Correlation between Soil pH, Heterodera glycines Population Densities, and Soybean Yield

Soybean cyst nematode (Heterodera glycines Ichinohe) is the most damaging pathogen of soybean [Glycine max (L.) Merr.] in the United States. Observations in fields suggest that high H. glycines population densities are associated with high soil pH, but H. glycines and soil pH have not been linked to soybean yield. The objective of our study was to assess the relationship between soil pH and H. glycines population densities and subsequent effect on yield. Experiments were conducted in Wisconsin from 1997 to 2000 and in Iowa from 1996 to 1998. Results were consistent among the experiments and showed a positive correlation between soil pH and H. glycines population densities and a negative correlation between yield and both soil pH and H. glycines population densities in both states. In the Wisconsin experiment, yield of both H. glycines–resistant and H. glycines–susceptible cultivars decreased as pH increased, but the decrease was less with H. glycines–resistant cultivars. Overall, results indicate that H. glycines population densities and the impact of nematode population densities on soybean yield are related to soil pH; however, the mechanism of these interactions is unknown.