Peanut (Arachis hypogaea L.) Residue Nitrogen Mineralization Under Contrasting Residue Loads and Tillage Systems.

Placement of peanut (Arachis hypogaea L.) residue in windrows after digging results in an uneven distribution of residue in the field, which may lead to spatial and temporal variability of plant available N for subsequent crops. The objective of this study was to quantify decomposition and N mineralization from peanut residue applied at different load sizes under simulated conventional and conservation tillage practices. A 365-day study was conducted in Citra, FL beginning in September 2015. Peanut residue was collected after harvest and placed in litterbags at loads equivalent to 2.2 Mg/ha, 4.1 Mg/ha, 6.3 Mg/ha, and 7.5 Mg/ha. Load sizes were selected based on measurements taken from windrows throughout the field. Litterbags were placed on the soil surface or fall-buried and retrieved periodically. In February 2016, a subset of surface-applied litterbags was buried (spring-buried) to simulate spring field preparation. Mass loss and N mineralization were determined at retrieval dates. Decomposition and N mineralization were affected by time x load size and time x residue placement interactions. Exponential decay models estimated that higher loads (6.3-7.5 Mg ha-1) would provide N credits of 75-92 kg N/ha to a subsequent winter wheat (Triticum sativum L.) crop in the Southeast compared to 23-47 kg N/ha provided by lower loads (2.2-4.1 Mg/ha). Smaller N credits of 42-51 kg N/ha and 10-24 kg N/ha for loads of 6.3-7.5 Mg/ha and 2.2-4.1 Mg/ha, respectively, were estimated for cotton (Gossypium hirsutum L.). Exponential models estimated that buried residue would provide a smaller N credit (40 kg N/ha) to a winter wheat crop than surface residue (66 kg N/ha) and that spring burial of residue would accelerate N mineralization compared to leaving residue on the soil surface. Fall and spring-buried residue were estimated to provide N credits of 28 kg N/ha to cotton, while surface residue would provide 42 kg N/ha.