Peanut residue distribution gradients and tillage practices determine patterns of nitrogen mineralization

Peanut ( Arachis hypogaea L.) harvest practices create residue distribution gradients in the field that lead to spatial and temporal variability in available nitrogen (N) during subsequent crop growth. The objective of this study was to quantify N mineralization from peanut residue loading rates that are reflective of postharvest residue distribution gradients under simulated conventional and conservation tillage. A field study was conducted in Florida, USA beginning in September 2015. Fresh shoot residues were placed in litterbags at loading rates (1.1, 2.2, 4.5, and 6.7 Mg ha −1 on an air-dry weight basis) that were based on the residue distribution gradient measured in the field following harvest. Three tillage scenarios were simulated by placing litterbags on the soil surface (no-till) or burying them at 0.10 m depth in fall or spring (fall and spring tillage, respectively). Litterbags were retrieved periodically over 365 days. Buried residues mineralized N faster than surface residues, even when buried residues had high levels of recalcitrant fractions, as was the case with spring-incorporated residues. Exponential models predicted that during a wheat ( Triticum aestivum L.) crop, residue loading rates of 1.1, 2.2, 4.5, and 6.7 Mg ha −1 would mineralize 3–6, 5–12, 24–34, and 35–41 kg N ha −1 , respectively, depending on tillage practice. At the same loading rates, N mineralization estimates dropped to 2–4, 3–6, 9–11, and 5–18 kg N ha −1 during a hypothetical cotton ( Gossypium hirsutum L.) crop planted the following spring. These results suggest that peanut harvest and tillage practices cause large spatial and temporal variability in available N following harvest and may partially explain inconsistencies and spatial variability in subsequent crop performance when peanut residues are relied upon as a N source and mineral N fertilization is reduced.