Introduction
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.
Water Erosion - Part I
Published July 9, 2017
The Barton County Fair ends this weekend. Hopefully everyone had the opportunity to enjoy this annual tradition and support our area 4-H youth. Recently we discussed wind erosion. Today let’s start examining water erosion. We may think of water erosion as more of a problem east of this area, however, water erosion is a potentially a significant problem from here to the Rocky Mountains. We think of wind erosion in our area, especially the area south of the Arkansas River, however, water erosion is a serious problem. Interestingly, because of our drier climate (less vegetation, less organic matter, and intense rainfall events) our soils can be more susceptible to severe soil loss if not properly managed. And while water erosion is typically associated with hillier areas, any slope that allows water to flow downhill can result in soil loss.
Water erosion is the detachment, movement, and deposition of soil particles from their original site. The smaller the particle, the further it can be moved and there are clay particles from Barton County deposited most years in the Gulf of Mexico. Clay from here makes it way to the Arkansas River to the Mississippi River and to the delta. Sand, being much heavier than silt and clay is deposited much closer to where it was eroded. The sandy soils south of the river in Barton and Stafford Counties are an example of this. The bend in the river that Great Bend was named for caused the water to slow down as it moved north and around this curve and deposited the sand.
Erosion is a natural process, think the Grand Canyon. The delta of the Mississippi River, the bayous of Louisiana, formed this way. Erosion becomes a problem when the rate of erosion is greater than the rate of soil formation and is termed accelerated erosion.
There are four types of water erosion: Sheet, rill, interrill, and gully.
- Sheet erosion is characterized by the removal of a fairly uniform layer of soil from the land surface by runoff water. It often goes unnoticed unless noticeable soil accumulation occurs downslope. However, sheet erosion typically results in the greatest soil loss. It removes finer particles, silt and clay, while leaving less fertile coarser sand particles that hold less water and are the result is poorer soil structure. It is this subtle loss that can allow for significant soil loss before it is noticeable.
- Rill erosion is the concentration of sheet flow into tiny channels, typically several inches wide. Rill erosion is most common on bare soil. These channels are small enough to smooth by normal tillage and present no special challenge. This results in the movement of silt, clay, and sand particles. Sheet and rill erosion account for most of the soil lost from water erosion.
- Interrill erosion is simply sheet erosion taking place primarily between irregularly spaced rills.
- Gully erosion is rill erosion further concentrated into deeper and deeper rills until an obstacle for equipment and cannot be fixed with ordinary tillage. While dramatic and noticeable, it accounts for the least amount of soil lost.
Next week – what determines the potential for soil water erosion.
Water Erosion - Part II
Published July 16, 2017
Last week’s column focused on the types of soil water erosion. While government help in understanding and controlling wind erosion was the focus in the Great Plains after the Dust Bowl, the focus in the eastern U.S. was water erosion. A series of research sites were set up with some still conducting research into the 2000s. The main focus was initially to determine what factors determine the degree of soil erosion and then how to control it. From this work, the Universal Soil Loss Equation or USLE was developed and it is probably the easiest, most concise way, to understand soil water erosion factors. There are new and modified USLE models but the original suits our purpose here.
The USLE is A = R x K x LS x C x P where:
- A – This is the predicted annual soil loss from water erosion based upon the factors described below. The key word here is predicted. As seen below, actual conditions will determine actual soil loss.
- R – This is the rainfall erosivity factor. This is not simply how much rainfall occurs but the intensity, how much rain falls in a given period of time, and the distribution, when it falls. Here, we think of hard, intense downpours when we think of rain, however, most of the rains we receive are 0.25 inches or less and light. Rainfall the equivalent of several inches per hour is more erosive. Distribution denotes when rain falls – winter, spring, summer or fall. Rainfall when vegetation is out is less erosive then say late fall or winter.
- K – This factor describes how susceptible the soil is to water erosion. A sandy soil erodes more easily than a silt loam or clay soil. Lower organic matter levels also lead to greater susceptibility to erosion. The ability of the soil to take in water, the infiltration capacity, and soil structure also matter here. This factor is determined using a 9 percent slope.
- LS – LS is the length and steepness of slope. As the percent slope increases so does the water erosion potential. The length of the slope is just that, how far along the slope can water flow uninterrupted. A steep slope that is 100 feet in length has a lower erosion potential then a less steep slope that is 1000 feet long. When you see terraces on a cropped hillside, it is decreasing the length the water can flow.
- C – This factor takes into account vegetative cover and cropping systems. A bare soil has a high C approaching one, cover and management factor, while a well-established alfalfa field a low number heading towards zero. Is the surface covered during critical periods for runoff? Simply this is the soil loss under actual conditions divided by the soil loss with bare soil.
- P – Finally we have P, the supporting practice factor. What is being done augment C? These are practices to supplement the cover and cropping system when that isn’t enough to control erosion.
Please remember this is a very brief description of the USLE. First a question to consider. What happens to erosion when any one factor goes to zero? Next week, using this equation to manage soil erosion.
Water Erosion Part III
Published July 23, 2017
Today’s column finishes up the discussion of water erosion with how to minimize soil loss based upon the USLE, the Universal Soil Loss Equation - A = R x K x LS x C x P. To mitigate the predicted annual soil loss, A, we will briefly deal with each factor of the equation.
- R – This is the rainfall erosivity factor. First, if it doesn’t rain, there is no water erosion. We cannot change when rainfall occurs or how intense it is. Simply, harder, longer lasting rainfall can result in more erosion. Harder because the greater the force the raindrops strike the soil surface with the more energy is available to break soil particles loose and longer because once the rainfall rate exceeds the ability of the soil to take in water, infiltration, water will flow and take soil particles along. We can’t change these factors but if we place a barrier, vegetation or crop residue on the surface, we can absorb the energy and soil can remain in place. A simple analogy if why a catcher in baseball wears a mask chest protector, they are going to be hit. The protective equipment absorbs much of the impact of the force of the ball. Not all of it but enough to normally prevent serious damage. Especially making sure the soil isn’t bare when the most likely erosive rains normally occur. And by promoting good soil structure, conservation tillage or no-tillage, we can increase the ability of the soil to take in water and store it.
- K – The soil erodibility factor describes how susceptible the soil is to water erosion. Producers can’t change the soil texture but can over time through crop rotations and reducing tillage increase organic matter to stabilize/improve soil structure and allow it to hold more water. They can accumulate residue at the soil surface to absorb rainfall impact and prevent surface crusting. If producers can eliminate tillage they can increase the number and connectivity of macropores which increases the infiltration rate and decreases runoff.
- LS – LS is the length and steepness of slope. Planting along the contour or at least across the slope where possible helps break up slope length. Those terraces you see on hillsides, mounded up soil across the slope, decrease slope length and trap dislodged soil. In some cases, establishing permanent vegetation such as perennial grasses is the best solution.
- C – This factor takes into account vegetative cover and cropping systems. This is discussed above. The key is to make sure the soil is covered and protected.
- P – Finally we have P, the supporting practice factor. What is being done augment C? This can be grassed waterways, buffer strips and other practices which supplement cropping practices.
Wind and water erosion are natural phenomena and only present problems when they become accelerated, where erosion is greater than soil formation. There is no way to totally eliminate erosion but it can certainly be minimized.