From 1980 to 1982 fungicide and aphioide sprays were tested in factorial combination with four amounts of nitrogen fertilizer, applied in one or two dressings to winter wheat, on three contrasting clay soils. These experiments were at Hexton (Burwell series) in Hertfordshire, at Billington (Evesham series) and at Maulden (Hanslope series) in Bedfordshire, following a 2–year break, an all-cereal rotation, and continuous wheat respectively. The nitrogen dressings were calculated after taking into account mineral N in the soil. In 1981 and 1982 soil density was measured by penetrometer. This showed compaction in soil at Maulden 28 cm deep which caused waterlogging in spring; this delayed growth which was not made good later.

At Hexton a small seed rate was used; plant losses during winter were proportionally larger than elsewhere. At Billington, the maximum number of stems occurred in March and elsewhere in April. Despite these differences in seed rate and number of plants, number of ears varied little, and each year the wheat at Hexton accumulated dry matter most rapidly. The growth rate there ranged from 20·0 to 21·8 g/m2/day during the linear growth phase as compared with 14·4 to 16·6 g/m2/day at the other two sites. Giving N in two dressings rather than in one increased dry-matter yield at all sites in May, but later this benefit remained static and so became a smaller proportion of the total. Fungicides increased post-anthesis dry-matter yield by 0·75 t/ha, most of which was incorporated in the grain.

Mean grain yields from 1980 to 1982 where nitrogen fertilizer was given were 9·86 t/ha at Hexton, 7·88 t/ha at Billington and 6–91 t/ha at Maulden. Additional nitrogen fertilizer always increased grain yield when fungicides and aphicides were given, but not where they were not. Grain yields in excess of 10 t/ha were achieved with numbers of ears ranging between 360 and 435/m2. The components of yield showed that grain yield was related to the number of grains per ear and 1000·grain weight, but not number of ears. Grain weight was increased by 3·1 mg by the fungicides.

The fungicides controlled the diseases eyespot (Pseudocercosporella herpolrichoides), Septoria spp. and yellow and brown rust (Pucdnia striiformis and P. recondita) where they occurred, but even where these diseases were absent or at very low levels the fungicides significantly increased grain yield. At Billington and Maulden take-all (Qaeumannomyces graminis) infected between 44 and 90% of the plants and sharp eyespot (Rhizoctonia cerealis) infected from < 1 to 20% of the stems because the wheat followed cereals. Yields of straw behind the combine-harvester were from 50 to 70% of those obtained from sheaves cut at ground level.