Assessment of elemental S-sludge mixtures and waste gypsum as fertilizer sources
Two separate studies (soil incubation and growth chamber) were used to assess the release of plant available sulfate from two alternative sulfur sources: (1) combinations of finely ground elemental sulfur, dried digested sewage sludge, and lime, and (2) waste gypsum. Bulk mixtures were created and subjected to a elemental-S oxidation stimulating period. Preparation of waste gypsum involved flail grinding of waste wallboard and sieving through a standard 2 mm sieve. All fertilizer treatments were subsequently added to soil at a rate of 100 ug S g-1 soil. The soil incubation parameters assessed included 0.01M CaCl2 extractable sulfate, and anion exchange membrane (AEM-exchangeable sulfate accumulation over time. The growth chamber study parameters included plant S uptake, residual soil sulfate and canola Brassica napus) yield. Results suggest an enhancement of elemental-S oxidation with addition of sewage sludge and lime as indicated by higher cumulative sulfate recoveries and plant yield. The potential exists for improving both the effectiveness and handling ease of finely ground elemental-S. Waste gypsum performance suggests intermediate release rates compared to conventional sulfate sources, but also points to a fertilizer less susceptible to gaseous and leaching losses under conditions of excess moisture.
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