Agriculture Reference
In-Depth Information
can have lower yields. This is one likely cause of the lower corn and wheat yields
observed in the MCSE Reduced Input and Biologically Based systems.
Opportunity costs are particularly acute challenges for farmers operating in
short growing season environments, such as the temperate U.S. Great Lakes region
and unimodal rainfall systems in other parts of the world. Farmers have developed
systems that maximize use of the biophysical environment (e.g., light, temperature,
and moisture) to produce marketable crops. In locations where there is a longer
growing season, such as in the southeastern United States, farmers develop double
cropping systems with two cash crops per season, rather than following a cash
crop with a biology-promoting cover crop (Cavigelli et al. 2008). This reflects the
reward structure of current policies, and indeed is a requirement for farm survival in
many socioeconomic environments. Overall, the costs and benefits associated with
biodiversity are complex and interact with management practices.
Organic row-crop production makes up a very small proportion of midwestern
agriculture, but organic acreage is increasing rapidly, even in the absence of policy
support for broader adoption (Dimitri and Greene 2002). This would seem to sug-
gest that organic row crops could be promoted in the United States without radi-
cally altering policy instruments or incentives. However, we note that as the supply
of organic products increases, prices are expected to decline, reducing the premium
that now compensates for lower yields.
On the other hand, the Reduced Input system has yields much closer to
Conventional, and shares most of the environmental benefits of the Biologically
Based system. Cropping systems based on the substitution of biological manage-
ment for most rather than all chemical inputs could be an attractive hybrid system
that optimizes yield and services. Such a system could be widely adopted with
proper incentives for farmers' providing desirable services.
Perennial Vegetation
The cumulative effect of perennial vegetation in agroecosystems is dramatic, par-
ticularly belowground. In a Russian study, substantial soil C gains to 2 m were
observed in grassland and forage systems compared to annual cropping systems
(Mikhailova et al. 2000). Perennial legume and grass plantings have been shown
to improve soil organic C by 35 to 58% compared to annuals (Bremer et al. 1994),
which is comparable to the 45% increase in soil C we observed in our MCSE con-
tinuous Alfalfa system (Fig. 15.1).
Nitrogen leaching losses in perennial vegetation vary, influenced by species
growth patterns and the importance of biological N fixation. Farming system man-
agement is also important, including reactive N inputs and harvest operations. In
the MCSE Early Successional community, very low levels of inorganic N have
been observed in soil, which is consistent with tight N cycling (Robertson et al.
2000). Alfalfa is intensively managed compared to this Early Successional system,
with biomass harvested three times per year, on average, and lime and fertilizers
other than N are applied as needed. Nitrogen leaching from the alfalfa system was
lower than from any of the annual cropping systems (Syswerda et al. 2012), as has
been shown in other shorter-term studies (Randall et al. 1997) despite high levels
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