Great Bend Tribune
Published June 11, 2017
On Wednesday a load of wheat was delivered to an elevator in Moundridge and test cutting is ongoing and the 2017 wheat harvest is underway, depending on the weather. The ninety degree plus temperatures will certainly accelerate wheat maturity. Now on to today’s topic.
The U.S., the United Kingdom and Russia were the three main countries that initiated the serious systematic study of soils in the 19th Century. We will skip the reasons here but suffice it to say they were large countries/empires with vast areas of arable land that varied greatly and presented many challenges. One of these challenges was the loss of topsoil, the A soil horizon. While U.S. scientists were aware of and concerned by erosion, there was no focused effort on addressing this condition until the 1930s. The Dust Bowl, combined with the Great Depression focused the attention of Washington on wind erosion in the Great Plains. Back in the Eastern U.S., erosion was also a major problem but water erosion was the main concern. Alarm over what was happening led to a concerted effort by the Federal Government to stop soil erosion (conserve) and restore productivity. This led to research sites and labs to study the phenomena and determine methods to prevent erosion. And it led to the agency termed the NRCS, the Natural Resources and Conservation Service, today and programs like the Conservation Reserve Program.
Over the last seventy years tremendous progress has been made in cultural practices providing producers with the tools necessary to dramatically and even reduce erosion. More than just planting techniques have played a role. The development of chemical pest control also played a major role as did the development of cultivars allowing for more diversity of crop rotations. However, soil erosion is still a problem today.
Over the last five years Kansas has experienced a drought far worse than the Dust Bowl and swung to extremely wet weather with torrential rains in many spots. The improvement in all aspects of crop production was evident during the drought and the deluges. However, these extremes still resulted in significant water and wind erosion in many areas of not just Kansas but the entire country.
Why does this matter so much considering the progress we have made? Aside from the damage both on-site and off, erosion robs producers of a resource, soil, that they cannot replace in their lifetime. On average, an inch of topsoil takes approximately 500 years to produce, longer in drier areas and less in wetter areas. The most fertile, productive and important part of the soil is the topsoil or A horizon. The A horizon is anywhere from several inches in depth to slightly over a foot typically. Any soil loss is significant but especially so in areas that have already lost soil due to erosion. It isn’t that the subsoil, B horizon can’t be farmed but it is typically less productive and requires significantly increased input costs and management.
Next week, how do wind and water erosion occur.
Wind Erosion - Part I
Published June 18, 2017
Wheat harvest is progressing as this is written and if the Thursday night storms hold off, harvest should be in full swing. And before discussing wind erosion, Happy Fathers’ Day to all the dads out there. Today we will start to tackle wind erosion. If you think soil erosion is soil erosion you would be wrong. While there are some similarities and both remove valuable soil particles, water and wind erosion differ in major ways. So today we will discuss wind erosion mechanisms. And remember that areas like Western Kansas experience both types of erosion and in fact damage from water erosion can be worse in an area like ours than in the traditional Corn Belt.
Wind erosion is the physical relocation of sand, silt, and clay, naturally by wind. This problem is worse in arid and semi-arid areas because of less vegetative growth, less organic matter accumulation and less soil development (less clay and more sand and silt sized particles). Before discussing wind erosion, one principle is key – wet soils don’t blow.
The three phases of wind erosion are detachment/abrasion, transportation, and deposition. Detachment has a snowball effect. Once a few soil particles break loose, they break loose more soil particles which break loose more and so on.
Transportation, the movement of soil particles is determined by the size of the soil particle. The larger the particle the less distance it will travel. The three types of transportation are:
- Saltation – movement of soil particles by a series of short bounces along the soil surface. This is 50 – 90% of total soil movement, especially sand sized, larger particles. These particles cause other particles to become dislodged and move.
- Soil Creep – next step after saltation. Rolling or sliding of larger soil particles along the soil surface. Particles up to about 1 mm in diameter and 5 – 25% of soil movement.
- Suspension – fine-sized sand and smaller particles. These get up into the atmosphere and stay there. Once suspended these particles can be transported thousands of miles. This resulted in the Dust Bowl in the 1930s and the dust storms we experience today.
Deposition, where the particles end up is a function of their size. The smaller the particle the further is can be transported. It may be tens of feet as in saltation, hundreds of yards with soil creep, and thousands of miles with suspension. For saltation and soil creep, particles are deposited when the wind speed is insufficient to move them. For suspension, particles will stay suspended until an event like rain deposits them. One last item to keep in mind, as the wind picks up past the threshold velocity where movement occurs, soil moves to the cube of the velocity. So as the wind speed increases say from one to two, it increases movement by a factor of 8, not 2. Next week, how to control wind erosion.
Wind Erosion - Part II
Published June 25, 2017
Wheat harvest in the area is in full swing with most yields respectable or better. Overall, protein levels are somewhat lacking and that may, the keyword is may, result in some protein premiums. And for another week Kansas is drought free without any abnormally dry parts of the state. Last week’s column described the mechanisms of soil erosion by wind. Today, how wind erosion can be eliminated or at least minimized.
First, scientists after the Dust Bowl developed the Wind Erosion Equation and it’s a good place to start. The equation is E = f(I x C x K x L x V) where:
- E = Predicted Soil Loss
- I = soil erodibility factor
- C = soil-ridge roughness factor
- K = climatic factor
- L = width of field downwind
- V = vegetative cover
You can’t do much about the soil erodibility factor, I, in the short term. You aren’t going to change the texture (sand, silt, and clay proportions) but over time you can alter other factors. Reducing or eliminating tillage serves several purposes. It always for the development of stable soil structure so soil can resist wind better. Over time it will increase soil organic matter which will aid in stability and increase water holding capacity (wet soils don’t blow). And finally, the accumulation of residue serves as a barrier to wind and provides surface roughness which also helps. This leads to C, the soil-ridge roughness factor.
Roughness, whether of the soil surface or from residue or plant cover breaks up the wind, slowing it down, and can trap particles that break loose. An analogy is the snow fences that would be put up to catch snow before it could blow onto the road. K, the climatic factor, is just what you think and involves precipitation amount and distribution as well as wind, humidity and temperature as it relates to evaporation. Arid and semi-arid areas, those areas receiving less precipitation than the amount of soil moisture that could be lost through evaporation and transpiration, are more susceptible to wind erosion. Areas with higher average wind velocities, like Western Kansas, also are more susceptible. We can’t control these factors directly but farm in a way to minimize their negative effects.
L, the width of the field downwind, can be addressed in several ways. The winds we typically deal with causing most wind erosion are S, SW, N, and NW depending on the season. The longer the unbroken run the wind has, the more soil it can move. First, wherever possible plant in an east-west direction. Than as the crop grows it is like a mini-windbreak decreasing field width. Second, break larger fields into smaller strips of crops and rotate so you decrease the run. This is especially important when using more tillage as it decreases the width of bare soil for wind to blow across. Finally, the one we are most familiar with is the shelterbelt. Again, established east-west, perpendicular to prevailing winds. Depending on the makeup of the shelterbelt, it will take from three to ten times the height of the belt for the wind speed to return to its original velocity. So a thirty foot high shelterbelt can protect a width from 300 to 500 feet. Unfortunately, many shelterbelts are in need of renovation or have been torn out.
V, vegetative cover, has been mentioned earlier. Cover is cover and soil well-covered with an actively growing crop will prevent erosion as described earlier.