Abstract
Direct and recursive estimation models for the oxidation rate of elemental sulfur (S°) in soil have been proposed, both essentially based on a constant oxidation rate per unit area of exposed surface. Fertilizer S° is taken to consist largely of blocky shaped particles, i.e. having similar dimensions along three axes, which can be treated as equivalent spheres. The most important implication in applying the rate assumption to these shaped particles is that the mass at any time is related to the cube of the time. This has been verified experimentally for oxidation by thiobacilli. Although the assumption is less likely for heterotrophs, experiments involving four soils conformed to the cubic relation.
Implications for the particle variables of size and size distribution have been given more limited testing. The data are generally consistent with theory, such as independence of the rate constant with particle size.
Assuming an activation energy for the oxidation process implies, in addition to the above, an exponential relation of rate constant with temperature. This is supported by experiment. Values for the activation energy are approximately 85 kJ mol−1, and therefore consistent with the rate limiting step for the oxidation being a chemical or biochemical reaction, rather than a diffusion process.
Because absolute rate constants are generated by the models, they are useful for examining the effects of environmental variables not hitherto included. Empirical relationships, once established, can then be included in the model, such as the quadratic relation between rate constant and soil moisture, with the maximum at approximately field capacity.
The delay time (the time to reach maximum oxidation rate) was useful, together with the rate constant, for distinguishing species of oxidizing microorganisms. Typically, under optimum conditions at 25°C, thiobacilli have a delay time of several days and a rate constant of 50µg cm−2 day−1 S, while heterotrophs have a negligible delay time but a rate constant of only 5µg cm−2 day−1 S.
The cubic model with a single rate constant gave a surprisingly good fit to the oxidation rate over 12 months in New Zealand pastoral soils under field conditions of varying temperature and moisture. This was attributed to the balancing effect of moisture and temperature on the rate constant under the cool temperate climate. A knowledge of the annual average soil temperature is sufficient to provide advice on the optimum particle size for S° fertilizer.
Article PDF
Similar content being viewed by others
Explore related subjects
Discover the latest articles, news and stories from top researchers in related subjects.Avoid common mistakes on your manuscript.
References
Barrow NJ (1971) Slowly available fertilizers in southwestern Australia. 1. Elemental sulfur. Aust J Exp Agric Anim Husb 11: 211–6
Chapman SJ (1989) Oxidation of micronized elemental sulphur in soil. Plant and Soil 116: 69–76
Chapman SJ (1990) Thiobacillus populations in some agricultural soils. Soil Biol Biochem 22: 479–482
Chatupote W (1990) An investigation of some factors influencing the rate of oxidation of elemental sulphur fertilizers. PhD Thesis. Palmerston North, New Zealand: Massey University
Chopra SL and Kanwar JS (1968) Effect of some factors on the transformation of elemental sulfur in soils. J Indian Soc Soil Sci 16: 83–8
Dana M (1992) Sulfur sources for flooded and nonflooded rice and pastures. PhD Thesis. Armidale, Australia: University of New England
Deng S and Dick RP (1990) Sulfur oxidation and rhodanese activity in soils. Soil Sci 150: 552–560
Fawzi Abed MAH (1976) Rate of elemental sulfur oxidation in some soils of Egypt as affected by the salinity level, moisture content, temperature and inoculation. Beitr Trop Landwirtsch Veterinaermed 14: 179–85
Fox RL, Atesalp HM, Kampbell DH and Rhoades HF (1964) Factors influencing the availability of sulfur fertilizers to alfalfa and corn. Proc Soil Sci Soc Am 28: 406–408
Germida JJ, Lawrence JR and Gupta VVSR (1984) Microbial oxidation of sulphur in Saskatchewan soils. Proc Int Sulphur 1984 Conf: 703-710
Janzen HH and Bettany JR (1987) Measurement of sulfur oxidation in soils. Soil Sci 143: 444–452
Janzen HH and Bettany JR (1987) The effect of temperature and water potential on sulfur oxidation in soils. Soil Sci 144: 81–89
Kittams HA and Attoe OJ (1965) Availability of phosphorus in rock phosphate-sulfur fusions. Agron J 57: 331–4
Lee A, Boswell C and Watkinson JH (1988) Effect of particle size on the oxidation of elemental sulphur, thiobacilli numbers, soil sulphate, and its availability to pasture. New Zealand J Agric Res 31: 179–186
Lee A, Watkinson JH, Orbell G, Bagyaraj J and Lauren DR (1987) Factors influencing dissolution of phosphate rock and oxidation of elemental sulphur in some New Zealand soils. New Zealand J Agric Res 30: 373–385
Lee A, Watkinson JH and Lauren DR (1988) Factors affecting oxidation rates of elemental sulphur in a soil under a ryegrass dominant sward. Soil Biol Biochem 20: 809–816
Li P and Caldwell AC (1966) The oxidation of elemental sulfur in soil. Proc Soil Sci Am 30: 370–372
McCaskill, MR (1984) The residual effects of elemental sulfur as a pasture fertilizer. MRurSc Thesis. Armidale, Australia: University of New England
McCaskill MR and Blair GJ (1989) A model for the release of sulfur from elemental S and superphosphate. Fert Res 19: 77–84
Meyer B (1977) Sulfur, energy and the environment. Amsterdam: Elsevier
Moser US and Olson RV (1953) Sulfur oxidation in four soils as influenced by soil moisture tension and sulfur bacteria. Soil Sci 76: 251–256
Shedley CD (1982) An evaluation of elemental sulfur as a pasture fertilizer. PhD Thesis. Armidale, Australia: University of New England
Swartzendruber D and Barber SA (1965) Dissolution of limestone particles in soil. Soil Sci 100: 287–291
Watkinson JH (1988) Rate equations for the oxidation of elemental sulphur in soil. Massey Fertilizer and Lime Research Centre Occasional Report No. 2: 26-31
Watkinson JH (1989) Measurement of the oxidation rate of elemental sulfur in soil. Aust J Soil Res 27: 365–375
Watkinson JH (1993) Oxidation rate of elemental sulfur particles with a wide range of sizes. Aust J Soil Res 31: 67–72
Watkinson JH and Lee A (1992) A mechanistic model for the oxidation rate of elemental sulphur in soil tested on results by HPLC. Proc Middle East Sulphur Sym Feb 1990: 163–171
Watkinson JH, Lee A and Lauren DR (1987) Measurement of elemental sulfur in soil and sediments: Field sampling, sample storage, pretreatment, extraction and analysis by high-performance liquid chromatography. Aust J Soil Res 25: 167–178
Watkinson JH and Perrott KW (1990) A new soil test for sulphate and mineralised organic sulphur. Proc New Zealand Fert Manufacturers' Res Assoc Conf: 188-198
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Watkinson, J.H., Blair, G.J. Modelling the oxidation of elemental sulfur in soils. Fertilizer Research 35, 115–126 (1993). https://doi.org/10.1007/BF00750225
Issue Date:
DOI: https://doi.org/10.1007/BF00750225