Investigating potential hydrological ecosystem services in urban gardens through soil amendment experiments and hydrologic models

Urban Farm DB summary

A study quantifying leachate and soil moisture from experimental urban garden plots receiving various soil amendments — high and low levels of manure and municipal compost, synthetic fertilizer, and no inputs — over three years. A simple mass-balance hydrologic model was parameterized for high-input municipal-compost and no-compost garden plots plus reference turfgrass plots, and run over three growing seasons under ambient precipitation and three elevated-precipitation scenarios. Soil moisture varied across treatments, with the highest mean levels in manure-compost plots and the lowest in synthetic-fertilizer plots. Soil amendment treatments explained little of the variation in weekly leachate volume, but high municipal compost and synthetic fertilizer had the lowest leachate volumes, while high and low manure compost had slightly higher volumes. Garden plots received 12-16% greater total water inputs than turfgrass plots due to irrigation, but total leachate was 20-30% lower for garden plots across climate scenarios because evapotranspiration was 50-60% higher in garden plots. Differences between high-municipal-compost and no-compost garden plots were small relative to the difference between garden plots and turfgrass overall. The study concludes that garden soil amendments influence water retention, and that the higher water retention, infiltration, and evapotranspiration potential of garden soils relative to turfgrass indicate hydrologic ecosystem services may be an underappreciated benefit of urban gardens.