STUDY ON BIOAVAILABILITY OF SULFUR FRACTIONS IN SOILS

Soil S depletion study was conducted in a pot experiment with successive planting of corn or rice for 4 harvests. Changes of soil available S (MCP-S), ester sulfate (C-O-S), carbon-bonded S (C-S) and unidentified organic sulfur (UO-S) were investigated. Results showed that total S uptake by plant and sulfur concentration in plant shoot were gradually decrease from first harvest to forth harvest, which were related to soil MCP extractable S. During cropping soil MCP extractable S decreased gradually and the amount of MCP extractable S decreased was greater when planting corn than planting rice. Ester sulfate (C-O-S), carbon-bonded S (C-S) and unidentified organic sulfur (UO-S) could be mineralized for plant uptake. The total amounts of S uptake by corn or rice of 4 harvests altogether were greater than the amounts of MCP-S decreased, and the additional S came from organic S mineralization. The percentage of total S uptake came from different organic S fractions was C-O-SC-SUO-S. Also, the percentage of total S uptake came from organic S was greater with planting rice in waterlogged condition than that with planting corn in aerobic condition.