Profitable forage production depends on high yields. Most of the state has fully completed the first alfalfa cutting for the season, and regrowth is taking off. Of course, there continues to be a lot of discussion on the lack of rainfall over much of the region. Alfalfa can generally survive dry conditions extremely well. However, provided a good stand has been established, continued production and stand life depends on good management practices. Fixed operating costs (equipment, labor, etc.) stay relatively the same regardless of low production or high production alfalfa. Major keys to high production in alfalfa include managing other inputs: available soil nutrients, weed and insect pest management, and plant health management. Immediately after the first cutting is an excellent time to apply crop inputs to alfalfa, especially to insure rapid regrowth and healthy stands for future cuttings this season. With the dry conditions, high quality forage may be a valuable commodity later this year.
Crop Nutrition: Alfalfa is one of the larger users of crop nutrients among our major crops. Crop removal values are high for some nutrients compared to other commonly grown crops. Alfalfa needs relatively large amounts of phosphate and potash. Each ton of alfalfa dry matter harvested removes about 14 pounds of phosphate (P2O5) and 58 pounds of potash (K2O). Each ton of alfalfa also removes the calcium and magnesium found in about 100 pounds of aglime, and a significant amount of a few micronutrients, especially boron. The table at left lists the levels of nutrients removed by one ton of alfalfa. Adequate phosphorus is important for successful establishment and good root development.
Alfalfa is an especially heavy user of potassium. Even high potassium testing soils can lack enough available potassium to adequately feed a high production alfalfa stand for any length of time. Potash is essential for maintaining yields, reducing susceptibility to certain diseases, and increasing winterhardiness and stand survival. Potassium is also involved in nitrogen use efficiency and water management. Potassium deficiency in alfalfa results in light colored leaves that may show white spots around edge of leaf starting with lower leaves. In addition to yield loss, alfalfa quality is reduced if potassium levels are deficient. The micronutrient boron is needed in very small amounts, but is critical to alfalfa production. In addition to K, alfalfa removes approximately 1.5 oz. of boron per ton of dry matter. Boron deficiency is displayed by yellowing of leaves, shortened main stem growth between upper portion of shoots, and a dense plant top. Damage is often confused with leafhopper damage. Boron responsiveness is fairly common across the region.
Using tissue tests or soils tests as a guide, topdressing potassium, in the form of potash (0-0-60), can be a very economical way to boost productivity. Boron can be applied as a dry product, through liquid sprays or micronutrient blends. The Mosaic Company produces a dry fertilizer product called Aspire with Boron (0-0-58-0.5B), a granular product with boron plus potash in each particle of fertilizer. In 20 field trials over the Plains regions of the United States, applying a product like Aspire has improved alfalfa yields by 0.5 tons per acre over potash alone (Mosaic data).
Two application windows are critical for crop nutrition in alfalfa:
- Apply topdress nutrients immediately after harvest and as regrowth resumes. Topdress following first cutting to stimulate second and third cutting regrowth; and,
Topdress in early September to increase winterhardiness.
Insect Management: Two key insects are issues for alfalfa in the Northern Plains. The alfalfa weevil can be a continual pest in South and North Dakota. Alfalfa weevil larvae chew and skeletonize leaves. Damage normally only occurs to the first harvest, but both larvae and adults may damage regrowth when populations are high, resulting in both yield and stand loss. If greenup is slowed, look for issues with alfalfa weevil larvae feeding on the regrowth and be ready to spray immediately. The second insect pest of concern is potato leafhopper. Potato leafhoppers are mid- to late-season alfalfa pests that migrate to north central and eastern states from southern areas in late spring. First crop alfalfa harvested at the proper time in the Midwest usually escapes damage. However, subsequent crops and new seedlings should be monitored for leafhoppers. Look for speckling on leaves and use a sweep net to monitor populations. Insecticides are very effective and cost efficient.
Diseases: Although not especially common in the Dakotas, several plant diseases can affect alfalfa. Root and crown rots can be present, especially in older, poorly managed stands. Foliar diseases can reduce forage quality, and should be monitored closely. The most common leaf diseases are leaf spotting diseases, which include Lepto leaf spot, common leaf spot and black stem leaf spot. Fungicide applications in alfalfa can provide significant benefits to protecting the crop. Increased leaf retention and higher plant health leads to improved quality and yield potential.
Other Plant Management Options: Alfalfa can respond very well to products stress reducers and biostimulants, such as the plant growth regulator products. The low doses of PGR can stimulate rapid recovery after cutting and improve quality of regrowth on alfalfa.
The Bottom Line: Quality alfalfa production takes management. Have a conversation about alfalfa crop nutrition and plant health management. Improved yields are possible, and can be extremely valuable, especially in a dry season.
Resources: Alfalfa Management Guide. 2011. ASSA, Inc. CSSA, Inc. and SSSA, Inc.; Mosaic AgriFacts- Aspire Yield Trials