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Crop Rotation Basics Page 3
Full-Year Covers Tackle Tough WeedsContinued from page 2 |
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TROUT RUN, Pa. -- Growing cover crops for a full year between cash crops helps Eric and Anne Nordell control virtually every type of weed nature throws at their vegetable farm--even quackgrass. The couple experimented with many different cover crops on their north-central Pennsylvania farm before adapting a system used to successfully battle quackgrass on a commercial herb farm in the Pacific Northwest. Between cash crops, the Nordells grow two winter cover crops to smother weeds. A brief stint of aggressive summer tillage between the two cover crops keeps annual weeds from setting seed. Regular use of cover crops in their half-acre strips between rows of vegetables also improves soil quality and moisture retention while reducing erosion. "Vegetable crops return very little to the soil as far as a root system," says Eric, a frequent speaker on conservation practices at conferences in the Northeast. "You cut a head of lettuce and have nothing left behind. Growing vegetables, we're always trying to rebuild the soil." The Nordells' short growing season--which typically ends with the first frost in September--makes it challenging to squeeze in cover crops on their six cultivated acres. Yellow blossom sweetclover is overseeded at 20 to 24 lb./A into early crops such as onions or spring lettuce. Lettuce is overseeded a week or two after planting but before leaves open up to trap sweetclover seeds, while onions are overseeded near harvest. The Nordells walk up and down every other row with a manual Cyclone seeder (canvas bag with a hand-crank spinner). They harvest the cash crop, then let the clover grow through summer. Yellow blossom sweetclover--one of the best cover crop choices for warm-season nitrogen production--puts down a deep taproot before winter if seeded in June or July, observes Eric. "That root system loosens the soil, fixes nitrogen, and may even bring up minerals from the subsoil with its long tap root." He points out that the clover alone would not suppress weeds. The sole-seeding works on their farm because of their successful management efforts over a decade to suppress overall weed pressure by crop rotation and varied cover crops. In spring, the sweetclover grows until it is about knee-high in mid-May. Then the Nordells clip it just before it buds. They let the regrowth bloom to attract pollinators and beneficial insects to the field, before clipping it again in July. In early- to mid-July, the Nordells moldboard plow the sweetclover to kill it. They leave the ground in bare fallow, working it again with a springtooth harrow to hit perennial weeds at the weakest point of their lifecycle. After that, the couple harrows every two to three weeks to bring weed roots and rhizomes to the soil surface, where they bake in the summer sun. The harrowing also kills flushes of annual weeds before they can set seed. After five years in this weed-killing rotation, the Nordells were able to cut back on harrowing, which they now coordinate with rainfall and weed pressure. In the unusually dry summer of 1997, for example, they did not harrow at all after plowing. In mid-August, the Nordells plant a second, overwintering cover crop. In this rotation, they seed a mix of rye and hairy vetch. They broadcast and lightly incorporate about 80 pounds rye and 30 pounds vetch per acre. The rye establishes quickly, putting on good growth both above and below the surface, while the vetch fixes nitrogen. Another combination is yellow, red and white clover in a 2:2:1 ratio by volume. "We're looking for a green field by Labor Day," Eric says. "We want a good sod before we get our first freeze." Rye and vetch are a popular combination to manage nitrogen. The rye takes up excess N from the soil, preventing leaching. The vetch fixes additional nitrogen which it releases after it's killed the following spring prior to planting the next cash crop. With the August seeding, the Nordells' rye/vetch mixture produces most of its biomass in fall. The Nordells plow the rye/vetch mix after it greens up in late March to early April, working shallowly so as not to turn up as many weed seeds. They forego maximum biomass and N for earlier planting of their cash crop--tomatoes, peppers, summer broccoli or leeks--around the end of May. The bare fallow during mid-summer plus early spring incorporation of overwintering cover crops are the best preventive to slugs and grubs, they have found. Thanks to their weed-suppressing cover crops, the Nordells typically spend less than 10 hours a season hand-weeding their three acres of cash crops, and never need to hire outside weeding help. "Don't overlook the cover crops' role in improving soil tilth and making cultivation easier," adds Eric. Before cover cropping, he noticed that their silty soils deteriorated whenever they grew two cash crops in a row. "When the soil structure declines, it doesn't hold moisture and we get a buildup of annual weeds," he notes. The Nordells can afford to forego a cash crop to keep half their land in cover crops because their tax bills and land value are not as high as market gardeners in a more urban setting. "We take some land out of production, but in our situation, we have the land," Eric says. "If we had to hire people for weed control, it would be more costly." Excerpted from Managing Cover Crops Profitably, Second Edition, by the Sustainable Agriculture Network, reprinted 2000, SAN, Beltsville, MD, pp. 34-42. Complete text: http://www.sare.org/handbook/mccp2/index.htm To contact SAN off the Web: PHONE: (301) 504-6425; FAX: (301) 504-5207; EMAIL: san@sare.org.
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