Sulfur-induced changes in phosphorus distribution in Everglades Agricultural Area soils

Elemental S is used as an amendment for Everglades Agricultural Area soils of south Florida to decrease pH and increase P availability to crops. Our objectives were to determine how S application altered phosphorus distribution and availability in organic soils under sugarcane cultivation. Soils were sampled four times during the growing season at 2, 6, 9, and 13 months after sulfur application and subjected to chemical P fractionation. Sulfur application had minimal effect on soil pH and thus generally failed to increase P supply to sugarcane during the entire growing season at the application rates tested due to the high soil buffering capacity against acidification. Yet, a significant reduction in soil pH did increase P concentrations in labile P and Fe–Al bound P fractions at 2 months for the highest S rate. Concentrations of labile P and Fe–Al bound P declined during the sugarcane growing season. The size of Ca–P fraction remained unchanged during the early season but significantly decreased at the end of the growing season. Humic-fulvic acid P fluctuated seasonally, averaging 143, 172, 139, and 181 mg P kg−1 for 2, 6, 9, and 13 months, respectively. Residual P fluctuated in a contrasting pattern to humic-fulvic acid P and contributed approximately 50% to the total P. Overall, S application did not result in large P accumulation in labile pools, thus S application does not appear to enhance potential P export from fields into wetlands.