Organic Matter Stimulation of Elemental Sulfur Oxidation in a Calcareous Soil
- F. R. Cifuentes and
- W. C. Lindemann
Oxidation of So to H2SO4 in some calcareous soils is a slow process that often does not increase nutrient availability. Our objective was to determine the effect of organic matter on So oxidation and its subsequent effect on nutrient availability. Belen clay (clayey over loamy, montmorillonitic [calcareous], thermic Typic Torrifluvent) was amended with 2.5 or 5 g So kg−1 in laboratory and field experiments, respectively. Organic amendments were 6 g C kg−1 as glucose, starch, cellulose, or sawdust in the laboratory and 15 g kg−1 as composted horse manure, fresh cow manure, or bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon] clippings in the field. The response variables included soil pH, SO4, electrical conductivity (EC), available P and micronutrients, as well as the most-probable-number (MPN) of neutralphilic, chemoautotrophic So oxidizers in the laboratory experiment. Averaged across organic matter types and sampling dates, organic matter stimulation of So oxidation decreased pH values 0.24 and 0.16 units, increased soil SO4 246 and 1455 mg kg−1, and increased soil EC 0.42 and 0.48 dS m−1 in the laboratory and field, respectively. Organic matter amendment decreased the number of chemoautotrophic So oxidizers compared with soils amended with So alone. Organic materials capable of supporting microbial growth for longer periods resulted in greater stimulation of So oxidation. Enhanced So oxidation consistently increased only Mn availability in the field. Changes in soil EC, pH, and SO4 were highly correlated. In calcareous soils with low organic matter, addition of organic matter with So stimulates So oxidation.
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