OPTIMAL SIZE OF UNLINED ON-FARM POND FOR SIXTY PER CENT RICE SUBSTITUTION IN RAINFED UPLAND

摘要

The rainfed uplands of eastern India are facing two major problems viz. low productivity of rice (Oryza sativa L.) and low cropping intensity. Introduction of on-farm pond (OFP) in this topo-sequence, of course, is found to be a suitable measure for drought mitigation, but failed to ensure supplemental irrigation to second crop in winter grown in the same field. Consequently, the technology could not pick up due to its poor economic viability. In pursuit of harvesting two crops in sequence from uplands, the concept of partial rice substitution (PRS) along with harvesting rainwater in OFP was introduced. The PRS was accomplished by dividing the existing rice field into two compartments of maize (Zea mays L): rice at various substitution ratios such as 70:30, 60:40, 50:50, 40:60, and 30:70. The maize was grown in the upstream and the rice in the downstream compartments. In winter, the maize and rice compartments were replaced by black gram (Vigna mungo L.) and mustard (Brassica campestris), respectively. Water balance models for crop compartments and the OFP were developed to simulate soil moisture and available water storage, respectively. The optimal size of unlined OFP was simulated based on the present worth analysis of the system. The optimal size of the unlined OFP for the average land holding size in the region (1200 m2) with 60% rice substitution was found to be occupying 6% area of the crop field based on net profit and other economic indicators.