COUNTY AG NEWS

Recent rains have caused flooding and ponding in many farm fields, and we now have numerous fields that have turned yellow as a result.

The extent to which flooding injures corn is determined by several factors including: 1) timing of flooding during the life cycle of corn, 2) frequency and duration of flooding, and 3) air-soil temperatures during flooding. Respiration is the plant physiological process most sensitive to flooding. Flooding reduces the exchange of air (oxygen) between soil and atmosphere, eventually leading to decreased total root volume, less transport of water and nutrients through the roots to the shoot, and formation of sulfides and butyric acid by microorganisms that are toxic compounds to plants.

Soils contain pores filled with gas and/or water. The two main gases important for respiration are oxygen and carbon dioxide. The pathway for oxygen into the plant is from the atmosphere through soil pores to a thin water film surrounding plant root hairs. It is relatively easy for oxygen to diffuse into soil when pores are filled by air, but oxygen does not easily diffuse in water so the main constraint to oxygen movement is the thin water film surrounding root hairs. This boundary is magnified in flood/pond conditions. Roots are injured if the soil remains waterlogged. Continued poor aeration causes cell death and even death of roots. 

Measurable short term reductions for root and leaf growth rates begin immediately within one to 12 hours, but tend to recover quickly within two to three days. Almost immediately, leaf elongation ceases and N, P, and K concentration in leaves decrease, but in roots N, P and K concentrations increase.

Wet soils have a large heat capacity and considerable amounts of heat are required to raise their temperature. Thus, usually wet soils are cold and corn growth is slower. Lowering soil moisture content leads to higher soil temperatures and faster growth.

A considerable amount of oxygen is required in the soil for mineralization of nutrient elements from organic matter by microbes. Oxygen deficiencies reduce microbe activity, decreasing the rate at which ammonium and nitrate are supplied to plants resulting in nitrogen deficiency in waterlogged soils.

Additionally, flooding can reduce the activity of mycorrhizae essential for symbiotic phosphorus uptake. Flooding can also result in losses of nitrogen through denitrification and leaching. Where estimated nitrogen loss is significant in fields not yet tasseling and yield potential is reasonable, corn may respond to additional applied nitrogen fertilizer.

 

Cultivating corn is a practice that is not used much today in corn production. However, cultivation can be beneficial as a way to loosen up the soil and allow the entry of oxygen into the root zone in areas where rain or flooding have resulted in wet, compacted soil. Where fields have been pounded by heavy rains, especially sandy fields with low organic matter, row cultivation can enhance corn root development by breaking the dense surface soil layers, encouraging better soil aeration, closing in cracks that may form as the surface dries, and reducing puddling and runoff from future rainfall events.