Agriculture Reference
In-Depth Information
A
B
200
200
150
150
100
100
50
50
0
0
0 0.5 1.0 1.5 2.0 2.5 3.0
0 100 200 300 400
Stocking rate (LU ha
-1
)
Mineral nitrogen input (kg N ha
-1
)
120
120
C
D
100
100
80
80
60
60
40
40
20
20
0
0
0 0.5 1.0 1.5 2.0 2.5 3.0
0 100 200 300 400
Stocking rate (LU ha
-1
)
Mineral nitrogen input (kg N ha
-1
)
FIGURE 6.1
Relationships between earthworm biomass and grassland management intensity as measured by
stocking rate (A, C) and mineral nitrogen fertilizer use (B, D). For total earthworm biomass,
r
= 0.32,
p
< 0.001
(A);
r
= 0.26,
p
= 0.007 (B). For anecic species,
r
= 0.33,
p
< 0.001 (C);
r
= 0.31,
p
= 0.001 (D). (From
Muldowney et al. 2004. With permission.)
cover, reduced litter input, and more rapid oxidation of crop residues (Balesdent et al. 1988). Under
these conditions, earthworms may experience severe food limitations, and earthworm population
densities and biomass are likely to reflect the quality and quantity of crop residue input (Hendrix
et al. 1992). Earthworm populations benefit from tillage practices that return a high proportion of
crop residues to the soil, particularly when the residues remain on the soil surface, and from crops
such as cereals, for which significant amounts of residues are left behind compared with root crops,
for which most of the plant production is removed (Edwards 1983; Lofs-Holmin 1983; Hendrix et
al. 1986; Mele and Carter 1999).
Cereal-legume intercrops support much larger earthworm populations than those in conventional
monocrops (Schmidt et al. 2001), probably in response to reductions in tillage (direct drilling or
no till) and increased food supply in the intercrops. The relative importance of these two factors
was investigated in a field plot experiment at Long Ashton Research Station, U.K., in which the
earthworm populations in conventional wheat, direct-drilled wheat, and direct-drilled wheat-clover
intercrops were compared (Schmidt et al. 2003). The results indicated that reduced tillage alone
had only a modest effect on earthworm populations; the combination of reduced tillage and the
presence of a clover understory increased earthworm populations greatly (
Figure 6.2
)
. The authors
