Identification of critical dry spells for irrigation planning

Rainfall distribution in India is characterised by several wet and dry spells. Hence irrigation has to be planned to meet the crop water needs during the dry spells that become critical to crop growth. A criterion was developed to identify the critical dry spells in a given climate-crop-soil situation taking into account the soil moisture depletion from crop root zone, stage of crop growth, a root growth model and pan evaporation. Analysis of daily rainFall data From the command area of the 0–53 major distributary of Sri Ram Sagar Project (SRSP). Andhra Pradesh, indicated that crop specific critical dry spells occur in kharif season (June-October) and that all the dry spells in rabi season (November-March) become critical to all crops. Starting dates of critical dry spells and the standard week numbers recommended For irrigation to different crops were identified.