Soil Property Influences on Xiphinema americanum Populations as Related to Maturity of Loess-Derived Soils

Field populations of Xiphinerna americanum around roots of Syringa vulgaris 'President Lincoln' were larger in Marshall silty clay loam, a medially developed loess soil, than in Monona silt loam, a minimally developed loess soil. Most X. amerieanum occurred in the top 15 cm of soil, with few below 30 cm. Maximum numbers occurred in August of both years in the Marshall soil, and in August 1969 and June 1970 in the Monona soil. Population fluctuations during the growing season were coincident with changes in soil moisture content. Although the population fluctuation pattern was the same at each depth tested, the adult-to-juvenile ratio increased in one soil while it decreased in the other. Numbers of X. americanum decreased as root weights decreased within a soil profile, but they were not correlated with root weights over all soils and depths. More X. americanum were recovered from the Marshall than from the Monona soil, but fibrous root weights were greater in the Monona soil. Survival of X. americanum in soil columns in growth chamber experiments was better in the Marshall than in the Monona soil. Movement and survival were different in identically textured Monona A and B horizon soils. Factors related to the ion exchange sites may affect X. americanum.