One of the possible reasons for stand losses on sidehill slopes, also known as the mid-slope (Figure 2), is water seepage leading to continuously saturated conditions and thus a lack of oxygen supply for seedlings to develop. Areas with water seepage like this are called 'sidehill seeps.'
Sidehill seeps -- what causes them? Is there a practical way to avoid this problem?
One of the main reasons for sidehill seepage is existence of an impermeable layer or pan layer of soil that restricts vertical water movement into the soil profile (Fig. 2), note the two ISU Extension agronomists. Also, in some cases it can be related to lateral flow where a layer of sand and gravel sandwiched between glacial debris channels water to the side- or mid-slope. "This impermeable layer probably lies just below the area where the emergence failure occurred," says Al-Kaisi.
One of the practices to alleviate problems in areas with sidehill seepage is planting deep-rooted perennials. Either alfalfa or perennial grasses will reduce soil moisture and prevent potential saturated conditions in seep areas. Reduced or no-till alleviates the problem as well, say the ISU agronomists.
Do higher pH soils tend to be found in saturated areas of fields?
The potential for higher pH soils in saturated areas exists in addition to issues with stand establishment, notes Al-Kaisi. Generally, water associated with sidehill seeps is high in dissolved minerals such as calcium and may create an alkali condition. If highly dissolved salts exist, salinity may result in crop failure in these seep areas. Continuous row cropping in these areas may reduce soil quality and increase soil erosion and water ponding conditions at the lower portion of the slope length -- the toe-slope (Figure 2).
SUMMING UP: Extensive spring 2013 precipitation fostered ideal conditions for sidehill seeps. Soil profiles were saturated and excess water moved laterally due to downward vertical flow restrictions. This soil saturation occurred during critical stages of germination and early stages of growth. These conditions deprived seedlings of oxygen necessary for growth and/or slowed growth to the point where pathogens were able to overcome the struggling seedlings. Corn stands were compromised.
"Evaluate field conditions during wet conditions and document areas with sidehill seepage," says Al-Kaisi. "Develop a management plan that may include conservation tillage, use of no-till, tiling, and/or planting perennials with deep roots to utilize excess moisture. These practices will help alleviate sidehill seep problems in the future."