The portion of rainfall that infiltrates into the soil is influenced by soil type, slope, crop canopy, and storm intensity. Effective rainfall is best determined through observation. If runoff occurs, the efficiency will be reduced. Rainfall amounts of less than 0.3 inch are not effective as these small quantities are quickly lost to evaporation. Irrigation Net irrigation is that amount of water actually stored in the soil profile which adds to the water balance.
Gross irrigation is the total amount of water applied by the irrigation system.
See NebGuide G78-393, Water Measurement Calculations , to calculate the amount of water applied to a field. Efficiency of irrigation systems. Crop water use changes as the crop grows and also responds to changes in the environment. An estimate of future crop water use may also be obtained from these sources. Contact your Cooperative Extension Service or Natural Resources District offices for availability of crop water use reporting.