Carefully selected rotations, especial y when alternating between grains and broadleaf plants, can greatly assist control of plant diseases and nematodes. Sometimes a one-year break is sufficient for disease control, while for other diseases a number of years of growing a nonhost crop is needed to sufficiently reduce inoculum levels. Inclusion of pulse crops in a rotation seems to stimulate beneficial organisms and reduce the severity of cereal root diseases. Severity of common root rot of wheat and barley is reduced by a multiyear break of growing broadleaf plants. Rotations can be relatively easy to develop for control of diseases and nematodes that have a fairly narrow host range. However, some diseases or nematodes have a wider host range, and more care is needed in developing or changing rotations if these are present. In addition, some diseases enter the field on contaminated seed, while others, like wheat leaf rust, can travel with the wind for long distances. Other tactics, aside from rotations, are needed to deal with such diseases.
—KRUPINSKy ET AL. (2002).
In addition, when you grow a more diversified group of
oats, barley, and wheat, in the second or third year
crops, you are less affected by price fluctuations of one
after a legume sod.
or two crops. This may provide more year-round income
3. Grow the same annual crop for only one year, if
and year-to-year financial stability.
possible, to decrease the likelihood of insects, dis-
Although there are many possible benefits of rota-
eases, and nematodes becoming a problem. (Note:
tions, there are also some costs or complicating factors.
For many years, the western corn rootworm was
It is critically important to carefully consider the farm’s
effectively controlled by alternating between corn
labor and management capacity when exploring diversi-
and soybeans. Recently, populations of the root-
fication opportunities. You may need more equipment to
worm with a longer resting period have developed
grow a number of different crops. There may be conflicts
in isolated regions in the Midwest, and they are able
between labor needs for different crops; cultivation and
to survive the very simple two-year rotation.)
side-dressing nitrogen fertilizer for corn might occur
4. Don’t follow a crop with a closely related species,
at the same time as harvesting hay in some locations.
since insect, disease, and nematode problems are fre-
In addition, some tasks, such as harvesting dry hay
quently shared by members of closely related crops.
(mowing, tedding when needed, baling, and storing)
5. If specific nematodes are known problems, consider
can require quite a bit of labor that may not always be
planting nonhost plants (such as grain crops for root-
available. Finally, the more diversified the farm, the less
knot nematode) for a few years to decrease popula-
chance for time to relax.
tions before planting a very susceptible crop such as
carrots or lettuce. High populations of plant parasitic
gENERAl PRINcIPlES
nematodes will also affect the choice of cover crops
Try to consider the following principles when you’re
(see chapter 10 for a discussion of cover crops).
thinking about a new rotation:
6. Use crop sequences that promote healthier crops.
1. Follow a legume forage crop, such as clover or
Some crops seem to do well following a particular
alfalfa, with a high-nitrogen-demanding crop, such
crop (for example, cabbage family crops following
as corn, to take advantage of the nitrogen supply.
onions, or potatoes following corn). Other crop se-
2. Grow less of nitrogen-demanding crops, such as
quences may have adverse effects, as when potatoes
119
Building SoilS for Better CropS: SuStainaBle Soil ManageMent