AGRICULTURAL PRACTICES AND THE SPATIAL-DISTRIBUTION OF EARTHWORMS IN MAIZE FIELDS - RELATIONSHIPS BETWEEN EARTHWORM ABUNDANCE, MAIZE PLANTSAND SOIL COMPACTION

The relationships between the spatial heterogeneity of maize fields, d ue to row-cropping and farm machinery traffic, and earthworm abundance were studied in three plots receiving different organic matter treatm ents: no organic fertilizer, pig slurry and farmyard-manure. In all pl ots, there was no significant effect of farm machinery traffic althoug h there was a tendancy for earthworms to be less abundant under inter- rows (wheel tracks) than in traffic-free inter-rows. In both the maize field without organic fertilizer and the maize treated with pig slurr y, earthworms were primarily located along the maize row. Earthworm ab undances were greater within than between rows (16 vs 6 nos 0.1 m(-2) in control, 30 vs 15 nos 0.1 m(-2) in slurry). In the farmyard-manure treatment, no row effect on the spatial pattern in earthworm numbers w as found. However, worm biomass was approximately twice as high under the maize row as under the inter-row. This suggested a greater migrati on of adults to the maize roots or that juvenile worms grew faster the re. Earthworm populations showed spatial variance in life cycle stage with populations under the maize row having proportionally more adults than populations between rows. Soil bulk-density was lower in than be tween maize rows and lower in maize fields amended with organic matter . Soil bulk-density and earthworm biomass were shown to be negatively correlated (r = -0.92, n = 6). Image analysis of resin-impregnated soi l blocks within and between rows showed that the soil under the row wa s characterized by a higher macroporosity (5.7 vs 0.7%) and also a gre ater diversity in size and shape of the macropores than occurred betwe en the rows. (C) 1997 Elsevier Science Ltd.