TABLE CONTENTS

Skimming the Surface: The Effects of Organic Amendments and Tillage
on Soil Nematode and Protozoan Communities
Zasada, I. (1), A. Treonis (2), E. Austin (2) & L. Spicer (2)
(1) USDA-ARS Nematology Laboratory, Beltsville, MD, 20705, USA (2) Department of Biology, University of
Richmond, Richmond, VA, 23173, USA.
Soil microfauna (nematodes and protozoa) have been shown to be responsive to soil
manipulations, but few experiments have investigated whether these responses vary across
the soil profile. We investigated the response of the soil food web to organic amendments
and tillage at two depths in a field experiment. Organic amendments were incorporated into a
tomato:bean:corn rotation through application to soil in the spring and fall over a three-year
period. We hypothesized that the addition of amendments would positively influence
protozoa and nematodes primarily in the surface layers of the soil, but that this effect could
be extended into deeper layers via tillage. Soils were sampled (0-5 cm and 5-25 cm) at the
initiation and at the end of the growing season. Organic amendments had positive effects on
most measured variables on both sampling dates, but these results mainly were confined to
the top 0-5 cm of the soil. For example, organic amendments enhanced soil organic matter
content in the top 0-5 cm of the soil profile but not in the deeper layer. Amended soils also
had higher respiration rates in the top layer than control soils, and this effect was correlated
with higher densities of both protozoans (amoebae and flagellates) and nematodes
(specifically Rhabditidae and Panagrolaimidae). Nematode density was further enhanced by
tillage in amended soils, but tillage had no effect on the other measured variables. Nematode
and protozoan densities were lower in the 5-25 cm layer but did not vary between treatments.
The results of this study suggest that soil microfaunal responses to organic amendments tend
to be confined to the surface layer (0-5 cm) of soil regardless of tillage. Future research
evaluating the influence of agricultural management practices on soil microfauna should
employ sampling schemes to account for stratification of resources.
5 th International Congress of Nematology, 2008 274