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 °C. The leaching procedure was repeated every 2 wk for 26 wk. The leachates were analyzed for SO²⁻₄-S. The rate of SO²⁻₄ release from sewage sludges was rapid during the first 6 wk, followed by a slow linear release. The release of SO²⁻₄ from anhnal manures was linear with time of incubation. With the exception of alfalfa (Medicago sativa L.), which showed a rapid SO²⁻₄ 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). Journal Paper no. J-13691 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA. Projects 2112 and 2710.
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