Alfalfa establishment: Steps to maximize yield

Typical management involves the seeding year and three to four production years. Alfalfa management programs are designed to ensure highly productive alfalfa stands throughout the course of production.

There are more than 1 million acres of alfalfa in Minnesota, but the goal of maximizing yield isn’t always realized.

The University of Minnesota Alfalfa Variety Trials reported average yields in the range of 6 to 7 tons per acre (dry matter) across all locations in recent years. However, the statewide average during that time hovered around 3 tons per acre of dry matter (Figure 1).

Several reasons explain the lower county yields. Countywide yields typically include seeding- and production-year alfalfa, thereby reducing yield expectations. However, including both doesn’t fully explain the yield gap.

Effective management in both the seeding and production years is critical for optimal yield, quality and persistence. On this webpage, we’ll focus on strategies for maximizing yield in the first production year.

Site selection is important because alfalfa prefers well-drained, deep soils that don’t follow alfalfa. Under ideal growing conditions, alfalfa roots can explore soils to depths over 20 feet. When selecting fields, try to avoid hilltops, shallow and highly eroded soils and fields with low spots where water is known to pool (Picture 1). Wet soils not only reduce diffused oxygen (O2 (g)), but also benefit diseases and increase the risk of ice sheeting.

In addition to locating well-drained, deep soils, following alfalfa in the rotation with newly seeded alfalfa is not advisable due to autotoxicity. Alfalfa produces toxins that reduce germination and impair the development of taproots, limiting the uptake of water and nutrients. This directly impacts yield and performance (Figure 2).

After the selecting the field, soil sampling and analysis will identify soil nutrient deficiencies. Because alfalfa has both perennial (e.g., aglime) and annual fertilizer (e.g., potash) needs, yearly soil sampling will provide detailed information on available nutrients.

Fertility management ensures good stands and vigorous growth during the establishment years, while increasing productivity and persistence throughout the production years. Several parameters and nutrients are critical for optimal stand health, although here we’ll focus on soil pH, potassium and phosphorus.

More nutrient management guidance

Soil pH

Maintaining soil pH between 6.7 and 6.9 is extremely important because nutrients are most available (i.e., widest bars) to the alfalfa roots within that range (Figure 3).

Because buffering soil pH can take time, it’s advised to perform soil tests and apply and incorporate Ag-lime 12 months prior to alfalfa seeding based on soil reports. This will allow adequate time for the lime treatment to neutralize soil acidity and ensure pH in the 6.7 to 6.9 range. Typically, you won’t need to re-apply lime during alfalfa’s lifecycle.

Phosphorus and potassium

Unlike soil pH, you need to assess phosphorus (P) and potassium (K) levels throughout the alfalfa lifecycle. Maintaining soil potassium and, especially, phosphorus in a non-limiting status will improve alfalfa stand establishment, yield and survival (i.e., persistence).

Because alfalfa removes significant amounts of P and K (Table 1), fall soil sampling and analysis are needed on an annual basis to identify any P and K deficiencies. If prescribed by the soil test, you can apply P and K fertilizer in the spring.

When seeding alfalfa in Minnesota, there are two options for timing: Spring and summer.

Spring seeding dates of April 15 to May 15 are recommended for most of Minnesota. However, north of St. Cloud, later planting dates (May 1 to 30) are advised. Recommended late-summer seeding dates are Aug. 1 to 15 for southern Minnesota and July 20 to Aug. 1 for northern Minnesota.

Both seeding dates have pros and cons (Table 2). The University of Minnesota Alfalfa Variety Trial seeds all alfalfa in the spring, mainly due to the available soil moisture and better overall growing conditions compared to summer seeding dates.

Proper seedbed preparation is essential for  providing adequate seed-to-soil contact and controlling perennial and annual weeds. Many establishment failures can be avoided by using primary tillage (moldboard plowing or chiseling) followed by disking and secondary tillage (i.e., smoothing operation) in conjunction with cultipacker.

Ideal soil conditions should be smooth, firm and clod-free for optimal seed placement using drills and brillion seeders. When walking on soil prior to planting, the heel of your shoe shouldn’t sink more than 3/8ths of an inch into the soil. If it does, then use a cultipacker to firm the surface.

With a proper seedbed, the choice of planter type, when operated correctly, doesn’t impact alfalfa yield (Figure 4).

Once you’ve prepared the field and properly calibrated the seeder, the number one cause of poor stand establishment is seeding depth.

Seeding depth is an issue when seeding with a drill. There’s a direct relationship between stand establishment and seeding depth. Sandy soils are a bit more forgiving, but it’s a good idea to limit planting depth to a 1/2 inch regardless of soil type (Figure 5). A good rule of thumb is that about 10 percent of the seeds should be visible on the soil surface.

The goal of providing a proper seedbed is to ensure good seed-to-soil contact. Because most forage seeds must absorb more than their own weight in water, good seed-to-soil contact is essential for uniform emergence.

Soil particles hold the water needed for germination. The more particles in direct contact with the seed, the quicker the seed can absorb water and germinate (Figure 6).

Seeding rates should be between 12 and 15 pounds per acre. Prescribed seeding rates are designed to provide several times the seed needed to achieve optimal yield under ideal growing conditions.

Seeding rates above 15 pounds per acre have no positive impact on yield (Table 3). A seeding rate of 12 to 15 pounds per acre will provide 23 plants per square foot during the first production year, assuming best management strategies were observed.

In the University of Minnesota Alfalfa Variety Trials, we seed at 13 pounds per acre, which achieves the needed 23 to 25 plants per square foot in the first production year, maximizing yield. Even though increased seeding rates have no impact on yield (assuming ideal conditions), planting extra seed can provide insurance to high seedling mortality in years when cool wet weather persists (Figure 7).

In addition, it’s important to select alfalfa varieties that have adequate fall dormancy and disease resistances, and purchase high-quality, pure alfalfa seed.

Find more information on varieties:

• Tests to characterize alfalfa cultivars: From the North American Alfalfa Improvement Conference.

• Alfalfa field crop trials results: From the University of Minnesota