Excess phosphorus from compost applications in urban gardens creates potential pollution hotspots

Urban Farm DB summary

Survey data from 142 gardeners and urban farmers in the Twin Cities Metropolitan Area, USA, characterized phosphorus (P) and nitrogen (N) inputs and harvest, and measured soil P concentrations at a subset of sites. Median application rates were 300 kg P/ha and 1400 kg N/ha, with low nutrient use efficiencies (2.5% for P, 5.0% for N). Garden soils had a median Bray P value of 80 ppm, far exceeding recommended levels, indicating a buildup and potential loss of P and N. Urban gardens, though only 0.1% of land area, constitute one of the largest inputs of P to the watershed.