Phosphorus Forms in Alabama Decatur Silt Loam with Upland Cotton Production.

Alabama was historically known as "The Cotton State". It ranks 4th with 10.1% of U.S. cotton production. We assessed the forms and labile P in the Alabama Decatur silt loam cotton soils, and evaluated the impact of management practices on the soil P forms. We observed that manure and inorganic fertilization resulted in the accumulation of appreciable amounts of inorganic P. Higher levels of water, Fe and Al bound inorganic P were found in soils treated with poultry litter than in the control and some treated with inorganic fertilizer. Inorganic P associated to organic matter (NaOH extracted) increased in soils that have received inorganic fertilizer than in poultry litter applied soils. Chemical fractionation revealed that the majority of the soil organic P were associated with Al oxide (> 40%). The NaOH-organic P was the next most abundant. Bioavailable organic P in soils was investigated by using phosphate-releasing enzymes. Less than half of the organic P in Ca-EDTA was hydrolyzed by the tested enzymes. Simple monoester P was the major hydrolysable P in the H2SO4 fraction. Greater than 50% of organic P in NaOH was hydrolyzed by the various enzymes, which suggest that NaOH-extractable organic P is labile. Enzymes activities in soils treated with poultry litter were less than in soils treated with inorganic fertilizer. This trend was consistent for all the fractions and all the enzymes used in this study.