Twenty-six experiments were carried out in England and Wales from 1983 to 1985 to compare urea and ammonium nitrate (AN) as N top-dressing for cereals over the range 100-300 kg\ha N. Most of the experiments were sited on chalky or other soils of pH 7n0 where the greatest differences in effectiveness were expected.The results showed that while relative N offtake in grain was 2n5 % greater from AN, there was no difference in grain yield. Splitting the main N application increased N offtake from urea but not from AN. Overall, urea effectiveness from a single application at GS 31 increased with increasing rainfall on the day of application, but was not increased by subsequent rainfall. On chalk soils, urea effectiveness increased with increasing cumulative rainfall up to the fifth day after application. There was little effect of rainfall on urea effectiveness when the dressing was split. Although grain yield was unaffected by the type of fertilizer N applied, grain N concentration was usually less from urea.The fertilizer N requirement for optimum yield (N opt ) was similar for both fertilizers. Splitting the main N application had no effect on yield or N opt . We conclude that urea is a satisfactory source of N for cereals.

SUMMARYForty-one experiments were carried out in England and Wales between 1983 and 1985 to compare ammonium nitrate and urea as N top dressings for multicut silage.The results showed that relative dry matter yields from the two fertilizers differed considerably between sites. However, compared with ammonium nitrate, there was a mean yield decrease with urea of 2% at the first cut and 5% at the second cut. Mean herbage N contents and apparent N recoveries were lower with urea than with ammonium nitrate at both the first and second cuts. It appeared, at least for first-cut dressings applied in early spring, that urea effectiveness increased with the amount of rain falling within 3 days of fertilizer application. The effect was much less obvious at the second cut.Urea effectiveness was not markedly reduced on soils of high pH or light texture, where higher ammonia volatilization losses might have been expected.

Three trials were carried out in separate years during 1987-89 to investigate the effectiveness of cattle slurry as a source of sulphur (S) for grass cut four times per year for silage. They were located on different areas ofthe same field in Dorset, UK, in an area known to be sulphur deficient for intensive grass production. Yields of dry matter and S offtakes in response to sulphur in slurry were investigated and compared with those from gypsum treatments supplying 0-100 or 0-75kgSha~'. Slurry was applied at two times of year, November or February, and at two rates, either alone or in combination with the two lowest rates of gypsum.Annual increases in yield from the slurry applied in February compared with the yield when no slurry was applied were significantly related (r^ = 0-96) to the rate of slurry sulphur applied. For applications in November, the relationship was not significant. Sulphur in slurry increased annual dry-matter yield with an average efficiency of 55% when compared with the sulphur in gypsum. The annual apparent recovery in the herbage of S from slurry was 21-8%, compared with 44-7% from the two lowest rates of gypsum.Cattle slurry, in these and other trials in southwest England, contained on average 0-35 kg S m~' and, at rates currently applied in fanning practice or likely to be applied in the future, would be insufficient to satisfy annual requirements for silage in sulphur-deficient areas.

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