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Choosing
the Right Maturities for Late-Planted Soybeans
Unusually wet weather has led
to major delays in crop planting in many agricultural regions of the country.
In a previous article sent to grower’s in some of the affected areas
we addressed hybrid corn options for late planting. As the spring has
progressed some of those same areas are still wet and soybean planting
will also be delayed.
Corn maturation is largely
determined by the accumulation of heat units during the growing season,
so as planting is delayed past a certain date the amount of heat units
available to mature a crop decreases and it becomes necessary to switch
to earlier season hybrids. Soybean maturation, unlike corn, is based largely
on day length (actually, hours of darkness). This difference in the maturation
process means that choosing soybean varieties for late planting may be
quite different than corn.
Soybeans have two major growth
stages, vegetative and reproductive. In central regions of the country
the vegetative stage (planting to the beginning of flowering) is 45-60
days for full season varieties planted at normal planting dates. This
period may be reduced to as little as 25 days when the same varieties
are planted in late June or early July. The reproductive stage may also
be shortened by late planting, but it would be very minimal. The end result
is that as planting is delayed past normal dates soybean varieties will
mature in fewer days. Latitude and the total length of the growing season
also play a role in determining what soybean varieties are the best choice
for late planting.
Here are some general recommendations
for choosing correct maturities for late planting based on geography and
total length of the growing season.
Mid to Late Group IV Areas
- KS, MO, IL, KY, TN, OH and on East. In these more southerly areas
growers should stay with adapted full season maturities until early July.
Many growers who double-crop after wheat will actually go to later (Group
V) varieties. Staying with fuller season varieties is critical to get
adequate vegetative growth (height) before the plants go into the reproductive
stage.
Mid Group III to Early
Group IV Areas- KS, NE, IA, IL, IN, OH and on East. Stay with adapted
full season varieties until June 20-25. After June 25 it may be necessary
to back off maturities. Reduce maturites by half a maturity group at July
1 and a full maturity group at July 10.
Early Group II to Mid Group
III Areas - NE, IA, IL, WI, IN, MI, OH and East. Stay with adapted
full season varieties until June 15-20. After June 20 it may be necessary
to back off maturities. Reduce maturities one-half group at June 30 and
a full maturity group at July 10.
Group I Areas- Dakotas,
MN, WI, MI and East. Stay with adapted full season varieties until June
10 throughout Group I growing areas. In Group I and earlier maturity areas
there is considerably less season length the timely switching to earlier
maturities as planting becomes late is more critical.
Group 0 and 00 Areas- ND,
MN and East. Geographic maturity bands for soybeans become very narrow
in far northern growing areas. It may be necessary to back-off maturities
much sooner in some areas. Please contact your AM or Regional Agronomist
for their suggestions in your particular area. Some 00 soybeans are day-neutral
(photoperiod insensitive) and their maturity will be not influenced by
day length.
According to Gary Pepper, Extension
Agronomist at the University of Illinois, the following management practices
can potentially benefit late-planted soybean yields.
1). Move to narrower rows by
the use of a narrow row space planter or drill. Rearranging plants into
narrow rows allows plants with reduced vegetative development to fully
intercept sunlight. The abbreviated growing season of late-planted soybeans
needs to be fully used by the crop at the earliest possible date.
2). Increase plant
densities with major planting delays. The reduced plant size of late-planted
soybeans will reduce their tendency to lodge. Reduced leaf area on each
plant suggests that more plants per acre can be used to capture sunlight.
We can "guestimate" how much and when to increase planting rate
based on the experience of double-cropping after wheat.
-
Increase planting
rate 10 to 15 percent if planting after June 10th.
-
Increase planting
rate 20 to 30 percent if planting after June 20th.
-
Increase planting
rate 50 percent in planting after June 30th.
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