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Descriptions of Cover Crop Species
Tarwi (Lupinus mutabilis) Other names: Chochos, altramuz, tarhui, Andean lupin
(click on photo
to enlarge) Tarwi is a traditional Andean crop that produces a bean with high nutritive value. It is often used in the end of traditional rotation cycles when soil nutrients have been depleted by previous crops. In 1990 World Neighbors began trials with communities in highland Bolivia to use it as a green manure, tilling it in at flower and maximum biomass, to provide fertility for a subsequent crop of potatoes. In these trials, tarwi in flower provided 20 to 50 metric tons/ ha of fresh green biomass for soil organic matter, and potato yields in the subsequent growing season were doubled and tripled compared to unfertilized controls, and equal to a chemically fertilized control (Beingolea 1993). Yield benefits to potatoes were also greater in dry years. A Silsoe Research Institute study near Cochabamba, Bolivia found that a crop of Tarwi outperformed fava beans, Garotilla (Medicago hispida, see below), and a vetch/rye mix for dry matter production, nitrogen accumulation, speed of soil coverage (Sims 2001). In the Andes it is well adapted to altitudes between 2200 and 4000 meters. In Peru, tarwi is allowed to flower and produce pods so that a crop can be harvested before tillage of the residue for soil benefits (R. Bunch, Mulch-L discussions). Tarwi has also been promoted for this use in Ecuador, where it is grown in rotation and as an interseeded crop between maize. Although tarwi in this system is noted to give benefits to the subsequent crops, this strategy has not been compared directly to tilling in tarwi before pods are formed. There is some evidence that tarwi suppresses plant parasitic nematodes in a subsequent crop of potatoes (Cornejo 1977) and that this may be partly responsible for potato yield increases after growing tarwi. Tarwi does not make good forage, since foliage, pods, and beans contain bitter alkaloids. For human consumption, beans must be repeatedly soaked and rinsed to remove the bitterness, but the beans then make a nutritious food, high in protein. Sweetclovers
Sweetclovers are an excellent source of biomass, nitrogen fixation, and forage for nutrient-poor, neutral to alkaline soils. They are also especially effective at bringing phosphorous from unusable to usable forms in the soil, and have a strong taproot that can help to break compacted soil layers. They are also more drought-tolerant than other forage/cover crops. Varieties of sweetclover are either annual or biennial. Sweetclover can be grazed or cut, and regrows from buds on the stem unless it is cut too low. In highland Mexico, where competition with a subsequent crop had been a problem with using sweetclover, low cutting was used to kill sweetclover before planting maize (R. Bunch, Coberagri-L discussions).Sweetclover's deep taproot and extensive fine root system is especially good for improving soil structure. Over two years and with good growing conditions, sweetclover can accumulate up to 250 kg/ha of N and 9000 kg/ha dry biomass for incorporation into the soil. Sweetclovers grow in a wide variety of conditions, and can grow on as little as 150 mm rain per year (SAN 1998). However, their efficient scavenging of water can deplete water for a subsequent crop if used as a green manure. Sweetclovers are good honey flow species for honey production. If sweetclover is cut for hay and rots rather than curing properly, a compound develops in the hay called di-coumarin that can cause hemhorraging in livestock Varieties low in coumarin that avoid this problem are being developed. seeds/kg: 580,000 Garotilla
A major advantage
of Garotilla is that there is no seed or seeding costs; it is only
necessary to conserve it in the cropping system. However, it can
compete with the main crop and has been noted to reduce tuber yields,
a disadvantage which is balanced against the benefit of additional
forage for animals. Also, its relative lack of drought tolerance
may limit its use in areas with less rainfall than the 800 to 900
mm (monomodal) in the Cochabamba valleys. In trials by farmers with
the Silsoe Research Institute near Cochabamba, Garotilla was slower
in establishing ground cover than tarwi (Sims
2001). Choreque (Lathyrus nigrivalvis) and Grass Pea, (Lathyrus sativus) Other names: flat pea, chickling pea (L. sativus)
photo © Ann Butler, Institute of Archeology, London Choreque is an annual legume forage and cover crop that is in use among farmers in highland Guatemala at altitudes between 1750 and 2300 meters. Lathyrus sativus, also known as grass pea, is a forage and food crop grown in east Africa and South Asia, and may have potential as a high-altitude cover crop. Both are relatives of the ornamental sweet pea, L. odoratus. In the Guatemalan highlands, choreque is interseeded between maize, either broadcast at time of hilling of the maize (roughly corresponding to last cultivation in mechanized systems) or seeded individually at the rate of one choreque seed to every two plants of maize. It then grows well into the dry season, producing copious forage biomass for cut-and-carry feeding to livestock. Although it is quite drought-hardy, choreque requires fertile soils and grows best in cool conditions, without being frost-resistant (R. Bunch, Overstory #29). Grass-pea, Lathyrus sativus, is an annual pulse crop widely used for both human food and forage in India, Ethiopia, Nepal, and Pakistan. It also occurs from the middle east to eastern Europe and north Africa (Campbell 1997). Both immature pods and shelled peas can be used for human consumption, and the extensive viny plant can be cut for feeding to livestock. Similar to the interseeding of choreque in the guatemalan highlands, grass pea is sometimes grown as a second crop after rice in South Asia, where it uses remnant water to produce food and forage going into the dry season, and provides green-manuring benefits to subsequent rice crops (Campbell 1997). It grows well on poor soils but is not tolerant of acid conditions (Muehlbauer and Tullu 1998) Although occasional
eating or feeding of grass pea is harmless, if grass pea is consumed
as the principal item in the diet by humans or livestock, certain
varieties can produce a paralytic condition known as "lathyrism"
(Muehlbauer
and Tullu 1998). Varieties of grass pea low in ODAP, the
amino acid derivative that causes lathyrism, are under development
as part of an initiative by ICARDA and other groups. Frijol
Chinapopo/ Runner Bean (Phaseolus coccineus) Like choreque, frijol chinapopo is a locally developed technique from the highlands of Central America. In the area of use, farmers prefer it to common bean (P. vulgaris) for intercropping with maize because it is considered to have greater resistance to cutworms, leafhoppers, and other pests (Flores et al. 1992). In parts of Honduras, 80% of farmers were using chinapopo intercropped with maize. Although runner beans are known in many areas of the world as an ornamental and crop species, they are used as an interplanted food and cover crop in wet-climate highlands of Honduras, at elevations between 1400 and 2000 meters, with annual rainfall from 1500 to 2000 mm. Soil pH in the area of use ranges from 4 to 6.5, with high soil organic matter content and soil nutrient levels described as low. Runner beans are eaten as green pods, dry beans, and as a root, since the plant forms an underground tuber that is edible and also helps it to persist in the field from year to year. The plant produces about 35 Metric tons/ha of green matter, and is pruned away from the growing maizeor planted at reduced densities to avoid competition with the maize. In new plantings,
runner bean is usually seeded at a density of 4500 seeds/ha, or
one seed in a square area 1.5 meters on a side, with corn seeded
in rows or hills at densities ranging from 30,000 to 50,000 per
ha. When a field has already had chinapopo growing, corn is seeded
with mininum tillage - a planting stick - so as to not disturb the
runner bean tubers, which then sprout to produce the associated
bean crop. The lack of a need to reestablish the associated cover
crop decreases farmer labor and is an advantage of this use of runner
bean. Although detailed studies of potential competition or facilitation
for nutrients are not known, the yields of both maize and chinapopo
are felt by the farmers to be satisfactory. With addition of manure,
one farmer was able to produce about 2000 kg/ha of maize and 500
kg/ha chinapopo. Woolypod
Vetch
Woolypod vetch is a combination forage/cover crop that is well adapted to a wide range of soil types and can grow and accumulate nitrogen rapidly in cool, moist conditions, producing the highest amount of biomass of all the vetches (SAN 1998). It survives frost and brief periods of freezing. Woolypod vetch has been successfully used by the Silsoe Research Institute Hillsides Project in Bolivia as a forage/cover crop, and has been shown to successfully flower and produce seed in a variety of locations of the high-altitude tropics (Wheeler et al. 1999). In Bolivia at 3000m altitude, it was able to set seed in five months with between 550 and 900 mm of rainfall (Sims and Rodriguez 2001), and outyielded Hairy vetch, red clover, and white clover in forage dry matter production and forage nutrient quality when associated with a phalaris grass species (see below) Woolypod vetch has a fairly high proportion of hard seed, which may raise concerns about weediness in some systems, since hard seed will persist and germinate over a number of years. Woolypod vetch grows quickly once established, but emergence is slower than small grains and annual grasses; mixed seeding with low rates of a quicker-emerging nurse crop will maximize soil cover, weed suppression, and forage and residue quality. Woolypod vetch can be either grazed or cut for forage, with dry cut forage reported to be more palatable than the grazed plants. It can survive dry periods, but its benefits are most evident during cool moist seasons like those found in Mediterranean winters and tropical highland summers. As an intercrop woolypod vetch will compete with the main crop unless planted after the main crop is established (Vanek 2002). Several cultivars of woolypod are available. "Lana" is used as a winter annual in mediterranean and mild-wintered areas of the temperate zone. Cv. "Namoi" is used as a forage in drought-prone areas of Australia, where it outyielded clovers and alfalfa during winter and spring seasons (Register of Australian Herbage Plant Cultivars 1972). It also set seed earlier than "Lana", which may be valuable to its persistence as a forage and cover in adverse years (ibid.). seeds/kg: 24,000 Phalaris
grass Phalaris grass have been the focus of a Silsoe Research Institute/ San Simon University project in highland Bolivia.. This perennial species related to a temperate forage called reed canary grass (P. arundinacea) is used as a quick-growing component of live barriers for terrace formation on sloped fields, rather than a cover crop over the whole field. In Bolivia, phalaris was planted in inter-Andean valleys at sites ranging from 3000-3500 meters elevation, and from 500-900 mm annual rainfall. Here it detained erosion, built terraces, and provided a good forage source, especially when accompanied by the legume woolypod vetch (see above) (Sims and Rodriguez 2001). In participatory evaluations, farmers cited greenness of the barriers through the dry season, high quality forage, and erosion protection as benefits, with costs of establishment and space taken up being principal disadvantages. In the Silsoe/San
Simon project, phalaris is established vegetatively by the planting
of two rows of vegetative grass slips along a contour line, with
associated legumes seeded between the two rows of grass. Alfalfa (Medicago sativa) 
Alfalfa during vegetative growth (click on photo to enlarge) photo © Steven Vanek Alfalfa is a deep-rooted forage perennial grown worldwide in a range of climates, and may be promising as a managed fallow crop in highland areas that can provide a grazing resource. Some varieties are highly drought tolerant such as those grown in areas of the Middleast with a mediterranean winter rainfall of only 300 mm per year. A study in Syria was able to document long-term increases in organic matter content of soils using grazed alfalfa as a fallow cycle in a system with annual grain and vegetable crops (Jenkinson et al. 1999). Alfalfa is sucessfully used as a forage species in highland pasture
areas, such as puna or páramo areas of the
Andes above 3500 meters elevation, where pasture is the dominant
land use (CONDESAN
1999). In a cropping system, alfalfa is best suited to a
managed, grazed fallow of several years or longer because it is
a perennial that establishes slowly. Alfalfa is not tolerant of
acid soil conditions, especially during establishment. In the United
States, a pH of 6.2 or above is required for good stand, and becauses
of slow initial growth alfalfa is often companion-seeded with an
annual grass or small grain like oats (Oregon
State Univ. 1996). Sainfoin
(Onobrychis viciifolia)
Another deep-rooted, drought tolerant forage perennial, sanfoin is grown in warm-temperate parts of Europe and Asia, and the Rocky Mountain states of the United States as a hay crop. It has so far not received a great deal of attention as a highland managed fallow species, although it combines excellent drought and frost tolerance with tolerance of low soil phosphorous. In the U.S.A., sainfoin requires at least 250 mm rainfall to provide adequate production. Like alfalfa, it is a slow-establishing perennial, uncompetitive with weeds, that may require companion seeding with a grass or small grain, or by undersowing into a grain crop (Frame 2001). It also requires a low-acid soil. Sainfoin is long-day for flowering, and it is not known whether there are varieties that can flower and produce seed under the daylengths found in tropical areas. seeds/kg: 40,000 |
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last updated: October 18, 2002
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