Compost Layering Effects on Poultry Litter Leaching: A Column Study

Incorporation of poultry litter (PL) into the nutrient management strategy of crop producers in South-western British Columbia is an important end-use for this agricultural waste product. Environmental and ecological concerns associated with leaching of nutrients by over-winter field storage of PL need to be addressed. To mitigate some of these concerns, some farmers store the manure on a base pad of City of Vancouver yard trimmings compost (YTC), with an additional covering layer of YTC. An outdoor column leaching study was designed to observe the effects of the YTC base pad and covering on the quality of leachate emanating from the PL, as well as to determine the maximum leachability of nutrients from these materials over the storage period. The YTC cover increased (P<0.05) the leaching of nitrogen (N), copper (Cu), and zinc (Zn) from the PL below. The YTC base pad under the PL decreased (P<0.05) the cumulative Cu, Zn and P leached as compared to the PL alone by 50%, 54% and 30%, but had little ability to retain N or soluble salts. Concentrations in the first flush of leachate out of the PL were reduced by the YTC base pad from 25 to 1.3 mg Cu L^?1, 11 to 0.95 mg Zn L^?1, and 430 to 40 mg P L^?1. The high calcium content and cation exchange capacity of the YTC are credited with much of this retention. We recommend that farmers continue to store PL on a base pad of YTC with some improvements, and that the YTC cover is used to isolate the PL from wildlife.