Response of soil nitrogen mineralization to warming temperatures depends on soil management history

Rising global temperatures have the potential to increase soil nitrogen (N) mineralization from soil organic matter (SOM). By increasing SOM over time, management practices that increase SOM through the addition of soil amendments, such as compost, have been recognized as effective strategies for mitigating the effects of climate change and building resilience in agricultural ecosystems. However, the effects of these strategies on temperature-induced changes to soil N cycling are unclear, particularly when soils are managed to increase SOM. To determine how agricultural management history and compost amendments affect net N mineralization, net nitrification, and nitrous oxide (N2O) production, we performed a laboratory incubation of soils with two distinct agricultural management histories under three incubation temperatures. Three compost treatments (green-waste compost, food-waste compost, and no compost) were applied, each with and without the addition of synthetic urea fertilizer. We found that organically managed soil exhibited higher rates of net N mineralization and nitrification than conventionally managed soil, leading to greater nitrate production. The rate of N mineralization in organically managed soil was also more sensitive to temperature increases. Although compost addition stimulated microbial activity, it did not affect the N-cycling processes measured in this study at any temperature. Therefore, the implementation of climate change resilience and mitigation strategies aimed at augmenting stocks of soil carbon may render agricultural soils more susceptible to increased N mineralization and subsequent losses under warming, particularly if plant uptake of the mineralized N does not occur concurrently. Moreover, the effects of compost application to stimulate the immobilization of excess N is likely limited in soils with low background C.