of earthworms, as well as other soil organisms. More
the time that living roots are present during a rotation is
complex rotations increase soil biological diversity.
also important. The period that active roots are present
Including perennial forages in the rotation enhances
varies considerably, ranging from 32% of the time for a
this effect.
corn-soybeans rotation to 57% for a beans-wheat rota-
tion to 76% for a three-year beans-wheat-corn rotation
RESIDUE AVAIlAbIlITY
(table 11.1). As mentioned above, when soils are covered
As pointed out in chapters 3 and 9, more residues are
with living vegetation for a longer period of time, there
left in the field after some crops than others. High
tends to be decreased erosion as well as a decreased loss
residue-producing crops—especially those with exten-
of nitrate and less groundwater contamination.
sive root systems—should be incorporated into rotations
whenever possible. There is considerable interest in the
ROTATIONS AND WATER QUAlITY
possible future use of crop residue for a variety of pur-
When annual crops are grown and planted in the spring,
poses, such as for biofuel production. However, farmers
there is a considerable amount of time when the soil is
should keep in mind that frequent removal of significant
not occupied by living plants. This means that for a large
quantities of residue from their fields—and there may be
portion of the year there are no living plants to take up
more pressure to remove them if production of biofuels
nutrients, especially nitrate, that can leach out of the
from crop residue becomes economically viable—can
soil. This is especially a problem in the Midwest, where
have a very negative effect on the soil’s health.
many soils have tile drainage, which accentuates the
discharge of high-nitrate water into streams and rivers.
SPEcIES RIcHNESS AND AcTIVE ROOTINg PERIODS
In addition to not taking up nutrients, the lack of grow-
In addition to the quantity of residues remaining follow-
ing plants means that the soils are wetter and more apt
ing harvest, a variety of types of residues is also impor-
to produce runoff and erosion as well as leaching. Thus,
tant. The goal should be a minimum of three different
rotations that include perennial forages and winter
species in a rotation, more if possible. The percent of
grains help maintain or enhance the quality of both
ground and surface waters. And, while intensive use of
Table 11.1
Comparison of Rotations:
cover crops helps water quality in a similar way, cover
Percent of Time Active Roots Are Present and Number of Species
crops should not be viewed as a substitute for a good
Rotation
Years
Active Rooting Number of
rotation of economic crops.
Period (%)
Species
Corn-soybeans
2
32
2
FARM lAbOR AND EcONOMIcS
Dry beans–winter
2
57
2
wheat
Before discussing appropriate rotations, let’s consider
some of the possible effects on farm labor and finances.
Dry beans–winter
2
92
3
wheat/cover
If you grow only one or two row crops, you must work
Dry beans–winter
3
72
3
incredibly long hours during planting and harvesting
wheat–corn
seasons, and not as much at other times. Including for-
Corn–dry beans–winter
3
76
4
wheat/cover
age hay crops and early harvested crops along with those
that are traditionally harvested in the fall would allow
Sugar beets–beans–
4
65
5
wheat/cover–corn
you to spread your labor over the growing season, mak-
Source: Cavigelli et al. (1998).
ing the farm more easy to manage by family labor alone.
118
Building SoilS for Better CropS: SuStainaBle Soil ManageMent