Agriculture Reference
In-Depth Information
Row Crops and Weed Communities
Research at KBS LTER has documented how management practices affect the com-
position and diversity of weeds in agricultural systems, both aboveground and in the
soil seed bank (Smith and Gross 2006, Davis et al. 2005). While many studies have
examined the effects of different cropping systems on weed communities, few have
followed these changes over decades. This extended temporal focus allows us to detect
whether weed community composition and productivity respond to longer-term driv-
ers, including changes in climatic factors such as precipitation (Robinson 2011).
Although the MCSE allows us to make such comparisons, the lack of rotation
“entry point” replication limits our ability to compare systems across years (i.e.,
each year has only one crop in the rotation). Also, the design of the MCSE (see
Table 7.1) limits our ability to draw conclusions about the role of cropping system
diversity in enhancing ecosystem services from agriculture. To address these con-
straints, in 2000 we established the Biodiversity Gradient Experiment to directly
examine how variations in crop diversity (number of crops in a rotation) affect
weeds, crop yields, and other agronomic and ecological factors.
Biodiversity Gradient Experiment
The Biodiversity Gradient Experiment includes a total of 21 treatments with mono-
cultures and rotations of three grain crops (corn, soybean, and wheat), with and
without cover crops, as well as spring and fall fallow treatments and a bare soil
treatment (Table 7.2). All entry points of the rotations are included in the design,
so we can quantify treatment effects on all crop yields in every year and directly
determine how interannual variation in climatic factors affects crop yield and weed
biomass. Crop treatments are classified into six systems that differ in the number of
annual grain and cover crop species in the rotation (Table 7.2). Additional details on
the management and design of this experiment are described in Smith et al. (2008)
and at
http://lter.kbs.msu.edu.
Early Successional Plant Communities
The MCSE Early Successional system allows us to quantify successional trajecto-
ries and dynamics in a midwestern U.S. landscape (Huberty et al. 1998, Gross and
Emery 2007). Since 1997 these plots have been burned annually (or nearly so) in
early spring to prevent colonization by trees and shrubs (see Foster and Gross 1999).
Although historically the frequency and season of burning of midwestern grasslands
likely varied depending on climate and other factors (Andersen and Bowles 1999),
today annual spring fires are used to manage them (Packard and Mutel 1997).
When the MCSE was initiated (1989), an experiment was established within
the Early Successional system with subplot manipulations of disturbance (tillage)
and nitrogen (N) fertilization (the Disturbance by N-Fertilization Experiment). This
experiment allows us to examine how disturbance and resource enrichment affect
(1) productivity and species richness in successional communities (Gough et al.
2000, Dickson and Gross 2013), (2) the composition and stability of aboveground
