IMPACT OF ELEMENTAL SULFUR FERTILIZATION ON AGRICULTURAL SOILS. I. EFFECTS ON MICROBIAL BIOMASS AND ENZYME ACTIVITIES

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Abstract
This study investigated the impact of repeated application of S° fertilizer on microbial and biochemical characteristics of two Grey Luvisolic soils. The Waitville pasture plots received Agri-Sul at a rate of 22 or 44 kg S° ha−1 yr−1 for 5 yr, whereas the Loon River canola-summerfallow plots received single or double applications of Flow-able Sulfur (50 kg S° ha−1) or Agri-Sul (100 kg S° ha−1). Application of S° fertilizer significantly decreased the pH in both soils. Organic C declined in S°-treated plots of the Waitville soil, and there was a narrowing of C:N:S ratios in both soils. Application of S° fertilizer significantly increased the total S, HI-S and sulfate sulfur levels of both soils. There was a 29–45% and 2–51% decline in microbial biomass carbon content due to S° fertilizer application in Waitville and Loon River soils, respectively. Repeated application of S° also resulted in a decline in respiration, dehydrogenase, urease, alkaline phosphatase and arylsulfatase activities, along with populations of protozoa, algae and nitrifiers in both soils. Significant correlations observed among related characteristics further emphasized the treatment effects. These results indicate that the impact of repeated application of S° fertilizer on microbial biomass and activity should be considered when recommending S° as a fertilizer for sulfur-deficient soils. Key words: Sulfur (elemental), microbial biomass, dehydrogenase, urea, phosphomonoesterases, arylsulfatase