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

Stanford University, Stanford CA

Investigators

Abstract

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.