From 1980 to 1983 factorial experiments at Saxmundham were made on winter wheat following beans, so as to minimize losses from foot and root rots and increase potential yields. All tested seed-bed N, and amounts and times of application of N in spring, both with and without sprays intended to limit losses from aphids and from diseases. The tests were made on one semi-dwarf variety in 1980 and on two contrasting varieties from 1981 to 1983. In 1982 and 1983 a comparison was made between wheat following beans and wheat following wheat; all treatments were applied cumulatively to the two successive wheat crops.
In 1980 and in 1981 N given in March greatly increased the number of shoots in April but had little effect on the final number of ears. Yields of grain were greatly increased by N given during April and by sequential sprays with fungicides and aphicide; these two factors interacted so that responses to N were larger with the sprays than without. Yield responses to seed-bed N, although small, were greater than the benefits from applying divided instead of single N dressings in spring. The number of ears was greatly increased by increasing the amount of N given in April, but only slightly by any of the other treatments. The weight of 1000 grains was greatly increased by the sprays of aphicide and fungicides and was decreased by N in 1981, but not in 1980. Largest yields of grain were 10·14 t/ha in 1980 and 10·91 t/ha in 1981 when N was given in spring at 160 and 200 kg/ha respectively, and the crops were sprayed with pesticides.
In 1982 and 1983 N applied in March again greatly increased the number of shoots in April, but not the final number of ears. Yields of grain were larger after beans than after wheat, mainly because the number of ears and the weight of 1000 grains were greater. This may have been because take-all (Gaeumannomyces graminisvar. tritici) was more severe where wheat followed wheat. Previous cropping also interacted with variety; Avalon yielded slightly less than Norman where take-all was slight but much less where take-all was severe. Where N was given the mean loss in yield from growing Avalon rather than Norman in the 2 years was 2·47 t/ha after wheat and 0·37 t/ha after beans. The take-all disease ratings of Norman and Avalon after wheat were 132 and 197 respectively. Yields of grain were greatly increased by N given during April, especially of wheat following wheat and where it was protected with sprays; then the mean yield was only 2·79 t/ha without N but 8·78 with 235 kg N/ha. Where wheat followed beans, yields were 6·89 t/ha without N and 11·07 with 175 kg N/ha. Applying N to the seed bed increased yields slightly, and again by more than by dividing the dressing of N in spring. The number of ears was greatly increased by N in spring and a little by all the other factors that increased grain yield. The weight of 1000 grains was increased greatly by the sprays of aphicide and fungicides, was decreased by N, and was larger for Norman than for Avalon.
In 1980–1, after beans, the mean amounts of N removed by the grain (where aphicide and fungicides were given) ranged from 81 kg/ha without N fertilizer to 167 where most N was given. In 1982–3 comparable values ranged from 86 kg N/ha to 191 where wheat followed beans and from 35 kg N/ha to 168 where wheat followed wheat.