Proper Late Summer Harvest Management of Alfalfa

By Dennis Cash (994-5688), Ray Ditterline and Mark Manoukian
MSU Professor/Extension Forage Specialist, Professor, and Phillips County Agricultural Agent

Irrigated alfalfa hay is a major crop for livestock producers. Summer hay harvest conditions are generally good for second and third harvests across Montana. However, in many regions, persistent showers in June delay harvest of first-cut alfalfa (which is the highest-yielding cut). Rain damage can cause forage quality losses in alfalfa, but the significant effect is often the delayed regrowth schedule for second and third cuts. Under irrigation, and with late first harvests, many alfalfa producers are faced with a dilemma in the late summer – when to harvest second (or third cut) alfalfa. The timing of late summer harvests is very critical for optimum alfalfa winter survival in northern areas. Alfalfa and all perennial plants require a proper “hardening” period in late summer and fall to assure that they are healthy next year.

Professor Ditterline recommends the following three-step program for optimal alfalfa stand life:

1. determine your average, long-term date of first frost (mid-September),
2. avoid cutting or grazing 30 to 45 days prior to average first frost, until
3. several consecutive mornings of mid-twenty degrees (mid-October).

In most of Montana, this means not harvesting alfalfa between August 15 and mid-October.

So what are the consequences of a poorly-timed harvest in late summer? Since 2000, we have tested the effects of harvesting irrigated alfalfa on September 1 at Bozeman, MT. Paired plots of all 63 varieties in the MAES yield trials seeded in 2000, 2001, 2002 and 2004 were evaluated. The paired plots were managed identically in our normal three-cut system (2 cuts by August 1), but half received their third cut on September 1 (“intensive”), and the other half received their third harvest in October after a “killing frost” as per our recommendation (“normal”). Forage yield in the final year is used to measure the effects of poorly-timed summer harvests. To date, the results have been very striking:

These results confirm that poor harvest scheduling in late summer reduces subsequent alfalfa yields. Obviously the impact is more severe when improper harvest occurs repeatedly. Aside from yield, the harvest on September 1 resulted in increased weed invasion (Fig. 1), more root and crown rot, and lower stand densities – all factors that reduce stand life. Under “normal” or ideal harvest scheduling, the range between the highest and lowest-yielding varieties was about 18%, so crop management can be more important than differences among varieties.

Note that the calendar dates of these trials are not as important as the alfalfa growth stage during frost – the alfalfa should either be dormant or have a minimum of 12 inches of growth when 20-degree weather occurs (unpredictable in August). The 30 to 45 day period prior to first frost assures that significant regrowth should occur prior to freezing weather. If hay or pasture is desperately needed, then late summer cutting should only occur on older fields destined to be replaced earlier – avoid this practice on newer productive stands that are needed long-term. Dryland alfalfa would behave similarly, however early dormancy is induced by our typically dry conditions in late summer which restricts forage regrowth.

Fig. 1. Field demonstration of the effects of September 1 harvest on alfalfa stands. Photo taken May 20, 2005 in the 2002 trial (see Table 1). ‘Shaw’ alfalfa is shown in the foreground in plots where the third harvest occurred on September 1 (“I”) or in October (“N”) as per our normal recommendation.

Return to regular view	Text-only	Updated: 11/27/2007