have more scab following peas or oats.
the Great Plains to replace the wheat-fallow system,
7. Use crop sequences that aid in controlling weeds.
resulting in better use of water and less soil erosion.
Small grains compete strongly against weeds and
(It is estimated that less than 25% of the rainfall that
may inhibit germination of weed seeds, row crops
falls during the fourteen-month fallow period in the
permit midseason cultivation, and sod crops that
Central High Plains is made available to a following
are mowed regularly or intensively grazed help
crop of winter wheat.) (See box “Flexible Cropping
control annual weeds.
Systems” and table 11.2, p. 121, for discussion and
8. Use longer periods of perennial crops, such as a for-
information on flexible, or dynamic, cropping sys-
age legume, on sloping land and on highly erosive
tems.) As discussed above (see point 5), reconsider
soils. Using sound conservation practices, such as
your crop sequence and cover crop use if nematodes
no-till planting, extensive cover cropping, or strip
become a problem.
cropping (a practice that combines the benefits of
rotations and erosion control), may lessen the need
ROTATION ExAMPlES
to follow this guideline.
It’s impossible to recommend specific rotations for a
9. Try to grow a deep-rooted crop, such as alfalfa, saf-
wide variety of situations. Every farm has its own unique
flower, or sunflower, as part of the rotation. These
combination of soil and climate and of human, animal,
crops scavenge the subsoil for nutrients and water,
and machine resources. The economic conditions and
and channels left from decayed roots can promote
needs are also different on each farm. You may get
water infiltration.
useful ideas by considering a number of rotations with
10. Grow some crops that will leave a significant
historical or current importance.
amount of residue, like sorghum or corn harvested
A five- to seven-year rotation was common in the
for grain, to help maintain organic matter levels.
mixed livestock-crop farms of the northern Midwest and
11. When growing a wide mix of crops—as is done on
the Northeast during the first half of the 20th century.
many direct-marketing vegetable farms—try group-
An example of this rotation is the following:
ing into blocks according to plant family, timing of
crops (all early-season crops together, for example),
Year 1. Corn
type of crop (root vs. fruit vs. leaf), or cultural prac-
Year 2. Oats (mixed legume–grass hay seeded)
tices (irrigated, plastic mulch used).
Years 3, 4, and 5. Mixed grass–legume hay
12. In regions with limited rainfall, the amount of water
Years 6 and 7. Pasture
used by a crop may be a critically important issue—
usually one of the most important issues. Without
The most nitrogen-demanding crop, corn, followed
plentiful irrigation, growing high-water-use crops
the pasture, and grain was harvested only two of every
such as hay, as well as sunflower and safflower, may
five to seven years. A less nitrogen-demanding crop,
not leave sufficient moisture in the soil for the next
oats, was planted in the second year as a “nurse crop”
crop in the rotation.
when the grass-legume hay was seeded. The grain was
13. Be flexible enough to adapt to annual climate and
harvested as animal feed, and oat straw was harvested to
crop price variations, as well as development of
be used as cattle bedding; both eventually were returned
soil pathogens and plant parasitic nematodes. For
to the soil as animal manure. This rotation maintained
example, dryland rotations have been introduced in
soil organic matter in many situations, or at least didn’t
120
Building SoilS for Better CropS: SuStainaBle Soil ManageMent