Net nitrogen mineralization enhanced with the addition of nitrogen-rich particulate organic matter

Particulate organic matter (POM) is a labile fraction of soil organic matter (SOM) that can contribute to nitrogen (N) mineralization. We added native and non-native POM to soils with contrasting properties and assessed net N mineralization during a 28days incubation study. Soils (0-15cm depth) for this study were a clay soil with a 3-year history of corn (Zea mays L.), a loam soil with a 2-year history of alfalfa (Medicago sativa L.) and sandy-loam and silty-clay-loam soils that were cropped in the previous 5years with a corn-soybean (Glycine max L.) - corn-forage-forage [45% alfalfa+55% timothy (Phleum pratense L.)] and corn-soybean-forage-forage-forage rotation, respectively. The POM was separated by size fractionation (>53μm) from coarsely sieved (>6mm) soil. The N concentration in POM followed the order loam>silty-clay-loam>clay>sandy-loam, whereas the acid unhydrolyzable fraction, a proxy for the lignin concentration, was the reverse. Compared to soil only, addition of N-rich POM from the loam soil increased net N mineralization in the clay soil and gave similar net N mineralization in the other soils, while addition of N-poor POM from the sandy-loam soil resulted in lower net N mineralization in the loam and silty-clay-loam soils. Multiple stepwise regression analysis showed that net N mineralized due to POM addition was related to the N concentration in the POM (partial R2=0.54) and the initial soil mineral N concentration (partial R2=0.33), suggesting that N mineralized from POM was related more to POM chemical composition than soil properties. We propose that information on POM chemistry in conjunction with soil mineral N concentration and texture could be useful for constructing N mineralization prediction models to improve N fertilizer management in agricultural soils.