Agriculture Reference
In-Depth Information
Based system, only soybean, which provides its own nitrogen, matched the yields
of crops managed with synthetic chemicals. In organic agriculture, manure or
compost is generally required to achieve high yields in nonleguminous crops (e.g.,
Liebman et al. 2013). However, in another experiment at the KBS LTER site,
designed specifically to address the impact of rotational diversity on yield in the
absence of confounding management practices, Smith et al. (2008) found that a
3-year, six-species rotation of corn, soybean, and wheat, with three cover crops to
provide nitrogen, could produce corn yields as high as the county average. In addi-
tion to yield, rotational complexity benefits other ecosystem services, as we will
discuss below.
Providing Pest Protection through Biocontrol Services
Biodiversity at the landscape scale also affects the capacity of agriculture to deliver
ecosystem services, especially those related to biocontrol and water quality. For
example, ladybird beetles (Coleoptera: Coccinellidae) are important predators of
aphids in field crops. In KBS LTER soybeans, ladybird beetles are responsible for
most soybean aphid (
Aphis glycines
) control and are able to keep aphid populations
below economic thresholds (Costamagna and Landis 2006); absent such control,
soybean yields can be suppressed 40-60%. Coccinellid diversity is an important
part of this control.
Because different coccinellid species use different habitats at different times for
foraging or other purposes, such as overwintering, the diversity of habitats within
a landscape becomes a key predictor of biocontrol efficacy (Fig. 2.2A). About a
dozen coccinellid species with moderate to strong habitat preferences are present
in the KBS landscape (Maredia et al. 1992a, Landis and Gage 2014).
Coleomegilla
maculata
, for example, overwinters in woodlots and, prior to the summertime
development of soybean aphid populations, depends on pollen from early flowering
(A)
(B)
r
2
= 0.39
1.0
1.0
P < 0.001
r
2
= 0.31
0.5
0.5
P < 0.01
0.0
0.0
1
2345678
0.1
0.2
0.3
0.4
0.5
.6
0.7
Simpson's Diversity (D) at 1.5 km Scale
Proportion Corn at 1.5 km Scale
Figure 2.2
. Biocontrol services from coccinellids as a function of landscape diversity (A) and
the dominance of corn within 1.5 km of soybean fields (B). Panel (A) is redrawn from Gardiner
et al. (2009) with permission from the Ecological Society of America; permission conveyed
through Copyright Clearance Center, Inc. Panel (B) is redrawn from Landis et al. (2008).
