Northwest Minnesota continues to be plagued by excess precipitation. Consequently many field or lower lying portions of fields are repeatedly flooding or are - at a minimum - completely waterlogged. Flooding and water logging causes a rapid depletion of oxygen in the root zone. In turn, this oxygen deficiency affects several physiological processes such as the uptake of water, the uptake and transport of nutrients, and the root/shoot hormone relations.
Wheat can probably handle 3 to 4 days of flooding and/or water logged soils before grain yield is impacted negatively as long as some of the leaves are above water. Higher temperatures will hasten the depletion of oxygen and increase the risk of damage to the crop. Acute nitrogen deficiencies are most commonly observed with the crop yellowing quickly. The waterlogged soils not only impair nitrogen uptake, denitrification and leaching further exuberate the problem. Extended periods of water logging reduce leaf elongation, kernel number, and ultimately grain yield.
Yield losses than have been reported in the literature range between 20 to 50% when soils were water logged in excess of 10 days. One study in winter wheat reported a yield loss of about 2% for each day soils were waterlogged. Several study, however, have also noted differences in water-logging tolerance among wheat varieties.
One of the characteristics that were observed of varieties that handled water logging better than other varieties was the ability of varieties to initiate adventitious roots of the first node (Photo 1). I have observed this trait in some of our spring wheat varieties but neither I nor any of the breeding program in the region have dedicated screening or evaluation nursery for this trait.