FERTILIZER NITROGEN REPLACEMENT VALUE OF FOOD RESIDUALS COMPOSTED WITH YARD TRIMMINGS, PAPER OR WOOD WASTES

Composting offers an opportunity to recycle food waste as a soil amend ment. A three year growth trial was conducted to determine the fertili zer nitrogen (N) replacement value of food waste composts for cool sea son perennial grass production. Six composts were produced in a pilot- scale project with two composting methods (aerated static pile and aer ated, turned windrow). The aerated, tuned windrow method simulated ''a gitated bay'' composting systems, which utilize routine mechanical agi tation. 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 sa ndy loam soil at application rates of approximately 155 Mg/ha (about 7 yd(3)/1000 ft(2)). Tall fescue (Festuca arundinacea Schreb. 'A.U. Tri umph') was seeded after compost incorporation, and was harvested repea tedly at a late vegetative growth stage (April to November; approx. 35 days regrowth between harvests). Grass yield and grass N uptake did n ot respond to compost application during the first year. During the se cond and third years after application, composts were a consistent sou rce 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 applicat ion 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 signifi cant slow-release N properties were produced with either the aerated s tatic pile composting method or the aerated, turned windrow method. Co mposts with higher N concentrations had higher fertilizer N replacemen t value. The slow release N supplied by food waste composts is ideally suited for urban landscapes, where a moderate, consistent rate of pla nt growth is highly desirable.