Monday, 7 November 2005

Effect of Soil pH on Performance of Soybean Cyst Nematode Resistant Varieties.

Vladimir Costa1, Palle Pedersen1, and Greg Tylka2. (1) Department of Agronomy, Iowa State University, 2104 Agronomy Hall, Ames, IA 50011, (2) Department of Plant Pathology, Iowa State University, 351 Bessey Hall, Ames, IA 50011

Soybean cyst nematode (Heterodera glycines; SCN) is the biggest yield robber on soybean [Glycine max L. (Merr.)] in Iowa. Previous research has shown that H. glycines populations tend to be higher on high soil pH. Our hypothesis is that we may need to change current H. glycines management recommendations under high soil pH. The objective of this study was to determine yield impact of ten soybean varieties with different reactions to H. glycines (PI88788, Peking, Hartwig derived and susceptible) in fields with different soil pH. The experiment was conducted at two northern and two southern locations in Iowa. The experimental design was a randomized complete block in a split-split-plot arrangement with four replications. Main plots were two planting dates (early versus late May). The sub-plots were 4 treatments of a nematicide (Aldicarb). The sub-subplots were ten soybean varieties. Soil samples were collected from each plot at planting and at harvest to determine the initial (Pi) and final (Pf) population densities of H. glycines. Nematicide data will not be presented in this poster. No effect of soil pH was observed on varieties in either zone. A planting date by variety interaction was observed in the northern zone. Early planting date yielded 8.3% and 9.6% greater than the late planting date in the northern and in the southern zone, respectively. At the northern locations, susceptible and PI88788 resistant varieties yielded better than Hartwig derived varieties and reduced Pf significantly. Nevertheless, at the southern locations susceptible varieties yielded better than PI88788 or Hartwig derived varieties with no impact on Pf. Research will continue in 2005 and 2006 to see if it will be beneficial to alter current SCN-management recommendations based on soil pH.

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