farm in Iowa practices an alternative five-year corn belt
from alfalfa (fourth year) back to corn. This caused the
rotation similar to the first rotation we described—corn/
investigators to use fall tillage followed by a cover crop
soybeans/corn/oats (mixed/grass hay seeded)/hay. For
mixture of winter rye and hairy vetch. Some success
fields that are convenient for pasturing beef cows, the
was achieved suppressing the cover crop in the spring
Thompson eight-year rotation is as follows:
by just rolling over it with a disk harrow and planting
corn through the surface residues with a modified no-till
Year 1. Corn
planter. The heavy cover crop residues on the surface
Year 2. Oats (mixed/grass hay seeded)
provided excellent weed control for the corn.
Years 3 to 8. Pasture
Traditional wheat-cropping patterns for the semiarid
regions of the Great Plains and the Northwest commonly
Organic matter is maintained through a combina-
include a fallow year to allow storage of water and more
tion of practices that include the use of manures and
mineralization of nitrogen from organic matter for use
municipal sewage sludge, green manure crops (oats and
by the next wheat crop. However, the wheat-fallow
rye following soybeans and hairy vetch between corn
system has several problems. Because no crop residues
and soybeans), crop residues, and sod crops. These prac-
are returned during the fallow year, soil organic matter
tices have resulted in a porous soil that has significantly
decreases unless manure or other organic materials are
lower erosion, higher organic matter content, and more
provided from off the field. Water infiltrating below the
earthworms than neighbors’ fields
root zone during the fallow year moves salts through
A four-year rotation researched in Virginia used
the soil to the low parts of fields. Shallow groundwater
mainly no-till practices as follows:
can come to the surface in these low spots and create
“saline seeps,” where yields will be decreased. Increased
Year 1. Corn, winter wheat no-till planted into
soil erosion, caused by either wind or water, commonly
corn stubble
occurs during fallow years, and organic matter decreases
Year 2. Winter wheat grazed by cattle after harvest,
(at a rate of about 2% per year, in one experiment).
foxtail millet no-till planted into wheat stubble and
In this wheat monoculture system, the buildup of grassy
hayed or grazed, alfalfa no-till planted in fall
weed populations, such as jointed goat grass and downy
Year 3. Alfalfa harvested and/or grazed
brome, also indicates that crop diversification is essential.
Year 4. Alfalfa harvested and/or grazed as usual
Farmers in these regions who are trying to develop
until fall, then heavily stocked with animals to
more sustainable cropping systems should consider
weaken it so that corn can be planted the next year
using a number of species, including deeper-rooted
crops, in a more diversified rotation. This would
This rotation follows many of the principles dis-
increase the amount of residues returned to the soil,
cussed earlier in this chapter. It was designed by
reduce tillage, and lessen or eliminate the fallow period.
researchers, extension specialists, and farmers and is
(See box “Flexible Cropping Systems.”)
similar to the older rotation described earlier. A few
A four-year wheat-corn-millet-fallow rotation under
differences exist: This rotation is shorter; alfalfa is used
evaluation in Colorado was found to be better than the
instead of clover or clover-grass mixtures; and there is
traditional wheat-fallow system. Wheat yields have been
a special effort to minimize pesticide use under no-till
higher in this rotation than wheat grown in monocul-
practices. Weed-control problems occurred when going
ture. The extra residues from the corn and millet also
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Building SoilS for Better CropS: SuStainaBle Soil ManageMent