Agriculture Reference
In-Depth Information
means to enhance nutrient availability in synchrony with crop demand and to sup-
press weeds. Native vegetation was used as part of long “bush-fallow” crop rota-
tions to allow successional processes to rebuild soil fertility.
Successional processes can be used in a sustainable manner to produce food and
other agricultural products in contemporary agricultural systems, given sufficient
time and access to land. However, these resources are often in short supply due to
economic and population pressures, and modern agricultural systems rely instead
on intensive energy and chemical inputs (Tilman et al. 2002). As a consequence,
there has been limited attention paid to the underlying ecological processes that
mediate agricultural production and control the pools and fluxes of C and nutrients
in agricultural soils.
The KBS Main Cropping System Experiment
The Main Cropping System Experiment (MCSE) evaluates agricultural row-
crop systems that vary in management intensity (Table 15.1); see Robertson and
Hamilton (2015, Chapter 1 in this volume) for a full description. In brief, we com-
pare four management strategies for a corn-soybean-winter wheat rotation: (1) the
Conventional system uses fertilizer and herbicide inputs, and conventional tillage
as recommended by Michigan State University Extension; (2) the No-till system
uses conventional management but for permanent no-till soil management; (3)
the Reduced Input system uses biologically based management, including winter
cover crops, to reduce synthetic chemical inputs to ~one-third of those used in
the Conventional system; and (4) the Biologically Based system uses biologically
based management to eliminate synthetic chemical inputs altogether. No systems
receive manure or compost. The Reduced Input and Biologically Based systems
include cover crops of red clover interseeded in wheat in the spring, and annual rye
planted after corn harvest in the fall. Wide row spacing and mechanical cultivation
are used to control weeds in these two systems. A fifth system, Alfalfa, is managed
conventionally as a continuous forage crop, replanted on a ~6-year schedule fol-
lowing a break year in a grain crop.
The Reduced Input and Biologically Based systems model alternative agricul-
ture practices that make up a small but active sector of U.S. agriculture (Swinton et
al. 2015b, Chapter 13 in this volume). For example, the Biologically Based system
simulates organic management practices and is USDA-certified organic, although it
is unconventionally organic in that neither manure nor compost are used as inputs.
The total acreage of certified organic cropland in the U.S. has increased more than
6-fold from 1992 to 2008 and made up 0.7% (1.1 million ha) of total U.S. cropland
in 2008 (ERS 2011). The Reduced Input system includes integrated nutrient and
pest management practices such as closely monitoring nutrient availability and pest
and beneficial insect populations, which allows external inputs to be reduced by
about two-thirds in this system. Herbicide application was banded within the crop
row until the shift was made in 2011 to broadcast application, and N fertilizer is
applied at lower rates. This reduction in N fertilizer use is significant in light of
the fact that in many cropping systems fertilizer is frequently applied in excess
of crop demand (Robertson 1997, Gardner and Drinkwater 2009). The effects of