SummaryThe effect of previous rotations maintained for 21 years on wheat and potatoes grown after 5 years of uniform cropping are described and discussed. Effects of length of ley in the rotation were detected in soil organic carbon, yield of wheat and yield of potatoes 6, 6 and 7 years respectively after the last ley was ploughed up. The effect of grazing the leys compared with mowing was detected in soil organic carbon and in yield of potatoes, and that of applying dung was detected in soil organic carbon and in yield of potatoes 12 and 13 years, respectively, after the last application.

A trial to investigate possibilities of berry control by cultivation depth is described. Tubers planted at 10 cm produced significantly more potato plants in flower than those planted at 30 cm at the commencement of flowering. However, 3 weeks later the difference in numbers of flowers had disappeared. Emergence of overwintered tubers was about 53%, and of spring-planted tubers about 97%. Depth of planting did not affect emergence. A comparison of overwintered and spring-planted potato tubers showed earlier flowering and berry production by the overwintered tubers of about 1 week on average compared with the spring-planted tubers.

An experiment comparing continuous winter wheat with the two wheat crops in a rotation of beans, oats, wheat, wheat, with four rates of application of N fertilizer, is described and the results discussed.The wheat following wheat in the rotation consistently outyielded the wheat following oats, but the continuous wheat yielded on average less. Response to N fertilizer was not affected by sequence of cropping and since there was practically no response to the highest increment of N, it is clear that additional N could not have brought the yield of the continuous wheat up to the level of the wheat in rotation.

Soils derived from Gault Clay in the eastern region of England are notorious for giving very variable yields of wheat. Whereas in recent years yields on other soil types have increased remarkably, largely owing to the use of high-yielding varieties and increased use of nitrogen (e.g. Holbrook, Osborne & Ridgman, 1982), yields from Gault Clay soils have remained at much the same level as the best crops of 30 years ago.

Hanley & Ridgman (1979) reported the results from three cycles of six-course rotations on light land. The report was based on a rotation of sugar beet, barley, barley, potatoes, barley, barley, with treatments involving replacement of one, two or three of the first three crops by 1-, 2- or 3-year leys, the last three crops acting as test crops. One of the problems of drawing general conclusions from rotation experiments is that the test crops are really part of the experimental treatments and may not be the most suitable crops for determining either the direct effects of the ‘treatment’ crops or the longer-term effects of the rotations themselves.