Modern agriculture has significantly disrupted the global phosphorus cycle through heavy use of fertilizers derived from non-renewable sources of mined phosphates, which accumulate in agricultural soils and greatly increase the potential for nutrient loading and eutrophication in connected ecosystems. Utilizing ecological processes and approaches to soil fertility management in the context of regionalized food systems has been proposed as an excellent means of addressing these issues and increasing food system resilience. Yet alterations to farm soils can hinder the ability of farmers to close nutrient loops and utilize ecological soil management practices. This analysis utilizes a holistic soil health approach to examine soil phosphorus cycling and soil fertility resilience on regional vegetable farms that sell their produce through a network of farmer’s markets in New York City. This analysis assesses 1) the sets of soil fertility practices used by farmers in this regional context, 2) how closely linked these practices are to the importation of mined phosphorus, and 3) the extent to which these management practices are able to close phosphorus nutrient loops and utilize in situ soil resources. To address these questions, soil from farm fields (n=227) was assessed with a suite of biological (organic matter, labile carbon, labile organic phosphorus, phosphatases, soil respiration) and chemical (soil test phosphorus, pH, cation exchange capacity) assays, and nutrient supply networks were mapped based on information from farmer interviews.
Farmers in this study tend to fall into three general categories: biomass-based fertility, mineral fertility, and synthetic fertility. Links between farm field fertility and mined phosphorus are longest among biomass-based fertility farms, yet nearly all farms in this analysis depend on the regular importation of non-renewable forms of phosphorus. Chemical soil analyses show no significant differences among management groups, with 85% of farm fields having excessive levels of soil test phosphorus. Preliminary results from biological assays find that farm fields amended primarily with biomass have greater potential for ecological nutrient cycling, yet the majority of farm soils exhibit only low to medium reliance on in situ phosphorus resources. These findings suggest that building more resilient soil fertility through regionalization must focus on capacity building among farmers so that they can develop more renewable sources of fertility, and soil ecologies that can effectively support in situ nutrient cycling.