Up and Coming Cover Crops
Identified as a promising new cover crop in screening trials throughout the Southeastern U.S., balansa clover (Trifolium michelianum Savi) is a small-seeded annual legume with superior reseeding potential compared with other legumes, including crimson clover. Well-adapted to a wide range of soil types, balansa performs particularly well on silty clay soil with a pH of about 6.5. Established stands tolerate waterlogging, moderate salinity, and soil pH from 4.5 to 8.0. It does not do well on highly alkaline soils (30). It is considered marginal in Zone 6B.
Balansa and other reseeding legumes were screened in Zones 6, 7, and 8 (from the Gulf Coast to northern Tennessee, and from Georgia to western Arkansas). TIBBEE crimson clover (Trifolium incarnatum) was used as a phenological check. Growth was terminated 2 to 3 weeks after TIBBEE bloomed at each location to identify adapted cover crops that reseed earlier than TIBBEE. Spotted burclover (Medicago arabica) and balansa clover were the best reseeding legumes that were hardy throughout zone 7a. Of these, only balansa clover is commercially available.
Balansa clover is open pollinated. Flowers vary from white to pink and are attractive to bees. Ungrazed, it grows up to three feet high and produces thick hollow stems that are palatable and of good feed value. It becomes more prostrate when grazed.
Balansa clover was named Trifolium michelianum Savi in 1798. It is sometimes called Trifolium balansae or Trifolium michelianum subsp. balansae. A landrace of balansa clover collected in Turkey in 1937 was released in 1952 by the Alabama office of NRCS with the name MIKE. Small amounts of seed of this accession are available from the Plant Introduction Station in Athens, Ga.
Balansa clover seed is quite small, so planting only 5 lb. /A gives a dense stand. Seed is produced commercially only in Australia. Balansa clover requires a relatively rare inoculant, designated “Trifolium Special #2” by Liphatech, Inc., manufacturer of “Nitragin” brand inoculants. Kamprath Seed Co. imports balansa seed (See Seed Suppliers). Some seed suppliers offer coated seed that is pre-inoculated. The price per pound of coated seed is about the same as bare seed, but 1/3 of the weight is coating so the seeding rate for coated seed should be increased to 8 lb./A.
PARADANA is the cultivar that has been most widely tested in the U.S. It was released in 1985 by the South Australia Department of Agriculture. It was derived from Turkish introductions crossed and tested at Kangaroo Island, NSW, Australia. Seed yields over 550 lb. /A have been obtained. BOLTA is 1-2 weeks later than PARADANA and FRONTIER is 2-3 weeks earlier. FRONTIER, a selection out of PARADANA, has replaced its parent in the seed trade in recent years.
While PARADANA seed matures slightly earlier than crimson clover, it often does not produce as much biomass. Nitrogen accumulation in above ground biomass is about 60 lb. /A at full bloom. Balansa can reseed for several years from a single seed crop, due to its relatively high amount of hard seed. It reseeded for four years following maturation of a seed crop in 1993 in Senatobia, Miss., and for at least two years in no-till systems at several other locations in Alabama, Georgia and Mississippi. Neither TIBBEE nor AU ROBIN crimson clover reseeded for more than one year at any location in those tests. Balansa clover does not reseed well after tillage, probably because the small seeds are buried too deeply.
Allowing balansa clover to grow for 40 days past first bloom every 3 to 4 years will allow stands to persist indefinitely in no-till systems. Reseeded stands are denser, bloom 5 to 7 days earlier, and are more productive than planted stands because growth begins as soon as conditions are favorable and seedling density is higher. However, seed cost is minor compared to opportunity cost and risk associated with delaying main crop planting. Waiting past the optimum planting date to encourage reseeding is only practical in rotations that include main crops optimally planted in May in the Southeastern U.S.
Balansa is less likely than crimson clovers to host root-knot nematodes (Meloidogyne incognita, race 3).Gary Windham, USDA-ARS, Starkville, Miss., found that balansa had egg mass index scores between 2.3 and 2.9. For comparison, a very resistant white clover scored 1.5, most crimson clovers score between 3 and 3.5 and very susceptible crops like REGAL white clover score 5 on a scale from 1 to 5.
USDA-ARS National Sedimentation Lab
P. O. Box 1157 Oxford, MS 38655-2900
662-232-2975; firstname.lastname@example.org .gov
Black oat (Avena strigosa L.) is the No. 1 cover crop on millions of acres of conservation-tilled soybean in southern Brazil, and has potential for use in the southern USA (Zones 8-10).
Black oat produces large amounts of biomass, similar to rye. It maintains a narrower carbon to nitrogen (C:N) ratio than rye so it cycles nitrogen better than rye, important for nitrogen management in conservation tillage systems. It breaks disease cycles for wheat and soybean and is resistant to root-knot nematodes. It is very resistant to rusts and has exceptional allelopathic activity for weed control. It is easy to kill mechanically.
Black oat is adapted for use as a winter cover crop in the lower Coastal Plain of the USA, including Zones 8b-10a. It has done well in fall plantings in Zone 8b, but winterkilled one year of six at some locations within this zone, dependent on planting date.
Planting dates are similar to common oat. If planted too early, it is more susceptible to winterkill and lodging. Planting in late winter (early February) yielded good biomass and ground cover for late planted cash crops in the lower Coastal Plain.
Seed 50-70 lb. /A for use as a cover crop, 40 lb./A for seed production. In the Southeast, fall plantings (November) result in seed ripening in mid May through early June. Seed yields range from 800 to 1400 lb./A. Seed is available commercially in limited amounts.
One cultivar, SOILSAVER, was selected for increased cold tolerance and released by Auburn University and IAPAR (Institute of Agronomy of Paraná, Brazil). Auburn University and USDA-ARS researchers developed it from a population of IAPAR-61-IBIPORA, a public variety from the Institute of Agronomy of Parana, Brazil (IAPAR) and the Parananese Commission for Evaluation of Forages (CPAF).
SOILSAVER black oat has several advantages as a cover crop. It tillers well, producing good soil coverage in relation to total biomass produced. It suppresses broadleaf weeds extremely well. In one study, weed control in conservation tillage cotton (Gossypium hirsutum L.) averaged 34% with black oat compared to 26% for rye, 19% for wheat, and 16% with no cover crop.
—D. W. Reeves
USDA-ARS, J. Phil Campbell Sr. Natural Resource Conservation Center
1420 Experiment Station Road
Watkinsville, Ga 30677
706-769-5631 ext. 203
SoilSaver— a Black Oat Winter Cover Crop for the Lower Southeastern Coastal Plain. 2002. USDA-ARS National Soil Dynamics Lab. Conservation Systems Fact Sheet No. 1.
Lupins are cool-season annual legumes that provide plenty of N and can be grown widely in the USA and southern Canada. Lupins have aggressive taproots, especially the narrow-leaf cultivars. You can kill lupins mechanically or with herbicides. Their hollow stems crush or break readily, making it easy to plant cash crops using conservation tillage equipment.
White lupin (Lupinus albus L.) and blue or narrow-leaf lupin (Lupinus angustifolius L.) species were originally named after their flower colors, but both species now have cultivars with white, blue or magenta /purple flowers. Blue lupin is adapted to the lower Coastal Plain and is more readily identified by its narrow leaflets (about 0.5- inch wide) rather than flower color.
As a fall and winter cover crop in the southeastern USA, white lupin is the most cold-tolerant. Some cultivars overwinter as far north as the Tennessee Valley. They typically produce 100 to 150 lb. N/A when fall-planted and killed in early spring.
Seed spring cultivars in early April in the northern U.S. and southern Canada. Kill in June when they’re at peak biomass (early-bloom to early-pod stage).
For use as a cover crop, drill lupins no deeper than 1 inch at 70 lb. /A for small-seeded blue varieties to 120 lb. /A for larger-seeded white varieties. At $30 to $40 per acre, the seed is relatively expensive. Be sure to inoculate lupin seed with compatible rhizobia.
Three winter-hardy lupin cultivars are readily available on a commercial scale. TIFWHITE-78 white lupin and TIFBLUE-78 blue or narrow-leaf lupin were both released by USDA ’s Agricultural Research Service in the 1980s. These two varieties, and other modern varieties, are “sweet” types as opposed to “bitter” types that were widely grown in the South prior to 1950. Sweet varieties have a low concentration of naturally occurring alkaloids. Sweet lupin is favored by wildlife, especially deer. Sweet lupin cover crops may act as a trap crop for thrips (Frankliniella spp.) in cotton plantings, but this has yet to be confirmed by research.
AU HOMER bitter white lupin is a new release by Auburn University derived from Tifwhite-78. It was selected for increased alkaloid content for use as a cover crop. Alkaloids make lupin seed and forage unpalatable for livestock, but also play a major role in resistance to disease, insects and nematodes.
Lupins are susceptible to many fungal and viral diseases and should not be grown in the same field in successive years. Rather, rotate lupin cover crops with a small grain cover crop, ideally in a rotation that allows three years between lupin plantings. Lupin are intolerant to poorly drained soils.
For information about lupins and seed sources, contact: Edzard van Santen, Professor Crop Science, Agronomy & Soils Dept., 202 Funchess Hall, Auburn University, Auburn, AL 36849; 334-844-3975; fax 334-887-3945 email@example.com
A tropical legume, sunn hemp (Crotalaria juncea L.) can produce more than 5,000 lb. dry matter/A and 120 lb. N/A in just nine to 12 weeks. It can fill a narrow niche between harvest of a summer crop and planting of a fall cash or cover crop and is especially fitted to vegetable production. Sunn hemp sown by September 1 following a corn crop in Alabama, for example, can produce an average of 115 lb. N/A by December 1.
Sunn hemp is not winter hardy and a hard freeze easily kills it. Sow sunn hemp a minimum of nine weeks before the average date of the first fall freeze. Seed at 40 to 50 lb. /A, with a cowpea-type inoculant.
Sunn hemp seed is expensive, about $2.25/lb., so the cost may be prohibitive for large-scale plantings. Seed can be produced only in tropical areas, such as Hawaii, and currently is imported only by specialty seed companies.
A New Alternative for South Florida Producers
A study by the NRCS Plant Materials Center (PMC) in Brooksville, Florida, concluded that sunn hemp seed can be a viable alternative cash crop for southern Florida growers. Sunn hemp is an annual legume that suppresses some types of nematodes and can produce over 5,000 pounds of biomass and 100 pounds of nitrogen per acre within a few months. Because of its potential use in alternative pest management systems and as a sustainable biological source of nitrogen, sunn hemp is a promising cover crop for rotation with vegetables throughout the Southeastern U.S.
Unfortunately, its use has been limited by the high seed cost—most is shipped from Hawaii as seed production requires a tropical climate. Two years ago, the NRCS PMC in Brooksville initiated a study to determine which zones in Florida could most economically produce sunn hemp seed. Seed was distributed to 15 growers throughout Florida and although many locations lost their crop to frost, sunn hemp stands in coastal counties below the 27th parallel consistently produced up to 370 pounds of seed per acre. Growers in more southern areas, such as Homestead, obtained even higher yields. Your contact is Clarence Maura, Manager, NRCS Brookville Plant Materials Center, at 352-796-9600 or firstname.lastname@example.org.
A management caution: Many Crotalaria species contain alkaloids that are poisonous to livestock. However, the sunn hemp variety TROPIC SUN, developed jointly by the University of Hawaii and USDA-NRCS, has a very low level of alkaloid and is suitable for use as a forage.
Research suggests that sunn hemp is resistant and/or suppressive to root-knot (Meloidogyne spp.) and reniform (Rotylenchulus reniformis) nematodes.
—D. Wayne Reeves (see Black Oats)
Mansoer, Z., D. W. Reeves and C. W. Wood. 1997. Suitability of sunn hemp as an alternative late-summer legume cover crop. Soil Sci. Soc. Am. J. 61:246-253.
Balkcom, K. and D. W. Reeves. 2005. Sunn hemp utilized as a legume cover crop for corn production. Agron. J. 97:26-31.
Sunn Hemp: A Cover Crop for Southern and Tropical Farming Systems. USDA-NRCS Soil Quality Technical Note No. 10.May 1999. Available at: https://soils.usda.gov/sqi/management/files/sq_atn_10.pdf
K. H. Wang and R. McSorley. Management of Nematodes and Soil Fertility with Sunn Hemp Cover Crop. 2004. University of Florida Cooperative Extension. Publication #ENY-717. https://edis.ifas.ufl.edu/NG043
Valenzuela, H. and J. Smith. 2002. Tropic Sun’ Sunnhemp. University of Hawaii Cooperative Extension. Publication #SA-GM-11.