Tillage and amendment effects on soil carbon and nitrogen mineralization and phosphorus release

The influence of tillage and nutrient amendment management on nutrient cycling processes in soil have substantial implications for environmentally sound practices regarding their use. The effects of 2 years of tillage and soil amendment regimes on the concentrations of soil organic matter variables (carbon (C), nitrogen (N) and phosphorus (P)) and C and N mineralization and P release were determined for a Dothan fine-sandy loam soil in southeastern Alabama. Tillage systems investigated were strip (or conservation) and conventional tillage with various soil nutrient amendments that included no amendment, mineral fertilizer, and poultry waste (broiler litter). Surface soil (0–10 cm depth increment) organic matter variables were determined for all tillage/amendment combinations. Carbon and N mineralization and P release were determined on surface soils for each field treatment combination in a long-term laboratory incubation. Soil organic P concentration was 60% greater in soils that had been conventionally tilled, as compared with strip-tilled, both prior to and following laboratory incubation. Carbon and N mineralization results reflected the effects of prior tillage amendment regime, where soils maintained under strip-till/broiler litter mineralized the greatest amount of C and N. Determination of relative N mineralization indicated that strip tillage had promoted a more readily mineralizable pool of N (6.1%) than with conventional till (4.2%); broiler litter amendments had a larger labile N fraction (6.7%) than was found in soils receiving either mineral fertilizer (4.1%) or no amendment (4.7%). Tillage also affected P release measured during the incubation study, where approximately 20% more inorganic P was released from strip-tilled soils than from those maintained under conventional tillage. Greater P release was observed for amended soils as compared with soils where no amendment was applied. Results from this study indicate that relatively short-term tillage and amendment management can significantly impact C, N, and P transformations and transfers within soil organic matter of a southeastern US soil.