Effect of fertilizers and of liming acid soil on common root rot in wheat, and of chloride on the disease in wheat and barley.
Field experiments were conducted in Saskatchewan, Canada, to investigate the effect of fertilizers and of liming acid soil (pH 4.8 (CaCl2)) on common root rot (CRR) and yield of wheat. The effect of potassium chloride (KCl) fertilizer on these variables in wheat and barley was also examined at several locations. Application of lime to raise soil pH to 6.5 or 7.0 in 1963 or 1965 had no influence on CRR severity in spring wheat that was rated over 8 years during 1973-82. However, grain yields were improved by the lime treatments in 5 of 7 years, with an overall mean increase of c. 15% for the wheat on soil limed to pH 6.5. On soil limed to pH 7.0, mean yields over 3 years were improved by 27%. Disease severity was not affected by phosphate (P) or nitrogen + phosphate (NP) fertilizer, but was significantly reduced by KCl in 5 of the 8 years studied. A yield increase averaging c. 12% was associated with P fertilization. The response to P fertilizer was most pronounced in the untreated soil and least in the limed soil. It is suggested that this differential response was probably due to the lower availability of soil P in the unlimed than limed soil. In an experiment on fertilizer rates and K sources, both added K and Cl significantly reduced CRR of wheat in 1 of 4 trials conducted during 1980-82, and over the 4 trials. However, applied K reduced the average yield compared with the control. Mean disease severity and grain yield increased as rates of NP increased. Chloride, but not K, significantly reduced the severity of CRR in 4 of 11 wheat trials and in 7 of 11 barley trials conducted during 1987-89. The Cl effect was consistent in wheat at Swift Current, and in barley at Saskatoon and Scott, suggesting a differential influence of the fertilizer on CRR in these crops. In 7 trials for each of wheat and barley, neither K nor Cl provided a yield benefit. The total N and P contents of wheat and barley foliage were not modified consistently by K or Cl fertilizers. Cochliobolus sativus was identified as the primary cause of CRR, and was isolated from >80% of subcrown internodes from wheat and barley plants in the 1988 and 1989 trials.