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Pennsylvania vegetable farmer
Steve Groff, (posing here with eight-year-old daughter, Dana),
pairs no-till with well-managed crop rotations and cover crops,
enabling him to reduce herbicides.
Photo by Ray Weil. |
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Composting imported organic-waste residues before applying them
to soils may help fight crop diseases. Good composts are costly
to buy and slow to produce, but they can pay their own way — especially
on farms that produce high-value vegetables and small-berry fruits.
At Ohio State University, plant pathologist Harry Hoitink and his
co-workers have found that compost may suppress root and foliar
diseases. Among the possible reasons:
 compost-treated
plants are usually healthier and better able to resist infection,
compost
feeds microorganisms, which produce plant growth hormones and
chelates that make micronutrients more available to plants, and
compost
hosts beneficial organisms that feed directly on disease organisms,
compete with them for nutrients or produce antibiotics.
Some soils or potting mixes blended with medium- maturity compost
— which still contains enough food for microorganisms — have sparked
systemic resistance in plants, Hoitink says. “These plants have
elevated levels of biochemical activity relative to disease control
and are better prepared to defend themselves against diseases.”
Not all composts provide this beneficial effect. In fact, composts
and other biological materials that are rich in available nitrogen
may actually stimulate some plant diseases. Among these diseases
are Phytophthora root rot in soybeans, Fusarium wilts
in vegetable crops and fire blight in fruit crops. To reduce the
risk of initiating disease, spread these materials many months before
cropping, allow the salts to leach away, or blend in low-nitrogen
materials before application.
In Ohio, vegetable grower John Hirzel recorded 25-percent yield
increases in tomatoes that were started in the greenhouse in mixtures
of one-third compost, then transplanted to the field into soils
amended with 10 to 12 tons of compost per acre. Hirzel, who died
in 2000, found that tomatoes grown with more compost have better
resistance to bacterial canker, bacterial spot and bacterial speck,.
“As soon as they germinate, they are living in a soil that has natural
bacteria and fungi,” he said in a 1999 interview.
On the other hand, farming practices that cause imbalances in nutrition
or other factors can lower natural resistance. High nitrogen fertilizer
levels can fuel the germination and growth of many weed species,
boost the incidence of diseases such as Phytophthora, Fusarium
and corky spot, and stimulate outbreaks of aphids, mites and other
insects.
Some herbicides lower the resistance of crops to invading disease-causing
organisms. Even more serious, as it decays, glyphosate-treated vegetation
can create flushes of Fusarium, Rhizoctonia and other
pathogenic fungi.
Rotation, in the absence of known pests, has improved growth and
yields in many crops by about 10 percent. Longer rotations tend
to increase crop yields more than shorter rotations; yields of corn
and wheat grown as part of three-year rotations exceed those in
two-year cycles or in continuous monocultures. Adding organic matter
— through cover cropping, animal manures and crop residues — boosts
crop performance and may improve pest tolerance.
For three decades, Dick Thompson has planted cover crops, managed
weeds like covers instead of like pests, and lengthened and expanded
his crop rotation. “I’m not saying we don’t have any insect problems,
but they do not constitute a crisis,” Thompson says. “We don’t have
to treat for them. We haven’t done that for years.”
| A word of caution regarding no-till.
If not managed properly, eliminating tillage can provoke problems.
Annual weed populations can build more rapidly if seeds stay
on the soil surface, soils may warm up more slowly in the
spring and, under some conditions, no-till may increase plant
disease because some pathogens survive better in undisturbed
soils.
You may need to till to control perennial
weeds that crop up in undisturbed fields. Soils — especially
wet, poorly drained ones — may need tillage to alleviate compaction
by heavy machinery. In such cases, devise a rotation that
involves tillage only during selected years or seasons, or
use strip-till or ridge-till instead of no-till. In regions
with cool, wet springs, no-till may not work well for early
planted crops. You may want to talk to professionals from
the Extension Service or the Natural Resources Conservation
Service before changing your tillage regime. |
On his Boone, Iowa, farm, Thompson uses a corn- soybean-corn-oats-hay
rotation, with at least four different kinds of hay. He shreds weeds
in his ridge-till system, then cultivates and lays them between
the rows, turning a pest into a mulch.
At 6 percent, his soil organic matter is now double that of neighboring
conventional operations. “You can tell it by working it,” Thompson
says. “I can do things with a cultivator that others can’t do. I’m
not moving big clods but fine soil. The dirt flows and allows you
to cover up the weeds.”
Because his soil no longer blows or washes away as easily as it
once did, Thompson’s high ground is becoming more productive. “Our
yields are just as good — if not better — on the hills as they are
on the low ground.”
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