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Minnesota Crop News > 2001-2008 Archives
September
21, 2005
Factors
Affecting the October Alfalfa Harvesting Decision
Paul Peterson
University of Minnesota Extension Forage Agronomist
Abundant late summer moisture and favorable temperatures
have many alfalfa stands in Minnesota looking very productive
this fall. Whether or not to harvest that growth can be
a difficult decision, but October harvesting makes sense
(and cents) in many situations.
Risk aversion. Cutting any time after the end of August
carries some risk of increased winter injury. If you are
unable or unwilling to take that risk for whatever reason,
it’s probably best to avoid cutting after September
1. But in many cases, fall cutting has minimal risk. The
amount of risk depends on the interaction of many factors;
some we can control, some we cannot. Some of those factors
are outlined below.
Stand length/rotation strategy. How
old is the stand and how long do you want/need to keep
it? If your goal is to keep the stand for 5 or more years,
fall harvesting may be too risky for you. If you plan to
keep the stand for 3 or 4 years to capitalize on the benefits
of shorter rotations, fall harvesting is a viable option
to maximize yields.
Feed supply. What is your feed inventory?
Do you need high quality feed? Fall alfalfa is usually
some of the highest quality alfalfa of the season.
Timing of the fall cut. It’s
generally best to try to avoid the “fall critical
period,” which is usually defined as September 1
to mid-October. This is because harvesting during this
window can result in inadequate time for regrowth to restore
root reserves prior to a killing frost. But the critical
period becomes less important as cutting frequency decreases.
For example, a second cutting in September is safer than
a fourth cutting in September. There is no need to wait
for a killing frost. In fact, it’s usually better
not to wait. A killing frost will induce leaf drop and
quality and yield decline. Dormancy is a response to the
combination of decreasing daylength and temperature. Once
October arrives, cut when weather and your time permit.
Previous cutting frequency. Stands
cut more frequently are at greater risk of winter injury
if cut during the fall. Fall cutting will be safer where
at least one crop during the year has reached the flowering
stage.
Stand age. Younger stands are less
susceptible to winter injury than older stands, because
young alfalfa plants are healthier than older plants. Thus,
younger stands are less likely to be injured by fall cutting.
Healthy stands seeded to winter hardy varieties in spring
2005 should be very tolerant of October harvesting.
Variety winter hardiness. Cheap seed
may or may not have good winter hardiness. Varieties with
known winter survival indices of around 2.0 or less should
be more tolerant of fall cutting.
Soil potassium. Alfalfa uses a lot
of potassium, and its winter survival has been linked to
soil K levels. Fields with medium or low levels of K will
be less tolerant of fall cutting.
Soil drainage. Alfalfa fields that are waterlogged now
or at any point during the season are less tolerant of
fall harvesting.
Ryegrass nurse crop or grass/alfalfa mixtures.
Alfalfa mixed with grass should be more tolerant of fall
cutting due to a greater ability to catch and hold insulating
snow cover and the soil insulating effects of grass crowns/residue.
Seeding-year stands where Italian or annual ryegrass was
seeded as a nurse crop may need to be harvested
in October to reduce competition and potential smothering
of alfalfa by the ryegrass.
Quality next spring. We’ve conducted
experiments on two farms in southeastern Minnesota . On
one farm, fall residue after a third cutting in mid-August
significantly reduced quality of the next year’s
first cutting. On the second farm, it didn’t. Some
Wisconsin data indicate little affect of fall residue on
spring quality. Thus, fall residue probably more often
then not has little detrimental affect on quality the next
spring. But if there is a lot of fall residue and it doesn’t
get matted down by snow over winter, it may reduce quality
next spring. If that is a concern next spring, fall residue
can be clipped when the ground is still frozen before spring
regrowth starts; this can be a challenge to time though
without damaging the stand.
Uncut strips. Leaving uncut strips about
every 20 feet can help catch insulating snow cover, especially
where winds have a tendency to blow snow off the field
(pretty much most of Minnesota, eh?).
Grazing. Grazing
is a great option for fall harvesting alfalfa. Patterns
of use by grazing animals often leave better stubble for
catching insulating snow. But don’t
graze when the soil is wet, lest stand damage occur.
Alfalfa-grass mixtures or alfalfa with a ryegrass nurse
crop can probably be grazed during somewhat wetter fall
conditions. Follow bloat precautions if grazing pure alfalfa,
especially right after a killing frost.
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