*Factors Affecting Yield of Crops DOI: http://dx.doi.org/10.5772/intechopen.90672*

*Agronomy - Climate Change and Food Security*

sustainable crop production [5].

**2. Environmental factors affecting crop yields**

pathogens, weeds, vertebrate pests) and anthropogenic evolution.

the environment.

**2.1 Abiotic constraints**

*2.1.1 Effects of climatic conditions on crops*

Organic crop production is one of the alternative agricultural practices promoted for the reduction of environmental pollution. As a result, several countries have introduced organic farming practices to replace the chemical-dependent ones [11]. To conserve and regenerate soil properties, the maintenance of soil organic matter (SOM) has received considerable attention. Although SOM is considered key to soil health, its relationship with yield is contested because of local-scale differences in soils, climate, and farming systems. The relationship between these factors should be quantified and proper soil management strategies set up to ensure

The impact of climate change in our agricultural systems is undoubtable. For example, drought followed by intense rain can increase the flooding potential, thereby creating conditions that favor fungal infestations of leaves, roots and tuber crops. In addition, reduction of bees' density due to global climate change has led to local extinction of several plant species [12]. The production of enough food to match population growth while preserving the environment is a key challenge, especially in the face of climate change. This chapter will review factors affecting yields of crops and provide some strategies to overcome yield loss while preserving

The environmental factors affecting crop yields can be classified into abiotic and biotic constraints. Actually, these factors are more intensified with global warming which leads to climate change. Abiotic stresses adversely affect growth, productivity and trigger a series of morphological, physiological, biochemical and molecular changes in plants. The abiotic constraints include soil properties (soil components, pH, physicochemical and biological properties), and climatic stresses (drought, cold, flood, heat stress, etc.). On the other hand, biotic factors include beneficial organisms (pollinators, decomposers and natural enemies), pests (arthropods,

Variations in annual rainfall, average temperature, global increase of atmospheric CO2, and fluctuations in sea levels are some of the major manifestations of climate change, which negatively impact crop yields [13]. Temperature and rainfall changes are expected to significantly have negative impact on wide range of agricultural activities for the next few decades. With the changing of climate, agriculture faces increasing problems with extreme weather events leading to considerable yield losses of crops. Most often, crop plants are sensitive to stresses since they were mostly selected for high yield, and not for stress tolerance. Climate change is the result of global warming. It has devastating effects on plant growth and crop yield which can affects directly, indirectly, and socio-economically reduce crop yields by up to 70% [14] (**Figure 1a**). Weather variations present positive and negative effects in the environment with very high expression of negative effects (**Figure 1b**). The regression analysis model between historical climatic data and yield data for food crops over the last 30 years in Nepal showed an increase in temperature of approximately 0.02–0.07°C per year in different seasons and a mixed trend in precipitation [15]. Additionally, no significant impact of climate variables on yields of all crops was observed and the regression analysis revealed negative relationships

**10**

#### **Figure 1.**

*General effects of climate change in agricultural production (a), the positive and negative impacts in the environment (b) [13].*

between maize yield and summer precipitation, between wheat yield and winter minimum temperature, and finally positive relationship was observed between millet yield and summer maximum temperature.

### *2.1.1.1 Drought*

Drought refers to a situation in which the amount of available water through rainfall and/or irrigation is insufficient to meet the evapotranspiration needs of the crop [16]. Climate change is driven by changes in water availability (volumes and seasonal distribution), and in water demand for agriculture and other competing sectors. The impending climate change adversities are known to alter the abiotic stresses like variable temperature regimes and their associated impacts on water

availability leading to drought, increased diseases and pest's incidence and extreme weather events at local to regional scale [16]. Moisture or drought stress accounts for about 30–70% loss of productivity of field crops during crop growth period [16]. Drought stress can induce abscisic acid (ABA) accumulation in guard cells to trigger stomatal closure [17]. Drought also results in abnormal metabolism that may reduce plant growth, and/or cause the death of entire plant. Drought has different effects at different stages of plant growth with the most sensitive growth stage being flowering period.

### *2.1.1.2 Heat stress*

Heat stress is the rise in temperature beyond a threshold level for a period sufficient to cause permanent damage to plant growth and development [18]. The Intergovernmental Panel on Climate Change (IPCC) projected rise of the temperature by 3–4° by 2050 [19, 20]. High temperature regimes due to climate change affect the percentage of seed germination, photosynthetic efficiency, crop phenology, reproductive biology, flowering times, pollen viability and pollinator populations [16, 21]. Under heat stress at reproductive growth stage, the increase of temperature prevents the swelling of pollen grains, which results in poor release of pollen from the anther at dehiscence. Heat stress is deleterious to plant developmental stages, including generation and function of reproductive organs. Furthermore, variable temperature regimes may result in unpredictable disease epidemics across geographic regions in the world. Heat stress contributed about 40% to overall yield loss of wheat [22], 1.0–1.7% yield loss per day in maize for every raise in temperature above 30°C [23].

#### *2.1.1.3 Cold stress*

Cold or chilling stress experiences by plants from 0 to 15°C [24], leads to major crop losses. Various types of crops in tropical or subtropical origin are injured or killed by non-freezing low temperatures, and exhibit different symptoms such as poor germination, stunted seedlings, chlorosis, or growth retardation, reduced leaf expansion and wilting and necrosis. In general, plants respond with changes in their pattern of gene expression and protein synthesis when exposed to low temperatures [25]. In general, plants from temperate climatic regions are considered to be chilling tolerant with variable degree compare to tropical and sub-tropical crops, and can increase their freezing tolerance by cold acclimation [26].

#### *2.1.1.4 Soil properties*

Soils are the uppermost part of the earth's crust, formed mainly by the weathering of rocks, formation of humus and material transfer. They vary in terms of origin, appearance, characteristics and production capacity. Soil fertility is the ability of a soil to deliver nutrients needed for the optimum growth of a specified crop. Soil fertility is one of the most important factors in crop production [10]. It has the ability to support crop production determined by the entire spectrum of its physical, chemical and biological attributes. Soil fertility is one important aspect of soil productivity since it is a major source of micronutrients (Fe, B, Cl, Mn, Zn, Cu, Mo, Ni) and macronutrients (N, P, K, Ca, S, Mg, C, O, H) that are needed for plant growth. The lack of these nutrients in the soil causes deficiencies in plants, and their excess leads to toxicities, which have negative impacts on crop yields.

**13**

*Factors Affecting Yield of Crops*

several years.

*2.1.1.6 Floods*

*DOI: http://dx.doi.org/10.5772/intechopen.90672*

*2.1.1.5 Soil salinity and acidity stress*

but will facilitate the entry of Na+

Several parameters can be used to determine the fertility status of a soil. Among them, the soil fertility index was found to be the most useful indicator that helps to improve sustainable land use management and achieve economical yield in crop production [27]. In several regions in the world, some croplands have undergone human-induced soil degradation resulting in poor yield production per unit area of crop harvest. Around 40% of agricultural lands are affected by human induced land degradation. Intensive agricultural production characterized by overuse of fertilizers and chemicals without adherence to agricultural sustainability leads to a decline of soil health, land degradation and severe environmental problems [28]. It is important to note that the deterioration of soil fertility normally takes pace over

Salinity stress affects crop production in over 30% of irrigated crops and 7% of dry land agriculture worldwide [29]. It is one of the major problems affecting crop production all over the world since around 20% of cultivated land and 33% of irrigated land are salt-affected in the world [30]. Salt causes osmotic stress and ionic toxicity in crop plants. Under normal conditions, the higher osmotic pressure in plant cells permits the absorption of water and essential nutrients from a soil solution into the root cells. However, under salt stress conditions, the high concentration of salts in the soil solution prevents absorption of water and essential minerals

toxic effects on cell membranes as well as on metabolic activities in the cytosol [31]. Low soil pH increases as a result of release of acidifying aluminum, iron and manganese ions, leaching of base ions such as calcium, magnesium, potassium and sodium, decomposition of soil organic matter and regeneration of organic acids, nitrification of ammonia-based fertilizers [32, 33] as well as land management practices. Low soil pH significantly affects crop growth and therefore decreases yield. In

Floods entail different stressful conditions to plants, mainly depending on water depth and its duration. Soil waterlogging damages most crops, with the exception of rice, which like other wetland species thrives when plants are not completely submerged. In view of the changing climate, flooding has become frequent in many lowlands and cultivated areas every year and causes a lot of damage to human

Flooding usually occurs with heavy rainfall, poor soil drainage and poor irrigation practices. Soil waterlogging has negative impacts on crop production especially for dryland species (such as most cereals, legumes, tubers, etc.) which include several crops. The excess water results in complex changes in plant physiology for non-adapted crops. This leads to restriction of gas diffusion between the plant and its surroundings (accumulation of high CO2 and ethylene in the root zone with very low O2), hypoxia (oxygen levels limit mitochondrial respiration) and anoxia (respiration is completely inhibited), often accompanied by increased of mobilization of 'phytotoxins' in reduced soils, leading to poor root metabolism (inability to absorb nutrients), lack of energy within plant cells, restriction of photosynthetic activities

The first constraint for plant growth under flooding conditions is the immediate lack of oxygen necessary to sustain aerobic respiration of submerged tissues [35–37].

maize for instance, soil acidity causes yield loss of up to 69% [34].

beings including losses in crop yields and food stuffs.

and therefore poor growth or death of plant roots and shoots.

and Cl<sup>−</sup> ions into the cells, which will have direct

#### *Factors Affecting Yield of Crops DOI: http://dx.doi.org/10.5772/intechopen.90672*

*Agronomy - Climate Change and Food Security*

being flowering period.

*2.1.1.2 Heat stress*

ture above 30°C [23].

*2.1.1.4 Soil properties*

*2.1.1.3 Cold stress*

availability leading to drought, increased diseases and pest's incidence and extreme weather events at local to regional scale [16]. Moisture or drought stress accounts for about 30–70% loss of productivity of field crops during crop growth period [16]. Drought stress can induce abscisic acid (ABA) accumulation in guard cells to trigger stomatal closure [17]. Drought also results in abnormal metabolism that may reduce plant growth, and/or cause the death of entire plant. Drought has different effects at different stages of plant growth with the most sensitive growth stage

Heat stress is the rise in temperature beyond a threshold level for a period sufficient to cause permanent damage to plant growth and development [18]. The Intergovernmental Panel on Climate Change (IPCC) projected rise of the temperature by 3–4° by 2050 [19, 20]. High temperature regimes due to climate change affect the percentage of seed germination, photosynthetic efficiency, crop phenology, reproductive biology, flowering times, pollen viability and pollinator populations [16, 21]. Under heat stress at reproductive growth stage, the increase of temperature prevents the swelling of pollen grains, which results in poor release of pollen from the anther at dehiscence. Heat stress is deleterious to plant developmental stages, including generation and function of reproductive organs. Furthermore, variable temperature regimes may result in unpredictable disease epidemics across geographic regions in the world. Heat stress contributed about 40% to overall yield loss of wheat [22], 1.0–1.7% yield loss per day in maize for every raise in tempera-

Cold or chilling stress experiences by plants from 0 to 15°C [24], leads to major crop losses. Various types of crops in tropical or subtropical origin are injured or killed by non-freezing low temperatures, and exhibit different symptoms such as poor germination, stunted seedlings, chlorosis, or growth retardation, reduced leaf expansion and wilting and necrosis. In general, plants respond with changes in their pattern of gene expression and protein synthesis when exposed to low temperatures [25]. In general, plants from temperate climatic regions are considered to be chilling tolerant with variable degree compare to tropical and sub-tropical crops, and can

Soils are the uppermost part of the earth's crust, formed mainly by the weathering of rocks, formation of humus and material transfer. They vary in terms of origin, appearance, characteristics and production capacity. Soil fertility is the ability of a soil to deliver nutrients needed for the optimum growth of a specified crop. Soil fertility is one of the most important factors in crop production [10]. It has the ability to support crop production determined by the entire spectrum of its physical, chemical and biological attributes. Soil fertility is one important aspect of soil productivity since it is a major source of micronutrients (Fe, B, Cl, Mn, Zn, Cu, Mo, Ni) and macronutrients (N, P, K, Ca, S, Mg, C, O, H) that are needed for plant growth. The lack of these nutrients in the soil causes deficiencies in plants, and their

excess leads to toxicities, which have negative impacts on crop yields.

increase their freezing tolerance by cold acclimation [26].

**12**

Several parameters can be used to determine the fertility status of a soil. Among them, the soil fertility index was found to be the most useful indicator that helps to improve sustainable land use management and achieve economical yield in crop production [27]. In several regions in the world, some croplands have undergone human-induced soil degradation resulting in poor yield production per unit area of crop harvest. Around 40% of agricultural lands are affected by human induced land degradation. Intensive agricultural production characterized by overuse of fertilizers and chemicals without adherence to agricultural sustainability leads to a decline of soil health, land degradation and severe environmental problems [28]. It is important to note that the deterioration of soil fertility normally takes pace over several years.

#### *2.1.1.5 Soil salinity and acidity stress*

Salinity stress affects crop production in over 30% of irrigated crops and 7% of dry land agriculture worldwide [29]. It is one of the major problems affecting crop production all over the world since around 20% of cultivated land and 33% of irrigated land are salt-affected in the world [30]. Salt causes osmotic stress and ionic toxicity in crop plants. Under normal conditions, the higher osmotic pressure in plant cells permits the absorption of water and essential nutrients from a soil solution into the root cells. However, under salt stress conditions, the high concentration of salts in the soil solution prevents absorption of water and essential minerals but will facilitate the entry of Na+ and Cl<sup>−</sup> ions into the cells, which will have direct toxic effects on cell membranes as well as on metabolic activities in the cytosol [31].

Low soil pH increases as a result of release of acidifying aluminum, iron and manganese ions, leaching of base ions such as calcium, magnesium, potassium and sodium, decomposition of soil organic matter and regeneration of organic acids, nitrification of ammonia-based fertilizers [32, 33] as well as land management practices. Low soil pH significantly affects crop growth and therefore decreases yield. In maize for instance, soil acidity causes yield loss of up to 69% [34].

### *2.1.1.6 Floods*

Floods entail different stressful conditions to plants, mainly depending on water depth and its duration. Soil waterlogging damages most crops, with the exception of rice, which like other wetland species thrives when plants are not completely submerged. In view of the changing climate, flooding has become frequent in many lowlands and cultivated areas every year and causes a lot of damage to human beings including losses in crop yields and food stuffs.

Flooding usually occurs with heavy rainfall, poor soil drainage and poor irrigation practices. Soil waterlogging has negative impacts on crop production especially for dryland species (such as most cereals, legumes, tubers, etc.) which include several crops. The excess water results in complex changes in plant physiology for non-adapted crops. This leads to restriction of gas diffusion between the plant and its surroundings (accumulation of high CO2 and ethylene in the root zone with very low O2), hypoxia (oxygen levels limit mitochondrial respiration) and anoxia (respiration is completely inhibited), often accompanied by increased of mobilization of 'phytotoxins' in reduced soils, leading to poor root metabolism (inability to absorb nutrients), lack of energy within plant cells, restriction of photosynthetic activities and therefore poor growth or death of plant roots and shoots.

The first constraint for plant growth under flooding conditions is the immediate lack of oxygen necessary to sustain aerobic respiration of submerged tissues [35–37].

**Figure 2.** *Different levels of excess of water in crop environment [38].*

As the duration of flooding increases, there is progressive decrease in soil reductionoxidation potential (redox potential) [38] (**Figure 2**). Flooding events can be classified by two categories: waterlogging where only the root system inside the soil is affected [39]; and submergence, where also parts or the whole shoot are under water [40]. In tree species with different flooding sensitivity, the importance of root-toshoot transport of metabolites to 'use rather than lose' is a relevant criterion used to identify the tolerant species [41]. Only non-wetland plants can survive flooding for a short period of time. The two survival strategies to flooding are plant avoidance of oxygen deficiency in tissues and the adaptation to oxygen deficiency [42].
