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

在国际水稻研究所的研究地点，ICON的第一阶段主要解决水稻系统中好氧土壤阶段的风险和权衡，第二阶段将重点关注这些新兴种植模式的机会和潜在的农艺效益，并将研究扩展到吕宋岛的主要水稻种植环境。好氧土壤阶段的整合为作物多样化、残留物管理和养分循环提供了机会。在占主导地位的水稻双熟制中，秸秆一般被除去并焚烧。另一方面，在亚洲和其他地方的许多生产系统中，将秸秆应用于旱地作物是常见的做法。在水稻后生态位中施用稻草可以使大量的钾和硅返回，暂时固定土壤硝酸盐的微生物，增强土壤（微）生物活性和改善土壤物理属性。此外，秸秆覆盖可以减少表层土壤水分的变化，从而可能减轻裂缝的形成。在菲律宾的大多数水稻种植环境中，产量差距（潜在或可实现产量与农民实际产量之间的差异）相对较大。我们假设，这些产量差距可以通过与残茬还田和旱地作物和豆科覆盖作物在旱地作物生态位的整合相关的改进来部分缩小。这种影响的程度取决于当时的土壤条件和农业系统的特性。在吕宋岛的四个主要水稻种植环境中（包括国际水稻研究所的核心试验），我们将比较不同种植和管理制度（水稻双季作与水稻旱作，有无秸秆覆盖，有无硝酸盐捕获作物）的农艺表现并量化部分产量差距。实际农民和模拟（ORYZA2000）的潜在产量，以及水稻和旱季作物的营养平衡和农艺性状将在每个站点的农民管理的田间地块和研究人员管理的子地块（旱季作物和秸秆管理）中确定。收益数据将进行前沿和部分收益差距分析。在不同的管理方案下，确定干湿过渡季和湿转干过渡季土壤氮的季节性动态，建立部分养分平衡。随后将评估选定的处理组合对土壤生物群（SPs 1、2和3）、土壤物理属性（包括裂缝形成（SPs 4））、微量气体排放（SPs 5和7）和水预算（SPs 6和7）的影响。将详细说明相关期权的可能外推范围及其对缩小收益率差距的影响。

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.