Calculation of Crop Coefficient With Meteorological Data

Crop coefficient was estimated with Penman-Monteith formula and the NWSE (Non-Water Stress Evapotranspiration) model driven with daily meteorological and crop data during reviving and harvest of winter wheat. The results showed that crop coefficient varies among years and remains a clear trend during growth season. When surface soil water content is set at 60% of field capacity approximately, the average crop coefficient of years estimated with NWSE model fits well with the experimental data. The average standard deviation and variation coefficient of crop coefficient estimated with NWSE model were 0.13 and 0.12 respectively. Analysis shows that the effect of net radiation, relative humidity and wind speed on crop coefficient variation is obvious, but the effect of temperature is negligible. Crop coefficient increases as wind speed increases, or net radiation or relative humidity declines.