By Roger Elmore and Mahdi Al-Kaisi
Iowa State University
Iowa’s wet spring and cool temperatures not only slowed planting progress but also slowed Growing Degree Day accumulations. These factors contributed to yellow corn plants across the state as well as within-row variability in plant to plant growth and development. Seedling diseases reduced stands.
We might expect all of those problems to surface considering the conditions the crop has experienced to date. We expect stand losses in low areas of fields in wet years due to prolonged standing water on planted or emerged corn (see link). However, one rarely-seen problem has developed: corn stand losses on side hills.
Saturated soils on sloped areas with corn planted in the 2nd or 3rd week in May resulted in poor germination and damping off and in some cases dramatically reduced stands. Soil temperatures at and soon after planting were conducive for rapid germination and emergence. So, we can rule out temperature as a causal agent. In some cases the seed swelled (imbibed water) but neither the radical nor mesocotyl emerged. In cases where the radical and/or mesocotyl did emerge, they died before much growth occurred (colleagues at the Plant and Insect Diagnostic Clinic are examining seedlings for pathogens as we write).
One of the possible reasons for stand losses on side slopes is water seepage leading to continuously saturated conditions and thus a lack of oxygen supply for seedling to develop. Areas with water seepage like this are called ‘side-hill seeps.’
Field with reduced stands on side hills due to saturated soils (foreground and just below the crest of the hill in the background). The field slopes down in the foreground to the lowest area – which ponded and has no surviving plants – and then back up the other side. Boone County, 11 June 2013.
One of the main reasons for side-hill seeping is an impermeable layer or clay-pan layer that restricts vertical water movement into the soil profile. This impermeable layer probably lies just below the area where the emergence failure occurred. This causes lateral water movement towards the back slope and creates saturated surface soil conditions.
Extensive spring 2013 precipitation fostered ideal conditions for side-hill seeps. Soil profiles were saturated and excess water moved laterally due to vertical flow restriction. This soil saturation occurred during critical stages of germination and early stages of growth. These conditions deprived seedlings oxygen necessary for growth and/or slowed growth to the point where pathogens were able to overcome the struggling seedlings. Corn stands were compromised.