**2. Environmental factors affecting crop yields**

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, pathogens, weeds, vertebrate pests) and anthropogenic evolution.

#### **2.1 Abiotic constraints**

#### *2.1.1 Effects of climatic conditions on crops*

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

**11**

*2.1.1.1 Drought*

*environment (b) [13].*

**Figure 1.**

*Factors Affecting Yield of Crops*

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

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

*General effects of climate change in agricultural production (a), the positive and negative impacts in the* 

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

millet yield and summer maximum temperature.
