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Ecology of Nematodes in Clarion-Webster Toposequences Associated With Glycine Max (L.) Merrill¹

ABSTRACT

Toposequence variations in soil and plant properties were characterized and related to nematode populations associated with soybeans. The smallest populations of Aphelenchus avenae, Helicotylenchus pseudo-robustus, Tylenchorhynchus nudus, Tylenchus spp., and non-stylet-bearing nematodes occurred at the toeslope position within the toposequences. Increases in soil pH, soluble salts, percentages of the soil pores filled with water, soil moisture relative to field capacity, silt plus clay, and soil organic matter within the toposequences were associated with decreases in nematode populations, plant top weight, and the concentrations of nitrogen, potassium, and barium in the plant tops. Factor analysis of the data revealed that 67–73% of the total site-sampling period variance could be accounted for by soil structure, root activity, soil fertility, dry matter production, and nematode factors. However, nematode populations were more closely correlated with plant variables than with soil variables at each toposequence.

¹ Journal Paper no. J-6720 of the Iowa Agr. & Home Econ. Exp. Sta., Ames, Iowa 50010. Project no. 1337. This investigation was supported by US Department of Agriculture, Agricultural Research Service Grant 12-14-100-9168 (34).

² Research Associate, Colorado State Univ.; Professor of Agronomy, Iowa State Univ.; and Professor of Plant Pathology, Iowa State Univ., respectively.

Received for publication January 1, 1971. Accepted for publication October 20, 1971.