Microbial Response of a Calcareous Histosol to Sulfur Amendment

The objective of this study was to assess the functional response of microbial communities to sulfur amendment in calcareous organic soils of the Everglades Agricultural Area in south Florida. Soils under sugarcane cultivation were amended with elemental S at four rates up to 448 kg S ha to decrease pH and enhance nutrient availability. Soil samples were collected 2, 6, 9, and 13 months after S application and subjected to microbial, enzyme, and nutrient analysis. Application of S at rates up to 448 kg S ha enhanced labile P availability by 103% compared with unamended soils. Nonetheless, stimulatory effects were limited and temporary because of the high buffering capacity of this calcareous organic soil against acidification. Activities of leucine aminopeptidase and sulfatase were independent of S application. Phosphatase activities were 115% higher and glucosidase activities 573% higher for soils receiving the highest S rates than unamended soils at 2 months. Microbial biomass C and N were not affected by S amendment, but biomass P was 314% higher for soils amended with the highest S rates at 2 months than soils receiving the lowest rates, primarily as a result of increased P availability. The C, N, and P mineralization rates were not affected by S, although all rates varied seasonally, suggesting that S application did not stimulate soil oxidation. Overall, application of S generally did not result in pulse or flux of nutrients from soil, suggesting that S application had minimal benefits for increasing nutrient availability to sugarcane.