Phosphorus and nitrogen losses from poultry litter stacks and leaching through soils

Abstract

Stacking poultry litter in fields prior to land application is a common practice that provides important logistical benefits to farmers, but may lead to environmental losses of nutrients. A 2-year field study was conducted to evaluate phosphorus (P) and nitrogen (N) losses from poultry litter stacks with and without a protective cover. Surface runoff from the litter stacks and leachate through two texturally contrasting soils (sand and silt loam) was monitored using a combination of runoff collectors and zero-tension lysimetry. Nutrient losses in surface runoff were small (total P < 3 g m−2; total inorganic N < 7 g m−2), particularly when compared with losses in leachate (total P < 60 g m−2; total inorganic N < 290 g m−2). Covering stacks reduced leachate total P losses by 25–100 times and total inorganic N losses by 25–770 times, such that leachate nutrient losses from covered stacks were similar to that in the controls with no manure stacking. Despite relatively small nutrient losses from litter stacks over the 2-year study, results point to substantial nutrient accumulation in soil after repeated stacking. Water-extractable P concentrations in upper 5-cm soils were similar between covered (120–240 mg kg−1) and uncovered stacks (140–250 mg kg−1), but soil nitrate-N concentrations were much higher under the covered stack (80–140 mg kg−1) than the uncovered stack (<5 mg kg−1). This study clearly points to benefits of covering litter stacks, but highlights long-term concerns with regard to soil nutrient accumulation.