Producing Seeds of the Legumes

M. W. PEDERSEN, L. G. JONES, AND T. H. ROGERS.

SEVERAL botanical features are a bane and a boon in the production of seed of the legumes.

The growth of legumes generally is indeterminate growth continues from the terminal and axillary buds while flowering and formation of seed are both in progress. Mature seed therefore is ready to harvest on the lower part of the plant while new flowers are still forming at the top. The decision as to when to harvest always is arbitrary. Cutting too late permits ripe seed to shatter to the ground and be lost. Cutting too early means an excessive amount of green, shriveled seed.

In some species, such as the trefoils, the pods open and the seed drops as soon as it is ripe. In others, special equipment is needed to remove the pods from the seeds. Strawberry clover is unique in that it has an inflated calyx, which lets it float on water. Such characteristics sometimes may complicate the harvesting.

The size of the seed about 3 thousand seeds in a pound of field peas to about 2.5 million in a pound of large hop clover affects many of the cultural practices, especially the rate and depth of planting and methods of harvest.

Most of the small-seeded legumes have hard seed and so cannot take up water promptly. The proportion of hard seed varies in species. The percentage of hard seed of most species is reduced by aging. In harvesting and cleaning operations, some of the seeds are scratched. The seedcoats of some species, such as sweetclover, are so hard that scarification is necessary before the seed will germinate.

Longer lived species tend to spread. Whiteclover and kudzu spread by stolons. Rambler and some other varieties of alfalfa spread by creeping roots. Crown vetch, Kura clover, big trefoil, and zigzag clover spread by rhizomes.

All of these species, except alfalfa, spread vigorously and are hard to maintain in rows for seed production. Cultural practices are affected.

The seed of many legumes need to be inoculated. Bacteria must be applied to the seed to insure the development of the symbiotic relationship in which nitrogen from the air is fixed in the plant. The inoculum varies from one species to another. Most seed dealers can supply the proper inoculum with seed that requires it.

The variability of legumes applies to genera, species, varieties, and to plants within varieties. Cultural practices for the production of legume seeds have distinctive features for each species.

PERENNIAL legumes include alfalfa (Medicago saliva), red clover (Trifolium pratense), alsike clover (T. hybridum), white or Ladino clover (T. repens), birdsfoot trefoil (Lotus corniculatus and tenuis), Kura clover (T. ambiguum), strawberry clover (T.fragiferum), zigzag clover (T. medium), sericea lespedeza (Lespedeza cuneata), big trefoil (Lotus uliginosus), crown vetch (Coronilla varia), and kudzu (Pueraria lobata).

ALFALFA for seed usually is planted on a firm, well-prepared seedbed in spring or fall, depending on the location, at a seeding rate of two-thirds to 4 pounds of seed per acre in rows 22 to 40 inches apart or as much as 15 pounds per acre in solid stands.

M. W. Pedersen and associates at Logan, Utah, used a four-dimensional scheme to explain the relationship between density of stand and production of seed. The space between rows and the distance between plants within the row are the first two dimensions.

Plant height is the third dimension. Pollination is the fourth.

The best plan probably is to space the plants equally within and between rows on about 2-foot centers. From a practical standpoint, however, it is better to have enough plants in the rows to crowd out weeds and volunteer alfalfa plants. A greater stand density can be tolerated if the plants are short and if pollination is rapid. Generally, however, seed setting is better on thin stands.

At Logan, Utah, the best yields have been obtained on 24-inch rows planted at 1 pound of seed per acre. The average annual production in a 4-year period was 211 pounds of seed per acre from a stand planted in 8-inch rows at a rate of 12 pounds of seed per acre, and 385 pounds from a stand planted in 24-inch rows at a rate of 1 pound of seed per acre.

When the forage stand was thinned, the yield of seed was increased to a level equal to or better than that from a stand that was originally thin. For example, a yield of 183 pounds of alfalfa seed per acre was obtained from a dense stand in 1955, compared to 427 pounds when the stand was thinned to 12-inch hills in 24-inch rows.

In the Delta area of Utah, thicker stands were better. In California, 40-inch rows planted at about 1 pound of seed per acre have given good results.

Solid-seeded stands often have given good results, but only when pollination was good. Much of the alfalfa seed is produced on stands that are utilized for both hay and seed.

At Logan, the yield of seed from the first crop is nearly twice the second, but about one-half of the seed produced in the State nevertheless is grown on the second crop. Governing factors include the relative values of hay and seed, date of the first frost, synchronization of bloom with the activity of pollinators, and weeds.

Fertilization with phosphorus is necessary in many sections. An application of 200 pounds of triple super-phosphate often is used when the need is established.

Scientists at the Utah Agricultural Experiment Station noted, however, that seed yield of alfalfa dropped when the soil phosphorus content exceeded 17 parts per million. This depressing effect would probably be most apt to occur when stands are dense, irrigation is excessive, and pollination is slow.

Until more exact information is available, caution should be exercised in the application of phosphorus for the production of alfalfa seed.

Potash and such minor elements as boron, zinc, sulfur, and molybdenum also are required in some places.

The results of several years of study of irrigation in the production of alfalfa seed in Utah showed that when the root zone contained 15 inches of available water when flowering began, no benefit was derived from additional irrigation. When the soil contained only 7 inches, however, irrigation following full bloom was considered to be of value.

An advantage of 22 percent for furrow irrigation over sprinkler irrigation for alfalfa seed production also was reported.

Weeds must be controlled. If the seed is to be certified, the volunteer alfalfa plants (plants developed from shattered seed of the harvested crop) must also be killed.

Cultivation is done by row machinery, spring-tooth harrows, disk harrows, and tillers. Once a stand is established, it is necessary sometimes to cultivate across the rows to kill volunteer plants and weeds in the row.

Scientists at Oregon State College reported the effective use of diuron [3-(3,4-dichlorophenyl)-1, 1-dimethylurea] and IPC [isopropyl N-phenylcarbamate] or CIPC [isopropyl N-(3- chlorophenyl) carbamate] for the over-winter control of weedy annual grasses and broad-leaved weeds. A combination of dalapon and 4-(2,4-DB) [4- (2,4-dichlorophenoxy) butyric acid] was also suggested for establishing weed-free stands. EPTC [ethyl N,N-di-n-propylthiolcarbamate] was suggested as a preplanting treatment. Contact weedkillers of the Dow general type [dinitro ortho secondary butylphenol] can also be used on established stands.

Harmful insects must be controlled without killing a disproportionate number of beneficial ones. Many beneficial and harmful insects are present in alfalfa.

Serious pests include the alfalfa weevil (Hypera postica), lygus bugs (Lygus species), pea aphid (Macrosiphum pisi), clover seed chalcid (Bruchophagus), spotted alfalfa aphid (Therioaphis maculata), and spider mites (Tetranychus).

A treatment of DDT (dichloro-diphenyl-trichloroethane) or dieldrin in the bud stage followed by toxaphene in the bloom stage controls lygus bugs. Demeton can be added to control mites and aphids.

One to five colonies of honey bees per acre are needed for pollination if enough native pollinators are not present to pollinate the crop.

Harvesting can be done by combining from cured windrows or from the standing crop. If combined direct, a defoliant spray (such as a dinitro product of the Dow or Sinox-general type) often is applied.

RED CLOVER is grown in all sections of the United States where there is sufficient rain or irrigation.

A fine, firm seedbed is essential to good stands of red clover. The surface should be firmed by settling by irrigation or rain, cultipacking, or rolling before seeding.

A medium soil of the loam, sandy loam, or clay loam type is preferred. Alkaline and extremely sandy soil should be avoided.

Red clover is planted between September and November and in February in California. In other areas, it is planted in the spring and late summer except in the Southeastern States, where fall plantings are made.

Broadcast seeding requires 10 to 20 pounds per acre; 8 to 10 pounds is enough when drill seeded. One or two pounds make satisfactory stands in row plantings. Spacings from 20 to 30 inches result in maximum seed yields in row plantings.

Tests in Minnesota indicated that red clover in 18-inch rows, planted at a rate of 2 pounds of seed per acre, and broadcast stands, planted at 4 pounds per acre, were superior to stands in 18-inch rows planted at a rate of 4 pounds and 36-inch rows planted at 1 or 2 pounds per acre.

Investigations in Kentucky led to recommendations of fall plantings, broadcast at the rate of 6 pounds of seed per acre.

The seed should be sown at a depth of about one-half inch or less.

Seeding rates are usually 8 to 10 pounds when drill seeded and 10 to 12 pounds per acre when broadcast. Red clover commonly is seeded in established stands of small grain or in grain stubble.

Inoculation is often necessary. Red clover will thrive only if enough legume bacteria are present. These may be lacking in soils where true clovers (Trifolium) were not grown a year or two previously.

Red clover needs more moisture than alfalfa. For maximum yield of seed, the plants should be kept growing vigorously throughout the growing and seed-setting period.