a lot of nitrate is left in the soil at the end of the season,
the rye is stimulated (reducing leaching losses). When
little nitrogen is available, the vetch competes better
with the rye, fixing more nitrogen for the next crop.
A crop that grows erect, such as winter rye, may pro-
vide support for hairy vetch and enable it to grow better.
Mowing close to the ground kills vetch supported by rye
B
easier than vetch alone. This may allow mowing instead
of herbicide use, in no-till production systems.
Planting
If you want to accumulate a lot of organic matter, it’s best
to grow a cover crop for the whole growing season (see
figure 10.5a), which means no income-generating crop
A
C
will be grown that year. This may be useful with very
a) Root of forage radish.
infertile or eroded soils. It also may help vegetable pro-
b) Root holes (bio-drilling) and root remains in spring following fall
duction systems when there is no manure available and
forage radish. Black pen (see arrow) in hole for scale.
where a market for hay crops justifies a longer rotation.
c) Horizontal cracks with rye (left) and vertical cracks with forage
radish (right).
Planting after economic crop harvest. Most
Figure 10.4. Brassica cover crop roots. Photos by Ray Weil.
farmers sow cover crops after the economic crop has
been harvested (figure 10.5b). In this case, as with the
much water in dry climates or by becoming a weed in
system shown in figure 10.5a, there is no competition
subsequent crops.
Mixtures of Cover Crops
a
main crop
Although most farmers use single species of cover crops
cover crop
in their fields, mixtures of different cover crops offer
combined benefits. The most common mixture is a grass
and legume, such as winter rye and hairy vetch, oats
b
main crop
main crop
and red clover, or field peas and a small grain. Other
mixtures might include a legume or small grain with
cover crop
forage radish or even just different small grains mixed
together. Mixed stands usually do a better job of sup-
c
main crop
main crop
pressing weeds than a single species. Growing legumes
with grasses helps compensate for the decreases in
cover crop
cover crop
nitrogen availability for the following crop when grasses
are allowed to mature. In the mid-Atlantic region, the
January
July
January
July
January
winter rye–hairy vetch mixture has been shown to pro-
Figure 10.5. Three ways to time cover crop growth for use with a summer
vide another advantage for managing nitrogen: When
crop.
108
Building SoilS for Better CropS: SuStainaBle Soil ManageMent