Gross Nitrogen Mineralization in Corn Is Influenced By Soil Organic Carbon and Nitrogen Management Strategy.

Nitrogen management strategies for annual grain cropping systems that can improve agricultural production efficiency and environmental quality are needed. Plants’ ability to access actively cycling N calls for a greater focus on gross N cycling rates which could help inform the design of efficient N management strategies. A long-term cropping systems experiment in Iowa comparing diverse rotations receiving manure inputs with a simple rotation receiving solely inorganic N fertilizer was utilized to explore the effect of N management strategy and soil organic C (SOC) on gross ammonification rates. Gross ammonification and SOC were measured three times during the growing season at two soil depths (0-10cm and 10-20cm). Gross ammonification but not SOC was significantly different across the three measurement events. SOC and gross ammonification rate were positively correlated. While cropping system did not have a statistically significant effect on SOC levels, at a given SOC level cropping system influenced gross ammonification rate where rates were higher in the diversified systems than in the simpler system. Cropping system effects on SOC and gross ammonification were observed in the 10-20cm depth, but not the 0-10cm depth. Stratification was greater in the simple cropping system, with greater gross ammonification rate and SOC in the 0-10cm depth than the 10-20cm depth. Our results suggest that N management strategies focused on optimizing microbial N cycling rates could enable annual grain production that is more nutrient retentive.