Nutrient Science

Alfalfa Development and Growth Staging

eKonomics News Team

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This interactive diagram demonstrates the different growing stages of alfalfa. These elements are important for understanding nutrient and fertilizer management. Click on the MORE buttons below for further information on each factor.

Vegetative

Germination and Emergence
The seeds will begin to absorb water about 24-48 hours after planting, if enough moisture is available. Temperatures between 65- and 72-degrees Fahrenheit (18- and 22-degrees Celsius) are optimal for alfalfa germination. As water uptake begins, a radical root emerges forming a taproot anchoring the seed to the ground. The hypocotyl, the initial seedling stem, forms and straightens, pulling the seed coat up through the soil. Seeds should not be planted deeper than half an inch and at the recommended seeding rate. A soil test should be done, and nutrients should be applied according to soil-test results. Soil preparation before planting is the best time to apply important immobile nutrients like phosphorus and potassium.

Seedling Growth and Establishment
Cotyledons are the first visible structures above the ground. A unifoliate leaf is the first true leaf produced. If the alfalfa seed is not fungicide treated, apply fungicide to prevent seedling diseases. Control weeds within the first 60 days to prevent stand loss.

First Trifoliate Lead and Buds
During this stage, the first trifoliate is formed. This is a second leaf and has three leaflets. As the plant is maturing it produces alternately arranged trifoliate leaves. During this stage, photosynthesis is sufficient to meet all energy requirements by the alfalfa seedling. The first few buds develop in the axils of all leaves, where secondary stems can originate.

Contractile Growth and Crown Development
This stage begins one to two weeks after emergence and is completed at 16 weeks. Contractile growth is a process in which the hypocotyl shortens and grows thicker. This is a result of carbohydrate storage within the plant. This stage pulls the cotyledonary node and the unifoliate node beneath the soil to form the crown. Critical crown buds form during this time.  Alfalfa should be planted in time to allow the crown and crown buds to fully develop before winter.

Root Development Nitrogen Fixation
During this stage, the alfalfa will cold harden. The plant needs shorter days and a minimum of two weeks of near-freezing temperatures to become dormant. The plant will convert starch in the crown to anti-freezing sugars to help keep the plant alive through winter. Before the winter dormant stage, the last cutting should leave eight to 12 inches of stubble, or four to six weeks of growth time. This will allow adequate time for root reserve replenishment. Adequate potassium improves winter survival by improving carbohydrate storage in the roots.

Spring Green-Up
This stage begins when the crown buds start to grow in response to warmer temperatures during the spring. Spring growth comes from crown buds formed during the previous summer and fall. Spring green-up is affected by plant health, dormancy requirements, and fall weather conditions. Uneven growth indicates winter injury. Injured plants are less vigorous and lower yielding. A soil test will help determine the nutrients needed.

 

Cutting Management

When to Cut
When deciding to cut, consider forage yield, quality, and stand presence. The forage yield will increase until the plant reaches full flower, but the quality will decrease with maturity. The optimum time to maximize both yield and quality is around the late bud stage to early bloom, depending on the nutrient requirement and livestock species. Scout for alfalfa weevils and potato leafhoppers, as both feed on the buds.

Growth after Cutting
Ideally, cutting should occur two inches above the soil surface to preserve axillary buds and next cutting yield. Cutting shorter than two inches will impact regrowth. Regrowth will commence more rapidly if alfalfa is harvested before axillary buds reach cutting height and new growth is not disturbed by cutting.

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