Effects of nitrogen sources on development of netted scab

In a field trial series different nitrogen sources and rates of seed infection with netted scab were compared regarding their effects on plant development, yield, tuber size distribution and the prevalence of netted scab in the progeny. Nitrate stimulated netted scab infection in the progeny more than ammonium ions did, although the differences, on average, were moderate. However, in 3 out of 14 trials calcium nitrate application resulted in a much higher level of netted scab infection in the progeny compared with NPK and ammonium sulphate fertilizers. Reasons for the variations in results are discussed.