Changes in soil extractable sulphate under field fallow conditions after application of three contrasting sulphur fertilizers

Abstract

A field fallow soil monitoring method was used to evaluate the time of appearance of inorganic sulphate-S from two types of fertilizer S, elemental and sulphate, under the humid weather conditions of coastal British Columbia. In addition to both these types being applied as commercially produced granules, elemental S was applied as a powder. All three S-fertilizers were surface applied, but not incorporated as would likely occur when applied to forages. Soil analyses on a control (no S added) showed that there was limited evidence of leaching of sulphate beyond 30 cm. This meant sampling the soil to 30 cm depth was sufficient to examine the effect of a single spring application of the fertilizer over a full year. Differences in appearance of sulphate in the soil from the three fertilizer sources were distinguished by soil analyses, but the relatively large variability of the measurements limited the precision of time differentiation. The recovery calculations showed that inorganic sulphate from the fertilizers changed to another form (assumed to be organic S) as the season progressed. Maximum recovery of the granulated gypsum fertilizer (62–80%) was greater than for powdered elemental S (36–65%), which was slightly greater than for the SulFer 95 granulated elemental S fertilizer (33–48%).Key words: Elemental S, granulated S, gypsum, S fertilizers, extractable inorganic sulphate