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Soil Management-Cover Crops
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Planting no-till
corn into soybean residue improves water infiltration and slows
evaporation.
Photo by USDA-NRCS |
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Cover crops, seeded between or amid cash crops, contribute a variety
of conservation benefits. For water conservation, they offer a triple
bonus. A living cover crop traps surface water. When killed and
left on the surface, cover crop residue increases water infiltration,
lessens erosion and reduces evaporation. Finally, when incorporated
into the soil, residue adds organic matter that increases infiltration
to the root zone.
Palm date growers in California’s dry Coachella Valley asked
USDA Agricultural Research Service (ARS) researchers to help them
improve their soil, which is both stratified with clay layers and
compacted by frequent cultivation with deep plows. Led by now retired
ARS researcher Aref Abdul-Baki, more than 40 growers helped test
lana vetch, a heat-tolerant legume cover crop, in their orchards,
despite concerns that the cover crop would out-compete the trees
for water.
The growers, flood-irrigating from the Colorado River, applied
six inches of water every two weeks. Yet, much of that evaporated
rather than infiltrated.
Research over a decade proved that adding lana vetch improved
the soil and thus water availability, to the date trees. The study
helped convince growers that cover crops aren’t water hogs.
“Population growth in Los Angeles will demand that the water
be channeled to the city of LA rather than to irrigate dates,”
said Abdul-Baki, whose lifetime of research on the soil-building
benefits of hairy vetch cover crops attracted the date growers’
attention. “We proved to them that the cover crop wasn’t
taking water.”
Instead, by shading the soil, the vetch lowered the soil temperature
by 7 degrees, reducing evaporation. Lana vetch also bound the soil
at the surface, preventing erosion and evaporation-promoting cracks,
while its root system opened up channels for infiltration. Perhaps
most important, the vetch also increased date yield by 15 percent
and, growers said, improved fruit quality.
Soil compaction, and the water loss it allows, occurs all over
the country. In Illinois, Ralph “Junior” Upton farmed
poorly drained land that was constrained by a “plow pan,”
a tough clay layer six to eight inches deep. The plow pan was so
thick, crop roots couldn’t penetrate. It also affected his
drainage, causing even moderate downpours to saturate his topsoil
and run off. Crops quickly used up the small amount of moisture
in the shallow top layer above the plow pan.
To break through, Upton began planting cover crops – rye
grass, cereal rye and hairy vetch – after harvesting beans
and corn. Following soybeans he now seeds rye grass, which breaks
up his soil with its deep roots.
Combined with no-till planting, Upton’s cover crops have
enhanced the soil’s ability to store water, and the additional
water available to the crop during the growing season has improved
grain yields. Short-term drought matters less, crop health has improved,
and when water does leave the farm, it isn’t carrying much
soil with it.
To improve soil aggregation, consider adding grass, either as
a hay crop or forage, into your rotation, since the complex root
systems of grass loosen soil. Some grass cover crops have especially
deep roots that do a yeoman’s job of breaking up compacted
soil. David Wolfe, a Cornell plant ecology researcher, studied the
effectiveness of sudangrass to improve soil in vegetable systems.
“As our research showed, the roots are relatively good at
proliferating into soil that is moderately compacted,” said
Wolfe, who received a SARE grant. “This would tend to improve
both water infiltration and drainage for subsequent crops.”
University of California-Davis researchers funded by SARE measured
as much as 50 percent higher water infiltration and 35 percent lower
runoff in the cover crop-heavy organic plots in a long-term trial
comparing organic and conventional cropping systems.
“Nobody could have possibly predicted such a dramatic difference
in the water runoff and infiltration between the organic and conventional
systems,” said project leader Steve Temple. “It’s
given us a new appreciation of the importance of cover cropping
and residue management.”
While Florida enjoys bountiful rainfall, the challenge for growers
is to capture precipitation for plant growth before it percolates
through sandy soils. Vegetable farmers like Gainesville grower Rose
Koenig and citrus farmer Lynn Steward in Arcadia use cover crops
such as sunn hemp with a lot of biomass to build the soil.
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