Baseline: Conventional till = 1.036 t/y sediment delivery
Absolutely, when it comes to reducing sediment delivery, there are BMPs that definitely outperform buffer strips. Using science developed by USDA’s Agricultural Research Service and Agren®, I looked at the efficacy of buffer strips compared to other practices. Using SoilCalculator®, I modeled the sediment delivery from a 302-acre farm in Western Iowa to a nearby stream. For the baseline conditions, I assumed a corn-soybean rotation farmed with conventional tillage. The resulting sediment delivered to the stream was 1,036 tons/year, with no other BMPs modeled.
By adding a 50-foot wide buffer, the sediment delivery was reduced by 114 tons/year, or a 11% annual decrease. That’s right, only 11%.
82-100% of water enters streams through CFPs
The marginal reduction in soil loss is due to the concentrated flow paths (CFPs) within the field. CFPs have long been identified as a weakness in sediment-reducing buffers. In a study of the Cache River Watershed, in Southern Illinois, Dr. Jon Schoonover found that between 82-100% of the water flowing from fields flowed into streams through CFPs.
Runoff entering field through concentrated flow paths
Again, using my example of the 302-acre field with conventional tillage, I modeled the CFPs through SoilCalculator. Clearly, a large portion of water runoff in this field enters the stream through concentrated flow (shown in red).
When identifying alternatives to a 50-foot buffer that achieve equal or lower sediment delivery, I considered three options; two being tillage options and one option being retention structures.
Reduce tillage:
Changes in tillage provide a significant reduction in both erosion and sediment delivery. Going to just one year of no-till reduces sediment delivery by 41% (or a reduction of 421 tons/year from the baseline). Moving to two years of no-till reduces sediment delivery 10-fold (a reduction of 935 tons/year).
Retention Structures:
Two basins reduce sediment delivery by 385 t/y.
Another way to achieve a reduction in sediment delivered to the stream is by constructing retention structures, or more specifically, water & sediment control basins. In this 302-acre field, there are multiple potential sites for basins. In the image on the right, I sited 2 different water & sediment control basins. The combination of these 2 basins will reduce the sediment delivery by 385 tons/year, or a 37% reduction. As a bonus, water and sediment control basins reduce rapid runoff thereby changing/improving, the hydrology of the stream.
Costs:
It is important to consider the cost of each of the three options — a 50-foot buffer, change in tillage practices, and water & sediment control basins. A 50-foot buffer strip on this site would take 12.3 acres of land out of row crops. Assuming the farmer had no use for hay or grazing and the land was valued at $8,500/acre, the buffer could cost upwards of $100,000. (The filter strips could be hayed or grazed but then sediment delivery to the stream would increase.) The planning tools estimated the two water & sediment control basins would cost $25,000, but tile lines used to drain the basins would improve drainage and improve yields. Switching to one or two years of no-till is more difficult to quantify, given such variables as soil types, fertility, weed control and equipment needs. Some farmers say no-till is a break even compared to conventional tillage. Some farmers say no-till reduces yield. Individual farmers, as always, will need to determine the cost/benefit to their unique operation.
If we are going to advance soil and water conservation, we need to stop thinking that one size fits all. Effective conservation planning must analyze the nuances of farmland so we can make the best recommendations to farmers and landowners. The idea of conservation planning has been around for years. Some planning is done on the back of a napkin. Some planning is done with aerial photos and topographic maps. However, the ability of whole farm planning has never been realized, until now, because of lack of science-driven technology. Agren’s sustainability platform allows ag retailers to effectively and efficiently assist farmers with their resource needs and prescribe the all-important precision conservation.
Drop the tillage and plant no-till and add cover crops. See what the Soil Calculator shows. My guess is that runoff should drop about 80-90% after 2-3 years. Add a 25′ buffer for additional insurance.
Dan, I understand your passion for no-till and cover crops. They are a great combination. You have always led that charge. However not everyone agrees on the same path forward. As conservationists we need to keep the toolbox open with all available best practices at our disposal. I for one am not ready to give up on any practice; not even buffer strips. We need to use the right practice is the right place, at the right scale. That is the definition of precision conservation…not everyone should be expected to do the same thing.
Surface water filtering is only one sediment reducing result of stream buffers. One factor left out of the analysis is the effect of deep rooted perennial stream buffers in removing water from streambank soils and reducing bank slumping. That is the principal reason that ditch buffers have been in public drainage system law for many years in Minnesota.
Les, I agree there are benefits to buffers other than just filtering sediment. In certian landscapes the rooting system can have a significant reduction in nitrates. However in a tile drained landscape much of the water still reach the stream or river unfiltered.
Les, again I agree deep rooted vegetation can stabalize some streambanks. There can be significant benefits, but the efficacy of that vegetation is based on factors such as the stage of the stream. If I remember the training I recieved from Dr. Isenhart at the Minnesota conference on buffers, there are stream stages that vegetation does very little in protection; specifically stages 3 and 4. Again there is no one size that fits all.
https://riverrestoration.wikispaces.com/Channel+evolution+model
Hi Tom,
Yes, buffers are not the end all. They do however provide streambank stabilization and wildlife corridors. I think of them as last ditch sediment catchments, and yes, concentrated flow is not stressed enough.
If we add them to no-till …
If we put livestock back in the picture and use the hay …
Seems we should have the “final word” on no/strip till by now. Farmers everywhere make it work and they make more profits overall, no? If all the corn and bean acres were no till (+cover crops) we would substantially solve the water quality problem; erosion rates under a ton per acre every where, every year. We need to get our soils to breathing again.
$8,500/acre?! Whoa. Is the strip along the stream as good as the rest of the field?
Tell me more about the soil calculator. Does it let you calculate your erosion rates more accurately than RUSLE2? Quickly?
Thanks, Karl Hakanson
Karl, I agree that strip till and no-til work. However I have worked with farmers who really tried to make these tillage systems work but could not. That should not be seen as something bad, as long as that farmer is willing to use other conservation practices. SoilCalculator uses RUSLE2. It calculates RUSLE2 70,000 in 160 acres by using the slope lenght and slope steepness derived by Minnesota’s LiDAR data. It is the best estimate of soil erosion available. I am happy to talk to you more about it. I have posted past blogs on the technology.
I’m curious about the farmers who tried it an gave up – what wasn’t working for them?
Hi Jean, most of the farmers I talked to saw a reduction in yield and therefore profitability.
I’m curious where the 50 foot buffer was added in this scenario? What about grassed waterways in the concentrated flow paths? Thanks for any clarification you can provide.
Brian, I am not sure what you mean by “50 foot buffer was added in this scenario?”
When designing grassed waterways the goal is almost always to design the waterway so that the water has enough velocity to flush the sediment all the way through the waterway. The goal is to eliminate deposition so the waterway doesn’t need constant maintainence. I do not necessarlily agree with this design methodology, but it is very common. In a previous post I wrote a post on my thoughts on using grassed waterways to trap sediment. https://www.agrentools.com/old-dog-new-tricks-conservation-pioneer/
Hi Tom,
Thanks for the reply. I was referring to the part that stated “By adding a 50-foot wide buffer, the sediment delivery was reduced by 114 tons/year, or a 11% annual decrease.” I’m familiar with grassed waterway design and agree with other posts here that it is much better to prevent soil from moving in the first place with no till, cover crops, etc. rather than try to catch it after it starts moving. I was just curious if the Soil Calculator program is able to model grassed waterway performance and how that would compare to the 50 ft. buffer with 11% reduction as stated above.
Brian, thanks for the clarification. At this time SoilCalculator only uses RUSLE2 to model soil erosion. As you know RUSLE2 only models sheet and rill erosion. It does not model the ephemeral erosion that waterways are designed to prevent. Over the last year we have worked with USDA’s ARS to integrate EphGEE (Ephemeral Gully Erosion Estimator) into our SoilCalculator. When this is done we will be able to model the effectiveness of grassed waterways and then compare them to other practices. In general I can tell you the effectiveness of grassed waterways and filter strips is a bit of apples vs. oranges. As we discussed grassed waterways are typically designed to stop ephemeral erosion and not to trap sediment. On the other hand filter strips are not designed to stop ephemeral erosion, but instead trap sediment. If we wanted to design grassed waterways to trap sediment we would make them wider and more shallow to slow the velocity of water. If did slow the velocity of water, grassed waterways could be great for trapping sediment…but it would take a lot more work to maintain the waterways.
Tom
Gee you sure did get some response on this one. Tonight I am sitting in Africa. Here on a lowland irrigation problem. With these much different conditions really no compassion, other than the conservation planning approach and working with to meet stake holders needs is much the same. Some of your comments were off site and other users. I think that is great. What I did not see is anyone agree with your general premise that the drains in your example were the unaddressed problem for the individual field. I remember seeing that myself and being up the oversight to higher. I am getting much better acceptance here to logical suggestions that that particular one.
Keep up the efforts.
Great points by you and those who replied, especially Dan Towery. About 10 years ago I was asked to write an article that included analysis of research on buffers. Concentrated flow is the biggest issue. And, the first foot of buffer provides about 90% of the total value. So, having more than a few feet along a stream is wasting land.
I think everyone will agree with this point: the best place for “sediment” is right where it started. And the best way to accomplish that is for every drop of rain to stay (and infiltrate) where it lands.
So, how can you get the soil particles and raindrops to “stay in place” and still raise corn and soybeans? Continuous no-till with cover crops is the best option today. This system adds soil organic matter which also increases water holding capacity. Of course there will be some runoff and erosion, but the soil loss is measured in pounds per acre, not tons, as proven by ARS at Coshocton, Ohio.
Most other practices, including terraces and grass waterways, are designed to catch soil after it has already left the productive part of the field. Our research needs to be 100% no-till (or strip-till). Dwayne Beck, Dakota Lakes Research Farm, has been preaching and practicing this for many years.
Thanks Randall. I agree soil it is best to stop soil erosion before it starts. I have never seen the value of trapping sediment in a filter strip just 50 feet from public waters. Legacy phosphorus is an enorumous issue already. Of course in Minnesota farmers are given the option to use filter strips or alternative practices. They can make the choice.
Tom
First of all, thanks for the development of the soil calculator, which I think accurately and visually shows everyone the results of more than just soil loss, and also allows the evaluation of several end results.
Secondly, the description of CFP’s sounds exactly like the definition of an ephemeral ditch to me. The ED ( my abbreviation) is a form of erosion that has never been adequately scientifically studied during the soil conservation era of the USA. I worked my whole career in western Iowa ( Cass, Sioux, Crawford Co’s) and control of ephemeral erosion was always a priority, not because of water quality, but to keep your farm farmable.
Third, my experience in the field validates Dr. Schoonover’s research. In steeper topography, a lot of soil moves around when row cropped and tilled, you knew it because of all the rill and ephemeral erosion visible. But, you didn’t see any silt deposits anywhere. Where did all that silt go? I think we all know. The alternative proof was the same scenario, but there was a wide bottomland ( flat land) before the runoff reached the main channel. In this case, you would see large silt fans.
Keep up the good work. I read the blog every time posted. You are unique in that you have a good understanding of all sides of the soil conservation issue. Science, Farmer, Government, Public.
JF
Thanks Jay, that means a lot coming from someone with your experience.
This is another case to call transitional no-till what it is…not TRUE no-till. Hence if continuous corn or corn soy farmers suffer yield loss in the first years they probably had N immobilization or N loss from denitrification or volatilization. Typical in high residue systems due to urease enzymes in the residue. Hence as Dan Towery has pointed out.. the need to start with cover crops with legumes in the mixture or after soybeans to prime the N cycle to handle increasing residue levels with High C:N ratios on the surface such as corn after corn.
Stubble over the soil talks about increasing N rates 25% in the transition years of no-till to maintain corn yield. We lost 2 & 3 year no-till farmers in the early no-till adopters because we did not understand this one key concept to maintain yields in high C:N residue transitional no-till systems.