EFFECTS OF EARTHWORMS IS ON SOIL AGGREGATE STABILITY AND CARBON AND NITROGEN STORAGE IN A LEGUME COVER CROP AGROECOSYSTEM

We investigated the effects of earthworms on soil aggregate size-distr ibution, water-stability, and the distribution of total C and N among aggregates of different sizes. Earthworm populations were experimental ly manipulated (reduced, unaltered or increased) in field enclosures c ropped to soybean (Glycine max). Soil samples were collected and sieve d (10 mm) field-moist, then air-dried and re-sieved to obtain dry-siev ed aggregates (DSA) of six size classes. The percentage water-stable a ggregates (WSA) in each size class was determined by wet-sieving DSA. There was no effect of earthworm manipulations on the depth-distributi on of total soil C and N or the distribution of DSA of different size classes. In the earthworm addition treatment, DSA in 1-2, 2-4, and 4-1 0 mm size classes contained more WSA than DSA of the same size class f rom the unaltered earthworm treatments. WSA had higher C and N content s than DSA of the same size class. Our results suggest that earthworm activity can increase soil structure stability and the storage of soil C and N in large WSA. (C) 1997 Published by Elsevier Science Ltd.