Emery Tschetter, Director of Communications & Marketing, SDSU College of Agriculture & Biological Sciences
BROOKINGS, S.D. - Over the last five days, some areas have received more than 6 inches of rainfall leading to ponded or flooded areas in fields. Water saturated or waterlogged soils lack enough oxygen for root respiration and many wonder, "How long can corn and soybeans plants at early growth stages survive in these waterlogged soils?" There are many factors that lead to this question's answer says Nathan Mueller, SDSU Extension Agronomist.
"We know that the crop growth stage, variety/hybrid, duration of ponding/saturation, soil type, soil/air temperature, and other factors can affect the survival of corn and soybean plants under these waterlogged conditions," Mueller said. "Unfortunately other factors reduce plant population related to flooding including crusting, plants covered in sediment or buried under residue, and increase in seed/seedling diseases like damping-off in soybean."
Currently, the crop growth stages of most corn and soybean range from germination to V3 and germination to V1, respectively. At these early growth stages of germination, emergence and early vegetative, Mueller says both corn and soybean plants are negatively impacted quite quickly by waterlogged conditions.
"Crops that are not completely submerged have some limited capacity for diffusion of oxygen to occur from the shoot to the root, which increase survival time," he said. "Oxygen is needed by plant cells for growth and development including germination."
Mueller points to research data which shows that waterlogged conditions experienced by corn seed for two or more days is a long enough time to decrease final corn emergence and is more detrimental at soil temperatures in the 70s than the 50s.
"In general, young corn plants can survive about two to four days of flooded conditions," he said.
Although the effect of waterlogging on soybean germination and early growth has not been widely studied or written about. Mueller says the presence of waterlogged soils at any time and for any duration during the germination process in soybeans will reduce the final germination and emergence percentage.
"A germination decrease of 20-43 percent can occur from a 48-hour flooding that occurs after the start of seed imbibition or swelling," he said referencing research. "Even after waterlogged conditions are removed, researchers have found that seedling growth was reduced by more than 50 percent from 24 to 48 hours of flooding when temperatures were near 77°F."
He adds that on-farm research and observations also say not to give up hope as soybean plants at the V2-V3 growth stage can survive on soils flooded up to eight days.
" If enough plants survive the temporary soggy conditions, yields in depressional areas can be equal to or better than upland areas during dry summers," Mueller said.
Soybean yield reductions from 0 to 100 percent can occur from three days of flooding at the V2 to V3 stage compared to adjacent non-flooded areas. However, he says low plant populations and shorter plants resulting from ponding/flooding often result in decreased yield. The probability of yield loss increases as final soybean plant population decreases below 100,000 plants/acre.
For growers needing to replant acres lost due to flooding, Mueller says there should be plenty of seed available in the maturity range they need, but they won't have the luxury being picky in their hybrid or variety selection.
To access delayed/ prevent planting provisions, growers should visit, http://www.extension.iastate.edu/agdm/crops/html/a1-57.html and to view final South Dakota planting dates they should visit iGrow.org (http://igrow.org/agronomy/corn/late-planting-dates-for-crop-insurance/).