The effect of sulphur application on the efficiency of nitrogen use in twocontrasting grassland soils

The effect of sulphur (S) application on the efficiency of nitrogen (N) use was investigated using cut plot experiments on two contrasting soil types. Nitrogen was applied at 200 and 450 kg N/ha per year, with and without 38 kg SO3/ha (15.2 kg S/ha) per cut. Over three conventionally timed silage cu ts for 2 years, measurements were made of herbage dry matter, the yield of N and S in herbage and losses of N and S by leaching, and N by denitrificat ion. Herbage dry matter and N yields were significantly increased by the applica tion of S at the high N level at the sandy loam site (Halse). At the clay l oam site (Great Close) the application of S had no significant effect on he rbage dry matter or N yields. At Halse, the pattern of response through the year was not the same in the 2 years studied, although in both, the effect of S was significant at third cut at high N. Deficiency was suggested by t he N:S ratio of herbage on the plots without S, especially at first cut, an d at later cuts at Halse. Nitrate leaching was reduced by S at Halse by 72% and 58% with high N in 1997 and 1998, respectively, and by 10% and 5% on t he low N treatments in 1997 and 1998, respectively. Application of S at hig h N at Halse reduced the peak concentration of nitrate-N in leachate from 2 7.3 mg N/l to 9.3 mg N/l. At Great Close, application of S had no significa nt effect on the amount or peak concentration of nitrate-N leached. The imp rovement in efficiency reported at Halse suggests that on permeable soils r eceiving high levels of N, the application of S could have a large effect o n nitrate leaching and its associated environmental impact.