Sustainable Agriculture Literature Review - Boulder County

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There are some tillage methods that are a combination of conventional-till and no-till,
such as ridge-till, mulch-till, and reduced-till. Both ridge-till and mulch-till are considered
conservation-till methods because they leave greater than 30 percent of past crop
residue on the land, however, reduced-till methods only leave 15 to 30 percent of crop
residue and thus are not considered conservation-till.
Ridge tillage consists of maintaining – permanent or semi-permanent – artificially
created ridge beds across an entire field. The ridge beds are established and maintained
through the use of specialized cultivators and planters designed to work with heavy crop
residues. The primary focus of ridge tillage is on row crops such as corn, soybeans, and
cotton. 377 In contrast to most forms of mulch tillage, more crop residue remains on the
soil surface for a greater portion of the season.
Mulch tillage is full-width tillage, meaning that all of the soil surface is disturbed, and is
done prior to and or during planting. Although some crop residue is left on the soil
surface, at least 30 percent of the soil surface is disturbed. Some examples of mulch
tillage are aerways, rotary harrows, and turbo tills. Some advantages of mulch tillage
practices are that it creates moderate erosion control and it helps the soil retain
moisture. 378
Soil that is not affected by erosion is considered stable soil. This typically occurs when
the topsoil and the subsurface soil are very similar. When there is a slight difference in
soil qualities between the topsoil and subsurface soil, causing it to erode initially but then
stabilize, it is considered neutral soil. Finally, when the subsurface soil below a good
layer of topsoil is poor in quality, causing erosion to be much more likely, the soil is
considered to be susceptible soil. Conventional-till agricultural practices, typically
associated with high levels of erosion, can be used if the soil is considered stable soil. 379
The negative effects of conventional-till on neutral soil and susceptible soil systems are
greater than on stable soil systems.
Grazing Practices and Crop Rotation
Boulder County has historically been a grassland region, however, only about 15 percent
of the original grasslands remain because of an increase in irrigated cropland,
development, and recreation. 380 Due to this decrease in the abundance of grasslands,
grazing practices have an important impact on the surrounding systems. Not only do
native grasses provide food to livestock, but they also protect soils from wind and water
erosion, sequester carbon, keep watersheds below grazing areas clean, 381 and increase
soil water infiltration.
Grazing frequency intensity and timing (seasonality) influence how grasses respond to
grazing practices. 382 Proper grazing strategies allow grasses to recover, however, there
is no umbrella grazing strategy since the proper time to move livestock from one area to
another is based on the amount of green leaf material left in the grass. 383 Grazing can
also affect the water infiltration rates of soil. A study conducted near Nunn, CO,
compared the infiltration rates of three different soil types at three different grazing
levels. The three types of soils studied were Ascalon sandy loam, Shingle sandy loam,
and Nunn loam. On areas with the three soil types, three grazing rates were used: light,
moderate, and heavy. To test the infiltration rates, rainfall was simulated and the
difference between application and runoff rates were calculated. It was concluded that
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