Agriculture Reference
In-Depth Information
than two decades, providing practical, hands-on advice for how to use
them effectively. He is critical of most UC cover crop research because it
either has not used the correct seed mix, or has not matched the seed mix
to the soil needs, or is not replicated properly.
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Thomas has a cover crop
mix for every purpose. Legumes fix nitrogen. Tap-rooted bell beans and
oats break up plowpan. Perennial grasses provide soil stability allowing
tractor access during wet winters. A diverse mix of cover crop species
can occupy the ecological niches of weeds. Specialized mustard species
can reduce the populations of nematodes, microscopic soil-dwelling
organisms that can torture orchard trees. For growers concerned about
the potential of increased frost damage from cover crops he recommends
species that can survive low mowing in the winter. For growers con-
cerned about high irrigation costs he recommends mixes that go summer
dormant. Thomas guardedly suggests that cover crops can aide in insect
pest management by providing nectar, pollen, or alternate hosts for ben-
eficial insects, but cautions that the generalist predators do not have the
ability to control pests with explosive growth, such as prune aphids.
Thomas emphasizes that cover crops are not a panacea.
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Cover crops
can work wonders with farm soils, but they have to be tied to realistic
biological goals and growers have to be able to adapt their approach to
orchard floor management. No one cover crop mix can perform all func-
tions. If growers want to improve winter access to their orchards, they
should sow grasses, not tall growing leguminous plants. If they want an
immediate fertility boost, they should plant legumes, although these
grow tall enough that they can increase the risk of frost damage to trees
in some regions. They also preclude equipment access during the spring,
when chemical disease treatments can be crucial. Cover crops with the
most nutrient value usually have to be purchased and planted each year.
Permanent cover grasses allow equipment access in the winter, but
require water during the summer. Permanent cover crops work well in
orchards with flood irrigation, which tend to have affordable water, but
they can be quite expensive for a grower trying to conserve water with
drip irrigation. Some growers have balanced orchard access with other
cover crop benefits by planting them in alternate middles.
To effectively incorporate cover crops into their operations, growers
must be open to re-thinking some aspects of their farming and have the
ability to match the variable performance of different cover crops to the
