Can I harvest alfalfa this fall?

Paul Peterson, Dave Nicolai and Dan Martens, Cooperative Extension, University of Minnesota

Historically, we have avoided harvesting alfalfa after September 1 but in recent years have been less cautious, with good reason. Let’s review a few of the key factors most relevant.

Stand health and stem density
Alfalfa stands need a minimum of 40 stems per square foot to be productive and preferably more than 55 stems per square foot. Healthy roots and crowns produce more shoots (stems) which drives yield. The fixed costs of alfalfa hay/haylage production are too great to limp along with marginal stands. Thus, older stands and stands that are weak or thin are often good candidates for fall cutting since they generally should be terminated after this growing season anyway.

Dig up some plants and examine them. Healthy roots are bright white on the inside from crown to tip. Stands with significant signs of root decay are unlikely to produce well next year so should be fall-harvested if the forage is needed.

Climatic factors
Drought slows alfalfa growth before it slows photosynthesis. Thus, drought-stunted, flowering alfalfa that had or maintained decent leaf area likely stored away a good supply of root reserves – important to regrowth and winter hardiness. However, severely stunted alfalfa with little leaf area or significant leaf drop may not have been able to store reserves.

Also, winter hardening is a gradual process influenced by changes in temperature and daylength as we progress into and through fall. Waterlogged soils are not conducive to good winter hardening, and obviously quite conducive to rutting, so should not be fall-harvested.

Feed supply
If your inventory of high-quality forage is low, risks associated with fall cutting become less important.

Timing of the fall cut
Data continue to mount supporting the concept that timing of the fall cut matters little as long as other factors favor fall-cutting tolerance. Farmer experience must agree, as I have noted more and more September cutting in my travels over the last several years. However, for the risk-averse, either avoiding a fall cutting or waiting until mid-October may be better options.

Waiting until mid-October minimizes the chances of significant regrowth and root reserve depletion after cutting. But don’t be concerned about waiting for an alfalfa-killing frost (around 20°F) before harvesting. That approach risks significant leaf loss and unfavorable curing conditions.

Previous cutting frequency
Stands cut more frequently are at greater risk of winter injury if cut during the fall. Thus, when other factors favor fall-cutting tolerance, a third harvest during fall is rarely risky, a fourth harvest during fall can be somewhat risky and a fifth harvest during fall can carry considerable risk. Key to enhancing winter survival is allowing at least one crop to mature to mid-bloom. Thus, stands of fall forage that have previously been cut at pre-bloom stages should be well-flowered if fall harvest is considered.

Alfalfa-grass mixtures
Mixtures are good candidates for fall cutting. Grasses such as orchardgrass and tall fescue have good fall growth, and grasses in general improve snow catch and insulation and reduce heaving potential.

Winter survival is a complex process influenced by many factors. But in general, fall cutting is often a good option for healthy, well-managed alfalfa stands. PD

—Excerpts from Minnesota Crop eNews, September 2007