Yield gap analysis and the effect of nitrogen and water on photoperiod-sensitive Jasmine rice in north-east Thailand

Yield constraint analysis using a combination of experiments and crop growth models has been useful for quantifying the relative role of yield-limiting factors, and for prioritizing management interventions aimed at increasing the yields of non-photoperiod-sensitive rice grown under rainfed conditions. The use of a systems approach for photoperiod-sensitive varieties is constrained by the lack of crop growth models that can simulate the varieties’ photoperiod response. This study used data from the literature, from a controlled-growth experiment, and from multi-location field experiments to determine the photoperiod-sensitivity parameters of Jasmine rice grown in north-east Thailand, and incorporated these in the ORYZA2000 model. Next, the model was used to analyse yield gaps by comparing yields in farmers’ fields with the simulated attainable yields with an adequate N supply (60 kg ha−1) under irrigated conditions. The ORYZA2000 model adequately simulated growth, development, and yield of Jasmine rice over a 0–150 kg N ha−1 range under irrigated and normal to above-normal rainfall conditions. The simulated attainable yields ranged from 3.47 to 5.96 Mg ha−1. A simulated yield gap of 1.76 Mg ha−1 (41%) currently exists in rainfed rice farmers’ fields. Yield gaps could be substantially reduced by 1.48 Mg ha−1 (34%) through improved N-management practices. The yield gap caused by water limitation was small (0.02 Mg ha−1, <1%) during the study period, when rainfall was normal to above normal. The large yield gap beyond the farmers’ current fertilizer level suggests considerable scope for increasing yields through site- and time-specific nutrient management. A long-term simulation study including years with rainfall below normal is needed to comprehensively quantify yield gaps caused by water limitation. Such long-term simulation is hindered by the lack of long-term groundwater depth measurements.