Agriculture Reference
In-Depth Information
Cropping System Diversity and Yield
Species diversity is important is determining the productivity of unmanaged her-
baceous communities, but what about managed systems? How does cropping sys-
tem diversity, via crop rotation and cover crops, affect productivity and agronomic
yields? An important component of an ecological framework for understanding crop
production and other ecosystem services from agriculture involves understanding
how cropping system diversity affects these services. The annual row-crop sys-
tems in the MCSE provide insights into the potential for biological processes (e.g.,
N-fixation or weed suppression by cover crops) to replace reliance on chemical
inputs (e.g., pesticides and fertilizers) in row crops. However, they cannot be used
to evaluate the role of cropping system diversity (via crop rotation or cover crops),
because they differ in a variety of inputs and all follow the same crop rotation
(Table 7.1). The Biodiversity Gradient Experiment was established to explicitly test
the effects of crop species and diversity (Table 7.2), not only on yield but also on a
suite of ecosystem variables. Because no fertilizers or pesticides are used in these
treatments, variation in crop yield and other system responses is directly attribut-
able to the number of different crops planted in the rotation (Smith et al. 2008), pro-
viding insight into the potential for biological processes (e.g., N-fixation or weed
suppression by cover crops) to replace or reduce reliance on chemical inputs.
For the first 3 years of the Biodiversity Gradient Experiment, cropping system
diversity showed no effect on the yield of any of the crops (Smith et al. 2008).
But by the fourth year (2003), the number of species in the rotation had a signifi-
cant effect on grain yield in corn (Fig. 7.7). Although the magnitude of this effect
has varied annually, typically corn grain yields have been highest in the two high-
est diversity treatments (five and six species over a 3-year rotation; Fig. 7.7). In
Number of Species
Six
Five
Three
Two
One (corn monoculture)
10
8
6
4
2
0
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
Year of Experiment
Figure 7.7
. Effects of rotational diversity treatments on average annual corn grain yield
from 2000-2010 in the Biodiversity Gradient Experiment. Treatments are coded based on
the number of species in the rotation. Values are means ± SE, n = 4. See Table 7.2 for descrip-
tion of treatments.
