Sulfur-Induced Changes in Extracellular Enzyme Activity in Everglades Soils.

Soil microorganisms play important roles in the decomposition of organic matter and nutrient regeneration.  In natural systems, soil microbial activities are related to the efficiency of nutrient cycling.  Elemental S is applied in the Everglades Agricultural Area (EAA) to reduce the soil pH and increase the availability of micronutrients and P to crops.  Alterations in soil physical-chemical properties by S amendment are likely to change microbial activity and function, which may in turn affect nutrient availability and organic matter turnover rates. The objectives were to investigate the seasonal response of soil microbial activities to sulfur addition.  Soils were amended with S at rates up to 448 kg S ha^-1.  All enzyme activities fluctuated seasonally and were affected by weather patterns and sugarcane growth.  Leucine aminopeptidase activity was independent of S application, averaging 63, 87, 63, 60 mg MUF kg^-1 h^-1 for 0, 112, 224, and 448 kg S ha^-1, respectively, yet it was significantly correlated to soil pH (r² = 0.42) and dissolved organic C (r² = 0.57).  Phosphatase activity increased with the addition of S, while glucosidase decreased.  Phosphatase was not correlated to soil C, N, P, and S chemical parameters.  Yet, glucosidase was significantly correlated to extractable P (r² = 0.35), extractable SO₄ (r² = 0.39), extractable NH₄ (r² = 0.30), and soil pH (r² = -0.28).  Overall, sulfur applied to reduce pH had minimal observable effects on enzyme activity, especially compared to strong seasonal effects and sugarcane growth patterns.