Increasing rainfed rice productivity in Central Java, Indonesia: a modeling approach

The typical rainfed cropping system in Central Java includes a dry-seeded rice crop grown from November to February (gogorancah), followed by a transplanted rice crop from March to June (walik jerami). This study assessed the climatic and agrohydrologic constraints to rice production and explored management strategies to increase the yield and yield stability of the double-rice cropping system using the crop growth simulation model ORYZA2000. The model was parameterized and evaluated using eight seasons of field experiments from 1995 to 2000 in Jakenan Experiment Station. The root mean square error between simulated and measured grain yields is considered low (10-20%). Simulation of potential and rainfed rice yield was carried out on a 15-d planting interval for the period 1977-2000. The average simulated potential yield of walik jerami rice was higher than that of gogorancah rice, indicating that radiation and temperature are not determinants of the observed relatively low yields of walik jerami rice. Simulated rainfed yields of walik jerami crops declined sharply if planted later than early March. Deep tillage, additional N fertilizer, and supplemental irrigation increased the yields of rainfed walik jerami crops. The results highlight the importance of timely planting and management to increase rice yields and yield stability in the area.