Leaching losses of sulphur from different forms of sulphur fertilizers: a field lysimeter study

Inputs and outputs of sulphur (S) were quantified over a three year period using field lysimeters containing undisturbed 60 cm deep soil monoliths of a sandy loam. There were four treatments, including a control (no S) and three forms of sulphur fertilizers: ammonium sulphate (AS); micronized elemental sulphur (MS0); and bentonite clay and elemental sulphur mixture (BS0). Sulphur was applied at the beginning of the experiment in autumn at 50 kg ha(-1). Atmospheric deposition varied between 6.7 and 7.8 kg S ha(-1) yr(-1). Leaching losses of S ranged from 35 kg ha(-1) in the control to 83 kg ha(-1) in the AS treatment over three years, with dissolved organic S accounting for 6-10% of the S leached. In the first year, 7, 26 and 72% of the applied S was lost to drainage water in the BS0, MS0 and AS treatments, respectively, and the percentages increased to 33, 75 and 96% by the end of year 3. No significant differences in sulphur uptake by herbage were found in any of the harvests except a significant increase in the BS0 treatment in the second cut of the second year. Over three years, total S outputs exceeded total S inputs in all treatments, with the control and the AS treatments showing a larger S deficit (34-35 kg ha(-1)) than the MS0 (23 kg ha(-1)) and BS0 (7 kg ha(-1)) treatments. The deficits indicate a depletion of soil S, probably through net mineralization of organic S. The results confirm that sulphate was highly mobile and prone to leaching under the experimental conditions, whereas the slow release characteristics of elemental S, particularly BS0, led to smaller leaching losses and larger residual values.