Nitrogen Dynamics Associated with Organic and Inorganic Inputs to Substrate Commonly Used on Rooftop Farms

Urban Farm DB summary

This study evaluated the effects of organic and inorganic nitrogen (N) inputs on N dynamics within substrate typically used on rooftop farms during an 8-week greenhouse experiment in the United States. Substrate without added N inputs (control) was compared with synthetic fertilizer and three organic N inputs: composted poultry manure, municipal green waste compost, and vermicompost. Few differences in N cycling and yields were found among treatments receiving organic N inputs, despite differences in carbon-to-nitrogen ratios. Crop yields from the synthetic fertilizer and municipal green waste compost treatments were higher than other organic N input treatments. Inorganic N levels in the synthetic fertilizer treatment decreased from 129 mg N/L to 113 mg N/L, while control and organic N input treatments showed nearly 10-fold decreases from 79.5–117.8 mg N/L to 12.8–16.6 mg N/L over 8 weeks. The greatest losses of ammonium and nitrate via leachate were measured from the synthetic fertilizer treatment.