Cover Crops for Organic Farms

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nitrogen in 45 to 60 days. Seed is notreadily available at this writing in early2006, but availability may increase ifdemand increases. While some Crotalariaspecies are toxic to animals, sunnhempforage is not. Sunnhemp should not to beconfused with showy crotalaria, a noxiousweed species.Summer NonlegumesBuckwheat (Fagopyrum esculentum).Buckwheat is a very rapidly growingbroadleaf summer annual, which canflower in four to six weeks. It reaches 30inches in height and is single-stemmedwith many lateral branches. It has both adeep taproot and fibrous roots. It can begrown to maturity between spring and fallvegetable crops, suppressing weed growthand recycling nutrients during that period.It is succulent, easy to incorporate, anddecomposes rapidly. Buckwheat flowers arevery attractive to insects, and some farmersuse this cover to attract beneficial insectsinto cropping systems. Buckwheat is aneffective phosphorous scavenger. The maindisadvantage to buckwheat is that it setsseed quickly and, if allowed to go to seed,may become a weed in cash crops. Thus,the optimal time to incorporate buckwheatis one week after flowering, before seed isset. Buckwheat can be planted anytime inthe spring, summer, or fall, but is frostsensitive.Sorghum sudangrass (Sorghum bicolor ×Sorghum sudanense). Sorghum sudangrass isa hybrid of grain sorghum and sudangrass.It is a warm-season annual grass, most oftenplanted from late spring through midsummer.It grows well in hot, dryconditions and produces a large amount ofbiomass. Often reaching 6 feet in height, itcan be mowed to enhance biomassproduction. Sorghum sudangrass is veryeffective at suppressing weeds and has beenshown to have allelopathic properties. Theroots of sorghum sudangrass are goodforagers for nutrients and help controlerosion. Sorghum sudangrass does wellwhen planted in mixtures, providingeffective support for viney legumes likevelvetbean. If frost-killed, the residue canprovide a no-till mulch for early plantedspring crops like broccoli. When stressed bydrought or by frost, this cover crop canproduce prussic acid, which is toxic tocattle.German (foxtail) millet (Setariaitalica). German or foxtail millet is anannual warm-season grass that maturesquickly in the hot summer months. It isone of the oldest of cultivated crops.German millet has a fairly low waterrequirement. Because of its shallow rootsystem, however, it doesn’t recover easilyafter a drought. Grain formation requires75 to 90 days. German millet forms slender,erect, and leafy stems that can vary inheight from 2 to 4 feet. The seed can bedrilled from mid-May through August at arate of 10 to 15 pounds per acre. A smallseeded crop, German millet requires arelatively fine, firm seedbed for adequategermination. To avoid early competitionfrom germinating weed seed, it should beclosely drilled in the row or sown in a staleseedbed—a seedbed that has been prepared,with early emerged weeds killed just beforeplanting the cover crop. Coarse, sandy soilsshould be avoided.Pearl millet (Pennisetum glaucum). Pearlmillet is a tall annual bunchgrass thatgrows 4 to 10 feet tall. It is also oftenreferred to as cattail millet because its long,dense, spike-like inflorescences resemblecattails. Though it performs best in sandyloam soils, pearl millet is well adapted tosoils that are sandy, infertile, or both. PearlOrganic Production—Cover Crops for Organic Farms 16
millet can be planted from late Aprilthrough July at a rate of 15 to 20 poundsper acre. Pearl millet matures in 60 to 70days. In North Carolina studies, pearl milletwas not as readily killed by mechanicalmethods (mowing and undercutting) asGerman or Japanese millet.Japanese millet (Enchinochloa frumentacea).Japanese millet is an annual grassthat grows 2 to 4 feet tall. It resembles andmay have originated from barnyard grass.Japanese millet is commonly grown as alate-season green forage. If weatherconditions are favorable, it grows rapidlyand will mature from seed in as little as 45days. Japanese millet can be planted fromApril to July at a rate of 10 to 15 pounds peracre. It performs poorly on sandy soils.RECOMMENDED READINGSources CitedAltieri, M.A., and D.K. Letourneau. 1982.Vegetation management and biologicalcontrol in agroecosystems. Crop Protection.1:405-430.Andow, D.A. 1988. Management of weeds forinsect manipulation in agroecosystems. InM.A. Altieri and M. Liebman (Eds.). WeedManagement in Agroecosystems: EcologicalApproaches. pp.265-294. CRC Press. BocaRaton, FL.Allison, J.R., and S.L. Ott. 1987. Economics ofusing legumes as a nitrogen source inconservation tillage systems. In (J.F.Power, Ed.) The Role of Legumes inConservation Tillage Systems. pp.145-150.Soil Conservation Society of America.Barnes, J.P., and A.R. Putnam. 1986. Evidencefor allelopathy by residues and aqueousextracts of rye (Secale cereale). WeedScience. 86:384-390.Bending G.D., and S.D. Lincoln. 1999.Characterization of volatile sulphurcontainingcompounds produced duringdecomposition of Brassica juncea tissues insoil. Soil Biology and Biochemistry.31:695-703.Bollero, G.A., and D.G. Bullock. 1994. Covercropping systems for the Central CornBelt. Journal of Production Agriculture.7:55-58.Bugg, R.L., S.C. Phatak, and J.D. Dutcher.1990. Insects associated with cool-seasoncover crops in southern Georgia:Implications for biological control intruck-farm and pecan agroecosystems.Biological Agriculture and Horticulture.7:17-45.Clark, A.J., A.M. Decker, and J.J. Meisinger.1994. Seeding rate and kill date effects onhairy vetch-cereal rye cover crop mixturesfor corn production. Agronomy Journal.86:1065-1070.Clement, A.J., J.K. Ladha, and F.P. Chalifour.1995. Crop residue effects on nitrogenmineralization, microbial biomass, andrice yield in submerged soils. Soil ScienceSociety of America Journal. 59:1595-1603.Creamer, N.G., and M.A. Bennett. 1997.Evaluation of cover crop mixtures for usein vegetable production systems.HortScience. 32:866-870.Creamer, N.G., M.A. Bennett, B.R. Stinner, J.Cardina, and E.E. Regnier. 1996a.Mechanisms of weed suppression in covercrop-based production systems.HortScience. 31:410-413.Duke, J.A. 1981. Handbook of Legumes of WorldEconomic Importance. Plenum Press. NewYork, NY.Fawcett, R.S. 1987. Overview of pestmanagement for conservation tillagesystems. In R.J. Logan (Ed.). Effects ofConservation Tillage on GroundwaterQuality: Nitrates and Pesticides. pp. 17-37.Lewis Publishers. Chelsea, MI.Forney, D.R., and C.L. Foy. 1985.Phytotoxicity of products fromrhizospheres of a sorghum-sudangrasshybrid (Sorghum bicolor X Sorghumsudanese). Weed Science. 33:597-604.Fujii, Y., T. Shibuya, and T. Yasuda. 1992.Allelopathy of velvetbean: ItsOrganic Production—Cover Crops for Organic Farms 17
Page 2 and 3: • Cover crops for the Southeast.
Page 4 and 5: crops like rye (which has a C:N rat
Page 6 and 7: For instance, some green manure or
Page 8 and 9: As with just about everything else
Page 10: These calculations normally require
Page 14 and 15: clover is seeded at 8 to 15 pounds
Page 18 and 19: discrimination and identification o
Page 20 and 21: measurement. Australian Journal ofA
Page 22: The Organic Production publication

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