Turnover of Manure 15N‐Labelled Ammonium during Composting and Soil Application as Affected by Lime and Superphosphate Addition

Abstract

To determine N turnover and losses during aerobic composting of animal manure, a 41‐d laboratory study was performed on pig manure composting with three additive treatments (Straw: pig manure + straw only; Lime: pig manure + straw + quick lime; and SSP: pig manure + straw + single superphosphate). The NH4–N pool in the pig manure was initially labeled with 15N to determine the fate of manure NH4–N during composting. The composts were subsequently applied to soil to investigate the effects on soil mineral N and to trace the 15N during 60 d of incubation at 25°C. Of the initial manure 15NH4–N, approximately 30, 90, and 20% was lost by NH3 volatilization during composting in the Straw, Lime, and SSP treatments, respectively. Concurrently, 62, 16, and 41% of initial 15NH4–N was immobilized in the respective treatments. When the composts were applied to soil, the mineral N in soil with SSP compost was higher throughout the incubation than in soil with Straw and Lime composts. This was because of higher mineral N content in the SSP compost on application and higher net N mineralization from that compost in the soil. In soil with Straw compost, N mineralization and immobilization were slow or effectively in balance. In soil with Lime compost, net N immobilization was strong in the first 10 d, but then net N mineralization dominated the remaining period of soil incubation. Overall, adding lime before composting reduced the NH4–N content in the compost and the amount available in soil, while adding superphosphate increased the NH4–N content in both. Therefore, superphosphate addition increased the potential fertilizer value of composted pig manure.