Factors Influencing Crop Water Requirements for Irrigation
See Also: Crop Water Requirement
The following are the factors which affect on the water requirements of the crops,
In hot climate the evaporation loss is more and hence the water requirement will be more and vice versa.
A certain crop grown in a sunny and hot climate needs more water per day than the same crop grown in a cloudy and cooler climate. There are, however, apart from sunshine and temperature, other climatic factors which influence the crop water need. These factors are humidity and wind speed. When it is dry, the crop water needs are higher than when it is humid. In windy climates, the crops will use more water than in calm climates.
The highest crop water needs are thus found in areas which are hot, dry, windy and sunny. The lowest values are found when it is cool, humid and cloudy with little or no wind.
From the above, it is clear that the crop grown in different climatic zones will have different water needs. For example, a certain maize variety grown in a cool climate will need less water per day than the same maize variety grown in a hotter climate.
Table 4 - AVERAGE DAILY WATER NEED OF STANDARD GRASS DURING IRRIGATION SEASON (mm)
For the various field crops it is possible to determine how much water they need compared to the standard grass. A number of crops need less water than grass, a number of crops need more water than grass and other crops need more or less the same amount of water as grass. Understanding of this relationship is extremely important for the selection of crops to be grown in a water harvesting scheme (see Chapter 6, Crop Husbandry).
Table 5 - CROP WATER NEEDS IN PEAK PERIOD OF VARIOUS CROPS COMPARED TO THE STANDARD GRASS CROP
As different crops require different amount of water for maturity, duties are also required. The duty would vary inversely as the water requirement of crop.
The influence of the crop type on the crop water need is important in two ways.
a. The crop type has an influence on the daily water needs of a fully grown crop; i.e. the peak daily water needs of a fully developed maize crop will need more water per day than a fully developed crop of onions.
While, for example, the daily water need of melons may be less than the daily water need of beans, the seasonal water need of melons will be higher than that of beans because the duration of the total growing season of melons is much longer.
Data on the duration of the total growing season of the various crops grown in an area can best be obtained locally. These data may be obtained from, for example, the seed supplier, the Extension Service, the Irrigation Department or Ministry of Agriculture.
Table gives some indicative values or approximate values for the duration of the total growing season for the various field crops. It should, however, be noted that the values are only rough approximations and it is much better to obtain the values locally.
If the water table is nearer to the ground surface, the water requirement will be less & vice versa.
If the slope of the ground is steep the water requirement will be more due to less absorption time for the soil.
It is directly related to water requirement, the more the intensity greater will be the water required for a particular crop.
In sandy soil water percolates easily so water required is more. While in clayey soils water requirement is less.
In sprinkler method less water is required as it just moist the soil like rainwater whereas in flood more water is required.
In deep ploughing less water is required and vice versa.