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Renovating thin alfalfa stands

Bruce Anderson Published on 11 April 2014
Alfalfa stands thin out over time, often slowly but sometimes suddenly. And as stands decline, tonnage and economic returns decline with them. When yield gets too low, the usual suggestion is to plant new fields to alfalfa, but sometimes factors like the immediate forage need, the cropping plans or field location make this suggestion undesirable.

When planting new fields isn’t reasonable, renovating existing fields may overcome at least some of the production lost due to stand thinning. Before beginning the renovation, though, decide if the renovation is to last one year or multiple years and if it will be used for hay or for pasture. This will help determine what plant species to add to the thin alfalfa stand.

Trying to thicken alfalfa stands by interseeding more alfalfa often fails. Autotoxic compounds released into the soil from previous alfalfa plants can inhibit germination and growth of new alfalfa seedlings. The seedlings that do emerge usually experience heavy competition from the remaining alfalfa plants. Thus, it usually is best to renovate using other plant species.

All spring-planted cool-season species must be planted early to give them their best chance of establishing before competition from remaining alfalfa becomes excessive, especially for light. In fact, if the remaining alfalfa stand is dense enough to form canopy closure before alfalfa buds begin to appear, it is unlikely that the renovation will be successful unless the alfalfa is harvested and removed soon after the canopy closes.

Annual cereals like oats and spring barley are added successfully more often than most other options when planted in early spring. The proper seeding rate varies greatly, from 30 to 100 pounds per acre, depending on how much alfalfa remains. If first harvest occurs early, most of the yield contribution of the cereals will occur at second harvest. Nearly all of the cereal’s yield contribution will occur at first harvest if it occurs after the cereal heads out.

Other spring-planted annuals that may be used include annual and Italian ryegrass, various brassicas like forage rape, and other spring cereals. Some of these options may provide additional forage for more than one cutting.

Cool-season perennial grasses like orchardgrass, bromegrasses, fescues, wheatgrasses and ryegrass can be added to extend hay production for multiple years or to convert the field into a pasture. Because they establish more slowly than annuals, timely moisture is needed over an extended time period.

In addition, greater attention will be needed to control competition from the alfalfa and any other plants that may be present. If rainfall or irrigation is reliably available in late summer, these grasses often can be established into thin alfalfa stands more readily at that time due to the slower growth rate and reduced competition from alfalfa late in the growing season.

Warm-season annuals also can be used to increase tonnage from thinned alfalfa stands. Sudans and forage sorghums, millets, teff and even corn or forage soybeans might be planted. Because of their warmer temperature requirements, these species usually are planted into the stubble immediately after first harvest. Alfalfa usually regrows rapidly at this time so moisture to germinate these seeds quickly is needed for these additions to become established without use of herbicides or mowing to control the alfalfa.  FG

Bruce Anderson, Ph.D., is an agronomy and forage specialist for the University of Nebraska – Lincoln.

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