Agriculture Reference
In-Depth Information
use now dominate the landscape, and mixed cropping systems—in which livestock
are supported mainly or solely by crops grown on-farm—are rare.
Current policies support the production of inexpensive food and affect the liveli-
hoods of many rural communities. To remain economically viable, farmers neces-
sarily focus on maximizing cash crop production (Swinton et al. 2015b, Chapter 13
in this volume). Corn, soybean, and wheat are grown over wide areas due to supe-
rior biological traits—including rapid growth, effective resource acquisition, and
an ability to translate inputs into grain yield. Changing the portfolio of crops grown
and better integrating crops and livestock to improve the delivery of ecosystem
services face considerable challenges, in part because the contemporary socioeco-
nomic context and infrastructure reinforce current farming systems.
Further, in recent decades U.S. subsidy policies have favored corn, soybean, and
wheat among the few crops that are targeted for direct price support payments. In
this environment, it is not surprising that an increasingly narrow range of crops are
grown, with less production of forage and hay crops, small grains, minor legumes,
or specialty oil and grain crops. At the same time, awareness is growing that reli-
ance on these few crops has environmental costs and increases the vulnerability of
significant portions of the food production system.
Long-Term Agricultural Ecosystem Experiments at KBS LTER
The ecological principles that underpin the functioning of natural ecosystems
apply to agroecosystems as well, and KBS LTER cropping system experiments
are designed to elucidate key processes, population and community-level dynam-
ics, and interactions. The overarching research goal of the KBS LTER is to test
the hypothesis that biological processes can substitute for chemical inputs without
sacrificing high yields (Robertson and Hamilton 2015, Chapter 1 in this volume).
The Main Cropping System Experiment (MCSE) was established in 1989 to pro-
vide a practical range of model systems across which these key ecological attributes
could be intensively examined over long time periods. The LFL (Sánchez et al.
2004) was established in 1993 to extend MCSE findings to a broader range of farm-
relevant cropping systems and, in particular, to separate crop diversity as a distinct
factor from crop management. The LFL includes systems with a wider range of
crop diversity and nitrogen (N) sources than does the MCSE. Properties that differ
among various MCSE and LFL systems include perenniality (the duration of living
cover), plant diversity (the number of species in a rotation), types and quantities
of fossil fuel vs. biologically derived inputs (including energy), and management-
related disturbances (tillage regime).
Resource gradients and disturbances from fire, flooding, tillage, and pests are
common regulators of productivity and resource flux in agricultural ecosystems
across the world. Processes such as biological N fixation and organic matter accu-
mulation are at the foundation of traditional agriculture (Greenland and Nye 1959),
including the bush-fallow or swidden agriculture that was historically practiced
across North America prior to European contact (Sylvester and Gutmann 2008).
For thousands of years, farmers have used soil disturbance and burning as primary
