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What factors determine how much irrigation water a crop needs?

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Large wheeled irrigation sprinkler sprays water over green crops in a field, with mountains and cloudy sky in the background. — Irrigation Specialized irrigation equipment watering crops in a field.

The amount of irrigation water a crop requires is determined by a combination of weather conditions, the specific type of crop being grown, and the characteristics of the soil.1

Key Factors Influencing Water Needs

Weather and Climate: Atmospheric conditions significantly impact water loss through evapotranspiration, which is the primary driver of water loss during crop growth. Key variables include solar radiation, temperature, wind, and atmospheric vapor pressure. Additionally, the frequency and amount of natural rainfall dictate how much supplemental irrigation is necessary.213
Crop Characteristics: Different plants have varying water requirements based on their species, stage of growth, drought tolerance, and the density and depth of their root systems. For example, rice typically requires significantly more water than cereal grains or cotton.41
Soil Properties: The soil itself influences irrigation needs through its texture, structure, and water-holding capacity.4
System Losses: Beyond the direct needs of the plant, irrigation planning must account for water lost to evaporation and seepage during transport to the fields.14