Minnesota Crop News > 2001-2008 Archives
Fields and Soybean Survival
Seth Naeve, Soybean Agronomist
Each year thousands of Minnesota soybean
acres succumb to stresses from excess water. Typically and
primarily, this occurs in small, low-lying areas of farm fields
that "drown out" relatively often. This spring, however,
whole fields will be lost in northwest Minnesota. Eight to
twelve inch rains that fell over large areas earlier this week
have devastated farmers, business owners, and homeowners in
more than 12 northwest Minnesota counties. In many areas the
waters have not yet receded, and many farmers are seriously
concerned about their crops.
Although soybean is generally rather sensitive to excess water,
soybeans can survive underwater for a week or more under ideal
conditions. Generally, soybeans tolerate 48 hours under water
quite well, but flooding for 4 to 6 days can reduce stands,
vigor, and eventually seed yield. Many factors determine how
well a soybean crop will tolerate flooding.
First, a few important definitions must be adressed. Field
flooding may occur by either stream flooding or by lowland
flooding. The former results from creeks or rivers overflowing
their banks onto a flood plain. In this case silt and sand
is often deposited in the field and plant tissues are covered
with soil material. The latter case results from water accumulation
in depressional areas due to inadequate soil permeability or
surface drainage. These flooding types can be further divided
into soil waterlogging, where the soil is merely saturated,
or complete submergence where the crop is entirely submerged.
The type of flooding occurring on a farm directly impacts
the re-growth and yield potential of that field. Although stream
flooding can quickly recede, the resulting silt deposits can
burry the crop and cover leaf tissue with thick layers of soil.
Without rains to wash silt from soybean leaves, recovery is
greatly slowed. Fortunately, soil types prone to stream flooding
are often course textured. These sandy soils drain well, allowing
quick crop recovery or replanting. Flooding in depressional
areas can last many days. Soils in depressional areas often
retain water so that as the water disappears from the surface,
the soil profile may remain waterlogged for several more days.
Most of the flooded acreage in the Red River Valley, this year,
fits into this category.
The most important factors that determine the fate of flooded
soybean fields are: 1) duration of the flooding, 2) temperature
during the flood, and 3) rate of drying after the flooding
event, and 4) growth stage of the crop during the flood. Yield
losses are seldom noted in fields flooded for 48 hours or less.
Four days or more of flooding stresses the crop, delays the
plants growth, and causes the plants be shorter with
fewer nodes. Flooding for six days or more can depress yields
significantly, while flooding for a week or more may result
in significant (or entire) losses of stand.
Temperature during the flooding event plays a large role in
determining the fate of a submerged soybean field. Higher temperatures
cause the soybean plant to more quickly deplete its stored
energy. Additionally, soybean plants appear to be very sensitive
to high CO2 levels in
the soil. Higher temperatures cause plants and soil microbes
to respire at high rates that quickly deplete the water of
oxygen and increase CO2 levels.
Cool, cloudy days and cool clear nights greatly increase the
survivability of a submerged soybean crop.
The rate of field drying after a flooding event also plays
a large role in soybean survival. Researchers have found yield
reductions to be much greater on flooded clay soils than on
silt loam soils when flooded for the same period. These researchers
reported a 1.8-bushel per acre yield loss per day of flooding
on a clay soil and 0.8-bushel yield loss per day on a silt
loam soil. These losses were reported for flooding at the V4
growth stage. Flooding is more detrimental to soybean yields
in the early reproductive phases of development. Flooding at
the R1 stage caused losses of 2.3 and 1.5 bushel per acre yield
losses on clay and silt loam soils. Larger yield losses would
be expected in soybeans at the R3 to R5 stages.
Some of the main indirect effects of flooding on soybean yields
are; 1) root diseases, 2) N deficiency, 3) and other plant
nutrient imbalances. Caring for recuperating soybean stands
should focus on reducing stresses to the plant where possible.
Cultivation should be considered to increase soil aeration,
and post emergence herbicides should be applied to conventional
soybean crops judiciously. Herbicide stress should be minimized
and postponed where possible.
Sullivan, M., T VanTooai, N. Fausey, J. Beuerlein, J. Parkinson,
A Soboyejo. 2001. Evaluating on-farm flooding impacts on soybean.
Crop Sci. 41:93-100
Scott, H.D., J. DeAngulo, M.B. Daniels, L.S. Wood. 1989. Flood
duration effects on soybean growth and yield. Crop Sci. 81:631-636