Eric Mousel, Forage and Alfalfa Specialist, Millborn Seeds Inc.
The first thing that has to be considered when figuring out what to do with a pasture that has been flooded out; is to consider what shape the soil is in. Flood waters that stand for long periods of time can really cause a lot of problems for your soil. These waters will bring in a lot of debris and salt and leave a lot of silt, sand and other trash.
There are three major things we need to look at when evaluating the soil in a pasture that has been flooded.
Alkalinity
When soil first becomes saturated, the pH will drop and the soil becomes acidic as a result of the production of organic acids produced through fermentation. However, after being saturated for an extended period of time, the soil will become alkaline as the pH rises. The rise in pH is partly attributed to the denitrification of nitrate (NO3) to N2 nitrogen.
Unlike soil acidity (low pH), where plant species will actually die from exposure, soil alkalinity decreases respiration and nutrient uptake in plants and therefore can cause depressed yields for forage species that are not adapted to a high pH environment.
Salinity
Soil salinity can be a big problem caused by flood waters. The inflow and subsequent settling of salt from upstream will at best leave a salt crust on the soil surface as flood waters recede. In the worst case scenario the soil profile will be completely saturated with salt.
The problem with salt in the soil is that it suspends when it is mixed with water, rather than dissolving. Therefore, the soil profile will contain a salt solution that plants have difficulty absorbing. In saline soils, plants will experience severe water stress even when adequate moisture is available because they cannot absorb the salt solution.
Soil Biology
Probably the biggest problem flood waters cause is upsetting the soil biology. Microorganisms that live in the soil are an essential part of plant growth. These organisms are largely responsible for making soil nutrients available for plant absorption. Many of these microorganisms that make nutrients in the soil available to plant life require oxygen respired by the soil to survive. Obviously, when a soil becomes saturated with water, these organisms will die off and only organisms that can tolerate the lack of oxygen will remain.
The change in soil pH as described above also will negatively impact many important soil organisms as will increases in salinity.
Soil testing
So, what do we do about soils in these situations? The first thing that needs to be done is to do a soil test to see what condition the soil is in. An analysis of N, P, K, pH, and salinity is probably all that is needed to start. Most of the available N has probably leached out and P and K availability will vary depending on site. As stated before, pH probably will be high, but you need to know how high so you can select species that will tolerate it.
Most any local CO-OP will conduct as soil test for you or you can contact me and I can arrange a soil analysis for you.
Solutions
Correcting these soil problems is difficult at best and depending on severity, not very economical. But there are some short-term (inexpensive) things a person can do to get the healing process started for your soil:
Alkalinity – if pH is above 8.0, action will need to be taken.
Add organic matter by growing an alkaline tolerant cover crop:
Turnips, radishes, lentils
Barley
Alfalfa (moderate)
Russian wildrye
Altai wildrye
Tall or slender wheatgrass
Smooth bromegrass
Tall fescue
Add sulfur to the soil solution by adding gypsum or fertilize with ammonium sulfate and retest periodically (worst case scenario).
Salinity
Grow salt tolerant plants to remove salt from the soil solution over time:
Turnips, radishes, lentils
Barley
Sugar beets
Winter wheat
Sunflowers
Alfalfa (moderate)
Russian wildrye
Altai wildrye
Tall or slender wheatgrass
Smooth bromegrass
Tall fescue
Soil Biology
The most important thing is to get something growing; anything that will stimulate the soil solution.
If your soil test comes back relatively normal…we’ll talk about that and what to do about flooded out alfalfa next time.
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