Fertilizer Nitrogen Replacement Value of Food Residuals Composted with Yard Trimmings, Paper or Wood Wastes

Abstract

Composting offers an opportunity to recycle food waste as a soil amendment. A three year growth trial was conducted to determine the fertilizer nitrogen (N) replacement value of food waste composts for cool season perennial grass production. Six composts were produced in a pilot-scale project with two composting methods (aerated static pile and aerated, turned windrow). The aerated, turned windrow method simulated “agitated bay” composting systems, which utilize routine mechanical agitation. Compost bulking agents included yard trimmings, yard trimmings + mixed paper waste, and wood waste + sawdust. Finished composts had Kjeldahl N concentrations ranging from 10 to 18 g N/kg. For the growth trial, composts were incorporated into the top eight to 10 cm of a sandy loam soil at application rates of approximately 155 Mg/ha (about 7 yd3/1000 ft2). Tall fescue (Festuca arundinacea Schreb. ‘A.U. Triumph’) was seeded after compost incorporation, and was harvested repeatedly at a late vegetative growth stage (April to November; approx. 35 days regrowth between harvests). Grass yield and grass N uptake did not respond to compost application during the first year. During the second and third years after application, composts were a consistent source of slow-release N. They supplied the fertilizer N equivalent of 0.70 kg N/ha/day over a 140-day period (April to August) in both years. The N supplied by composts in the second and third year after application was valued at $0.70 to $1.90 per dry tonne (Mg) compost per year, using a fertilizer N cost of $1/kg N. Food waste composts with significant slow-release N properties were produced with either the aerated static pile composting method or the aerated, turned windrow method. Composts with higher N concentrations had higher fertilizer N replacement value. The slow release N supplied by food waste composts is ideally suited for urban landscapes, where a moderate, consistent rate of plant growth is highly desirable.