Potassium and phosphorus have no effect on severity of charcoal rot of soybean

Charcoal rot of soybean [Glycine max (L.) Merr.] caused by Macrophomina phaseolina is a disease of economic significance throughout the world. The effects of potassium (K) and phosphorus (P) fertilizer on disease development are unknown. Therefore, two separate trials were conducted in the field during 2008, 2009 and 2010 at Jackson and Milan, TN, USA to evaluate the effects of K and P on severity of charcoal rot. Rates of K (0, 45, 90, 134 and 179 kg K2O ha−1) and P (0, 22, 45, 67 and 90 kg P2O5 ha−1) were used, with a sixth rate ranging from 0–22 for P and 0–37 for K equal to the recommended K or P fertilizer application based on annual soil testing. The colony forming units of M. phaseolina in soil indicated no significant response for any P treatments in five of six location-by-year and for K applications in all six location-by-year environments. Similarly, no significant response in tissue CFU for all P and K treatments in all six location-by-year environments was observed, indicating that th...