By STEVE BROWN
Crop rotation is not only mandated by the USDA's National Organic Program, it is a practice organic farmers can use to their benefit in many ways, experts say.
Speaking in a webinar funded by the Natural Resources Conservation Service, Mark Schonbeck of the Virginia Association for Biological Farming listed typical practices and their benefits.
* Varying plant families year to year breaks the life cycles of weeds, pests and diseases.
* Including flowering legumes and other plants provides habitat and nectar for predator insects and pollinators. Alternating vegetables with cut flowers keeps profit going.
* Delaying planting beyond the earliest possible date lets the first flush of weeds emerge. Shallow cultivation can then clean up the small weeds and allow the soil to warm.
* Legumes such as clovers, alfalfa, vetches, peas and beans fix nitrogen, and there is less nitrogen leaching from living sources.
Harriet Behar, organic specialist at Midwest Organic Sustainable Education Service, said crop rotation should be the "foundation of an organic farmer's production system."
Even perennial systems like orchards can include alley cropping, intercropping and hedgerows. Schonbeck said practices like that are opportunities to grow predator and pollinator habitat.
Cover cropping works hand-in-glove with crop rotation, Behar said. It builds soil fertility and structure, increases organic matter and minimizes soil erosion.
"Organic farms should be the gold standard for protecting soil and water in their region," Behar said.
Schonbeck said when different cover crops are combined -- such as clover, winter grain and vetch -- the diversity benefits the soil life and adds even more biomass. A grass-legume combination balances carbon and nitrogen, increases nitrogen fixation, lessens nitrogen leaching or tie-up and increases weed control.
Killing cover crops with a roller-crimper or flail mower makes a good mat for planting into, whether it's seeds or transplants, Schonbeck said.
"Less disturbance equals more diversity of beneficial fungi, earthworms and arthropods," he said. "Till only when necessary."
Among the rotation-cover crop variations Behar and Schonbeck suggested:
* Row crops can be rotated with small grains undersown by nitrogen-fixing legumes. The legumes can be left for hay or forage, or incorporated as high biomass green manure.
* Habitat for beneficial insects can be mowed to drive predators over to adjoining cash crops.
* Including bio-energy crops (sunflowers, soybeans, canola, camelina) in the rotation facilitates on-farm biodiesel production.
* Spring oats and red clover can be planted after two years of vegetables and winter annual cover. Oats can be harvested for grain, and the clover allowed to grow through summer.
* When mixing species for seeding, including non nitrogen-fixing green manures such as rye, buckwheat, oats, wheat, barley, sorghum, sudan, tillage radish and mustards actually maximize nitrogen fixation.
* In high-tunnels, as lettuce and bok choy approach maturity, tomatoes -- interplanted later -- begin their rapid growth. The farmer then harvests greens instead of pulling weeds while waiting for tomato crop to begin bearing fruit.
* Applying animal manure onto a living cover crop captures nutrients, lessens leaching and releases them for the subsequent cash crop when incorporated. Sudan grass is excellent for this, Schonbeck said.