Agriculture Reference
In-Depth Information
and water; reduce soil erosion; and control plant diseases and weed pressure. These prac-
tices have largely been adopted without full knowledge of their impact on the soil biologi-
cal community or how the soil biological community may have an impact on the success
or failure of these practices. Here, we examine three sustainable agricultural practices:
reduced tillage, crop rotation, and overwintering cover crops; give a brief overview of their
goals; and then show how AM fungus communities are impacted by these practices and
contribute to the achievement of the goals of these practices.
7.2.1 Reduced tillage
7.2.1.1
Agronomic background
7.2.1.1.1 Brief history and definition.
Soil tillage had its beginning thousands of
years ago, although modern tools such as the moldboard plow were not introduced until
the 18th and 19th centuries. The replacement of animal power by tractors allowed large
areas of open grassland in the Great Plains of the United States to be turned into fields
with row crops. Tillage of the former grassland combined with drought caused severe soil
erosion and led to the Dust Bowl in the 1930s, making millions of acres of farmland unus-
able. Although the no-till movement first started in the 1950s and 1960s, made possible by
the invention of herbicides such as 2,4-D
®
and Paraquat
®
, it was not a common practice
at that time (Derpsch, 1997). The 1985 Farm Bill, which required farmers to prevent and
reduce erosion, may have been a major incentive for conservation tillage to become more
widely adopted in the United States (Brock et al., 2000).
In reduced or conservation tillage, crops are grown with minimal disturbance of the
soil. Methods differ from each other mainly in the degree to which the soil is disturbed
prior to planting. Even in “no-till” systems, the soil is opened to a certain degree (e.g., with
coulters or disk openers) to plant the seed. By definition, conservation tillage leaves at least
30% of the soil covered by crop residues (Day et al., 1999).
7.2.1.1.2 Effects of reduced tillage.
No-till practices were first introduced as a soil
conservation tool and to decrease labor requirements and fuel use (Doren and Linn,
1994; Sims et al., 1994). Numerous studies have shown that soil is more protected from
erosion and runoff in no-till systems (Gilley et al., 1997; Langdale et al., 1979; Shipitalo
and Edwards, 1998; Williams et al., 2009), and that yields in no-till systems can be as
good as or better than with conventional tillage (Day et al., 1999; Dick et al., 1991; Karlen
et al., 1994; Teasdale et al., 2007). Soil carbon (Berner et al., 2008; Halpern et al., 2010;
West and Post, 2002) and other soil quality parameters (aggregate stability, microbial
activity, earthworm populations) can increase significantly after switching from con-
ventional tillage to no-till (Karlen et al., 1994). Potential disadvantages of no-till are
compaction, flooding or poor drainage, delays in planting because fields are too wet or
too cold, and carryover of diseases or pests in crop residue.
When tillage is reduced, crop residues are not or only partially incorporated into the
soil. The new crop is planted into the stubble left on the soil surface or into small strips of
tilled soil; fertilizers and lime are generally placed on top of the soil. Weeds are usually
controlled with herbicides rather than by tillage or cultivation. This increased dependence
on herbicides for weed control (Day et al., 1999) is often considered unsustainable, possibly
leading to herbicide resistance in certain weeds and increased leaching of pesticides into
groundwater due to higher infiltration rates in no-till relative to tilled systems (Isensee
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