Use of crop water stress index as indicators for scheduling irrigation in winter wheat

Canopy-ambient air temperature differences(Tc-Ta)for six irrigation treatments of winter wheat were monitored during booting to grain filling period at Luancheng Station from 2000 to 2001 season．The results showed that the midday Tc-Ta was closely related to soil moisture condition Soil moisture at 60％ of field capacity for the 1m soil profile of winter wheat corresponded with the changing of Tc-Ta from positive to negative． For a non-water-stressed treatment，Tc-Ta was negatively related to the atmospheric vapor pressure difference(VPD)．A baseline equation of Tc-Ta with VPD was established to calculate the Tc-Ta under non-water-stressed condition for the purpose of calculation of crop water stres index(CWSI)．The relation of average CWS1 with grain yield was non-linear．With the decrease in CWSI，grain yield increased．When CWS1 was at about 0．1～ 0．2，the grain yield of winter wheat reached the optimum ． Thus，the average CWSI at 0．1～ 0 2 might be taken as the indicator for irrigation scheduling of winter wheat．