Effect of subsurface clay on nematode communities in a sandy soil

A variety of soil properties can directly or indirectly affect nematode community structure. The effects of subsurface clay content (at 20-40 cm depth) on nematodes in the surface layer (0-20 cm depth) of a sandy soil were examined in field experiments in Florida, USA. Plots were established in a site with a relatively uniform sandy upper soil layer (88-91% sand and 5-7% clay at 0-20 cm depth) but with varying levels of clay in the subsurface layer (3-35% clay at 20-40 cm depth). Nematode numbers in the surface soil layer were affected by the amount of clay in the subsurface layer. Population densities of a number of: different nematode genera were greater in the surface layer of plots with 35% subsurface clay than in plots with 3% subsurface clay. Indices of nematode community structure were largely unaffected, since effects of subsurface clay were observed across all nematode groups. Most nematodes (70-80% of total numbers) occurred at 0-20 cm depth, although Teratocephalus was more common at 20-40 than at 0-20 cm. Subsurface clay content indirectly affected soil moisture and other environmental factors in the upper soil layer in which most nematodes reside. (C) 2002 Elsevier Science B.V. All rights reserved.