Fertilizer Type, Tillage, and Application Time Effects on Recovery of Sulfate-S from Elemental Sulfur Fertilizers in Fallow Field Soils

Abstract

Elemental sulfur (S) fertilizers may cost less per unit of S than sulfate-S (SO4-S) fertilizers, but oxidation of elemental S to plant-available SO4-S depends on fertilizer type and soil conditions. The objective of this study was to investigate the effects of S source, time of application, soil type and tillage on recovery of applied S as SO4-S in fallow field soils. Field experiments were conducted at five locations on Black Chernozem (Udic Boroll), Dark Gray Chernozem (Boralfic Boroll) and Gray Luvisol (Boralfs) soils in the Parkland zone of Canadian Prairies. The recovery of <100% from previous season Na2SO4 application in some cases indicated loss of fertilizer S from the soil SO4-S pool. The recovery results showed that only up to 44% of the spring applied elemental S could be recovered during the same growing season. The greater recovery of spring applied elemental S in October compared to July suggests that there is a considerable potential for SO4-S loss from soil over the winter and in early spring. The higher SO4-S recovery from Na2SO4 compared to elemental S fertilizers [Fine S, Urea S (A), Urea S (B) and Bentonitic S (A)] following their application in the previous season showed no extra residual benefit from elemental S fertilizers relative to the SO4-S fertilizer. Among the elemental S fertilizers, Fine S gave more recovery of SO4-S compared to Urea S (A), Urea S (B) and Bentonitic S (A). Tillage increased SO4-S recovery from applied S in one experiment but had inconsistent influence in another. The substantial differences in the SO4-S recovery from different soils indicated the influence of soil type on oxidation rate and recovery of applied S at a given time. In conclusion, the findings suggest that only a portion of the applied elemental S could be recovered as SO4-S at any of the sampling times. The recovery of residual S in the following year was always lower from elemental S fertilizers than Na2SO4, and the recovery at a given time was influenced by soil type and tillage.