Urban agriculture has been expanding rapidly in recent years, and it has the potential to recycle nutrients from local food wastes into new foods through the use of compost as growth medium. Composts typically have low nitrogen: phosphorus (N:P) ratios, and in urban gardens, when composts are typically applied to soils annually to meet the N demand of crops, excess P can build up and be proneto leaching. We measured dissolved P (PO4 3−) and N (NO3 − & NH4 +) losses in the leachate from experimental raised-bed garden plots that received one of two commonly used composts (municipal organics compost derived from food scraps or cow manure derived compost) at three different application levels (15%, 35%, or 50% by volume). PO4 3− concentrations in leachate from garden plots receiving manure composts were high, ranging from 5 to 11 mg/L, depending on the application level. Leachate PO4 3− concentrations from plots receiving municipal organics composts were an order of magnitude lower, ranging from 0.5−1.2 mg/L, while leachate PO4 3− in garden plots receiving no compost was 0.3 mg L−1. Cumulative mass of PO4 3− lost through leachate during the growing season ranged from 1.2 to 4.2 g/m2 for manure compost treatments, compared to 0.12– 0.72 g/m2 for municipal compost treatments, and 0.06 g/m2 for soil with no compost. Leachate accounted for 0–37% and 18–45% of dissolved P and N exported from garden plots, respectively. The high application rate of municipal compost significantly increased crop yield relative to the control treatment. P lost from leachate and removed through harvest only represented 1–10% of total P applied as compost, suggesting that soil build-up was the dominant fate of P in this study. Our results illustrate the potential trade-off in urban agriculture between crop production and recycling P efficiently from urban food waste.
compost, nitrogen, nutrient leaching, nutrient recycling efficiency, phosphorus, urban agriculture, water quality
 Burger, J.R., Allen, C.D., Brown, J.H., Burnside, W.R., Davidson, A.D., Fristoe, T.S., Hamilton, M.J., Mercado-Silva, N., Nekola, J.C., Okie, J.G. & Zuo, W., The Macroecology of Sustainablility. PLoS Biology 10, p. e1001345, 2012.
 Rees, W.E. & Wackernagel, M., Appropriated carrying capacity: Measuring the natural capital requirements of the human economy. Investing in Natural Capital: Ecological Economics Approach to Sustainability, ed. A. Jansson, M. Hammer, C. Folke & R. Costanza, Island Press: Washington, DC, pp. 362–390, 1994.
 Baker, L.A., Can urban P conservation help to prevent the brown devolution? Chemosphere, 84(6), pp. 779–784, 2011. https://doi.org/10.1016/j.chemosphere.2011.03.026
 Grewal, S.S. & Grewal, P.S., Can cities become self-reliant in food? Cities 29(1), pp. 1–11, 2012. https://doi.org/10.1016/j.cities.2011.06.003
 Brown, K. & Jameton, A., Public health implications of urban agriculture. Journal of Public Health Policy, 21(1), pp. 20–39, 2000. https://doi.org/10.2307/3343472
 Smit, J. & Nasr, J., Urban agriculture for sustainable cities: using wastes and idle land and water bodies as resources. Environment and Urbanization, 4(2), pp. 141–152, 1992. https://doi.org/10.1177/095624789200400214
 Kleinman, P.J.A., Allen, A.L., Needelman, B.A., Sharpley, A.N., Vadas, P.A., Saporito, L.S., Folmar, G.J. & Bryant, R.B., Dynamics of phosphorus transfers from heavily manured coastal plain soils to drainage ditches. Journal of Soil and Water Conservation, 62, pp. 225–235, 2007.
 Heckrath, G., Brookes, P.C., Poulton, P.R. & Goulding, K.W.T., Phosphorus leaching from soils containing different phosphorus concentrations in the Broadbalk experiment. Journal of Environmental Quality, 24(5), pp. 904–910, 1995. https://doi.org/10.2134/jeq1995.00472425002400050018x
 Sharpley, A., Jarvie, H.P., Buda A., May, L., Spears, B. & Kleinman, P., Phosphorus legacy: Overcoming the effects of past management practices to mitigate future water quality impairment. Journal of Environmental Quality, 42(5), pp. 1308–1326, 2014. https://doi.org/10.2134/jeq2013.03.0098
 Taylor, J.R. & Taylor Lovell, S., Urban home food gardens in the Global North: Research traditions and future directions. Agriculture and Human Values, 31(2), pp. 285–305, 2014. https://doi.org/10.1007/s10460-013-9475-1
 Rosen, C.J., Bierman, P.M. & Eliason, R.D., Soil Test Interpretations and Fertilizer Management for Lawns, Turf, Gardens, and Landscape Plants. University of Minnesota Extension, St. Paul, MN, 2008.
 Dewaelheyns, V., Elsen, A., Vandendriessche, H. & Gulinck, H., Garden management and soil fertility in Flemish domestic gardens. Landscape and Urban Planning, 116, pp. 25–35, 2013. https://doi.org/10.1016/j.landurbplan.2013.03.010
 Metson, G.S. & Bennett, E.M., Phosphorus cycling in Montreal’s food and urban agriculture systems. PLoS ONE, 10(3), p. e0120726, 2015. https://doi.org/10.1371/journal.pone.0120726
 Abdulkadir, A., Leffelaar, P.A., Agbenin, J.O. & Giller K.E., Nutrient flows and balances in urban and peri-urban agroecosystems of Kano, Nigeria. Nutrient Cycling in Agroecosystems, 95(2), pp. 231–254, 2015. https://doi.org/10.1007/s10705-013-9560-2
 Murphy, J. & Riley, J.P., A modified single solution method for the determination of phosphate in natural waters. Analytical Chimica Acta, 27, pp. 31–36, 1962. https://doi.org/10.1016/s0003-2670(00)88444-5
 Tilman, D., Global environmental impacts of agricultural expansion: The need for sustainable and efficient practices. Proceedings of the National Academy of Sciences of the United States of America, 96(11), pp. 5995–6000, 1999. https://doi.org/10.1073/pnas.96.11.5995
 Small, G.E., Sisombath, B., Reuss, L., Henry, R. & Kay, A.D., Assessing how the ratio of barley mash to wood chips in compost affects rates of microbial processing and subsequent vegetable yield. Compost Science & Utilization, 25(4), pp. 272–281, 2017. https://doi.org/10.1080/1065657x.2017.1329038
 Amlinger, F., Götz, B., Dreher, P., Geszti, J. & Weissteiner, C., Nitrogen in biowaste and yard waste compost: Dynamics of mobilization and availability – A review. European Journal of Soil Biology, 39(3), pp. 107–116, 2003. https://doi.org/10.1016/s1164-5563(03)00026-8
 Gabrielle, B., Da-Silveira, J., Houot, S. & Michelin, J., Field-scale modelling of carbon and nitrogen dynamics in soils amended with urban waste composts. Agriculture, Ecosystems & Environment, 110(3–4), pp. 289–299, 2005. https://doi.org/10.1016/j.agee.2005.04.015
 Edmondson, J.L., Davies, Z.G., Gaston, K.J. & Leake, J.R., Urban cultivation in allotments maintains soil qualities adversely affected by conventional agriculture. Journal of Applied Ecology, 51(4), pp. 880–889, 2014. https://doi.org/10.1111/1365-2664.12254
 Booth, M.S., Stark, J.M. & Rastetter, E., Controls on nitrogen cycling in terrestrial ecosystems: a synthetic analysis of literature data. Ecological Monographs, 75(2), pp. 139–157, 2005. https://doi.org/10.1890/04-0988
 Chapin, F.S., Matson, P.A. & Vitousek, P.M., Nutrient cycling. Principles of Terrestrial Ecosystem Ecology, pp. 259–296, Springer: New York, 2011.
 Palmer, L., Urban agriculture growth in US cities. Nature Sustainability, 1(1), pp. 5–7, 2018. https://doi.org/10.1038/s41893-017-0014-8
 Lee-Smith, D., Cities feeding people: An update on urban agriculture in equatorial Africa. Environment and Urbanization, 22(2), pp. 483–499, 2010. https://doi.org/10.1177/0956247810377383