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Figure 1. Forage production in tons per acre from
Minnesota Ag News, 2013 (top) and 2014 (bottom),
Hay County Estimates, USDA 2013 and 2014.
There are over 1 million acres of alfalfa in Minnesota and typical management involves the seeding year and 3 to 4 production years. Alfalfa management programs are designed to ensure highly productive alfalfa stands throughout the course of production. The goal of maximizing yield is not always realized. For example, the University of Minnesota Alfalfa Variety Trials reports yields in the 6 to 7 ton/acre (dry matter) range, on average, across all locations over the last few years. In contrast, the statewide average hovers around 3 ton/acre (dry matter) (Figure 1).
The natural question is why is there such a difference in yields between the UMN Alfalfa Variety Trials and the statewide averages? This question has been asked repeatedly, and there are several reasons that can explain the lower county yields. Dr. Michael Russelle (USDA–ARS, retired) stated that countywide yields typically include seeding and production year alfalfa, thereby reducing yield expectations (Russelle, 2007). However, the inclusion of seeding and production–year alfalfa yields does not fully explain the yield gap and best management in both the seeding and production–years are critical in ensuring optimal yield, quality and persistence. For the remainder of this article we will focus the discussion on maximizing yield through best management related to establishing alfalfa.
Since alfalfa production spans several years, it is important to start off with the highest productive stands possible. In the UMN Alfalfa Varity Trials, we adhere to the six following management strategies for optimal alfalfa establishment: (i.) field selection, (ii.) fertility management, (iii.) seeding dates, (iv.) field preparations and seeders, (v.) seeding depth, (vi.) seed-to-soil contact, and (vii.) seeding rates.
Along with the aforementioned establishment strategies, selection of alfalfa varieties that have adequate fall dormancy and disease resistances, as well as purchasing high-quality pure alfalfa seed, is extremely important. For information on varieties, please visit http://www.naaic.org/resource/ stdtests.php and the UMN Alfalfa Varity Trials.
Figure 2. Impacts of waiting periods when
establishing alfalfa following alfalfa. Note that
even though the number of plants is similar for
all but fields planted with no waiting, yield
increases dramatically. Adapted from Alfalfa
Site selection is important since alfalfa prefers well–drained deep soils that do not follow alfalfa. Under ideal growing conditions, alfalfa roots can explore over 20 feet deep. 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 not only reduce germination but also impair the development of taproots, thereby limiting the uptake of water and nutrients, which directly impacts yield and performance (Figure 2).
After the field is selected, soil sampling and analysis will identify soil nutrient deficiencies. Since alfalfa has both perennial (e.g. aglime) and annual fertilizer (e.g. potash) needs, soil sampling yearly 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, but for this discussion we will focus on soil pH, potassium, and phosphorus. For more details on nutrient management please visit http:// www.extension.umn.edu/agriculture/nutrient-management/.
Maintenance of soil pH between 6.7 and 6.9 is extremely important since soil nutrients are most available (i.e. widest bars) to the alfalfa roots within that range (Figure 3). Since buffering soil pH can take time, it is advised that soil tests be performed and Ag-lime applied and incorporated 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 – 6.9 range. Typically, the re–application of lime will not be needed during alfalfa's life cycle.
Phosphorus and potassiumUnlike soil pH, phosphorus (P) and potassium (K) levels need to be assessed throughout the alfalfa life cycle. Maintaining soil potassium and phosphorus in a non-limiting status, especially phosphorus, will improve alfalfa stand establishment, yield, and survival (i.e. persistence). Since 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, P and K fertilizer can be applied in the spring.
Table 1. Pounds of nutrient removed from the soil per ton of
alfalfa produced on a dry matter basis.
|Adapted from Alfalfa Management Guide|
When seeding alfalfa in Minnesota, there are two options for timing: spring and summer. Spring seeding dates of April 15th to May 15th are recommended for most of Minnesota. However, north of St. Cloud, later planting dates are advised (May 1st to May 30th). Late-summer seeding dates for southern Minnesota are August 1st to 15th and for northern MN July 20th to August 1st are recommended. Both seeding dates have pros and cons. See the summary in Table 2. The UMN Alfalfa Variety Trial seeds all alfalfa in the spring, mainly due to the available soil moisture and better overall growing conditions when compared to summer seeding dates.
Table 2. Pros and cons of spring and summer alfalfa seeding dates.
|Spring||More soil moisture
Longer growing season
Excessively wet springs
|Summer||Herbicides typically not needed||Lack of available soil moisture
Sclerotinia crown rot may be prevalent
Need 6 to 7 weeks of growth to survive the winter
Field preparation and seeders
Proper seedbed preparation is essential in providing adequate seed–to–soil contact and controlling perennial and annual weeds. Many establishment failures can be avoided by utilizing 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 should not sink more than 3/8 of an inch into the soil. If it does, then use a cultipacker to firm the surface. Providing a proper seedbed is achieved, the choice of planter type when operated correctly does not impact alfalfa yield (Figure 4).
Figure 5. Alfalfa emergence as determined by
ing depths and soil types. Alfalfa Management Guide.
Once the field is prepared and the seeder is properly calibrated, the number one cause of poor stand establishment is seeding depth. Seeding depth is an issue when seeding with a drill, and there is a direct relationship between stand establishment and seeding depth. Sandy soils are a bit more forgiving, but it is a good idea to limit planting depth to ½ inch regardless of soil type (Figure 5). A good rule of thumb is that about 10% of the seeds should be visible on the soil surface.
Figure 6. The impacts of proper seed–to–soil
contact. Soil particle (gray) and soil water (blue).
The seed on the right will absorb the required 125%
of its mass in water quicker than the seed on the left.
A consequence of seedbed preparation
The goal of providing a proper seedbed is to ensure good seed–to–soil contact. Since most forage seeds must absorb more than their own weight in water, good seed–to–soil contact is essential for uniform emergence. The water needed for germination is held by the soil particles, and 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 lb/acre. Prescribed seeding rates are designed to provide several times the seed needed to achieve optimal yield under ideal growing conditions; therefore, seeding rates above 15 lb/acre have no positive impact on yield (Table 3). The 12 to 15 lb/acre seeding rate will provide 23 plants per square foot during the first production year, assuming that best management strategies were observed.
In the UMN Alfalfa Variety Trials, we seed at 13 lb/acre, which achieves the needed 23 to 25 plants per square foot in the first production year, thereby 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).
Table 3. Effect of seeding rate on first–year
alfalfa dry matter yields.
|Seeding rate||Dry matter yield|
|Adapted from the Alfalfa Management Guide|
The above guidelines are followed in the UMN Alfalfa Varity Trials, and have ensured optimal yield year after year. We are confident that if you select fields of deep and well-drained soils, sample soils annually to mitigate soil nutrient deficiencies, spring seed in clod-free smooth but firm seedbeds with at least 13 lb-seed/acre, and plant seeds at no more than a ½ inch depth, you will have sufficient alfalfa plants to maximize your yields in the first production year.
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