Limit wind erosion
Soil erosion caused by heavy rains and water running off fields gets more attention. But wind erosion also occurs in Iowa, even during winter. It’s especially noticeable when snow in roadway ditches is covered with black sediment from the erosive force of wind, even at subzero temperatures.
Of course, water erosion is a major concern. “Erosion caused by water far exceeds the amount of sediment loss by wind because of the high volume of precipitation Iowa receives during the year,” says Mahdi Al-Kaisi, an Iowa State University agronomy professor and Extension soil management specialist.
The powerful erosive effects of water erosion on removing sediment and associated organic matter and nutrients from fields and moving it into waterways, streams and rivers is another reason why erosion caused by water gets more attention. The water quality issue is making headlines these days.
“However, wind erosion also contributes to a significant loss of topsoil, especially the loss of organic matter at the soil surface,” says Al-Kaisi. “It’s certainly worthwhile to do what you can to try to prevent wind erosion from occurring on your fields.”
Driving around Iowa, particularly in January and February, you notice the volume of sediment accumulated in ditches or near farm fences, with the snow looking black.
“This phenomenon is observed in many parts of the state, and it is worse where fields are tilled or have no crop residue or cover crop to prevent the wind from dislodging soil particles,” says Al-Kaisi. “The misconception is that the soil is frozen; therefore, wind erosion is not a concern in detaching soil particles. However, wind can have a significant effect on soil erosion during winter, and what we see in the ditches and close to fields is only a small portion of the total soil loss during the wind erosion process.”
Effects of topsoil loss
During wind erosion, three distinct processes occur to displace soil particles, he explains. These include the initial process (saltation), when the wind’s force detaches and removes soil particles, which subsequently return to the soil surface and dislodge other soil particles. This creates the “creeping effect” — another process in wind erosion.
During the creeping process, sand particles move slowly along the soil surface, striking other soil particles, says Al-Kaisi. Then these dislodged particles are transported (suspension phase) airborne for an extended period of time. Those sediments and airborne particles are deposited at different distances from the point of origination or source.
“The heaviest particles are deposited closer to the source, and that is what we see as sediment-covered snow by the roadside, in ditches and near fences,” he notes. “However, significant amounts of eroded materials with lighter density are transported greater distances and may end up in water bodies and other places across the landscape and in cities.”
Regardless of the type of soil erosion, the loss of topsoil can have a profound effect on soil productivity, in addition to impacting water quality and air quality, says Al-Kaisi. “The loss of organic matter, sediments and attached nutrients is highly driven by the intensity of tillage and lack of crop residue, or lack of a cover crop on the soil surface.”
No-till and cover crops
Generally, three management practices — intact crop residue cover, no-till and cover crop, — will reduce wind erosion significantly, says Al-Kaisi. “Crop residue and cover crops create conditions at the near surface to increase soil roughness to deflect the wind profile above the soil surface. This results in less erosive effects of wind to remove soil particles. Also, crop residue and cover crops slow down water movement on the soil surface, and provide better soil structure for increased soil porosity and water movement into and through the soil profile.”
The combined effects of crop residue on the soil surface and cover crops growing in the field lead to less eroded sediment, and they reduce wind erosion. “Crop residue and cover crops have the dual effect of stabilizing the soil structure and reducing the effect of wind and water erosion,” says Al-Kaisi.
Time to check your fields
Al-Kaisi encourages farmers to give some thought to fields that experienced wind erosion this winter. Are there areas of fields that would benefit by leaving crop residue untouched in the fall? Would the entire field or even part of the field benefit from planting a cover crop?
Once the snow cover is gone this spring, it’s also a good time to evaluate rill and gully erosion in fields that has occurred since last fall, he says. Spring rains tend to cause these areas to show up more strongly. But often you can determine these areas before planting and see where grass waterways and other soil conservation measures are needed.
This article published in the March, 2015 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2015.
Field Conservation Maintenance/Practices
Photos credit: Richard Schultz