Plant-soil interactions in changing rice cropping systems: Nutrient balances and yield gap analysis

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While phase I of ICON mainly addressed the risks and trade-offs associated with an aerobic soil phase in rice-based systems on the research site at IRRI, phase II will focus on the opportunities and potential agronomic benefits of these emerging cropping patterns and expand the studies to the major rice-growing environments in Luzon. The integration of an aerobic soil phase offers opportunities for crop diversification, residue management and nutrient cycling. In the predominating rice double cropping system, straw is generally removed and burnt. The application of straw to upland crops, on the other hand, is common practice in many production systems in Asia and elsewhere. Application of rice straw in the post-rice niche allows for the return of substantial amounts of K and Si, the temporary microbial immobilization of soil nitrate, enhancement of soil (micro-)biological activity and improvement of soil physical attributes. In addition, straw mulch can reduce variations in topsoil moisture and thus possibly mitigate crack formation.The yield gaps (differences between the potential or achievable, and farmers¿ actual yields) are relatively large in most rice-growing environments of the Philippines. We hypothesize that these yield gaps can be partially closed through improvements associated with residue return and the integration of upland crops and leguminous cover crops in the niche following wet season rice. The extent of such effects depends on prevailing edaphic conditions and farming systems¿ attributes. In four major rice-growing environments of Luzon (incl. the core experiment at IRRI), we shall compare the agronomic performance and quantify partial yield gaps in different cropping and management systems (rice double crop vs. rice ¿ upland crops, with / without straw mulch, with / without ¿nitrate catch crops¿). Actual farmer¿s and simulated (ORYZA2000) potential yields, as well as nutrient balances and agronomic attributes of both rice and the dry season crops will be determined in farmer¿s-managed field plots and in researcher-managed subplots (dry season crop and residue management) at each site. Yield data will be subjected to frontier and to partial yield gap analyses. Seasonal soil N dynamics during the dry-to-wet and the wet-to-dry transition seasons will be determined under different management scenarios, and partial nutrient balances will be established. Selected treatment combinations will subsequently be evaluated regarding their effects on soil biota (SPs 1, 2, and 3), soil physical attributes, incl. crack formation (SP 4), trace gas emissions (SP 5 and 7) and water budgets (SPs 6 and 7). Possible extrapolation domains for relevant options and their impact on closing the yield gap will be specified.