Soil Property and Landscape Position Effects on Seasonal Nitrogen Mineralization of Composted Dairy Manure

Abstract

To develop better management practices that optimize the N derived from manure, additional research is needed regarding the mineralization and dynamics of N under field conditions. Thus, an in situ field study using three different soil types located in an agricultural field was conducted to evaluate N mineralization patterns during the summer and winter months. The three Coastal Plain soils (Ultisols) investigated were Bama (sandy loam), Lynchburg (loam), and Goldsboro (loam), representing the landscape position of a summit, drainageway, and sideslope, respectively. Composted dairy manure was incorporated into in situ soil cores, at a rate of 350 kg N ha−1, to evaluate mineralization rates of the soils and their landscape position during the summer and winter months. Addition of composted dairy manure on N mineralization was impacted by season and soil type. This was most evident during summer months (N mineralization was 24%), suggesting that seasonal timing of application will influence mineralization. The seasonal patterns of N mineralization were affected mostly by temperature; N mineralization was minimal during winter (N mineralization was 2%) when temperature was low (∼10 °C) but was greater during summer with higher temperatures (25 °C-30 °C). Landscape and soil texture played an additional role in mineralization. The soil type with the greatest percentage of sand and located in a low-lying area, although N mineralization was low during the winter months, significantly lost more of the added N from dairy compost (80%-90% more) compared with the other soils. During the summer, the loam soil with the greatest water-holding capacity mineralized the most N, significantly mineralizing 9% to 10% more than the other soils. These results show that soil variability, temperature, and landscapes need to be considered when applying manure to agricultural fields.