Nitrogen Fertilization Effects on Soil Respiration and Mineralogy in an Agroecosystem.

Additions of nitrogen fertilizer to surface soil (0-5cm) under no-tillage can trigger an increase in soil organic carbon (SOC) levels, however, the storage and stability of this SOC in no-till agroecosystems are unclear. This study addresses the relationship between decomposition of SOC and soil properties as influenced by increasing levels of added N fertilizer (0, 168, and 336 kg N/ha) in a long-term no-till agroecosystem. The soil type is a Maury silt loam (Typic Paleudalf) with mixed mineralogy. At the conclusion of the 34-day aerobic incubation period, there was a 24% decrease in SOC-normalized respiration values in the 336 kg N ha^-1 treatment when compared with the control (0 kg N ha^-1). The decrease in respiration with added N agrees with previous studies in other undisturbed ecosystems. There was a concurrent increase in poorly-crystalline iron and organo-iron complexes based on selective chemical extractions with N additions which might explain the lower respiration rates. Further experiments will help tease out the contributions of iron fractions to SOC storage and stability as influenced by anthropogenic N additions.