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
cuts 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 denitrification.
Herbage dry matter and N yields were significantly increased by the application of S at the high
N level at the sandy loam site (Halse). At the clay loam site (Great Close) the application of S had
no significant effect on herbage 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 the N[ratio ]S ratio of herbage on the plots without S, especially
at first cut, and 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 the low N treatments in 1997
and 1998, respectively. Application of S at high N at Halse reduced the peak concentration of nitrate-N in leachate from 27·3 mg N/l to 9·3 mg N/l. At Great Close, application of S had no significant
effect on the amount or peak concentration of nitrate-N leached. The improvement in efficiency
reported at Halse suggests that on permeable soils receiving high levels of N, the application of S
could have a large effect on nitrate leaching and its associated environmental impact.