Agriculture Reference
In-Depth Information
dairy compost for fertility and tillage for weed management, while the Integrated
Conventional system uses herbicides at rates one-third of conventional rates and
composted manure and synthetic N fertilizers at rates two-thirds of conventional
(Sánchez et al. 2002, 2004). Five entry points for cropping system diversity are
included within each management system, where one plot is continuous corn and
the other four plots represent each phase of a 4-year rotation of corn-corn-soy-
bean-wheat. Cover crops are grown on half of each plot (red clover, crimson
clover [
Trifolium incarnatum
L.] and annual ryegrass); the other half is winter
fallowed, with some limited plant cover provided by the presence of winter annual
weeds (Smith and Gross 2006a).
It is experimentally challenging to manipulate crop diversity in isolation from
management, as management practices are typically “bundled” and therefore multi-
functional (Snapp et al. 2010a). In conventional management, for example, reliance
on chemical inputs for pest control and nutrient supply allows simplification of the
system to a few highly productive species. In contrast, biologically based manage-
ment, including organic management, commonly relies on a mixture of species that
promote internal processes such as N fixation, mineralization, and pest suppression
(Lowrance et al. 1984, Drinkwater and Snapp 2007).
Agronomic Lessons from the KBS MCSE
Productivity
Agronomic productivity in the MCSE annual crops over 17 years (1989-2007)
has shown consistent responses to management. The No-till system has the over-
all highest average annual grain yield across all three crops at 4.2 Mg ha
−1
and
the Biologically Based system the lowest at 2.9 Mg ha
−1
(Table 15.2; Gelfand
et al. 2010). Grain yield in the cereal crops—corn and wheat—has been sub-
stantially reduced under biologically based management, compared to no-till. In
contrast, soybean yields have not been reduced under biologically based man-
agement compared to conventional. Although soil moisture and weed pressure
likely contribute to low yields in some years, insufficient N supply appears to
be the key factor influencing biologically based corn and wheat production. This
is supported by the success of soybeans, which provide their own N via bio-
logical N fixation, and by low levels of soil inorganic N (nitrate [NO
3
−
] and
ammonium [NH
4
+
]) in soils of the Biologically Based system during other parts
of the rotation. For example, at midseason in the corn phase of the Biologically
Based system, soils contain 17 mg N kg
−1
, on average, as compared to 29 mg
N kg
−1
at midseason in soils of the Conventional system (Millar and Robertson,
2015, Chapter 9 in this volume). Nitrogen deficiency in organic systems has
been observed in other agroecosystem experiments (Cavigelli et al. 2008), and it
is typical of agriculturally converted grassland areas where minimal agricultural
inputs are applied (Smith et al. 2008). Biological management for the MCSE
relies on N fixation from legumes in the rotation, with no supplementation from
manure or compost.
