Exploring variations in potential carbon and nitrogen mineralization in managed grasslands among the diversity of soils in North Carolina

Abstract Background Nitrogen availability from mineralization of organic matter in managed forage and grazing lands can be substantial, but little is known of how it varies with management within and among farms within a region and across regions. Methods Soil samples ( n = 648) were collected at 0–10‐cm depth under grasslands and woodlands across three physiographic regions of North Carolina, United States, which has a warm‐humid climate. Potential C and N mineralization and inorganic N were classified by physiographic region, soil texture, and farm management to characterize influences. Results Potential C and N mineralization were strongly associated across both grasslands and woodlands. Although physiographic region explained 27% ± 5% of the variation in C and N mineralization, it was individual farm locations varying by management and soil type that contributed the most to this variation (48% ± 2%), whereas field within a farm (11% ± 3%) and duplicate sampling within a field (11% ± 3%) were minor components. Soil‐test biological activity was the best predictor of net N mineralization, with some modifications based on pasture age and quantity of hay fed on the farm. Apparent nitrification was inhibited under woodlands and in ~20% of samples under grasslands. Conclusions Pasture age and management were key factors controlling C and N mineralization. Widely varying soil N supply from mineralization suggests that N fertilizer recommendations for pastures should be adjusted for soil texture and management conditions, and use of the soil‐test biological activity assay could be a simple indicator of N availability to guide these recommendations.