Risk analysis for rice ratooning

Experiments have demonstrated that lock-lodging, a new ratooning method, consistently produced higher grain yield than conventional methods. On-farm experiments have shown, however, that ratooning was risky. Success of the ratoon crop was strongly dependent upon conditions being favorable for crop growth in the period immediately following stubble lodging. Should short-term waterlogging, submergence, or cloudy conditions coincide with the critical period of ratoon tiller emergence, fewer ratoon tillers would survive. If weeds or diseases were carried over from the main crop, yield of the ratoon would be reduced. Also, if a farmer relied on rainfall or had only a limited capacity for supplementary irrigation toward the end of the wet season, the ratoon crop may fail due to drought stress. The objective of this study was to examine the sensitivity of a ratoon crop to conditions which may be encountered over a range of seasons and with different standards of crop management. Modifications were made to the CERES-Rice model to permit it to stimulate the performance of a ratoon crop. This required a reduction in the juvenility phase in order to align crop phenology and leaf area development in the second crop. Data from field experiments conducted at IRRI in 1993 and 1994 were used to develop the routine, which was validated against data from experiments conducted in Camarines Sur, Laguna [Philippines] and Iloilo. Sensitivity analysis was used to determine which factors were most likely to adversely affect performance of a ratoon crop. Finally, cumulative distribution functions for grain yield were obtained for ratoon crops grown at Iloilo and Tarlac under fully irrigated or rainfed conditions. These functions were used to assess the risks associated with ratoon cropping for different locations, seasons, and management systems