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Soil is the primary medium for crop growth, where water,
nutrients, soil microbes, and other factors interact.
It supports the fundamental physical, chemical, and biological
processes that must take place in order for plants to
grow. It regulates water flow between infiltration, root-zone
storage, deep percolation, and runoff. And it acts as
a buffer between production inputs and the environment.
How well these functions are performed depends on soil
quality.
Contents
Importance of Soil Management
Soil management is one of the most important components
in a crop production system because it has a major impact
on:
- Current and future yield levels
- Food quality and safety
- Environmental pollution
- Global climate change.
Soil is the primary medium for crop growth, where water,
nutrients, soil microbes, and other factors interact.
It supports the fundamental physical, chemical, and biological
processes that must take place in order for plants to
grow. It regulates water flow between infiltration, root-zone
storage, deep percolation, and runoff. And it acts as
a buffer between production inputs and the environment.
How well these functions are performed depends on soil
quality.
A high-quality soil exhibits parameter values (related
to soil texture, bulk density, rooting depth, permeability
and water storage capacity, carbon content, organic matter
and biological activity, pH level, and electrical conductivity)
that promote the growth of crops. Soil can also function
as a “degrader” or “immobilizer” of
agricultural chemicals, wastes, or other potential pollutants,
and act as a carbon sink.
Beneficial soil management practices maintain the quality
and long-term productivity of the soil and reduce potential
environmental damages from crop production. These practices
include:
- Efficient use of nutrients, pesticides, and irrigation
water
- Soil- and water-conserving cover crops, crop rotations,
cropping systems, and crop residue management strategies
- Field/landscape-scale engineering structures and
buffer zones (e.g., grass waterways, terraces, contour
farming, strip cropping, underground drainage outlets,
and surface diversion and drainage channels).
The extent to which these practices are carried out
depends on site-specific technical and economic feasibility
considerations, as well as farmer attitudes, perceptions,
and resources. Most farmers recognize the importance of
good soil management to their income and long-term economic
viability, and to environmental quality. To this end,
farmers commonly use crop rotation, crop residue management,
and soil conservation structures.
- Many farmers are rotating the crops they grow from
year to year and the mix of crops in a field to improve
soil fertility; control insects, diseases, and weeds;
reduce soil erosion; and reduce water pollution often
associated with runoff and leaching. Crop rotation
also reduces the use of chemical inputs in the production
process over a period of years. In 1997, the majority
of acreage in corn, soybeans, and wheat were in a rotation
system, with corn and soybeans in a 3-year rotation.
- Crop residue management can reduce soil losses
from wind and water erosion. Through the use of cover
crops and special tillage and cultivation operations,
postharvest residue is left on field surfaces, minimizing
soil disturbance and exposure to the elements.
- Soil and water conservation structures may
be used in conjunction with other practices to control
runoff water after heavy rains. These structures allow
for surface water to be captured on site or slowed and
diverted from the field via erosion-resistant waterways,
channels, or outlets.
Effect of Crop Residue Management
on Soil and Water Resources
Crop
residue management (CRM) calls for fewer and/or less
intensive tillage operations and preserves more residue
from the previous crop. CRM can protect soil and water
resources by reducing soil erosion and interrupting movement
of nutrients and pesticides off the field. CRM is generally
cost-effective in meeting conservation requirements and
can lead to higher farm economic returns by reducing fuel,
machinery, and labor costs while maintaining or increasing
crop yields.
Crop residue management systems include reduced tillage
or conservation tillage practices such as no-till, ridge-till,
and mulch-till, as well as the use of cover crops and
other conservation practices that provides sufficient
residue cover to mitigate wind and water erosion. Conservation
tillage was used on over 109 million acres in 1998,
or over 37 percent of the U.S. planted cropland area.
For more information, refer to the soil management chapter
in Agricultural Resources
and Environmental Indicators.
Extent of U.S. Cropland
Acreage under Crop Residue Management
Soil conserving crop residue management systems such
as conservation tillage, crop rotations, and cover crops
are increasingly being used on all field crops across
the United States. The use of conservation tillage and
reduced tillage systems on all cropland acreage has increased
from around 50 percent in 1989 to almost 65 percent in
1998. Since the early 1990's, 50 percent of soybean acreage
has been devoted to conservation tillage, along with 40
percent of corn, 35 percent of sorghum, 30 percent of
small grains, and 10 percent of cotton.
Since 1991, 75, 95, and 70 percent of corn-,
soybean-, and wheat-planted acreage has been in some form
of crop rotation system. And as a result of farmer willingness
to participate in USDA conservation programs, grassed
waterways, terraces, drainage systems, and other structural
measures are found in most regions. Recent data for 16
corn producing States show that at least one of these
types of measures is found on 75.3 million acres.
Adoption of conservation tillage and a corresponding
decline in clean tillage has been stimulated by the prospects
of higher economic returns with conservation tillage and
by public policies and programs promoting conservation
tillage for its conservation benefits. The major limitations
to adoption of soil-conserving tillage systems for some
farmers include additional management skill requirements,
expectations of lower crop yields and/or economic returns
in specific geographic areas or situations, negative attitudes
or perceptions, and institutional constraints.
For more information, refer to Agricultural
Resources and Environmental Indicators.
Impact of Conservation
Tillage on Pesticide Use
Tillage, whether conventional, reduced-till, or conservation-till,
is integral to crop production. The choice of tillage
type may affect other production processes as well. For
example, conservation tillage does away with some, or
all, mechanical weed control and emphasizes chemicals
for weed control. Recent comparisons by ERS of conventional
tillage practices to conservation tillage in corn, soybeans,
and winter wheat found that conservation tillage tends
to require more herbicides but less insecticides for each
crop.
Another investigation of conventional versus conservation
tillage in nonirrigated corn production found a statistically
significant difference in per-acre herbicide application
rates only with no-till and ridge-till systems. Five tillage
practices were compared: conventional with moldboard plow,
conventional without moldboard plow, and conservation
mulch-till, no-till, and ridge-till. Findings include:
- As tillage changed from conventional systems to conservation
no-till, herbicide use per acre tended to increase.
- With ridge-till systems, herbicide rates decreased.
- Conventional tillage with moldboard plow used less
herbicide than no-till, about the same as mulch-till,
but more than ridge-till.
- Conventional tillage without moldboard plow used less
herbicide than no-till, and more than ridge till or
mulch-till.
- For insecticides, application rates under conservation
tillage were no higher than under conventional tillage,
and often lower. The key variable that determined total
pesticide loadings in the study area was the number
of acres treated in each tillage type and not differences
in per-acre application rates between types. Conventional
tillage used more insecticides than no-till and about
the same as mulch-till, except that plow systems used
more than ridge-till. For more information, “Pesticide
Use in U.S. Corn Production: Does Conservation Make
A Difference?” Journal of Soil and Water Conservation,
Vol. 54, No. 2, 1999.
Conservation Practice
Trends for Corn and Soybean Production
The use of conservation practices in corn and soybean
production is generally stable, with slight year-to-year
variability, over 1996-2000. Grassed waterways and drainage
are the only conservation practices for corn that are
decreasing. The use of conservation practices in soybean
production followed the same pattern as corn from 1996-2000.
Corn acres in conventional tillage and mulch tillage
have been increasing, while acres in no-till and ridge
till dipped slightly. Soybean acreage in conventional
tillage has been increasing, particularly in 1999 and
2000. This increase is concurrent with declines in reduced-till
acreage during the same period.
Extent of the Combined Use of Soil Conservation Practices
in Corn and Soybean Production
Terraces and grassed waterways are regarded as complementary
soil conservation activities. Corn and soybeans had only
a small share of acreage in fields containing both terraces
and grassed waterways from 1996 to 2000 — 5-10 percent
for corn and 4-8 percent for soybeans, and the trend
in their use is downward.
Grassed waterways are applied singly on more acreage
than are terraces for both corn and soybeans. However,
the majority of acreage in both crops has neither grassed
waterways nor terraces; 59-74 percent for corn and 65-86
percent for soybeans.
Similarly, the combined use of contour farming and strip
cropping occurred on 0.5 to 1.4 percent of corn acreage
from 1996 to 2000. Contour farming alone is much more
prevalent than strip cropping alone, but as with waterways
and terraces, most corn fields (80-88 percent) have
neither practice in place.
Extent of Corn Acreage Received
Technical Assistance and Cost Sharing for Conservation
Practices
Terraces and grassed waterways are regarded as complementary
soil conservation activities. Corn and soybeans had
only a small share of acreage in fields containing both
terraces and grassed waterways from 1996-2000, 5-10
percent for corn and 4-8 percent for soybeans. And the
trend in their use is downward. Grassed waterways are
applied singly on more acreage than are terraces for
both corn and soybeans. However, the majority of acreage
in both crops has neither grassed waterways nor terraces;
59-74 percent for corn and 65-86 percent for soybeans.
Similarly, the combined use of contour farming and strip
cropping occurred on 0.5 to 1.4 percent of the corn
acreage from 1996-2000. Contour farming alone is much
more prevalent than strip cropping alone, but as with
waterways and terraces, the majority of the corn fields
(80-88 percent) have neither practice in place.
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