Two experiments compared yields of spring barley following barley, oats, beans {Viciafaba), red clover (cut) and (one experiment only) oil-seed rape, and tested effects of trefoil (Medicago lupulina) undersown in the preliminary crops of barley and oats. N fertilizer was applied at two rates to preliminary crops, and four rates to the final crop in each experiment. Barley following barley suffered severely from take-all disease (Qaeumannomyces graminis var. tritici); barley after other crops was little affected. Other recognized soil-borne diseases were unimportant. Barley yielded less after barley than after other crops except where excessive N fertilizer caused lodging. Clover and beans left N residues equivalent to about 88 and 44 kg fertilizer N/ha respectively; undersown trefoil left inconsistent N residues. Couchgrass (Agropyron repens) was more prevalent after barley than after other crops.

SUMMARYThe yield of wheat and the incidence of take‐all were measured in crops grown in six different 4‐year sequences, repeated in 3 successive years. The first crop of winter wheat grown after oats or beans yielded 13–23 cwt/acre (1632–2887 kg/ha) more grain than wheat after wheat or barley. Spring wheat after oats yielded 2–5 cwt/acre (250–625 kg/ha) more than spring wheat after wheat. The smaller yields of wheat after wheat or barley were caused mostly by greater prevalence of take‐all. Regression analysis indicates that each 1 % increase in straws with take‐all decreased yield of winter wheat by 0·6%. Take‐all was more prevalent in the second and third successive wheat crops after oats than in the fourth crop.

SUMMARYAssessments of Phialophora radicicola var. graminicola (PRG) and Gaeumannomyces graminis var. tritici (GGT) were made by culturing and by direct microscopic examination of pieces of seminal roots from 16 winter wheat crops grown in different cropping sequences and with different phosphate manuring. PRG occurred on all wheat crops, but was abundant only on wheat after grass, where it seemed to delay the onset of damaging take‐all by 1 yr. Delayed occurrence of take‐all by phosphate fertiliser was not related to differences in populations of PRG. Wheat grown in ‘take‐all decline’ soils had only small amounts of PRG, indicating that the development and the decline of take‐all epidemics may be influenced by different biological control mechanisms; breaking sequences of wheat crops by 1 yr grass leys might harness the advantages of both mechanisms.

7 7 With 1 text-figure Printed in Great BritainTake-all, Gaeumannomyces graminis var. tritici, and yield of wheat grown after ley and arable rotations in relation to the occurrence of Phialophora radicicola var. graminicola

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