University of Wisconsin-Extension
Many
factors affect the extent of crop damage after a flood. Seasonal
temperatures can be a major factor. A July flood, for example,
is often much worse for crop survival than a spring flood.
The warmer mid-summer weather increases the rate of damage
and death to submerged plants. During spring flooding, temperatures
are colder and plants can survive longer under water.
Plants
that encounter flash-flooding along creeks where the water
rises and recedes quickly are most likely to survive. They
will experience less oxygen depletion than submerged plants.
Other factors for survival include water movement and plant
height. Standing water is more harmful than moving water.
Plants with some leaves protruding from the water are more
likely to live. Restoration of alfalfa, irrigated pastures,
perennials and hay will depend heavily on all of these factors.
But it a so depends on the steps you take toward recovery.
Alfalfa
can withstand submersion for a limited time, depending on
its stage of growth. Dormant plants may withstand submersion
for as long as seven to 10 days. Growing plants can usually
withstand submersion for less than three to four days without
damage.
Alfalfa
can recover from moderate silt deposits. Silt deposits of
over 2 to 3 inches will weaken the stand, and you may need
to regrade and re-establish in places.
Limit
reseeding of established fields to silted patches within the
field. If the entire field is silted, rework and reseed the
field. Where alfalfa stand is over two years old, overseed
with temporary crop and reseed alfalfa at least one month
after having reworked the field.
You can
reseed small areas with fast-growing grasses. This will help
provide forage until the entire field can be reworked. In
old fields, seeding to annual crops such as ryegrass will
provide some hay and also will help control weeds.
You probably
can restore irrigated pastures without serious production
losses if silt deposits are not over 2 inches and erosion
is minimal. Recovery usually depends on the type of legume.
Alfalfa probably will recover from moderate silting better
than white clover varieties. White clover will not survive
silting that covers the ends of the growing stems or stolons.
Ladino clover, however, will fill in stands from a few surviving
plants if the area is not too large.
Grasses
such as ryegrass, orchard grass, fescue and meadow foxtail
will probably grow through a moderate silt deposit, and can
stand several days of flooding without injury. Tall fescue
will tolerate more water than ryegrass or orchard grass. Meadow
foxtail and reed canary grass can stand longer submersion
than other perennial grasses.
Subsurface
water saturating the root zone of deep-rooted crops such as
alfalfa can damage the plant as much as surface water. To
take care of excess soil moisture, open drainage ditches as
soon as possible.
Some
overly mature alfalfa or clover grass can be partially salvaged
by mixing with less mature forage and ensiling the crop. Although
nutritional value will be low, this is a fast method of removing
the crop to ensure a good second cutting.
Ensile
perennials in either conventional upright or temporary trench
silos. To make a trench silo:
- Locate
the trench where drainage is good.
- Design
the trench for efficient feeding. A long, narrow, deep trench
results in less feeding loss than a wide, shallow trench.
To make
the silage:
- Direct
cut or wilt to 65 to 70 percent moisture.
- Chop
fine.
- Pack
thoroughly.
- If
available, add 100 to 200 pounds of corn and cob chop per
ton of ensiled nutrients. This will improve fermentation,
quality and palatability.
To minimize
damage to flooded hay crops:
- Remove
old growth from fields that have not been harvested. This
will encourage a good aftermath crop.
- Make
this crop into hay or silage.
- If
crop is silt-damaged, chop it uniformly back onto the field.
Then topdress immediately with fertilizer. You also may
want to apply nitrogen to stimulate legumes as well as grasses.
Check with an agronomist for recommended application rates.
- On
fields harvested just prior to the flood, make crop into
hay or silage. Then topdress field with fertilizer. Check
with your county agricultural agent for specific recommendations.
- If
growth is short or yellow, topdress immediately.
Additional resources:
Your county agricultural agent
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NASD Review: 04/2002
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