Sulfur Distribution and Availability in Alkaline Subtropical Soils Affected by Organic Amendments

Abstract

Sulfur availability depends upon the distribution of S forms in soil, interaction among them, and soil microbial properties. Organic amendments play a vital role in maintaining adequate S reserves in soil. However, two important questions in this regard are (i) the effect of microbial activity on sulfur oxidation in soil, and (ii) the relationship of sulfur fractions to available S pool in soil. The present experiment was designed to assess the effect of organic amendments on sulfur fractions, availability, and microbial properties in soil. Two alkaline subtropical soils belonging to Missa (silt loam Typic Ustochrept) and Kahuta (sandy loam Udic Haplustalf) soil series were amended with organic amendments, viz. farmyard manure (FYM), poultry litter (PL), and sugarcane filter cake (SF), at 1% w/w and incubated at 25 °C for 56 days maintaining soil moisture at 50% WHC. CO2-C evolution rate, the ∑CO2-C, and also the ∑CO2-C to microbial biomass C differed with the soils and were higher in poultry litter–amended soils. Dissolved organic C (DOC), microbial biomass C (MBC), and dehydrogenase activity (DHA) were also higher in poultry litter while the microbial biomass S (MBS) and arylsulfatase activity (ASA) were higher in the sugarcane filter cake–amended soils. Organic amendments significantly increased plant-available SO42− and enhanced C-bonded S, and inorganic S fractions in the following order: sugarcane filter cake > poultry litter > farmyard manure. Organic amendments significantly improved microbial activity and S availability in soil depending upon their labile organic C, organic S, and available S contents.