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Hana Newcomb stands by the
vegetables produced by her 30-acre organic farm in northern
Virginia. She and her mother, Hiu, rely on mulches to control
weeds — from onion plants blanketed by composted leaves, to
blueberry bushes rising through mounds of sawdust, to cucumber
plants pushing protective sheets of white polyester. Photo by
Valerie Berton. |
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Reduce tillage for healthy soils. Many people
consider tillage necessary for crop production. However, this seasonal
practice can destroy some vital processes by depleting organic matter,
intensifying the loss of topsoil to erosion and destroying soil
tilth. Damaged soils are less able to provide nutrients, hold water
and support biological activity. The net result: less diversity
in crucial soil organisms.
“In my opinion, there’s no single greater catastrophic event in
the life of the soil than to have some big piece of tillage equipment
run across it,” says Luna. “Worms and bugs are killed, fungi are
broken up and destroyed, and you end up with a much more simplified
biological system.”
To plant and establish vigorous crops, you need to clear vegetation
and residues from at least a portion of your field. Some equipment,
however, minimizes soil disturbance. No-till planters, which cut
a slot just wide enough to insert seed, disturb soil the least.
Strip-tillage disrupts only a band of soil along the crop row, leaving
untilled areas between rows. Ridge-till systems produce only shallow
soil disturbances. Chisel plows do disturb soil structure, but,
unlike moldboard plows, they do not invert or pulverize soils. No-till,
zone-till and ridge-till also leave accumulations of plant residues
covering the soil.
In a 1997 vegetable trial, Oregon State University researchers
found a Willamette Valley farmer improved corn yields after strip-tilling
into a winter cover of oats, vetch and Austrian winter peas. The
farmer planted in eight-inch strips cut into the cover crop residue.
The new system returned $100 per acre more than the standard tillage
system.
Surface plant-residue mulches supply organic matter that reverses
many of the detrimental effects of tillage. They take the edge off
soil temperature extremes and keep soil moisture more consistent,
thereby favoring a wide group of organisms. These factors combine
to improve biological activity, soil tilth and nutrient- and water-holding
capacity.
In Lancaster County, Pa., Groff says his cover crops — along with
his “full time, 100-percent commitment to no-till” — have increased
his soil organic matter from 2.7 to 4 percent in the last decade.
Although he farms on slopes as steep as 17 percent, his annual erosion
losses are only a fraction of the county’s average.
When putting in underground irrigation lines, Groff found “roots
of my rye cover crop 40 inches deep and earthworm holes 36 inches
deep. By not tilling the soil, by leaving all of that structure
intact, over several years I have a soil that begins to open up.”
Maintain surface residues. More diverse biological
and physical environments at the soil surface spark more bountiful
opportunities for regulating pests. The living and dead plant materials
linked with no-till management readily establish biological activity,
which can contribute to natural suppression of pests. The soil organic
matter and fertility generated by cover cropping and reduced tillage
also lessen pest damage simply by improving the growth and vigor
of crops.
Cover crops supply generous amounts of surface vegetation and residue
that can be customized for specific needs. Live, they furnish excellent
habitat and food for beneficial insects. Strip-tilling a cash crop
into a winter annual cover crop or overseeding the cash crop with
a cover crop after the last cultivation allows bands of live covers
to flourish between rows without over-competing.
In some systems, cover crops eliminate the need for pre-plant herbicides
and reduce the need for post-emergence herbicides. (See Resources
for information about the comprehensive book, Managing Cover
Crops Profitably.) Winter annual cover crops continue to yield
crop benefits even after they have withered. Along with residue
from previous crops, they can interfere with pest populations by:
 hindering
weeds or other soil pests by physically obstructing their growth,
tampering with soil temperature or moisture, or unleashing plant-inhibiting
allelopathic chemicals,
preventing
fungal spores from being dispersed by water or wind, thereby curbing
foliar diseases, and
enhancing
populations of predatory insects such as ground beetles and spiders.
“We see it over and over in our research,” says weed specialist
Teasdale: “The tomatoes in the vetch cover crop system stay green
and healthier longer than tomatoes grown on a black plastic mulch.”
Indeed, the tomatoes maintain healthy green foliage about 50 percent
longer.
Other practices for building healthy soils. Good
management of soil organic matter — reducing tillage, applying animal
manures and composts, and rotating with such soil-building crops
as sod-forming grass and legume forages — forms the basis for healthy
soils. Develop strategies to encourage on-farm nutrient cycling
and help organic matter accumulate. Take care to avoid compacting
soils. You may need to keep heavy equipment off wet soils, maintain
controlled traffic zones on soils susceptible to compaction, or
use some tillage to break up compacted layers. Many of the soil-building
practices discussed above help reduce soil erosion. On soils that
are prone to erosion damage, consider strip cropping, grassed waterways
to conduct runoff off fields, and soil terracing to help keep topsoil
in place.
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