The influence of different agricultural management practices on earthworm
abundance
Tommy D’Hose1, Mathias Cougnon2, Alex De Vliegher1, Geert Haesaert3, Veerle Derycke3,
Lucien Carlier1, Erik Van Bockstaele1,2, Dirk Reheul2
1
Institute for Agricultural and Fisheries Research ILVO, BE-9820 Merelbeke, Belgium
Department of Plant Production, Ghent University, BE-9000 Gent, Belgium
3
University College Ghent, Faculty of Biosciences and Landscape Architecture, BE-9000
Ghent, Belgium
2
Abstract
Earthworms are considered the most important soil invertebrates in most soils worldwide, in
terms of biomass and activity. They are also known to influence soil structure, soil chemistry,
and, in particular, processes like organic matter decomposition. When present, earthworms
can play a major role in soil fertility and productivity. For these reasons, earthworms are
regarded as useful indicators of soil quality and sustainable crop production. The activity of
earthworms in agricultural soils depends strongly on management practices, such as tillage,
crop rotation, residue inputs, manure and compost additions and fertilizer and pesticide use.
To examine the effect of different management practices on the earthworm population, the
numbers and weights of earthworms were measured in the top 20 cm of soil of four long-term
field experiments, using a combined method of extraction by a mustard powder solution and
handsorting. The earthworm samples were collected in the fall of 2008 except for the
fertilization experiment which was sampled in the fall of 2007. The fertilization experiment
started in 2005 and investigates the influence of different types or qualities of exogenous
organic matter (farmyard manure, cattle slurry and three different types of compost, compared
with mineral fertilization, and two unfertilized treatments, cropped and uncropped). The
organic matter applications had a significant effect on the earthworm populations. Earthworm
abundance was highest on all organically amended plots, while the lowest number and
biomass was found on plots without fertilization at all. The highest earthworm biomass was
recorded on plots amended with farmyard manure. The VFG-compost (Vegetable, Fruit and
Garden waste compost) experiment started in 1997 and examines the influence of a various
application rate of VFG-compost (yearly addition of compost, every three year or no addition)
and the addition of cattle manure in a monoculture silage maize. A comparison of the
earthworm population in the different compost amended plots, produced a trend. Earthworm
densities declined in the order of application rate with the highest earthworm numbers and
biomass in the yearly amended plots. The effect of the cattle manure remained unclear. The
crop rotation experiment, started in 2006, consists of eleven different crop rotations (Figure
1). The permanent grass-clover of CR4 (Crop Rotation) showed the greatest earthworm
abundance followed by the temporary grass-clover of CR6. Remarkable was the very low
level of the earthworm numbers and biomass in the maize of CR7 suggesting a rapid decrease
in earthworms after ploughing down the grass-clover ley. The CMC-compost (Controlled
Microbial Composting) experiment commenced in 2004 and combines a crop rotation of
potatoes, fodder beet, maize and Brussels sprout with the addition of CMC-compost. The
rotation takes four years and every crop is grown every year. In the objects with potatoes and
maize, the earthworm numbers and biomass were rather low and no clear trend was observed.
In the objects with fodder beet and Brussels sprout, on the contrary, the compost amended
plots showed higher earthworm densities than the unamended plots. The highest earthworm
numbers and biomass were registered in the Brussels sprout plots. Overall, the addition of
organic matter and crop type are important factors in increasing earthworm abundance.
Figure 1: Schematic presentation of the crop rotation experiment (CR: crop rotation)