy production [5, 6].

However, the fall in oil prices in the 1990s tempered the markets, resulting in hindering green energy development and limiting them to small ones.

Nevertheless in our day and age, global energy requirements have increased sharply due to the rapid increase in both the population and the technology. Therefore, alternative forms of energy are imperative. Research has shown that by 2030, the world's population will have grown from 6 to 8bn (33%) and the demand for energy will increase by 50% [7, 8].

Hopefully, there are many possible alternatives to fossil fuels, especially for heat and power generation. In recent years, we have seen a strong desire for some nations to reduce their confidence in fossil fuels and turn to new forms of energy. Three new markets have emerged for energy crop plants:


Energy crops are either cultivated or native species, traditional or new, which produce biomass as the main product that can be used for various energy purposes [11]. The biomass produced can be used for combustion or cogeneration for coal, electricity and heating as raw material for thermochemical processes such as pyrolysis and gasification for the production of methanol, biogas and pyrolytic oils and for biochemical processes (for example, fermentation) for the production of ethanol or methane [12, 13].

Their main advantage is that their stable production can ensure a large-scale long-term raw material supply with uniform qualitative characteristics in liquid biofuels and energy plants.

Traditional crops whose final product is used to produce energy and biofuels are also considered as energy crops, such as wheat, barley, maize, sugar beet, sunflower, etc.

"New" energy crops are species with high biomass productivity, per unit of land and divided into two categories which are agricultural and forestry. Agricultural energy crops are further distinguished in annual and multiannual years.

Biofuel compared with fossil fuels is considered to be more effective. For example with coal, oil and natural gas to produce 1 MJ of electricity; non-renewable energy consumption is projected to be between 1.7 and 4.2 MJ; biomass values range from 0.1 to 0.4 MJ. In the case of thermal energy, prices are 1.1 and 1.5 for fossil fuels and only 0.01–0.15 for biomass. Although the energy is considered to be CO2 neutral, in fact there is actually a burden on greenhouse gas emissions due to the process of cultivation and harvesting. However, this charge does not exceed the total emissions of fossil fuels which results in being up to 90% reduced [14].

The amount of land devoted to the cultivation of energy crops for biomass fuels is estimated to account for only 0.5–1.7% of the available agricultural land. Although there are still strong concerns about the production of plants for energy and not for the classic crops purposes such as fee [15], human food production [16] and other related issues [17], there is no doubt that plant biomass is of paramount importance in this field of renewable energy sources, particularly, in the production of biogas and biofuels, through well-designed and organized development programs [15, 18]*.*

### **2. Energy crops**

Energy crops include plants intended for energy production. One of their main strengths is stable production, which can ensure a large-scale, long-term raw material supply. In particular, new crops have significantly higher yields per unit area than conventional ones. Energy plants produce different types of biomass as main products, which can be used for various energy purposes [19].

**5**

*Maize as Energy Crop*

*DOI: http://dx.doi.org/10.5772/intechopen.88969*

**2.1 Advantage***s* **of energy crops**

maize and others can be used to produce biofuel gas [20, 21].

potentially eligible for energy crops in the United States.

dioxide released during combustion, unlike fossil fuels.

has significant economic social costs [23].

regional development of the country [24].

pollinated*,* both self and cross pollinated.

the genome of the plant [29].

transport [23].

cally negligible.

*2.1.1 Zea mays L.*

For the production of liquid biofuels, the energy crops that can be grown are: sunflower and soybeans. For the production of solid biofuels, plants such as cardoon, eucalyptus, canary grass and switchgrass can be used. Finally, sunflower,

There are many potential benefits using energy crops such as increased economic rural development, energy security and environmental benefits [22]. Rural economic development, a compulsory reason for producing energy from crops is the development of a new and profitable crop market taken into account that in recent years, crop prices have been extremely low, which means low profits. Energy crops can be planted in degraded cultivated land, pastures and land which is currently used for traditional crops. There are 392 million acres of land

Using energy crops to produce transport fuels could increase our energy security. Currently, the US is importing over 50% of the oil used for transport fuels and is estimating that imports could increase to 75%. Dependence on foreign imports

The environmental benefits of using energy crops include water and soil improvement. By reducing the use of herbicides and pesticides that reduces the chances of water pollution and other environmental problems are also reduced due to non-point pollution. Compared to traditional crops, energy crops have increased soil stability, reduced surface water run-off and reduced nutrient and sediment

Reducing the emissions of energy crops against fossil fuels for power generation unlike fossil fuels, plants grown for energy crops absorb the amount of carbon

Another advantage of using biomass is the avoidance of atmospheric pollution with sulfur dioxide (SO2) produced during combustion of fossil fuels which contributes to the phenomenon of "acid rain." The sulfur content of biomass is practi-

Finally, energy crops can ensure employment and the retention of rural populations in the border and other agricultural areas, thus contributing biomass to the

Maize (*Zea mays* L*.*) is a member of the *Poaceae* family. It originates from the American continent where thousands of ancient cultures, such as the Indians, the Magyars and the Aztecs, used to grow it. Today, it is one of the most popular cultivations around the world, such as the United States, China, India and Brazil and produces the largest quantities. Maize is a monocotyledon annual plant wind

Since the sixteenth century, its cultivation has spread to all tropical, semi-tropical and many temperate regions worldwide. It is a crop mainly used for human and animal nutrition [25], but in recent decades, the production of biofuels from maize has redefined the purpose of its cultivation. Today, the contribution of maize to biofuels and especially to bioethanol has increased at levels equal to or higher than all energy plants [26–28]. Nitrogen and ash concentrations as well as lignocellulose are two very important factors that define the quality of the raw material in ethanol. These characteristics, in most cases, are based on climatic conditions as well as on

#### *Maize as Energy Crop DOI: http://dx.doi.org/10.5772/intechopen.88969*

For the production of liquid biofuels, the energy crops that can be grown are: sunflower and soybeans. For the production of solid biofuels, plants such as cardoon, eucalyptus, canary grass and switchgrass can be used. Finally, sunflower, maize and others can be used to produce biofuel gas [20, 21].

### **2.1 Advantage***s* **of energy crops**

*Maize - Production and Use*

• bioenergy;

• biofuels; and

ethanol or methane [12, 13].

biofuels and energy plants.

for energy will increase by 50% [7, 8].

• biorenewable materials [9, 10].

new markets have emerged for energy crop plants:

2030, the world's population will have grown from 6 to 8bn (33%) and the demand

Hopefully, there are many possible alternatives to fossil fuels, especially for heat and power generation. In recent years, we have seen a strong desire for some nations to reduce their confidence in fossil fuels and turn to new forms of energy. Three

Energy crops are either cultivated or native species, traditional or new, which produce biomass as the main product that can be used for various energy purposes [11]. The biomass produced can be used for combustion or cogeneration for coal, electricity and heating as raw material for thermochemical processes such as pyrolysis and gasification for the production of methanol, biogas and pyrolytic oils and for biochemical processes (for example, fermentation) for the production of

Their main advantage is that their stable production can ensure a large-scale long-term raw material supply with uniform qualitative characteristics in liquid

considered as energy crops, such as wheat, barley, maize, sugar beet, sunflower, etc. "New" energy crops are species with high biomass productivity, per unit of land and divided into two categories which are agricultural and forestry. Agricultural

Biofuel compared with fossil fuels is considered to be more effective. For example with coal, oil and natural gas to produce 1 MJ of electricity; non-renewable energy consumption is projected to be between 1.7 and 4.2 MJ; biomass values range from 0.1 to 0.4 MJ. In the case of thermal energy, prices are 1.1 and 1.5 for fossil fuels and only 0.01–0.15 for biomass. Although the energy is considered to be CO2 neutral, in fact there is actually a burden on greenhouse gas emissions due to the process of cultivation and harvesting. However, this charge does not exceed the total emissions of fossil fuels which results in being up to 90% reduced [14]. The amount of land devoted to the cultivation of energy crops for biomass fuels is estimated to account for only 0.5–1.7% of the available agricultural land. Although there are still strong concerns about the production of plants for energy and not for the classic crops purposes such as fee [15], human food production [16] and other related issues [17], there is no doubt that plant biomass is of paramount importance in this field of renewable energy sources, particularly, in the production of biogas and biofuels, through well-designed and organized development

Energy crops include plants intended for energy production. One of their main strengths is stable production, which can ensure a large-scale, long-term raw material supply. In particular, new crops have significantly higher yields per unit area than conventional ones. Energy plants produce different types of biomass as main

products, which can be used for various energy purposes [19].

energy crops are further distinguished in annual and multiannual years.

Traditional crops whose final product is used to produce energy and biofuels are also

**4**

programs [15, 18]*.*

**2. Energy crops**

There are many potential benefits using energy crops such as increased economic rural development, energy security and environmental benefits [22]. Rural economic development, a compulsory reason for producing energy from crops is the development of a new and profitable crop market taken into account that in recent years, crop prices have been extremely low, which means low profits.

Energy crops can be planted in degraded cultivated land, pastures and land which is currently used for traditional crops. There are 392 million acres of land potentially eligible for energy crops in the United States.

Using energy crops to produce transport fuels could increase our energy security. Currently, the US is importing over 50% of the oil used for transport fuels and is estimating that imports could increase to 75%. Dependence on foreign imports has significant economic social costs [23].

The environmental benefits of using energy crops include water and soil improvement. By reducing the use of herbicides and pesticides that reduces the chances of water pollution and other environmental problems are also reduced due to non-point pollution. Compared to traditional crops, energy crops have increased soil stability, reduced surface water run-off and reduced nutrient and sediment transport [23].

Reducing the emissions of energy crops against fossil fuels for power generation unlike fossil fuels, plants grown for energy crops absorb the amount of carbon dioxide released during combustion, unlike fossil fuels.

Another advantage of using biomass is the avoidance of atmospheric pollution with sulfur dioxide (SO2) produced during combustion of fossil fuels which contributes to the phenomenon of "acid rain." The sulfur content of biomass is practically negligible.

Finally, energy crops can ensure employment and the retention of rural populations in the border and other agricultural areas, thus contributing biomass to the regional development of the country [24].

#### *2.1.1 Zea mays L.*

Maize (*Zea mays* L*.*) is a member of the *Poaceae* family. It originates from the American continent where thousands of ancient cultures, such as the Indians, the Magyars and the Aztecs, used to grow it. Today, it is one of the most popular cultivations around the world, such as the United States, China, India and Brazil and produces the largest quantities. Maize is a monocotyledon annual plant wind pollinated*,* both self and cross pollinated.

Since the sixteenth century, its cultivation has spread to all tropical, semi-tropical and many temperate regions worldwide. It is a crop mainly used for human and animal nutrition [25], but in recent decades, the production of biofuels from maize has redefined the purpose of its cultivation. Today, the contribution of maize to biofuels and especially to bioethanol has increased at levels equal to or higher than all energy plants [26–28]. Nitrogen and ash concentrations as well as lignocellulose are two very important factors that define the quality of the raw material in ethanol. These characteristics, in most cases, are based on climatic conditions as well as on the genome of the plant [29].

#### *2.1.1.1 Maize production*

The main root system of maize is rich and can reach a depth of 2.5 m, although its main bulk grows in the first 60 cm of soil.

The pH range for ideal yields is 6–6.5 while a range of 5.8–7 is generally shown, and there are reports that mention an even greater range of 5–8. Generally, attempts have been made to create varieties that adapt to high or low pH in acidic pH, expecting only 35% of ideal yields and being defined as an optimum pH of 6.8 [30].

The water requirements of maize range from 744 to 901 mm. The irrigation frequency affects the yield of corn seed as they propose an irrigation program where a dose of 15% of the water capacity of the soil will be applied irrigation every 9 days [31, 32].

Increased salinity results in reduced plant leaves, decreased green weight, fresh weight, shorter shoots and root lengthening. However, varieties that are ideally adapted to conditions of high salinity have been developed, as they have particular durability [33, 34]. Still hybrids with respect to pure maize rows show greater tolerance to salts [35].

Corn seed germination may be affected even slightly from 28°C or above as the activity of certain protein-producing enzymes is inhibited by this critical temperature and then [36]. When the temperature increases (in the range of 13–38°C), there is a similar increase in leaf growth rate and photosynthesis rate. Also it was found an increase in photosynthesis rate by increasing the temperature (study range, 13–28°C).

The nutrition of the cobbler in continuously cultivated soil suggests 17–23 kg of nitrogen per hectare, while when there is an increase in organic matter, the addition may be twice as low. For high yields, it is necessary to add potassium as a mature crop of maize which may contain up to 30 kg of potassium per hectare in its plant parts. An experiment in Brazil showed that nitrogen application increased the productivity of grains and dry matter, the calorific power, and the potential for energy generation from maize. Maximum grain yield was obtained with an application of 226 kg ha<sup>−</sup><sup>1</sup> N, resulting in 13.647 kg ha<sup>−</sup><sup>1</sup> of grain yield and 10.968 kg ha<sup>−</sup><sup>1</sup> of total biomass. This biomass presents an energy potential of 11.050 kWh ha<sup>−</sup><sup>1</sup> . Taking the use of only husks and cobs into consideration, it is possible to generate 2712 kWh ha<sup>−</sup><sup>1</sup> of bioenergy [37].

Like energy crops, maize is mainly used for two reasons: (i) for the starchy raw material contained in seeds and the material from which bioethanol is mainly produced [38, 39] and (ii) for the biomass (crop residues) resulting from the removal of the seeds and consisting of leaves, stems and a cone of the blade. Biomass can be used for combustion or production of second-generation bioethanol [27, 40, 41].

The appropriate time of harvesting is when the moisture content of the seeds is between 20 and 30% [42]. Late maturation and flowering of maize cause a greater accumulation of lumps with reduced grain yields and a reduced number of cores per plant.

Maize requires more nitrogen and pesticides than many other crops, thus affecting its energy balance. Increasing the energy potential with ethanol from maize is significantly less than with sugar cane [43].

The choice of varieties with a dry matter content of 30–32% is very important for harvesting date to facilitate the process. Based on the system, FAO maize needs about 45 units of heat to form a new real leaf and about 300 units of heat to fully populate the plant. Early varieties (FAO 150–160) require about 2100 heat units, late (FAO 180–210) approximately 2400 units, while biogas crude maize hybrids (FAO 240–260) require a longer period of 2800–3000 heat units.

**7**

**Table 2.**

**Table 1.**

*Maize as Energy Crop*

**3. Βiofuels**

**3.1 Biodiesel**

*3.1.1 Production*

*DOI: http://dx.doi.org/10.5772/intechopen.88969*

each continent separately, up to 2017.

The use of corn-based biofuels was first introduced into the US as a food additive, but ethanol-maize production increased drastically when conventional fuel prices doubled between 2004 and 2007. Biofuels and rising food prices have contributed to the accumulation of wealth in the agricultural sector, thus increasing the income of farmers, potential value to agricultural land and shifting the relative allocation of resources to the agricultural sector in relation to the rest of the economy [44].

The use of biofuels in the transport sector has become very timely recent years. In **Tables 1** and **2** below, we can see the liquid biofuel production globally and in

The European Commission has adopted the Biofuels Directive in 2009, which

The two main substitutes for conventional fuels are biodiesel and bioethanol. Biodiesel is used in diesel-powered vehicles, while bioethanol is used in gasolinepowered vehicles. The European Union is the major biodiesel producer. USA, Brazil, Argentina, Indonesia and Thailand along with the EU together produce 85% of all biodiesel worldwide. In 2016, 32.6 billion liters of biodiesel were produced globally. Global biodiesel production is expected to reach 39 billion liters by 2024, corresponding to a 27% increase from 2016. It is important to point out that the cost of biodiesel from the first generation biodiesel feedstock is currently 30% higher than of petroleum-based diesel [48]. Furthermore, it is estimated that 60–80% of the biodiesel production cost stems from the cost of raw materials. All this makes use of low-cost second generation biodiesel feedstock which is very attractive alternative [49].

Europe is the world's largest biodiesel producer (**Figure 1**). Total European production in 2016 is estimated at over 1.5 million tons, with Germany and France

Total 15.9 34.1 94.4 125 132 143 Bioethanol 12.2 24.5 60.5 82.0 85.6 biodiesel 0.78 3.42 18.9 28.9 32,6 — Other biofuels 2.97 6.16 15.0 14.6 13.6 —

Total 0.07 101 13.9 19.3 0.29 Biogasoline 0.07 72.1 5.95 4.42 0.2 Biodiesel 0.00 12.5 7.48 13.7 0.06 Other Biofu. 0.00 16.0 0.47 1.13 0.00

*Liquid biofuel production globally (all values in billion liters) [45].*

*Liquid biofuel production in continents in 2016 [45].*

**2000 2005 2010 2015 2016 2017**

**Africa Americas Asia Europe Oceania**

requires biofuels to contribute 10% of all transport fuels by 2020 [46, 47].
