ANALYZING THE LIMITATIONS SET BY CLIMATIC FACTORS, GENOTYPE, AND WATER AND NITROGEN AVAILABILITY ON PRODUCTIVITY OF WHEAT .2. CLIMATICALLY POTENTIAL YIELDS AND MANAGEMENT STRATEGIES

The objectives of this paper are to establish the climatically determi ned potential grain yields of wheat for different locations of India, to quantify the gap between actual and potential yields and to determi ne the optimal levels of irrigation and N required for given productiv ity levels. The analysis is based on simulations made with the crop gr owth model WTGROWS. Simulated potential grain yields, determined by so lar radiation and temperature, varied between 2.56 and 8.25 t ha(-1) f or 138 Iodations spread throughout India, In general, yields increased with latitude and inland locations had greater yields than the coasta l locations at the same latitude. These trends were related to mean te mperature differences over latitude/location. The results indicate a s trong linear decline in grain yield as mean temperature increased. Lat e sowings had smaller yields as well as increased variability. The dec rease for each day's delay in sowing was more when potential yield was high. The yield gap was at least 2 t ha(-1) irrespective of location and a significant portion of this was due to delayed sowing. Crop simu lation with different amounts of nitrogen and irrigation inputs showed significant interaction between water and N availability as well, as inter-seasonal climatic variability, particularly with low input of wa ter. The optimal N application depended on the amount of water availab ility. Yield variance of stressed wheat crops is moderated greatly by irrigation but reduced N fertilizer application may modify the respons e.