Improving resource use efficiency in rice-based cropping systems: experimentation and modelling

Key words: Nitrogen; Yield; Rice; Wheat; Environment; Simulation; Soil; Organic matter; Water; Denitrification To cope with the projected increase in food demand and increased environmental concerns, rice-based cropping systems combining high resource use efficiencies and high yields will be increasingly important. By combining experimental research with crop growth simulation, this study aims at a better quantitative understanding of crop production and nitrogen dynamics in irrigated rice-wheat (RW) systems to improve N management as a basis for the design of RW systems that combine high yields with high N use efficiencies. The various field experiments included different rice genotypes, environments, and N fertilizer and water management. Experimental data was used to evaluate the rice crop growth model ORYZA2000, which performed satisfactorily. The model was applied to explore options for different N management regimes combining high yields and high nitrogen use efficiency, and to identify the relative importance of environmental factors affecting yield and nitrogen use efficiency. Average rice yields of around 10-11,000 kg ha^‑1 were simulated with fertilizer N rates of around 200 kg ha^‑1, with high nitrogen use efficiency in three equal splits at transplanting, panicle initiation and booting at Nanjing, China. Indigenous soil N supply affects yield and internal N use efficiency (INUE, kg grain per kg N uptake) more than weather at low N rate, but its effect is reduced at high N rate. Temperature contributes more than radiation to the variation in rice yield, N uptake and INUE. The study resulted in better understanding of the relationship between yield and N dynamics in rice-based systems and in a RW model integrating existing crop and soil models and using results from own experiments. This model is a promising research tool to design and to develop rice-based cropping systems with high yields and high resource use efficiencies.