Cover Crops for Organic Farms

clover is seeded at 8 to 15 pounds per acrebetween mid-September and mid-October.Austrian winter pea (Pisum sativumarvense). Austrian winter pea is succulentand viney and can climb when plantedwith small grain crops. It grows vigorouslyand will suppress weeds while growing, butit decomposes rapidly and is not a goodchoice for a surface mulch and weedcontrol. Austrian winter pea does well in amixture with oats, barley, rye, or wheat.Seed is drilled at 60 to 90 pounds per acreand can be sown through October.Winter NonlegumesCereal rye (Secale cereale). Rye is one ofthe most commonly used winter covercrops. It grows 3 to 6 feet tall and has anextensive, fibrous root system. It performswell when mixed with hairy vetch, whichwill use it for climbing support. Rye cantolerate a wide variety of soil types andclimatic conditions and is considered to beweed suppressive when managed as amulch. Of all the small grains, rye is thebest scavenger of excess soil nitrogen in thefall. The seeding rate is 100 pounds peracre.Annual ryegrass (Lolium multiflorum).Annual ryegrass is a noncreepingbunchgrass. In the spring it can grow 2 to 4feet tall. Annual ryegrass can be difficult tocontrol and can become a serious weed if itproduces seed. Ryegrass requiresconsiderable nitrogen and water. If theseare limited, it may not be a good choice.Ryegrass has a very fibrous, dense rootsystem that protects against soil erosionwhile improving water infiltration and soiltilth. Dry matter yield can average between1,300 and 2,000 pounds per acre, with anaverage nitrogen content of 1.5 percent.Normally seeded in the fall, seeding ratesare between 20 and 30 pounds per acre.Other cereal grasses. All of the cerealgrasses will produce biomass ranging from2,000 to 6,000 pounds per acre withnitrogen concentrations between 1 and 2percent. Biomass accumulation depends, inpart, on how early in the spring the covercrop is killed. The high end of the rangerepresents a kill date in mid- to late May. Atthis late date, however, the biomass carbonto nitrogen (C:N) ratio will normally begreater than 50:1, a ratio at which soilmicrobes would immobilize anymineralized nitrogen. Small grains arenormally drilled at 100 pounds of seed peracre.• Wheat (Triticum aestivum) provides agood overwintering ground cover andalso provides the option of harvestingthe grain.• Barley (Hordeum vulgare) biomassproduction peaks about two weeksearlier than wheat, and about the sametime as crimson clover. Barley, grown asa smother crop, has been shown tosuppress winter annual weeds incropping systems, but must be plantedin September or early October to reducewinter kill.• Oats (Avena sativa) grow well in coolweather and provide rapid ground coverin the fall. Some growers plant springoats in the fall to produce a winterkilledmulch for early spring no-tillvegetable plantings. However, springoats may not always winter-kill in mildwinters.Recommended Summer SpeciesThere is growing interest in the use ofshort-season summer annual legumes orgrasses as cover crops and green manures incropping systems. Summer annual legumesOrganic Production—Cover Crops for Organic Farms 14