Biosolids Type, Rate, and Receiving Soil Affect Anaerobic Incubation Nitrogen Availability Coefficients

Abstract

Core Ideas Potentially available N (PAN) differed greatly among biosolids, soils, and rates. Nitrogen availability coefficients (NAC) under or overestimated PAN from −140 to 181%. The effects of soil and biosolids on PAN and NAC were of similar magnitudes. Biosolids NAC might best be estimated with the receiving soil and a range of rates. Seven‐day anaerobic incubation can provide relatively quick and easy estimates of potentially available N (PAN), but has been little used to estimate N availability coefficients (NAC) of biosolids destined for land application. We hypothesized that waterlogged‐incubation estimates of PAN and NAC depend on biosolids type, application rate, and receiving soil. We applied three dissimilar biosolids at five rates to four representative southeastern US soils and measured NH4–N and NO3–N after a 7‐d laboratory waterlogged incubation. Target PAN rates were 0, 0.5, 1, 1.5, and 2× a realistic yield expectation (RYE) rate, 127 kg N ha–1, for tall fescue (Festuca arundinacea), a common biosolids‐receiving grass. Biosolids application rates were based on biosolids types, associated book‐value NACs, and biosolids total N. Anaerobic incubation of soil plus biosolids yielded predominantly NH4–N. There were three‐way biosolids × rate × soil interactions for NH4–N, PAN, and NAC. The PAN differed substantially among biosolids, rates, and receiving soils, ranging from –12.1 to 146 mg kg–1, while NAC ranged from ‐0.13 to 0.86. Negative values suggested N lost via denitrification or immobilization. The PAN trends reflected biosolids total N. At the highest application rate, soil had no detectable effect on the NAC; otherwise, soil affected NAC by as much as an order of magnitude. Presuming anaerobic incubation provides reasonable estimates of PAN, NAC of any particular biosolids might best be estimated via incubation with the receiving soil across an RYE‐based range of N application rates, rather than relying on book value NAC.