Nutrient and trace element changes during manure composting at four southern Alberta feedlots

Interest in composting as a means of handling the large volumes of manure generated by southern Alberta beef cattle feedlots has increased in recent years. We measured concentrations of 19 elements (C, N, P, Na, Ca, Mg, K, S, Al, Fe, Mn, Zn, Cu, Cr, Ni, Pb, Co, Mo and Cd) in fresh manure, interim-composted manure and finished compost, at four commercial feedlots. Thirteen elements showed increased concentrations (by 26-73%) with composting, while four (C, Cr, Ni and Mo) showed concentration declines. Of the remaining two, the trend in N concentration was feedlot dependent, while Pb was largely unaffected. Total mass loss during composting averaged 54%, which represents a substantial decrease in haulage requirements. Overall average C losses were 61% and N losses 33%. On an equivalent wet weight basis ("as-is"), composting allowed haulage of 56% more N, 84% more P, 91% more Zn, and 76% more Cu than fresh manure, which is advantageous in terms of moving nutrients and trace elements from high to low-loading areas. Our study quantifies nutrient and trace element behaviour during composting, provides comparative data with fresh manure, and helps tailor end-use decisions (e.g., haulage distance, application rate) on the compost product.