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June 16, 2005 Carefully Assess Flooded Crops Recent heavy rains in eastern North Dakota and western Minnesota will result in substantial crop damage and losses, according to a North Dakota State University agronomist. How serious will the damage be? "That depends," says Duane Berglund of the NDSU Extension Service. "Prolonged soil saturation definitely affects crop growth and yield, but the extent of the injury will depend on the type of crop, growth stage, duration of the flooding and the air and water temperatures at the time of ponding." The first major impact of soil completely covered with water is a rapid depletion of oxygen required for plant growth and development. The other major impact is a change in nutrient status by either leaching or changing its availability to the plant. Corn is very sensitive to flooding in the early vegetative stages, especially before the fifth or sixth leaf collar stage, Berglund says. In early growth stages, corn and soybeans can survive for only two to four days under water in anaerobic conditions. Moderate water movement can reduce flood damage by allowing some oxygen to get to the plants, keeping them respiring and alive. Drainage within one to two days increases the chances of survival. “If temperatures are warm during flooding (greater than 77 degrees), plants may not survive 24 hours,” Berglund says. “Cool temperatures may prolong survival. However, cold, wet weather favors disease development. Seed treatments are effective, but limited in protection. Seedling development slowed or delayed two to three weeks allows soil-borne pathogens a greater opportunity to cause damage.” Iowa studies found that flooding for 72, 48, and 24 hours, when corn is about 6 inches in height, reduced corn yields by 32 percent, 22 percent and 18 percent respectively, at a low nitrogen fertilizer level (50 pounds of nitrogen per acre). At a high level of nitrogen (350 pounds of nitrogen per acre), these yield reductions ranged from 14 percent to 19 percent in one year, to less than 5 percent the following year. "Even if flooding doesn’t kill plants outright, it may have a long-term negative impact on crop performance," Berglund says. "If excess moisture in the early vegetative stages retards root development, plants may be subject to greater injury during a dry summer because root systems are not sufficiently developed to access available subsoil water. "Seed rots, seedling blight, corn smut and crazy top affect corn plant development later, even though ponding occurred earlier,” says Berglund. “Delayed soybean growth in wet, saturated soils allows diseases, such as fusarium, phytophthora and pythium root rots, to establish and weaken or destroy seedlings. Carefully assess the damage and check with your crop insurance agent before deciding to replant or before tearing up the existing stand." At this late date, only a few crops should be considered for replanting. Early maturing sunflowers, buckwheat, proso millet and very early group 00 soybeans may be options, Berglund says. Before replanting, make sure herbicides used on the prior planting will not injure the replanted crop. In addition, don’t seed into a wet seedbed because crops "mudded in" will result in poor stands and limited yield potential. Look for rotted seed or damped-off seedlings to reveal probable crop losses, Berglund advises. To confirm plant survival, check the color of the growing point (it should be white and cream colored, while a darkening or softening usually precedes plant death) and look for new leaf growth three to five days after the water drains from the field. Compare the intended stand with the damaged stand and evaluate the uniformity of the stand, the original planting date versus a replant date, likely replant pest control and seed costs as well as projected crop prices. "Weigh these costs and price projections against replanting yield gains to evaluate crop injury and replanting gains," says Berglund. "On surviving stands, remember that favorable weather for plants after ponding is important," Berglund says. "Cultivation, once soils are dry enough, will open and aerate the surface soil and promote root growth, but be careful. Working wet soil causes compaction that reduces crop growth." An additional nitrogen application in corn may be necessary in fields that show signs of yellowing or uneven growth, he notes. A late test for nitrate when corn plants are still 6 to 12 inches tall can determine if more nitrogen is needed. Similarly, maintain a good weed control program so that plants are not robbed of nutrients and moisture later in the season. According to Berglund, wheat can withstand waterlogged soils for up to 24 hours without excessive damage. Barley is more susceptible to damage. Depending on the conditions, wheat probably can survive saturated conditions for up to two days. A younger crop has a smaller demand for oxygen and may be able to survive better. "Even so, a small-grain crop that is submerged in water for two days or longer has little chance for survival," Berglund says. "When a small-grain crop does survive flooding, recovery may be very slow and yields will be impacted dramatically." Soybeans tend to have better tolerance for standing water than dry beans and small corn seedlings. Sugar beets with five to six leaves can withstand more flooding than smaller seedlings. It also should be noted that established alfalfa could survive up to 10 days of flooding. ### Source: Duane
Berglund, (701) 231-8135, duane.berglund@ndsu.edu |
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