Summer-seeding perennial forages
Summer provides a window of opportunity to successfully establish alfalfa and other perennial forages, but timing and attention to seedbed conditions are essential. Of foremost importance are the presence or likely prospect of adequate soil moisture and a seedbed that maximizes seed-to-soil contact, both of which will ensure rapid and uniform emergence. There is a wealth of relevant research data, much of it from 40 to 50 years ago, that can help us make informed summer-seeding decisions.
Summer seeding offers a number of advantages over spring seeding:
- Less weed pressure, so this can be an optimum time to seed legume-grass mixtures, which have limited herbicide options.
- Spreads out the planting workload.
- Can harvest a crop (eg. small grain) followed by a full forage production year after seeding.
- Allows perennial forages to get a jump on the growing season and produce at or near established stand production the following year.
- Aids in wind and water erosion through the winter months.
- Can allow time to prepare a good, clean seedbed in summer.
Alfalfa needs 6 to 8 weeks of growth before the first killing frost. In northern Minnesota, the recommended window for conventional (tilled) legume summer seedings is between about July 20 and August 1. In southern Minnesota, seeding between August 1 and 15 is recommended. These dates apply to all legumes, reed canarygrass and probably tall fescue. Other more common perennial grasses, including smooth bromegrass, timothy and orchardgrass can be seeded in early August in northern MN and until late August in southern MN.
Research in central Pennsylvania (Table 1) demonstrated that for each day planting was delayed after August 1, total DM yield the year after seeding declined 160 lb/ac for alfalfa, 110 lb/ac for red clover, 80 lb/ac for birdsfoot trefoil, and 120 lb/ac for reed canarygrass. After mid-August, orchardgrass yield declined 90 lb/ac for each day planting was delayed. Conversely, perennial ryegrass yields increased 1.0 ton/ac by delaying seeding from early to late August. Planting perennial ryegrass after late August resulted in 130 lb/ac decreases per day. Perennial ryegrass seeded in early August and/or >6" tall in fall should be mowed or grazed to improve its persistent since shading reduces its tiller survival.
Table 1. Summer-fall seeding date influenced total season yields (ton DM/ac) of six forage species the year after seeding in central Pennsylvania. (Averaged over 2 establishment years; Hall, 1995.)
Virginia work in the 1950s demonstrated that with a firm and moist seedbed, summer-seeded alfalfa has the potential to establish rapidly. The Virginia researchers also suggest that when grasses are mixed with alfalfa, relatively heavier grass rates should be used with summer seeding when the grasses are relatively less competitive seedlings than alfalfa. Way back in the early 1950's, Minnesota researchers concluded that best stands were obtained with rolling, drilling, then rolling again. Rolling beforehand prevents drilling too deeply. They found that rain shortly after seeding favored broadcast seeding, while drought favored drilled seeding.
Firmness and good seed-to-soil contact are essential. Minimize the amount of tillage before a summer seeding to avoid unnecessary soil moisture loss. A loose, fluffy seedbed severely reduces germination success. Multiple passes with a roller seeder may be required to get adequate firmness. If the land is idle, it should be prepared in early summer for better moisture conservation. It's best not to use a companion crop with summer seedings. However, a very low rate can be used on sites with high erosion potential when moisture is adequate.
Summer seeding depth should be about ½", and somewhat deeper on sandy soil. Research in Wisconsin showed the influence of seeding depth in clay and sandy soils. In clay soil, the greatest stands were achieved with a ½" seeding depth. Orchardgrass was particularly sensitive to being seeded too deep. In sand, all species established equally well at ½or 1" seeding depths.
Perhaps the best way to provide a firm seedbed and favorable soil moisture is via no-till seeding. Four years of no-till research on a clay soil in Virginia showed consistent successful establishment and over-wintering by no-tilling 15 lb/ac of alfalfa 1" deep up to 3 weeks later than broadcast seeding with a cultipacker seeder in a prepared seedbed. They attributed the no-till advantage to: 1) consistently more rapid emergence with no-till; 2) greater root development due to less temperature extremes; and 3) less heaving losses.
The potential to seed up to 3 weeks later in Minnesota may be a stretch; a 10-14 day longer/later window for no-till seeding may be a safer bet. So for alfalfa (and other legumes, reed canarygrass and tall fescue), in northern MN, perhaps a no-till seeding could be done as late as August 15 instead of August 1; and as late as Sept. 1 in southern MN. Smooth bromegrass, orchardgrass, and timothy could be no-tilled even later. Dr. George Rehm (Minnesota) and co-workers assessed different methods and dates for establishing forage legumes on sandy soil, and found no-till seeding in early August to be very successful (Table 2).
Table 2. Average annual yields (ton DM/ac) for two years after the establishment year for three legumes as influenced by planting date and method on a sandy loam soil at Staples, MN. (Averaged over 2 establishment years; Rehm and co-workers, 1998.)
In conclusion, consider summer seeding as an opportunity to establish alfalfa and other perennial forages; but remember, timing and attention to seedbed conditions are essential.