Estimation of crop coefficients for sprinkler-irrigated winter wheat and sweet corn using a weighing lysimeter

Crop water demands for sprinkler-irrigated winter wheat and sweet corn were measured using a weighing lysimeter located in Beijing. Then the coefficients of two crops were calculated. The results showed that the relationships between crop coefficient and days after seeding can be represented by a fourth-order polynomial equation for both crops. Single and dual crop coefficients for winter wheat and sweet corn were computed based on the method recommended by FAO-56 and compared with the observed data. The comparison indicated that the variation of crop coefficients during the growing season for sprinkler-irrigated crops of Northern China Plains could be described by the patterns recomrnended by FAO-56, but the computed crop coefficients were usually smaller than the observed values. The single and basal crop coefficients suggested by FAO-56 were therefore modified based on the observed results and crop water demands for winter wheat and sweet corn were simulated. A good agreement between the simulated and the observed crop water requirements was obtained for different growing periods of the two crops.