Abstract
Tylka, G.L., C. Sanogo, and S.K. Souhrada. 1998. Relationships among Heterodera glycines population densities, soybean yields, and soil pH. Presentation at the 1998 Society of Nematologists Annual Meeting, St. Louis, MO.
A study area of 20.2 ha divided into 0.2-ha cells was established with global positioning system (GPS) technology in 1997 in an Iowa field infested with the soybean cyst nematode, Heterodera glycines. A twenty-core soil sample was collected from each cell at a randomly selected site located using a hand-held GPS unit prior to planting the field with a H. glycines-susceptible soybean variety. For each soil sample, pH was determined, cysts of H. glycines were extracted and counted, then eggs were extracted from the cysts and counted. Average yield of each 0.2-ha cell also was determined. Cyst population densities ranged from 2 to 463 per 100 cm3 of soil; egg densities ranged from 200 to 35,800 per 100 cm3 of soil. Soil pH ranged from 5.5 to 8.0; soybean yields of 820 to 3,258 kg per hectare were obtained. Significant linear correlations between soybean yield and cyst (r = -0.74) and egg densities (r = -0.56) were detected, as well as significant linear correlations between soil pH and cyst (r = 0.62) and egg densities (r = 0.48). The nature of the relationship between soil pH and H. glycines densities is not known.