Mineralization of sulfur in soils amended with organic wastes
Tabatabai, M.A. | Chae, Y.M.
This study was conducted to compare the mineralization of S in soils amended with various types of sewage sludges, animal manures, and plant materials. Field-moist soils amended with organic waste materials at a 50-Mg-ha-1 rate were mixed with glass beads, packed in leaching columns, leached with 5 mM CaCl2 to remove the mineral S, and incubated at 30 degrees C. The leaching procedure was repeated every 2 wk for 26 wk. The leachates were analyzed for SO4(2-)-S. The rate of SO4(2-) release from sewage sludges was rapid during the first 6 wk, followed by a slow linear release. The release of SO4(2-) from animal manures was linear with time of incubation. With the exception of alfalfa (Medicago sativa L.), which showed a rapid SO4(2-) release within the first 2 wk and a subsequent linear release with time up to 26 wk, the addition of all other plant materials resulted in net S immobilization. The total net S mineralized from the organic waste materials varied considerably, depending on the type of soil and the C/N/S ratio of the organic waste material. The amounts of S mineralized in soils amended with sewage sludges and animal manures ranged from 99 to 345 mg S kg-1 and from 32 to 52 mg S kg-1 soil, respectively. The total S mineralized in soils amended with plant materials ranged from 15 to 57 mg S kg-1. Expressed as a percentage of total organic S added to soils, the S mineralized ranged from 41 to 97% for sewage sludges and from -62 to 127% for animal manures. The percentage of organic S mineralized in the plant materials ranged from -510% for cornstalk (Zea mays L.) to 87% for alfalfa. Soil types have marked effects on the mineralizable S (S0) pool and first-order rate constants (k).
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