Eyespot in wheat after four‐course rotations and 3 1/2‐year leys

SUMMARY In a long‐term ley‐fertility experiment, on old arable land, the treatments include various 3 1/2‐year leys and an arable four‐course rotation—barley, fodder‐beet, barley, undersown with a 1‐year ley. The yields of winter wheat following most of the 3 1/2‐year leys are higher than after the arable rotation. To determine whether this is partly due to disease, the wheat was examined in 1957, 1958, 1959 and 1961 for soil‐borne diseases, mainly eyespot ( Cercosporella herpotrichoides) and take‐all ( Ophioboltis graminis ). Very little take‐all occurred. The amount of eyespot was negligible in 1957. In the other years, examination of the wheat suggested that the amount of eyespot in the soil was low during 1‐year leys and hayed 3 1/2‐year leys, and during grazed 3 1/2‐year leys not receiving nitrogen fertilizer, but possibly not during grazed 3 1/2‐year leys receiving heavy dressings of nitrogen. The 1‐year leys were probably as good as the 3 1/2‐year leys at controlling eyespot. The main factor affecting the level of eyespot in the wheat appeared to be the level of mineral nitrogen in the soil under the wheat. In wheat not receiving nitrogen fertilizer, between 4 and 24% of the culms bore eyespot. When the wheat received 78 lb. N per acre after the 1‐year ley of the arable rotation, up to 49% of the culms bore eyespot; and when the wheat received 52 lb. N per acre after heavily‐manured grazed leys (the residues of which contained much mineralizable nitrogen), up to 60% of the culms bore eyespot. Nevertheless, the increases in mineral nitrogen increased the yields of wheat. Although the wheat yields were probably not depressed by eyespot, the large amount of eyespot associated with some treatments, notably where both the 3 1/2‐year grazed leys and the subsequent wheat received nitrogen fertilizer, was potentially important to the survival of the disease.