Forage Legume Seed Crops: Establishment and Nutrient Management

Thomas G Chastain CROP 460/560 Seed Production

Forage Legume Seed Production • Several species of forage legumes are grown for seed production in the Pacific Northwest. • These include alfalfa, red clover, crimson clover, white and ladino clover, arrowleaf clover, subterranean clover, hairy vetch, and common vetch. • Red clover, crimson clover, and white clover are the top three forage legume seed crops in Oregon. Trends in forage legume seed production in the Willamette Valley

Forage Legume Seed Production • Seed yield of forage legume seed crops has increased over time in the Willamette Valley.

Crimson clover (TG Chastain photo) Trends in forage legume seed yield in the Willamette Valley

Establishment Practices

• Since forage legume seeds are small, a fine and firm seedbed is required. • The seed needs to be inoculated with the proper strain of Rhizobium for nodulation of roots. Alfalfa seed (near top), crimson clover seed (near bottom) – USDA photos, red clover seedlings (far right) – TG Chastain photo.

Establishment Practices • Planting date - Alfalfa and white clover are generally spring-planted perennials, although much of Willamette Valley white clover is fall-sown. • Red clover is a spring- or fallsown biennial, and crimson clover and subterranean clover are fall-sown annuals. Vetch is sown in autumn. • Not usually sown with cover or companion crops in the Pacific Northwest, but are often established with these crops in other parts of the world.

Red clover seedlings (TG Chastain photo)

Row spacing and seed yield in Willamette Valley red clover. 700

Seed Yield (lbs./acre)

Establishment Practices • Red clover, alfalfa and white clover are sown in rows while crimson clover and subterranean clover are often sown broadcast in solid stands. • Alfalfa is sown in 22-36 inch rows, red clover in 6-12 inch rows, white clover in 6-24 inch rows. • Rows are better than solid stands in red clover and alfalfa because: 1. Crop canopy is more open and plants are erect, improving bee pollination. 2. Less lodging of the stand. 3. Better penetration of pesticides. 4. Better volunteer control.

600

500

400

300

200

100

0 6

12

18

Row Spacing (inch)

24

30

Establishment Practices • Alfalfa is sown at 0.5 - 2 lb./A and red clover is sown at 1 - 2 lb./A. • White clover is sown at 2.7 4.0 lb./A, subterranean clover is sown at 10- 20 lb./A, and crimson clover is sown at 5 - 15 lb./A.

Alfalfa seed field (top), white clover seed field (bottom). TG Chastain photos.

Nutrient Management • Nitrogen is needed prior to nodule formation and is applied before seeding. • There is adequate nodulation and symbiotic biological nitrogen fixation to supply the needs of forage legumes in Willamette Valley soils once the crop is established. • The recommended N rate at seeding for alfalfa is 15 - 20 lb. N/A and for red clover, the N rate is 40 lb. N/A.

Alfalfa (TG Chastain photo)

Nutrient Management • Phosphorus is banded at planting. • P rate at planting is 40 - 90 lb. P2O5/A for red clover and is 15 20 lb. P2O5/A for alfalfa. P is broadcast as needed on established stands. Too much P may reduce seed yield in white clover. • Potassium is applied pre-plant at 40-100 lb. K2O/acre.

White clover seed

Nutrient Management • Sulfur applications range from 20 - 30 lb. S/A. The annual clovers tend to have higher S needs than perennial species. • Lime is needed when the pH falls below 5.5 in crimson clover, 5.8 in white clover, 6.0 in red clover.

Crimson clover seed field (TG Chastain photo)

Nutrient Management • Boron is applied in legume seed crops and applications range from 1-2 lbs B/A when soil B levels < 1 ppm. Boron is needed for pollen tube elongation. • B deficiency levels might be set too high (1 ppm) as seed yield responses were not evident in red clover on deficient soils (0.3 to 0.4 ppm). • Timing and rate of boron application had no effect on seed yield and seed quality in 1st and 2nd year stands of red clover.

Boron effects on seed yield in 1st and 2nd year stands of red clover (Anderson et al., 2015). Soil test B levels ranged from 0.3 to 0.4 ppm. Timing Control Fall Fall Summer Fall + Summer

Seed yield Rate 1st Year 2nd Year lbs B/acre -------- lbs/acre ------0 796 a 707 a 1 800 a 661 a 2 782 a 670 a 1 725 a 636 a 2 797 a 684 a

Nutrient Management

• Nitrogen, sulfur, and boron applications did not affect seed yield in 1st and 2nd year stands of red clover. • Timing of the application did not affect seed yield in red clover. • Molybdenum applications either in early spring, late spring, or split between the two timings, has no effect on red clover seed yield.

Nitrogen, sulfur, and boron effects on seed yield in 1st and 2nd year stands of red clover (Anderson et al., 2016) Treatment Control Fall Nitrogen Spring Nitrogen Fall Sulfur Spring Sulfur Fall Boron Spring Boron Fall N + S + B Spring N + S + B

Rate lbs /acre 0 40 40 30 30 2 2 40+30+2 40+30+2

Seed yield 1st Year 2nd Year -------- lbs/acre ------681 a 657 a 683 a 671 a 677 a 568 a 696 a 604 a 628 a 583 a 668 a 569 a 694 a 587 a 669 a 571 a 652 a 538 a

Nutrient Management

• Nitrogen in red clover plants generally declines as the biomass of the crop increases over the course of the spring and summer months.

Plant nitrogen in 1st and 2nd year red clover seed crops over spring and summer months (Anderson et al., 2016)

Grazing and Mowing • White clover – Grazing by sheep or defoliation of the canopy is a standard practice to promote flowering and seed yields in white clover. • Seed yield in white clover is related to the number of heads/area. • Heads arise in the leaf axils of stolons (horizontal above-ground stems) and to maximize the production of inflorescences, the stolons need unshaded space to grow into and the need to manipulate the canopy.

Developing white clover head and stolons (TG Chastain photo)

Grazing and Mowing • Red clover - Excess vegetative growth is often removed by taking a hay crop prior to harvest of the seed crop. • Crimson clover - Can be mowed without affecting yield, beneficial where lodging is a problem. • Alfalfa - No grazing or mowing is done in alfalfa seed crops.

Crimson clover plants (TG Chastain photo)

Grazing and Mowing Effect of spring hay crop harvest date on seed yield in red clover grown in eastern Washington. Seed yields are averaged over three years and four cultivars. (Dade, 1966)

Spring hay harvest date

Seed Yield (lbs/acre)

No hay crop

602

May 1

614

May 21

502

June 11

409

Red clover foliage (TG Chastain photo)