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COG Organic Field Crop Handbook
3.1 Alfalfa, Clovers and Forage Mixtures On the organic farm, legume forages are one of the most important mechanisms for soil building. A three- or four-year stand will improve soil structure and increase the humus level. It is one of the best ways to add fertility and although a large proportion of the nutrients will be released in the first year after it is plowed, the effects will last for several years. A forage mixture may not be practical for farmers without livestock and many prefer to use stands of clover for soil building. This section looks at some of the options.
When selecting a forage mixture that will work, your first consideration should be the nutrient balance of the soil, and then whether your need is for hay, pasture, erosion control or soil structure. Other considerations which are important are the condition of your soil, pH, drainage, compaction, and the lifespan of a stand.
Farmers without livestock may find there is a ready market for legume hay but in an organic system selling hay off the farm will seriously deplete the soil of organic matter and nutrients. (10 tons of alfalfa hay may remove up to 600lb N, 120lbs P and 600lbs K ) Organic farmers believe that hay should not leave the farm and that its nutrients should be recycled either as livestock feed or as a green manure. If hay is sold it is essential to return composted manure to the land.
• Reasons for crop selection
Legumes are valued in a rotation because of their nitrogen fixing ability. Amounts of nitrogen available to the following crop will vary depending on the species and the age of the stand. To give one example - a tonne of red clover green manure which includes the clover tops and roots, will supply 25 kg of nitrogen for the succeeding crop. They also act as cover crops and conservers of nutrients preventing losses due to leaching or soil erosion.
Some legumes such as sweet clover contribute considerable amounts of organic matter as well as nitrogen to the soil when incorporated.
All legumes and forage mixtures will build up the humus content of the soil. Microbial activity is also encouraged because the soil is protected from tillage and exposure and earthworm populations increase because the plant roots provide a good food supply.
The deep tap root of some legume crops breaks through a soil hardpan, and the fibrous root system of the grasses aid in soil aeration and nutrient recycling. The fibrous roots of red clover can extend up to 60 to 90 cm, and are more branched than alfalfa and thus are more useful in improving soil structure. Sweet clover and alfalfa have a deep penetrating taproot that opens up the subsoil reaching nutrients that are not available to shallower rooting crops.
A two to three year forage stand will control persistent weeds like milkweed and thistle. Clipping the forage weakens the root reserves of the weeds and the deep roots of alfalfa perfom the soil conditioning task that milkweed or thistle fulfill.
Forages are also important for soil conservation. Sod-forming grasses are used for erosion control for waterways or buffer strips.
Illustrations of alfalfa and clovers
Some of the options:
• Alfalfa, a highly nutritious feed that out-yields other legumes like birdsfoot-trefoil, or red and white clovers, is grown most often in combination with grasses such as bromegrass, timothy or orchard-grass. A properly managed mixture seems to be more productive and less prone to weeds than other legume species.
• Red clover is a short-lived perennial that will only last for two years. It can be included in forage mixtures but it is used primarily as a green manure to condition the soil and fix nitrogen for the following crop. It is usually incorporated in the late fall of the establishment year or early next spring if it is not left for forage or seed production. Double-cut red clover flowers in the seeding year and following the first and second cuts in the succeeding year. Therefore it is possible to take off a hay crop and have a seed crop, but its disadvantage is that it is not very winter hardy. Single-cut or mammoth red clover does not flower in the seeding year or after the first cut in succeeding years. The advantage of single-cut clover is that it is hardy and can be grown on the prairies and in more northern areas.
photo C1.1 Red clover
• Alsike clover is a short-lived perennial which is adapted to a wide range of soil types. It is used in the same way as red clover, although it will give lower yields. It is used instead of red clover on soils that are acidic or where excessive water or flooding is a problem. It can also tolerate more alkalinity than red clover. To ensure a uniform stand, farmers sometimes plant a mixture of alsike and red clover so that if the red clover fails to establish, the alsike clover will fill in. Alsike is also more resistant to diseases than many of the more commonly-grown forage legumes. It fixes nitrogen earlier in its development than red clover. When used as a green manure the best results are obtained if it is incorporated at about 10-20 percent bloom.
• Ladino clover or white clover is another alternative to red clover for more acidic moist soils.
• Sweet clover is a biennial and is generally used as a green manure. Because of its deep root system it is drought resistant and it is considered one of the best legumes for soil improvement.
• Birdsfoot-trefoil is a legume frequently used in pastures. It is non bloating and will keep the pasture productive when growth slows down in grasses during hot summer weather.
• Crop requirements
The soil drainage and pH requirements of forage species are given in figures 5 and 6 taken from the 1991-1992 OMAF Field crop recommendations.
Low soil fertility will lower the mineral content of the forage and cause growth deficiency. Avoid growing alfalfa or red clover on soil with low potassium and phosphorous. White spots around the outer edges of the forage leaves are an indication of potassium deficiency.
Potassium is needed by the plants for cold resistance. If soils are low in potassium, add compost or rock powders, to prevent the crop from being damaged by low winter temperatures. Composted manure can be applied lightly before seeding and in the early fall after the forage has established.
Sweet clover will thrive on the poorest of soils, but does not tolerate acid conditions. It is most productive on fertile, well-drained clay and clay loam soils.
Note that forages on an organic farm will probably green up later in spring than those on a conventional farm where nitrogen fertilizer is used. Nutrients are not made available until the soil warms up enough for the microorganisms to become active.
• Planting Methods
It is beneficial to inoculate all legumes with their specific strain of Rhizobium bacteria especially if the legume being planted has never been grown on the field before.
Forage stands are most frequently established with spring seedings. Legumes, unlike grasses, cannot be sown successfully in the fall (i.e. September or October). For good seedling development seed alfalfa when the soil has warmed up. Early seeding in cold weather results in weedier fields when alfalfa is grown without the use of high rates of synthetic phosphate. In areas where there is adequate moisture, you can seed in early August.
Red clover is best sown in early spring, but can be sown in the summer if there are favourable moisture conditions. It can also be broadcast over winter wheat in late March or early April.
Seeding with companion crops
Shade tolerant legumes, like alfalfa and red clover can be seeded directly, or undersown with a companion or nurse crop such as oats, barley or flax. The companion crop can be seeded at the same time or before the forage crop. Although winter wheat is very competitive a stand of red clover can sometimes be established if the clover is frost seeded. On the Prairies sweet clover is underseeded with spring cereals, oil seeds and grain legumes. Low seeding rates of oats and barley are recommended when establishing a forage stand.
When alsike clover is grown for seed production, a nurse grain crop is not recommended because alsike is non aggressive during establishment. However the advantages of a companion crop for weed control and as a cash crop can still be realized if the grain is seeded at half the recommended rate to reduce the competition.
As soon as the soil is dry enough to work, disc and/or cultivate to incorporate the residue and to prepare a fine, firm seed bed. Allow a short time for the soil to settle before seeding the forage. Harrowing immediately prior to or while seeding will eliminate early germinating weeds and leave a smooth seed bed which conserves moisture.
It is not recommended to try to broadcast a hay mixture in a fresh seed bed; use the seed drill instead. Forage seeds are small and should not be placed any deeper than 1 cm (1/2 inch) for good emergence.
Seeding rates for some green manure legume crops are given in table 3 in the green manure section. For forage stands seeding rates will depend on the desired mix. We recommend you follow the recommendations from your provincial ministry of agriculture for suitable mixtures and seeding rates.
The nurse crop and its straw should be removed as soon as possible to maximize the growth of the forage or green manure before fall freeze up.
Clipping will control annual weeds and some perennials in a forage stand. Disease problems such as lepto leaf spot, black stem, root rot and verticillium wilt can be reduced by choosing resistant varieties.
Green manure crops can be pre-cut or incorporated directly into the soil using discs or a chisel plow.
A cash crop farmer without livestock can have the benefits of a soil building crop and get a cash return from legume seed.
Farmers who wish to use red clover for just a one-year break crop, can get seed from double-cut red clover in the seeding year. The clover should be direct seeded in the early spring in a field that has no severe weed problems, and the first growth should be left for seed. Flowering will occur in late July and the seed can be harvested in early September. Harvest the seed when most of the heads and upper stems are brownish-black in colour. Direct combining of the crop is preferred. However farmers generally plant red clover with a cereal and leave it until the second year for seed production. An early cut of hay in year two could also be taken.
Alsike clover should be cut and swathed when 90 percent of the heads have turned brown, and then allowed to dry for seven to ten days before threshing.
There is no difference between organic and conventional practice for the harvesting of forage crops. Pay particular attention to forage quality and ensuring optimum winter survival of the stand.
It may not be possible to take off hay in the year the stand is established, but if you do, do not cut too early. It is also important that at least one cut allows the hay mixture to go to blossom otherwise the stand will be severely weakened. In the southern regions, two to three cuts may be possible, while in the north, you can expect only one to two. The last cut should be four weeks before the first killing frost to permit the plants to store carbohydrates, to develop cold resistance and to have grown enough to ensure that the stand can catch snow over winter. Pay attention to the “critical harvest date” for your area. To ensure persistence and maintain yields do not harvest alfalfa during a six week period following that date. An application of composted manure to an alfalfa stand after the last harvest will increase the level of cold tolerance. A stand of red clover usually thins during its second winter so it is usually treated as a biennial and incorporated the year following seeding.
fig. 7. Critical harvest date for alfalfa in Ontario
As the crop matures, the dry matter (fibre content), yield and ability to survive increases but the digestibility of the forage and the protein level decrease. The advantages need to be balanced with the potential disadvantages. The major factor affecting forage quality is the stage of growth when it is cut. The optimum maturity stage is usually when about ten percent of the flowers have opened.
Copyright © 1992 Canadian Organic Growers. Inc
Reprinted with permission. All rights reserved.
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