Increasing Rates of Gross Nitrogen Mineralization in Diversified Midwestern Cropping Systems.

Gross N mineralization is the total amount of nitrogen transformed by microbes from organic N to NH4+. Agroecosystems that achieve increased rates of gross N mineralization could potentially supply sufficient N to meet crop demand without depending on large fertilizer inputs and associated pools of mineral N, and reduce N losses to the environment. This study examines the effect of management of diversified cropping systems in the Upper Midwest US by focusing on three long term cropping systems experiments: the Marsden Farm experiment, the Variable Input Crop Management Systems experiment, and the Wisconsin Integrated Cropping Systems Trial. Specifically, the roles of manure application and increases in soil organic N in determining gross N mineralization rates are explored. Particulate organic N was found to be positively correlated with gross N mineralization rate, and manure application explained some of the variability in both particulate organic N and gross N mineralization rate. Manure application and associated increases in soil organic N fractions are likely significant factors in explaining gross N mineralization rates in corn-based systems in the Upper Midwest.