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 environme ntally sound practices regarding their use. The effects of 2 years of tillage and soil amendment regimes on the concentrations of soil organ ic 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 so il nutrient amendments that included no amendment, mineral fertilizer, and poultry waste (broiler litter). Surface soil (0-10 cm depth incre ment) organic matter variables were determined for all tillage/amendme nt combinations. Carbon and N mineralization and P release were determ ined on surface soils for each field treatment combination in a long-t erm laboratory incubation. Soil organic P concentration was 60% greate r 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 amend ment regime, where soils maintained under strip-till/broiler litter mi neralized the greatest amount of C and N. Determination of relative N mineralization indicated that strip tillage had promoted a more readil y mineralizable pool of N (6.7%) than with conventional till (4.2%); b roiler litter amendments had a larger labile N fraction (6.7%) than wa s found in soils receiving either mineral fertilizer (4.1%) or no amen dment (4.7%). Tillage also affected P release measured during the incu bation study, where approximately 20% more inorganic P was released fr om strip-tilled soils than from those maintained under conventional ti llage. Greater P release was observed for amended soils as compared wi th soils where no amendment was applied. Results from this study indic ate that relatively short-term tillage and amendment management can si gnificantly impact C, N, and P transformations and transfers within so il organic matter of a southeastern US soil.