Soil Organic Matter Pools Vary Across Management Systems but Weakly Predict Short-Term Nitrogen Cycling

Abstract

The dynamics of soil carbon and nitrogen are important for soil fertility and ecosystem functioning, and agricultural management and land use strongly affect them. However, it is still not clear how different management systems change soil organic carbon (SOC) and soil organic nitrogen (SON), or if larger SOC and SON pools go together with more available nitrogen through mineralization and nitrification. The data come from the Kellogg Biological Station Main Cropping System Experiment; this site has SOC and SON measurements for several years and depths, and its nitrogen cycling variables were monitored at 0–25 cm depth. Treatment comparison and linear regression were used to test the differences among systems and the relationships between soil organic matter pools and nitrogen cycling. SOC and SON differed significantly among the treatments; the long successional system had the highest concentrations and the conventional system the lowest. Nitrogen cycling had different treatment patterns, and only SON had a significant positive relationship with net nitrification (R² = 0.16, p = 0.007); the other three regressions were not significant. The analysis relied on one experimental site, and the datasets matched only partly in time; therefore, the results cannot be generalized very far. In general, management had a strong effect on SOC and SON, but these pools by themselves predicted short-term nitrogen cycling only weakly.