Interaction Of Sowing Date And Climatic Variability
The effect of sowing wheat at different dates was simulated for all 138 locations (Das and Karla, 1995). It was apparent that as potential yield increased. The reduction in yield per day delay in sowing also increased. In general, the yield decrease was between 0.25% and 0.75% of potential yield when the latter was less than 4% hari, between 0.5 to 1.00% for yield potential between A and 6% hart and between 0.75 to 1.00% for yield potentials greater than 6. It is interesting first irrespective of potential yield, a few location showed a small yield reduction (less than 0.25%) with delayed sowing. For New Delhi environment, the maximum grain yield was obtained for sowings done between 1 and 15 November.
The effect of varying amounts of post sown irrigation for wheat was tested for New Delhi environment with WIGROWS model in relation to the seasonal climatic variability (using 20 years runs from 1971 – 93). The amount of moisture at the time of sowing was assumed to be 75% of the field capacity. The amount of water applied at each irrigation was assumed to be 60 mm. Nitrogen application at the rate of 150 kg hart was applied at the time of sowing. The result showed increased yield with increase in number of post sown irrigations and stabilizing beyond three irrigation. Variability width seemed to be dependent of the amount of post – son water received. It is decreased with increase in post – son water received. It is decreased with increase in post – son water received by the crop, indicating the reduced effect of climatic variability on yields under increment moisture availability condition. The variability index values ranged from about 0.59 up to one irrigation to around 0.135 (beyond for irrigations) with intermediate values of 0.42 (Two irrigations) and 0.20 Three