The factors affecting the water requirement of crops are:

1) Type of soil, its texture, water holding capacity and drainage conditions:

The pores in a soil mass can be broadly classified into two types: 

i) large pores or non-capillary pores, and 

ii) small pores or capillary pores. 

Large pores do not hold water tightly, and hence a large amount of the water held by the soil is quickly drained off under gravity. 

On the other hand, small pores hold a large amount of water tightly and prevent it from being drained off under gravity. The relative magnitudes of the two types of pores in a soil depend on its texture and structure. 

In general, a sandy soil has large pores which result in better drainage and aeration but low-water holding capacity. 

On the other hand, a clayey soil has small pores which result in better water-holding capacity but poor drainage and aeration. 

Moisture extraction by the plant in the clayey soils is resisted by large forces and is difficult. 

Loams are ideal soils which posses fairly good moisture-holding properties and have good drainage and aeration as well. Such soils release their moisture relatively easily at low-suction.

The greater the porosity (or void ratio) of a soil, the greater is the water-holding capacity. The clayey soils because of their high porosity have a large water-holding capacity as compared to sandy soils.

The water held by the soil is extracted by the roots of the plants. This extraction of water is resisted by some forces in the soil which are greater in the case of clayey soils than in the sandy soils. Thus the large quantity of water held by clayey soils may not be easily available to plants. Hence in sandy soils water water requirement is more. While in clayey soils water requirement is less.

In loams, the small pores (capillary pores) and the large pores (non-capillary pores) are almost equal in number in the total pore space. Such a soil has enough number of small pores to have an adequate water-holding capacity and at the same time, enough number of large pores to permit adequate drainage and aeration. Loams are therefore ideal soils for cultivation.


 2) Sub-Soil Water Table:

Water requirements for the crop depend on the position of the water table. Water requirement will be less if the water table is nearer to the ground surface. 

But if the water table is much below to the ground surface, therefore water requirement will be more.

3) Slope of Ground:

If the ground slope is steep. The water flows down quickly along the slope of the land, and the soil gets less time to absorb required moisture for their growth, that means the water loss is more for steep ground. Hence, the water requirement will be more.

But if the ground is flat, the water flows gently and the soil gets enough time to absorb the required moisture. so the water requirement is less.

4) Climatic factors: 

Evapo-transpiration from the plants depends upon the climatic factors, such as temperature, wind, humidity and sunshine hours. 

Water requirements are more when the temperature is high and the humidity is low. Evaporation from plants and soil increase with wind velocity and hence more ater is required. 

Water requirements are also more if the sunshine hours are long, as in the case of long sunny days. If there is natural rainfall during the growth period, the water requirements are correspondingly reduced.

5) Method of Application of Water:

In surface method, evaporation loss is more. Hence, more water required to overcome the loss of water due to evaporation.  

But in sub-surface method, evaporation loss is less, so water requirement will be less.

6) Intensity of Irrigation:

It is directly related to water requirement, the more the intensity greater will be the water required for a particular crop.

7) Socio-economic factors:

The socio-economic factors and the skill of the cultivators also affect the water requirements of the crops. 

Practices which are based on superstitions and prejudices are prevalent in some regions. 

The cultivators do not easily adopt the scientific methods which are conducive to more economical use of water. These factors should be considered while arriving at the optimum water requirements for different crops in such regions.

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