Irrigators needs to plant for higher populations to optimize yields. Surface Cover and Tillage. The amount of soil surface cover influences soil evaporation. When the soil surface is wet, evaporation depends on the amount of radiant energy at the soil surface. Lowest evaporation rates occur from shaded and mulched soil surfaces.
Crops shade more and more of the soil as they grow, but soil evaporation continues.
However, crop residues can reduce soil evaporation by 1-3 inches during the irrigation season. Availability of Soil Water. Research shows soil water content cannot be considered alone as the single factor controlling whether crop ET is reduced below its potential rate. The ability of soil to transmit water to plant roots and the actual evaporative demand for a given day also are important. For progressively drier soil, actual crop ET is below the demand rate.