Ohio acreage enrolled in government programs should have adequate vegetative cover to both prevent soil and wind erosion and increase water infiltration. Plant vegetation contributes to soil organic matter, improves soil tilth and reduces the leaching of plant nutrients. Several forage legumes can be used to provide temporary soil cover.
Properly inoculated forage legumes will furnish nitrogen to the crops which are subsequently grown. This nitrogen contribution by legumes should be an important consideration in the selection of crops for soil cover. Legumes provide excellent soil cover and substantial nitrogen when used as green manure crops.
Table 1 shows the quantity of nitrogen contained in the plant parts of red clover, alfalfa and sweetclover during the fall following seeding and for a range of dates the following spring. The nitrogen and dry matter of the legume parts will vary with the stage of growth. Leguminous soil cover crops are ordinarily plowed during the fall, or killed for no-tillage or plowed during the April 15-May 15 period the year following seeding.
Sweetclover will "fix" the greatest quantity of nitrogen in the shortest period of time when compared to alfalfa and red clover. During the fall of the seeding year, the total amount of nitrogen will be greatest in sweetclover with lesser amount in red clover and alfalfa. The following spring, sweetclover will still contain the greatest amount of nitrogen, followed by alfalfa and then red clover. A summation of 14 years of Ohio data indicates corn yields following alfalfa and sweetclover were equal when both crops were plowed down one year following seeding. Mammoth and medium red clover were not as productive.
Yellow and white biennial sweetclover are the important strains of sweetclover. In general, the adaptations and uses of biennial yellow and biennial white sweetclover are the same. The yellow is earlier-maturing than the white. Yellow sweetclover always puts a higher proportion of the total first year's growth into the roots than does the white. Yellow sweetclover has much greater ability to establish itself in dry seasons and on dry seedbeds than white sweetclover.
Sweetclover should be seeded during the early spring months. The seeding-year growth of biennial sweetclover consists of a single stem with numerous branches. Biennial sweetclover does not bloom during the seeding year. During late summer and fall of the seeding year, several buds develop on the crown. These buds are usually just at or below the soil surface. Crown buds make rapid growth during the spring of the second year. Crown buds of biennial sweetclover are not killed by fall or winter plowing. These buds frequently produce volunteer growth unless plowing is delayed until spring growth has started. After spring growth has commenced, sweetclover is rather easily killed.
Sweetclover is capable of making considerable vegetative growth during the season it is seeded. Any clipping or harvesting reduces the vegetative growth of the seeding year and has a corresponding effect on root development. Table 2 indicates the nitrogen reduction when sweetclover was clipped the seeding year.
Table 1. Nitrogen and dry matter in legume roots and tops at various stages of growth (seeded in oats in early spring and not clipped after oats harvest, Columbus, Ohio) | ||||||
|---|---|---|---|---|---|---|
| Air-dry Yield (lb/A) | Nitrogen (lb/A) | |||||
| Plant Part | Red Clover | Alfalfa | Sweetclover | Red Clover | Alfalfa | Sweetclover |
| October 1 of seeding year | ||||||
| Tops | 2490 | 1670 | 2280 | 66 | 47 | 63 |
| Roots | 500 | 1080 | 1760 | 13 | 29 | 58 |
| Total | 2990 | 2750 | 4040 | 79 | 76 | 121 |
| Early November of seeding year | ||||||
| Tops | 2050 | 1350 | 1550 | 50 | 39 | 34 |
| Roots | 940 | 1270 | 2640 | 24 | 35 | 95 |
| Total | 2990 | 2620 | 4190 | 74 | 74 | 129 |
| April 24 to May 12 of year following seeding | ||||||
| Tops | 2010 | 2500 | 2100 | 58 | 83 | 78 |
| Roots | 900 | 1110 | 1170 | 20 | 25 | 37 |
| Total | 2910 | 3610 | 3270 | 78 | 108 | 115 |
| May 24 to June 22 of year following seeding | ||||||
| Tops | 4360 | 4040 | 5400 | 108 | 103 | 130 |
| Roots | 1050 | 1450 | 1080 | 22 | 33 | 25 |
| Total | 5410 | 5490 | 6480 | 130 | 136 | 155 |
Table 2. Effect of Clipping Sweetclover in July on Yield and Nitrogen when harvested November 1 (Columbus, Ohio). | |||||
|---|---|---|---|---|---|
| Height Clipped (in.) |
Air Dry Yield (lb/A) | Nitrogen (lb/A) | |||
| Tops | Roots | Tops | Roots | Total | |
| Not cut | 2940 | 3630 | 47 | 127 | 174 |
| 14-16 | 1900 | 2760 | 40 | 99 | 139 |
| 7-8 | 1130 | 1830 | 25 | 68 | 93 |
| 2-3 | 630 | 1090 | 14 | 37 | 51 |
Sweetclover should be seeded at 10 pounds per acre in the early spring. This species requires a pH of 6.5 or higher and a well drained soil. Sweetclover seed typically contains a percentage of hard seed which may produce volunteer plants for many years, once the seed has been introduced into the area. Use red clover or alfalfa on land destined for future production of animal hay as sweetclover forage is not desirable for animal feeding.
Medium red clover is a widely grown legume for both forage and soil cover purposes. Red clover is more easily established and is more tolerant of a lower soil pH and of poorly drained soils than sweetclover and alfalfa. Red clover is easier to establish in small grains than is alfalfa. Red clover can effectively be harvested after September 1 of the seeding year.
Mammoth red clover (Big English) is a variety or selection of red clover. It differs from medium red in that it is later maturing and for hay purposes it is considered a single cut clover. Contrary to popular opinion, mammoth does not have a larger root system than medium red clover. As temporary soil cover it is equal but not superior to medium red clover.
Alsike clover is a perennial but usually behaves agriculturally as a biennial due to its susceptibility to disease. It grows well on heavy, poorly-drained soils and will even withstand flooding for considerable periods of time. Alsike will grow on soils with pH levels too low to support satisfactory growth of red clover. It is extremely sensitive to heat and drought. It should not be seeded alone. Alsike should be seeded only when the above mentioned conditions exist. It will produce less vegetative growth and less nitrogen under favorable conditions than will red clover, sweetclover or alfalfa.
Alfalfa requires excellent surface drainage, good internal soil drainage and a soil reaction of pH 6.5 or higher. It would be preferred where the forage might be harvested or where the soil cover might be maintained for a longer period of time. Alfalfa is sensitive to competition at seeding. Seed at 10-12 pounds per acre in early spring.
Successful establishment of these forage legumes is highly dependent upon obtaining good seed-to-soil contact through proper tillage and/or seeding methods.
On sloping fields, the inclusion of a cereal grain will assist in providing adequate soil cover and reduce erosion. This will also reduce competition from weeds. When using this practice, seed one bushel or less per acre of cereal grain. Clipping will be required to reduce growth of the cereal grain.
Inoculate the legume seeds with the proper inoculum of rhizobia bacteria. This is most important when planting a legume in an area where that legume has never been grown. It certainly is good insurance to inoculate, even in those areas where the legume may have been planted within the past 2 or 3 years. Remember, it takes a specific bacteria inoculum for a specific legume.
Beware of herbicide residues. Moderate to high rates of atrazine or simazine (Princep) applied to corn one year can carry-over and injure legume and grass seedings the following spring. If more than 2 pounds per acre of atrazine and simazine were applied one year on corn, it is questionable if a seeding of forage legumes or grasses should be attempted the following spring. Rye is more tolerant to herbicide residue than the forage legumes and grasses, and is suggested if soil cover is required.
Prepared by:
Donald K. Myers
Extension Agronomist Emeritus
Revised by:
John F. Underwood
District Agronomy Specialist
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