Field evaluation of basal crop coefficients for corn based on growing degree days, growth stage, or time

Basal crop coefficients for estimating corn evapotranspiration that are based on time do not account for variations in plant development that occur due to differences in growing season temperature, hybrid maturity length, and planting date. Crop coefficients based on growing degree days (GDD) or observed growth stage (GS) are available that would adjust to abnormal growing conditions. This article reports the results of Colorado field tests of corn basal crop coefficients derived in Nebraska based on either GS or GDD. These crop coefficients were tested for a range of planting dates and corn hybrid maturities. Generally, these crop coefficients estimated corn evapotranspiration (ETcorn) more closely to water balance measurements of ET than did time-based (TB) crop coefficients. Coefficients based on observed growth stage or growing degree days simplify ET prediction and irrigation scheduling because adjustments for abnormal environmental conditions or planting dates are not necessary.