Managing Cover Crops Profitably - Valley Crops Home

OVERVIEW OF NONLEGUME COVER CROPS
Most of the commonly used nonlegume cover
crops are grasses. These include:
• Annual cereals (rye, wheat, barley, oats)
• Annual or perennial forage grasses such as
ryegrass
• Warm-season grasses like sorghum-sudangrass
Grass cover crops are most useful for:
• Scavenging nutrients—especially N—left over
from a previous crop
• Reducing or preventing erosion
• Producing large amounts of residue, and
adding organic matter to the soil
• Suppressing weeds
Annual cereal grain crops have been used successfully
in many different climates and cropping
systems.Winter annuals usually are seeded in late
summer or fall, establish and produce good root
and topgrowth biomass before going dormant
during the winter,then green up and produce significant
biomass before maturing. Rye, wheat, and
hardy triticale all follow this pattern, with some
relatively small differences that will be addressed
in the section for each cover crop.
Perennial and warm-season forage grasses also
can serve well as cover crops. Forage grasses, like
sod crops, are excellent for nutrient scavenging,
erosion control, biomass production and weed
control. Perennials used as cover crops are usually
grown for about one year. Summer-annual
(warm-season) grasses may fill a niche for biomass
production and weed or erosion control if the
ground would otherwise be left fallow (between
vegetable crops, for example). Buckwheat, while
not a grass,is also a warm-season plant used in the
same ways as summer-annual grasses.
Grass cover crops are higher in carbon than
legume cover crops.The high carbon content of
grasses means that they will break down more
slowly than legumes, resulting in longer-lasting
residue. As grasses mature, the carbon-to-nitrogen
ratio (C:N) increases. This has two tangible
results: The higher carbon residue is harder for
soil microbes to break down,so the process takes
longer, and the nutrients contained in the cover
crop residue usually are less available to the next
crop.
So although grass cover crops take up leftover N
from the previous crop,as they mature the N is less
likely to be released for use by a crop grown immediately
after the grass cover crop. As an example of
this, think of how long it takes for straw to decompose
in the field.Over time,the residue does break
down and nutrients are released. In general, this
slower decomposition and the higher carbon content
of grasses can lead to increased soil organic
matter, compared to legumes.
Grass cover crops can produce a lot of residue,
which contributes to their ability to prevent erosion
and suppress weeds while they are growing
or when left on the soil surface as a mulch.
Although grasses contain some nitrogen in
their plant tissues, grass cover crops generally are
not significant sources of N for your cropping system.
They do, however, keep excess soil N from
leaching, and prevent the loss of soil organic matter
through erosion.
Management of grasses in your cropping system
may involve balancing the amount of residue
produced with the possibility of tying up N for
more than one season. Mixtures of grass and
legume cover crops can alleviate the N-immobilization
effect, can produce as much or more dry
matter as a pure grass stand and may provide better
erosion control due to the differences in
growth habit.Suggestions for cover crop mixtures
are found in the individual cover crop sections.
In addition to grasses, another summer nonlegume
is buckwheat, which is described in
detail in its own section (p. 77). Buckwheat is
usually classed as a non-grass coarse grain.While
it is managed like a quick-growing grain, its has
a succulent stem, large leaves and white
blossoms.
54 MANAGING COVER CROPS PROFITABLY