A Review of Nutrient Losses to Waters From Soil- and Ground-Based Urban Agriculture—More Nutrient Balances Than Measurements

Urban Farm DB summary

A review of empirical peer-reviewed studies (2000-2021) on nutrient losses to water from soil- and ground-based urban agriculture. Of 241 publications screened for a stated concern with nutrient losses to water, 20 were retained, but only seven had actually measured losses to water. Of four experimental studies, three measured leachate losses under different garden management practices; of 16 real-world studies, only four quantified losses to water as leachate, with measured average losses ranging from 0.005 to 6.5 kg/ha for phosphorus and 0.05 to 140 kg/ha for nitrogen. Thirteen of the 16 non-experimental studies provided input and harvested-crop data allowing nutrient balances to be calculated; despite wide value ranges, most studied gardens showed nutrient surpluses (inputs exceeding crop harvest) for nitrogen and phosphorus but not potassium, identified as a risk factor for losses to water, though large surpluses were not always linked to higher leachate losses. The review concludes that more field studies measuring actual losses to water, and documenting contextual factors, are needed to determine whether urban agriculture can contribute to a circular economy without causing nutrient-related water quality impairment.