Dissertation Research: Phosphorus mobilization by legume cover crops in agricultural systems

农业生产力常常受到土壤养分（包括磷）可用性的限制。土壤中磷的有效性是有限的，因为大多数土壤磷不能直接被植物利用，而自然输入不足以取代收获所去除的磷。因此，需要施用肥料或粪肥来保持土壤肥力和产量，但经济上可行的磷储量正在下降，农业系统的磷损失使水生生态系统退化。本项目评估覆盖作物，特别是豆科作物，是否能够在为经济作物提供磷肥力的同时，通过动员土壤磷（将土壤矿物质和有机质中的磷转化为植物可利用形式）来减少磷的投入需求。中心目标是确定不同种类的覆盖作物如何调动磷。要做到这一点，互补的方法？长期试验的田间测量、温室研究和磷预算的计算？将被使用。将对不同形式的土壤磷、动员磷的过程、磷从覆盖作物向经济作物的转移率以及覆盖作物动员磷相对于农场规模上其他磷通量的总体重要性采取措施。该项目将有助于制定替代施肥策略，既能保持土壤肥力，又能减少昂贵的磷肥投入。它将测试使用覆盖作物是否有助于实现这一目标，并提供对不同植物生长的土壤中磷转化的更好理解。由于该项目的结果应与农场从业人员直接相关，因此这项研究将与广泛传播结果的外展活动相结合，包括公开提供数据，为覆盖作物数据库作出贡献，并通过在学术界以外举行的活动（实地考察日、非技术出版物）传播知识。该项目还将涉及本科生，并为他们提供生态系统科学的基础培训。

Agricultural productivity is often limited by the availability of soil nutrients, including phosphorus (P). Phosphorus availability in soils is limited because most soil P is not directly available to plants and natural inputs are insufficient to replace P removed by harvest. Applications of fertilizers or manures are thus required to maintain soil fertility and yields, but economically viable P reserves are declining and P losses from agricultural systems degrade aquatic ecosystems. This project evaluates whether cover crops, especially legumes, could provide P fertility for cash crops while reducing P input requirements by mobilizing soil P (converting P bound to soil minerals and organic matter into plant-available forms). The central objective is to identify how different species of cover crops could mobilize P. To do so, complementary approaches ? field measurements in long-term experiments, greenhouse studies, and computation of P budgets ? will be used. Measures will be taken of different forms of soil P, processes that mobilize P, transfer rates of P from cover crop to cash crop, and the overall importance of P mobilization by cover crops relative to other P fluxes at the farm scale.This project will contribute to the development of alternative fertilization strategies that could maintain soil fertility while reducing costly P inputs. It will test whether using cover crops could contribute to this goal and provide a better understanding of P transformations in soils where different plant species grow. Because results from this project should be directly relevant to farm practitioners, this research will be coupled with outreach activities to disseminate results widely, including making the data publicly available, contributing to cover crop databases, and transferring knowledge through activities held outside of academic circles (field days, non-technical publications). This project will also involve undergraduate students and provide them with basic training in ecosystem science.