Last year, I wrote a column entitled Unintended Consequences. The column was about how my grandpa straightened his stream many years ago and the unintended results of that action. Of course, at the time, he had no idea of the series of events he was about to set off.
I have a feeling I could start a whole new blog entitled “Unintended Consequences in Agriculture”. I doubt I would ever run out of material. Agriculture is complicated, and it is hard to predict what is going to happen and there seems to always be unintended consequences. As I was thinking about this post on tillage erosion, I decided it was time to write Unintended Consequences-Part II. So here it is…
Quantifying Tillage Erosion
Recently Dr. Seth Dabney, USDA’s Agricultural Research Service, reminded me about a type of erosion I have not heard mentioned for years. Dr. Dabney was referring to tillage erosion. Dr. Dabney said that tillage erosion has been well researched and definitely contributes to the decline in soil health. Since Dr. Dabney is one of the brainiest people I know, I decided I should take the subject of tillage erosion seriously and do my research.
Tillage erosion is defined by the Soil Science Society of America as the downslope displacement of soil through the action of tillage.
Coming from a scientific journal, that definition is not so hard to understand. Think about it this way. When you till a sloped field, the tillage implement will drag or roll the soil further down the hill than up the hill. I guess that is simple gravity stuff I should have remembered from grade school. Please note, I am not saying that zero soil is dragged or thrown uphill. Because of gravity, more soil is displaced downhill rather than uphill. And over the years, the disproportionate amount soil displaced can be drastic.
According to Dr. Dabney, the amount of soil displaced downslope with tillage is often as much as the amount of soil displaced downslope with water erosion. Think about that! In other words, within those few days of tillage, we are moving as much soil downslope as we are in an annual erosion cycle. Incredible!
Soil displacement from tillage erosion varies with slope steepness, implement design, direction of tillage, and speed of the tillage implement. In one study conducted in the Ontario Province of Canada, tillage erosion was estimated at 54 t ha-1 yr-1 which by my calculations is equivalent to 26 tons/acre/year. Wow, that is a lot of soil erosion! That is like losing 1.75 inches of topsoil over a 10 year period.
Dr. Dabney reminded me that the RUSLE2 model, the same model used for calculating water erosion, can also calculate tillage erosion. Unfortunately this feature of RUSLE2 is rarely used and the information is seldom presented to a farmer.
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Great article. Thanks! It is time to abandon the human manipulation mentality in all enterprises and learn to work with nature.
Tom.
You are correct. Seth is brainy, and tillage erosion is a very big problem.
The study you refer to from Canada was my MSc study from 25 years ago. Since then, there have been many studies clearly demonstrating that tillage erosion causes severe soil loss. It is important to note that all forms of soil disturbance can cause tillage erosion, not just the mouldboard plow. The chisel plow can be as erosive as the mouldboard plow, so can high disturbance seeders (erosivity of tillage is determined by the variability in how much and how far the soil moves). The soil disturbance associated with hilling and harvesting root crops can cause more tillage erosion than the primary and secondary tillage operations combined.
The thing to remember with soil loss by wind, water and tillage erosion is that the areas of severe loss can be fairly localized within fields. Water erosion soil losses are severe in areas of concentrated runoff, the convergent areas where rills always form within a field. Tillage erosion soil losses are severe on hilltops. Often the soil lost by tillage erosion accumulates in those areas of concentrated runoff, masking the effects of severe water erosion. To see this balancing act between the erosion processes, go to one of these areas of concentrated flow and look to the adjacent hilltops and see which has the most observable soil loss.
All of this has important implications for precision farming. To learn more about this, read an article I wrote for the Journal of Soil and Water Conservation, or contact me and I will send you a copy.
• Lobb, D.A. 2011. Understanding and managing the causes of soil variability. In: Recent Advances in Precision Conservation. Special issue of J. Soil Water Conservation, 66: 175A-179A.
David, that is really interesting work. I am especially intrigued how tillage erosion moves soil into those areas where concentrated flow is most likely to occur, and at a later time the soil is eroded (or transported) out of the field by the process of ephemeral erosion. This adds a whole new dimension to soil erosion. In an analogy by Dr Rick Cruse, this process is like corn and a grain sweep auger. The corn flows by gravity towards the auger (tillage erosion) and then the grain sweep (ephemeral erosion) transports that grain (or soil) efficiently to another location. See grain sweep video.
Great analogy. I normally talk about delivery mechanisms and dynamic equilibriums, but I also refer to loading a gun (tillage erosion) and shooting a gun (water erosion). Other analogies used include flushing the toilet…..
I encourage everyone reading the blog to try and map tillage speed and take note of upslope speeds versus downslope speeds. Speed is probably the major factor causing tillage erosion (the cause for great variability in how much and how far soil is moved — net movement being soil erosion), and the difference between upslope tillage speed and downslope tillage speed can be used can be used as an indicator for tillage erosion.
Great comments and words of wisdom. I often give the following example to farmers when I talk with them about tillage erosion, although I am far from an expert in this area. If we have a pan like a big cake pan or pizza pan and place 2 inches or sand uniformly in the pan, we have a model of a farm field – kind of like we used in the sand box when we were kids. If the pan is flat and we run our fingers through the sand for several minutes pretending we are tilling, the depth of the sand remains uniform at 2 inches deep. However, what happens to soil depth if we tilt the pan 5 degrees or 10 degrees and do the same tillage simulation? Farmers then understand the effect of their tillage on soil movement – gravity works.
I really appreciate you taking up this important topic, as well as the contributions of prior comments. Tillage is an important geomorphic and soil forming factor in agricultural areas. I think your description is very clear.
Tillage erosion contributes to the spatial soil quality patterns you describe, but also the development of ridges at the boundaries of tilled areas that affect surface runoff flow patterns. This affects where and how runoff concentrates and alters the effectiveness of vegetative buffers.