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Flooded cropland – many challenges ahead

Flooded cropland – many challenges ahead

Landowners of flooded acreage must manage a variety of issues, including oxygen-depleted soils, nutrient loss, soil compaction, debris removal and possible chemical contamination. Some acres may not be ready for planting again until next year.

Much of the flooded Delta was already planted for the 2011 season, and when it finally dries out, landowners will face challenges preparing it for planting.

Landowners of flooded acreage must manage a variety of issues, including oxygen-depleted soils, nutrient loss, soil compaction, debris removal and possible chemical contamination. Some acres may not be ready for planting again until next year.

Larry Oldham, soil specialist with the Mississippi State University Extension Service, said much of what is known about soil fertility following a flood was learned after the 1993 flood in the upper portion of the Mississippi River Basin.

“As the waters recede, a new landscape in both land and nutrient management will emerge,” Oldham said. “The soil chemistry that controls the bioavailability of most plant nutrients is very dynamic as soils transition from a normal state to flooded for several weeks, and then back to drier conditions.”

Oldham said conventional wisdom says soils are more fertile immediately after a flood, as upstream nutrients are deposited in downstream fields. But if this were true, the south Delta would not be as fertile as it is today since repeated flooding would have washed away nutrients.

“What is perceived to be better fertility from sediment on the surface is more likely a flush of nitrogen from organic residues in the pre-flood soil when soil microbes, which depend on oxygen from the air, become more active as the soil dries,” Oldham said. “This activity also increases when flooded soil warms as the soils dries.”

Landowners must consider several things when preparing to plant again.

“Remember that flood water carries materials such as pesticides, petroleum products and other substances swept up in its downstream progress,” Oldham said.

Debris removal can include dead animals, uprooted trees and garbage.

“Be safe and follow local, state or federal guidelines for debris disposal,” Oldham said. “Check with the Mississippi Department of Environmental Quality for guidelines.”

While many will be tempted to work in the fields as soon as the water recedes, Oldham urged growers not to do this. Driving heavy equipment on wet soil compacts soil 10 to 20 inches below the surface.

“These dense layers restrict the crop’s rooting zone and limit plants’ access to nutrients and water,” Oldham said. “Additionally, compaction limits the soil’s ability to absorb water, resulting in more runoff from the field.”

Another management challenge is the expected phosphorus deficiencies. After the 1993 floods, land that had adequate phosphorus levels immediately after the flood was deficient in this nutrient after crops were planted. This was especially true with corn fields.

“Among other factors, the deficiency problems came from the diminished activity of beneficial fungi that allow plants to take in phosphorus,” Oldham said.

Solutions to what is known as flooded soil syndrome may be to grow cover crops until planting next year if it is late in 2011 before fields can be worked. If corn is the desired crop in 2012, soil may require supplemental phosphorus fertilizer.

Consider soil’s nitrogen needs carefully after a flood. Oldham said nitrogen is lost at the rate of 5 percent per saturated day. As with phosphorous management, the best practice for the 2011 crop year may plant a cover crop on flooded land and use a starter fertilizer when planting certain crops in 2012.

“Soil testing is the foundation of proper nutrient management,” Oldham said. “Because the flood has created a new farming landscape, test fields before the next growing season even if they were tested going into 2011. The sampling should be done after the soils have dried.”

Wayne Ebelhar, Mississippi Agricultural and Forestry Experiment Station research professor at the Delta Research and Extension Center in Stoneville, Miss., said oxygen supply is a big issue in flooded land. Plants and organisms living in the soil need oxygen to survive.

“Soil aeration will be slow coming back to flooded land,” Ebelhar said. “Most of the flooded ground seals over with silt and clay particles, and it is slow to dry.”

In a normal wet-field situation, producers can till the soil to increase its oxygen capacity, but that is not possible in current super-saturated situations.

“We hit the flood stage in Greenville, Miss., April 28 and the river kept rising. They’re predicting the river won’t drop back to flood stage until June 20,” Ebelhar said. “That’s almost eight weeks of flooding.”

Ebelhar said without oxygen for this length of time, it will take a long time for aerobic microbial populations in the soil and helpful insects and animals such as earthworms to repopulate the affected land.

“An earthworm may be pretty virile, but I’m not sure he can tread water for eight weeks,” he said.

Many living things suffocate from the lack of oxygen when the land and vegetation is covered by water for an extended time.

“Anaerobic organisms, or those that don’t require atmospheric oxygen to function, can increase and consume oxygen that is combined with such things as nitrate, resulting in subsequent nitrogen loss as a gas,” Ebelhar said. “Aerobic populations, or those that require atmospheric oxygen for life, will build back up with rapid reproduction once things dry out.”

The bottom line for many landowners in the flooded region is that the 2011 crop season simply won’t happen, and preparing for the 2012 season will require extra management.

“For a lot of producers, this flooded land may not have much cropping opportunity for this year,” Ebelhar said. “With this flood being so high, it’s going to take a long time for the water to drop and the ground to dry out. With the cost of seed, it’s an awful risky situation to plant in the middle of July or later.”

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