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How does flooding impact row-crop soils?

Following non-stop rains, Mid-South farmland continues to go underwater. What should farmers do once water recedes?  

In early May, rains continue to fall across the Mid-South sending swollen rivers outside their banks and across row-crop acreage.

What are the effects of so much flooding on farmland? What should be done once the water recedes? A team of Texas A&M soil specialists has attempted to answer those questions.

For more, see Texas A&M paper

The prologue from a recent paper by the specialists reads: “The impact of flooding rivers, overflowing sewage and septic systems and other freshwater flooding scenarios has an immediate and dramatic effect on the lives of area residents, agricultural enterprises and the overall environment. After the water has receded, evaluation of damages typically is centered on homes and businesses, roads, utility services and other often life essentials. However, flood water also can have a pronounced influence on soil fertility and its physical and chemical properties, as well as creating potentially serious environmental issues.”

On April 29, Delta Farm Press spoke with one of the paper’s authors, soil chemist Tony Provin, about how flooding can affect soils, safety issues and soil tests. Among his comments:

Can you talk about when the study was done and the impetus?

“We followed up, from an Extension perspective, on general guidelines that individuals need to know about.

“Within Texas – really right after Hurricane Rita and, to some extent, Hurricane Katrina – we got a bit closer to the first responders. We were right behind the emergency personnel that went into the affected areas.

“After that, we tried to be a bit more proactive and educate people on these types of subjects and, hopefully, get this information in their hands before they need it.”

On specific soil concerns…

“From an agricultural standpoint, first and foremost, prior to or following a flood, know where the pesticides and petroleum products are stored. For the petroleum products, know everything all the way to propane tanks -- document where those are.

“Take care of pesticides. You don’t want those floating off or improperly contained. While we may want to take personal possessions out of a given area, certain pesticides may need to be the priority because of the long-term risks and potential movement of those products into very sensitive areas. You don’t want those ending up in your neighbors’ fields.”

Did you look at how long it takes for farmland to recover from a flood?

“If we look back to the 1990s flooding around Dubuque, Iowa, along the Mississippi River and some of the tributaries, the greatest long-term concern was what type of sediment would be deposited on the fields. If it’s a silt-loam on a silt-loam, the repercussions are modest to minimal.

“But in some areas, three and four feet of sand were put on silt-loam or silty-clay loam. The end result of that was devastating to the type of agriculture in that area. It went from very productive soils – as productive as northeast Iowa has – to soils that actually became quite droughty.

“The long-term ramifications for some of those areas is that corn/soybean-type agriculture would no longer happen. That is, unless we come up with a method of irrigating those areas. And that region of Iowa doesn’t have the infrastructure to support irrigation.”

First worries post-flood…

“In many cases, the first thing to worry about is pesticides, hydrocarbons and materials like that.

“The next concern is large debris removal – after Hurricane Ike there were debris fields 15 or 20 miles inland. Those debris deposits were often 20 to 25 feet tall with refrigerators and everything else mixed in.

“Simply going out and burning that debris like we would have done in the 1970s and 1980s is no longer an option. There may be tires, Freon-containing appliances and whatever else – you need to go through and segregate it.”

On the microbiological aspects of flooding…

“The farther north you go, the greater this is an issue. In Texas, we don’t have much soil organic matter.

“Heading north, under flooding conditions, there is a lot of soluble organic carbon within the surface soil and extending into the soil profile. That’s particularly true if there’s been a growing row-crop like corn or soybeans.   

“Looking at nitrogen availability following water receding, we often find that what nitrogen would’ve been available to growing plants is now lost to de-nitrification events. We have a leaching event that’s potentially occurring where water is perforating, or penetrating, through the surface and leaching soluble nitrate nitrogen down into a lower soil profile.

“At the same time, with warmer temperatures the soluble organic carbon that dominates many of the northern soils shows the microbic activity goes from aerobic activity to anaerobic. Instead of the soil microbes using oxygen to function, they look at other electron receptors – in this case, nitrate nitrogen. In a prolonged flood, you get into iron reduction.   

“Long-term that isn’t a big issue. Short-term, particularly in a pasture setting where water has been standing for a week, or two, recovery will be slower. That’s because there is a lot of mud and debris on the plant tissue (if it’s still alive) and, second, we’ve lost a lot of available nitrogen to those plantings.”

Advice on soil tests following a flood?

“We have a different philosophy here than in the Midwest. I’m originally from central Illinois where we’d soil test once every two or three years. Farther south, there is annual soil testing looking at residual nitrogen.

“The first thing I’d recommend after a flood is for a farmer to evaluate how much debris is out there and what type of debris is there. Debris could be anything from trees to buildings to sediment.

“If there is significant sediment, they need to go out and start digging into it to determine if it’s sandy material, a clay material. If it’s dramatically different than what was there originally, and is more than a couple of inches thick, they need to take soil samples. They’ll need to check the new fertility levels Mother Nature has dealt them.”

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