The results of 173 field experiments carried out between 1957 and 1986 are presented comparing ammonium nitrate and urea as top-dressings for winter cereals and grassland.The trials show that urea was an inferior nitrogen source to ammonium nitrate. The yield from ammonium nitrate was significantly greater than that from urea for winter wheat, winter barley and for first, second and third cut silage. The results suggest (a) that winter wheat and winter barley respond differently to the two nitrogen sources and (6) that yield losses from urea are just as likely on first cut silage as second or third cut.

Research conducted on sowing dates has shown a trend towards increased yield as sowing is advanced for winter wheat (Darwinkel, Hay & Kuizenga, 1977; Walker, 1980) and winter barley (Selman, 1980; White, 1981). Green & Ivins (1985) have quantified the rate of yield decline for winter wheat as sowing is delayed after mid-September, giving a mean value of 0–35% per day. For a similar study on winter barley (Green, Furmston & Ivins, 1985) a yield decline of 0–43% per day delay in sowing was attributed to reductions in the number of ears per unit area as planting was delayed.

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