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An Evaluation of Elemental Sulfur-Sewage Sludge Combinations and Waste Gypsum as Sulfur Sources

Sulewski, G.D. 1996. M.Sc. Thesis. Dept. Soil Science, University of Saskatchewan, Saskatoon, SK

Abstract

Elemental sulfur (So) was combined with dried anaerobically digested sewage sludge (DDS) from Saskatoon to form fertilizer mixtures. These So combinations were studied in both loose and pelletized form to discern the role of DDS as a fertilizer binder and a potential stimulator of heterotrophic So oxidation. Additionally, two waste gypsum sources from Saskatchewan were evaluated as sulfate fertilizer alternatives: (1) waste wallboard (23% S, air-dried, pulverized) and (2) sodium sulfate mining by-product (20.9% S, air-dried, crushed and sieved < 2mm). Elemental sulfur combinations consisting of various proportions of So, DDS and hydrated lime (Ca(OH)2 ) were created, incubated and microscopically examined. An incubation lasting 12 weeks was used to examine the short-term release of sulfate from wallboard as well as fine (mean particle size = 82 5 μm) and coarse (MPS = 353 5 μm) So combinations. Sulfate supply potential and the effects of granular So pelletization were studied in the growth chamber with canola as the test crop. An apparent link existed between enhanced So oxidation rate and a modified surface environment produced by the combination of So DDS lime. Soil amendment with So combinations containing DDS lime or lime alone showed superior initial oxidation rates than So alone. Growth chamber observations revealed higher canola yield and sulfate recovery with application of So combinations containing DDS lime over So alone. Attempts at pelletizing the So combinations resulted in improved handling characteristics, but lowered product performance due to poor dispersion in soil. The potential role of DDS, heterotrophic populations and lime on So oxidation were assessed through measurement of soil CO2 evolution. The addition of So DDS lime prevented the depression in soil CO2 evolution observed with So amendment alone. Compared to immediately soluble sulfate, the recovery of wallboard-derived sulfate in soil incubation (12 weeks) was lower. Growth chamber tests lasting six weeks revealed a 37% lower S recovery from wallboard gypsum than soluble sulfate. The potential for using DDS to enhance So oxidation and the sulfate release of waste gypsum was studied under field conditions at Star City, Saskatchewan using canola as the test crop. Yield and sulfur uptake were assessed at three rates of sulfur (20, 40 and 80 kg S ha-1 ) on a Gray Luvisolic soil (Porcupine Plain association). Variability and an underestimation of the soil sulfur supplying power obscured the effects of DDS lime on enhancing So oxidation. Based on crop sulfur uptake data, wallboard gypsum was often comparable to ammonium sulfate. Application of mine gypsum produced lower mid-season and final sulfur uptake compared to wallboard and ammonium sulfate. The crystalline nature of mine gypsum restricts product effectiveness, but it has better handling qualities than pulverized wallboard. The waste gypsum sources provided significantly lower sulfur use efficiency (SUE) at 20 kg S ha-1 than ammonium sulfate; however no difference was observed at 40 and 80 kg S ha-1.