Rainwater harvesting options for rice–maize cropping system in rainfed uplands through root-zone water balance simulation

• Root-zone water balance models for upland rice and maize fields were developed.
• Soil moisture balances of rice and maize crop fields were simulated.
• Need and scope of rainwater harvesting for the crops in uplands were assessed.
• Rainwater harvesting with rice substitution ensured double cropping in rainfed upland.

A root-zone water balance model was used to simulate the soil moisture storage of maize (Zea mays L.) and rice (Oryza sativa L.) fields in rainfed uplands of eastern India. The simulation study revealed that short duration (95 days) rice fields in uplands remained under ponding condition for a period of 32 days during the entire growing season. Based on the ponding depth requirement in rice fields (50 mm), excess ponding was found for seven days only out of the 32 days of ponding. In contrast, the maize field under similar length of growing season (95 days) and topographic condition could produce harvestable runoff for 23 days. Furthermore, the rice crop was to remain under moisture stress for eight days during its mid-season stage, whereas the maize was found to be without stress during entire growing season. Before sowing of winter crops, the soil moisture in the seeding zone was determined to be depleted below germination soil moisture for 18 and 19 years out of 30 years of simulation in rice and maize fields, respectively. This implies that a second crop, following withdrawal of monsoon, is not possible without pre-sowing irrigation in three out of five years in rainfed uplands. Thus, complete substitution of rice by maize in uplands would create a better scope for rainwater harvesting. Alternatively, partial replacement of rice could be a viable option for meeting both rice demand of the people and harvesting of adequate rainwater for supplemental irrigation to crops in rainy and winter seasons.