Soil organic sulfur mineralization in the presence of growing plants under aerobic or waterlogged conditions

Pot culture experiments are described which attempt to identify soil organic S mineralization and availability to plants under aerobic or waterlogged conditions. Several organic S fractions were determined using existing fractionation techniques before and after the growth of corn (Zea mays L.) or rice (Oryza sativa L.) seedlings for four successive harvests. Net mineralization occurred in organic S fractions including hydriodic acid-reducible S, Raney-nickel reducible S and non-reducible S and all fractions decreased gradually during plant growth and decreased more in the first two harvests. The amount of S mineralized from organic S during rice growth under waterlogged conditions was more than that during corn growth under aerobic conditions and this contributed to the greater amount of S taken up by rice seedlings. On average for the four soils tested, 70 and 82% of S taken up by four harvests of corn and rice seedlings, respectively, was derived from organic S calculated by the difference between the S uptake by plant and the decreased amount of inorganic sulfate in soils. All of the S fractions investigated contributed available S for plant uptake under either aerobic or waterlogged conditions.