PRF/J: Nutrient Cycling as a Measure of Agroecosystem Sustainability

该项目将通过比较中国古代复杂农业生态系统中的养分循环和传统农场的养分循环，将养分循环与农业生态系统的长期生产力联系起来。由于氮往往是这类系统中的限制性养分，氮(N)循环是本研究的主要重点，其他营养循环也有待于在有用的情况下进行表征。N循环模式将从村级农业生态系统的年度N转移预算中模拟出来。将比较N循环的食物链和营养链模型区分农业生态系统行为的能力，并评估各种计算方法在量化养分循环中的适用性。氮素循环措施与投入产出效率标准和土壤氮库大小相结合，将得到氮素循环效率指数。该指数将与生态可持续性有关，以数百年来保持高产的中国农业生态系统为基准。然后，将使用N循环指数来评估豆类种植对可持续农业生态系统生产力的当代重要性。中国传统农业生态系统及其衍生的生态农场是基于生态原理的环境管理的显著例子。这类系统的养分循环模式与只使用传统化学养分管理的中国农场形成了极好的对比。所有三种农业生态系统类型(传统、生态农场、常规)都可以在中国的同一生物气候区域找到；在比较研究中，所有三种类型的组合构成了发展可持续发展衡量标准的独特机会。

This project will relate nutrient cycling to long term productivity of agroecosystems by comparing nutrient cycles that prevail under agricultural methods in ancient and complex Chinese agroecosystems with those of conventional farms. With nitrogen often being the limiting nutrient in such systems, nitrogen (N) - cycling is the main focus of the study, with other nutrient cycles to be also characterized where useful. N-cycling patterns are to be modeled from annual N-transfer budgets of village-scale agroecosystems. Food web and trophic chain models of N-cycling will be compared for their ability to differentiate agroecosystem behaviors, and various calculations will be assessed for their suitability in quantifying nutrient cycling. A nitrogen-recycling-efficiency index will be derived from N-cycling measures combined with input/output efficiency criteria and soil N pool size. This index will be related to ecological sustainability using as a benchmark Chinese agroecosystems that have sustained high yields for centuries. The contemporary importance of legume cultivation to sustained agroecosystem productivity will then be evaluated using the N- recycling index. %%% Traditional Chinese agroecosystems and the eco-farms derived from them are striking examples of environmental management based upon ecological principles. Nutrient cycling patterns of such systems provide an excellent contrast to Chinese farms that use only conventional chemical nutrient management. All three agroecosystem types (traditional, eco-farm, conventional) may be found in the same bioclimatic area of China; the combination of all three types in a comparative study constitutes a unique opportunity to develop measurements of sustainability.