Unevendistribution pattern of monsoon rain and highly permeable soil type and poorrainwater management practices effect the crop yield. Also lands remain barrenin winter season due to lack of rainfall. There is need for rainwaterconservation and its optimum utilization for achieving maximum return from thefield. Daily water balance model for crop field and the on farm reservoir (OFR)is developed based on mass balance approach to assess water availability in theOFR and moisture content in the field. A Dynamic Programing (DP) model isdeveloped to allocate optimum supplemental irrigation to crop for receivesmaximum net annual return from the cropped area under land and wateravailability constraints in the OFR based rainfed agricultural system. The decisionvariable is optimum allocation of supplemental irrigation from the OFR anddecision interval is standard week. This model requires soil data, crop data,meteorological data and different level of water management strategies asinputs.
The model integrates the dynamics associated with the water released bysupplemental irrigation from the OFR to the actual water utilized by the cropsat farm level. It also takes into account the non-linear relationship of rootgrowth, soil moisture dynamics for multiple crops and yield response to waterdeficit at various growth stages of the crops. The DP model is simulated for 5%to 12% field area (800 m2 field) and economic benefits from thecrops takes into accounted for optimum size of OFR.Based on aforementioned modeling approach, optimum sizingof the on-farm reservoir will be determine that will provide supplementalirrigation to rice in monsoon season, to mustard in rabi season. Apply this model to 800 m2 fields that theoptimum size of the OFR varies with the combination of the crop (rice or rice -mastered) and the size of OFR reduces in 15% soil moisture depletion factorthan 10% soil moisture depletion factor also the OFR size is less for rice thanrice – mustard scenario.