Ronnie Schnell, Ph.D.
Cropping Systems Specialist
Texas A&M AgriLife Extension, College Station
Recent rain events have resulted in flooding or significant ponding of water in many corn and sorghum fields across Texas. While low-lying areas may be flooded, other areas of fields may be saturated for extended periods of time. How long can corn or sorghum survive under saturated or flooded conditions? What impact will these conditions have on grain yield, if any?
Oxygen is required by plants for respiration, including above ground (shoots) and below ground (roots) plant tissue. Respiration is the process where plants metabolize sugars, producing energy needed for growth and development. Soil contains about 50% pore space that is occupied by air and water. Flooding increases the proportion of pore space occupied by water and reduces exchange of air between the soil and atmosphere. Deep ponding has the same effect on above ground tissue. Oxygen does not easily move through water so saturated or flooded conditions will limit oxygen availability to plant tissue, especially roots. This can have detrimental affects on plants.
The growth stage of the crop will influence the plant’s ability to withstand flooded conditions. Younger plants are more susceptible to damage or death by flooding, especially when the growing point is at or below the soil surface. Younger plants are easily submerged compared to older, taller plants. Higher temperatures will exacerbate the effects of flooding. Young plants may survive for up to 48 in oxygen limited environments under cool conditions but may not survive 24 hours under warm conditions (>77°F). For this reason, yield loss is typically greater when young plants (< 6 leaves) are exposed to saturated or flooding conditions. Stand loss at early growth stages is a major factor in yield loss. Similar to freeze and hail damage, look for new growth several days after conditions improve to determine surviving plant populations.
Extended periods of saturation will affect plants of all ages. Root tissue can die and new growth will be stunted or delayed under saturated conditions. Reduction in root volume will reduce the capacity for uptake of water and nutrients during later growth stages. Flooding can induce nutrient deficiency symptoms. Nitrogen will be remobilized from older (lower leaves) to younger (upper leaves) resulting in yellowing of lower leaves. Purpling of leaf tissue is possible due to accumulation of carbohydrates in the shoot tissue under flooded conditions, a symptom usually associated with phosphorus deficiency. In addition, denitrification and leaching of nitrate can result in loss of nitrogen from soil and potentially reduce yield. Damaged root systems and associated stress can increase the potential for various plant diseases, including root and stalk rot diseases. The degree of flooding will ultimately determine the potential for yield loss.
A brief period of flooding will likely have minimal impact on grain yield, especially for older plants. Repeated or long-term saturation/flooding will increase the potential for yield loss due to a variety of complications.