Applied Soil Ecology 14 2000 213–222
Effects of soil compaction on the relationships between nematodes, grass production and soil physical properties
L.A. Bouwman
a,∗
, W.B.M. Arts
b
a
Alterra, Green World Research, P.O. Box 47, 6700 AA Wageningen, The Netherlands
b
DLO Research Institute for Agricultural and Environmental Engineering, P.O. Box 43, 6700 AA Wageningen, The Netherlands Received 18 October 1997; received in revised form 24 February 2000; accepted 1 March 2000
Abstract
As farm machinery has become heavier, concern has grown about its direct effects on soil physical conditions and its indirect effects on crop yields and soil biota. To study the relationships between these parameters, non-grazed temporary grassland
plots on a loamy sand soil were subjected to full-width load traffic with widely different loads 0, 4.5, 8.5 and 14.5 t one to four times per year for a period of 5 years. Soil bulk density was monitored as an indicator of soil compaction. Grass yield
was measured throughout the experimental period. Root distribution over the soil profile and nematodes populations were assessed during the final year of the experiment. Results indicate that a moderate degree of compaction ∼4.5 t load gave the
highest crop yield and that at higher degrees of compaction roots failed to penetrate into the deeper soil layers 20 cm depth. Total numbers of nematodes were not affected by compaction, but their distribution over the various feeding types shifted
towards a population with increased numbers of herbivores and decreased numbers of bacterivores and omnivorespredators. This change in the structure of the nematode assemblage is associated with poorer conditions for crop growth. © 2000 Elsevier
Science B.V. All rights reserved.
Keywords: Grass production; Habitable pore space; Nematode trophic structure; Root distribution; Soil bulk density; Soil compaction
1. Introduction
Soil compaction is an important form of physical soil degradation Van Ouwerkerk and Soane, 1994.
The use of heavy load traffic machinery in modern agriculture causes substantial soil compaction, coun-
teracted by soil tillage that loosens the soil. Higher soil bulk densities affect resistance to root penetration, soil
pore volume and permeability to air, and thus, finally the pore space habitable for soil organisms. Through
a combination of these factors, soil compaction will
∗
Corresponding author. Tel.: +31-317-474352; fax: +31-317-424812.
E-mail address: l.a.bouwmanalterra.wag-ur.nl L.A. Bouwman
affect crop growth Brussaard and Van Faassen, 1994; Soane and Van Ouwerkerk, 1994. Soil pores also ac-
commodate biological processes such as organic mat- ter decomposition and nutrient mineralization Elliott
et al., 1980; Hassink et al., 1993. Also, herbivorous organisms feeding on living plant roots live in the
interstitial spaces present in the soil. Conventionally, fields are regularly tilled for arable crop production
and the use of heavy load machinery creates a plow layer with increased bulk density, usually below 25 cm
depth, and with a decreased bulk density in the upper soil layers. The passage of heavy load traffic on peren-
nial grassland also causes compaction of the upper soil layers but there are no tillage operations to counter-
act this compaction. In perennial and temporary ley
0929-139300 – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 9 - 1 3 9 3 0 0 0 0 0 5 5 - X
214 L.A. Bouwman, W.B.M. Arts Applied Soil Ecology 14 2000 213–222
grasslands, compaction affects many physical and bio- logical soil properties and processes by various direct
and indirect mechanisms. To unravel these, we should know the relationships between the load of the passing
traffic and the resulting soil compaction, bulk density, root distribution over the soil profile, crop yield, and
finally the structure of the community of soil organ- isms and its functioning. This knowledge may help
farmers in their choice of machinery load, the width and the pressure of the tires and the frequency of traf-
fic, depending on soil type, weather conditions, and acceptable degree of compaction Arts et al., 1994.
Nematodes are involved in a wide range of activities and connections to other organisms in the soil food
web, comprising species feeding on living roots her- bivores H, on microorganisms bacterivores B;
fungivores F, and species feeding on larger organ- isms predators P or on mixed diets omnivores O.
Nematode communities in permanent grasslands are relatively stable with respect to numbers and have
a high species diversity. Numbers of specimens in trophic groups often decrease in the order BF
HOP Boström and Sohlenius, 1986. The various nematode trophic groups reflect important microbio-
logical and phytopathogenic processes such as organic matter decomposition, nutrient mineralization and her-
bivory. Although numbers of nematodes belonging to a particular feeding category are not always correlated
to the amount of specific food, numbers are correlated with process rates, e.g. numbers of bacterivorous ne-
matodes correlate with bacterial production Clarholm et al., 1981 and N mineralization rate, in particular,
in sandy soils with pore diameters between 30 and 90 mm Hassink et al., 1993, and herbivores correlate
with root growth, etc. Soil compaction affects nema- todes directly as well as indirectly. Vulnerable species
can be damaged during passage of the traffic Boag, 1985; decreased habitable pore space after passage
of the traffic affects probably all taxa except those that are intimately connected with root development, and
finally root dynamics in particular affects the numbers of herbivores and some root-generated microbivorous
taxa Griffiths et al., 1991; Bouwman et al., 1993. The effect of tillage and compaction regimes on total
numbers and dynamics of nematodes can therefore not be generalized, but feeding categories and taxa should
be examined individually Fortnum and Karlen, 1985; Parmelee and Aston, 1986; Thomas, 1978.
Trophic differences among nematode populations were observed to be indicative of variations in crop
yields Edwards, 1988; Edwards and Kimpinski, 1997 and also of decomposition and, in particular, N
mineralization processes Hassink et al., 1993.
A field experiment was carried out to study the relationships between traffic load and physical, bio-
logical and crop production characteristics of the soil. In 1988 the experiment Arts et al., 1994 was
established on a marine loamy sand soil in The Netherlands, where grass was sown on plots strips
previously tilled to a depth of 50 cm and consequently subjected to different degrees of soil compaction
over the whole surface of the plots. Soil physical characteristics as well as crop yields were measured
throughout the 5-year trial period and finally, in the last year of the experiment 1992, the distribution of
the roots over the soil profile and the nematode fauna were recorded in two plots with different degrees
of compaction. It was hypothesized that compaction may have positive as well as negative effects on
crop yield and thus, a site-specific optimum degree of soil compaction exists. Single season changes in
soil management regimes have little lasting effect on nematode communities Baird and Bernard, 1984;
Sohlenius and Sandor, 1989, but the nematode fauna in the upper 10 cm of the grass-sod of the experimen-
tal plots is assumed to be in a new equilibrium after 4 years of growth under experimental conditions.
2. Materials and methods
