Alfalfa Management Decisions for Early Spring: Spring Seeding Tips and Evaluating Existing Stands for Winter Injury
Tips for Spring-Seeded Alfalfa
Variety selection: Base variety selection on winter-hardiness, yield potential, and genetic resistance to key root rot diseases and insect pests.
Fertilization: Lime fields to achieve a soil pH of 6.8 or greater, preferably one year in advance to allow time for lime to react. Soil pH is important for N-fixing nodule formation and nutrient absorption.
Apply potassium well ahead of seeding to avoid injury during germination (salt effect). Maintain optimum potassium levels throughout the life of the stand to maximize yield and winter survival.
Apply Phosphorous to achieve optimum or above soil test levels which is critical for healthy root and plant development.
Field preparation: Prepare a firm seedbed. Your shoe should only sink ¼ to ½ inch into the soil surface. Firm seedbeds help prevent seed from being planted too deep and allows good seed-to-soil contact for improved emergence. No-till planting can also provide a firm seedbed and may be used in the spring when topsoil moisture is generally good.
Planting depth: Seed should not be planted too deep or too shallow! Planting depth is critical for a successful stand. Planting depth on clay or loam soils should be ¼ to ½ inch and on sandy soils ½ to 1 inch.
Planting rate: Seeding rates of 60-80 seeds per square foot is desired for most planting conditions. This is achieved by adjusting your planter to seed between 15 and 18 lb of Pioneer® brand light-coated seed per acre.
Planting date: Spring seeding can be flexible, but to maximize the first growing season yield, plan to seed between April 1 and May 15. Alfalfa seed starts to germinate at soil temperatures above 37°F. Early spring seeded alfalfa will generally encounter less moisture stress during germination.
Weed control: Alfalfa is a tender plant to establish and doesn’t like a lot of competition. Weed competition can reduced stand establishment success and puts excessive stress on alfalfa plants, especially in the seeding year. Whether using pre-emergence weed control or conventional tillage followed by post emergence weed control, scout the field and plan your weed management strategy. Today’s Roundup Ready® varieties offer an excellent tool for managing weeds throughout the life of the stand.
Nurse crops: Nurse crops can be used in the seeding year and help reduce erosion and compete with weeds. However, carefully manage nurse crops by harvesting early to avoid excessive competition for water, nutrients, and sunlight. Also, monitor insect pressure in the nurse crop canopy to avoid alfalfa damage, especially from potato leafhoppers.
Newly emerged alfalfa seedling.
Time to Assess Established Alfalfa Stands
Every spring, growers need to walk their alfalfa fields to assess winter survival and yield potential of the remaining alfalfa plants. Making early evaluation of winter damage helps with rotation decisions and forage inventory planning.
Diagnosing winter injury
Slow green-up - One of the most evident results of winter injury is slow green-up. If other fields in the area are starting to grow and yours are still brown, it is likely alfalfa plants have been injured or killed during the winter.
Heavy dandelion spring growth is a sign of winter injury in alfalfa.
Asymmetrical growth - Buds for spring growth are formed during the previous fall. If parts of an alfalfa root are killed and others are not, only the living portion of the crown will give rise to new shoots, resulting in a crown with shoots on only one side—or asymmetrical growth.
Uneven growth - During winter, some buds on a plant crown may be killed and others may not. The uninjured buds will start growth early while the injured buds must be replaced by new buds formed in spring. This results in the shoots from buds formed in spring several inches shorter than the shoots arising from fall buds.
Root problems - Probably the best way to diagnose winter injury is by digging up plants and examining roots. Healthy roots should be firm and white with little evidence of root rot; winter-injured roots have a gray, water-soaked appearance and/or a brown discoloration. If the root is soft and stringy looking, it is most likely winterkilled. If the root is firm but showing signs of rot, it can still produce new growth through the season, but may be lower yielding. If over 50% of the root is damaged, the plant will most likely die that year. If less than 50% is injured, the plant will likely survive for one or two years.
Evaluating yield potential in the field is best done by digging roots, counting the number of healthy plants, and looking at stem growth and uniformity. If you have 4-5 healthy plants per square foot, the field is still capable of giving adequate yields. The following tables give guidelines for evaluating alfalfa plant health and yield potential.
Table 1. Using stem density to evaluate alfalfa stands.
Table 2. Alfalfa root health effects on winter survival (ratings pertain to crown and roots)
Source: University of Wisconsin Extension Publication.
Table 3. Alfalfa root symptoms and diagnosis
A. No injury. Roots are solid white internally. Tillers are beginning to green and are solidly attached to the root.
B. Moderate injury. Roots are solid and white but brown damaged areas occur in old tissue of the crown down to 1 to 2 inches. Growth beginning. With favorable growing conditions and a delayed first cutting, many of these plants will survive.
C. Severe injury. Roots white on outside. Brown discoloration carries down in center of the root. The chances are not very good these plants will survive.
D. Dead plants. Roots are discolored, mushy and partly rotted. Top growth can be readily pulled from the crown.
Source: Rohweder and Smith, 1978.