Each year, my pharmacist, Dr. Jennifer Filloon, demands that I get a flu shot; no excuses. Flu shots are truly a part of precision medicine. Flu shots are designed to do one thing – prevent the flu. And the benefits are clear:
- The flu shot targets seasonal flu strains predicted by researchers.
- The flu shot has no appreciable side effects.
- Getting an annual flu shot boosts immunity to the flu and can prevent, or minimize, the flu.
- Getting the flu shot is simple and inexpensive.
In a recent webinar, Dr. Steven Hall (Assistant Professor of Department of Ecology, Evolution, and Organismal Biology at Iowa State University) talked about the disproportionate environmental impacts from partially drained prairie potholes. In Iowa, these depressional areas comprise about 9% of the Des Moines Lobe, a geologic region in central Iowa where prairie potholes have been drained and cropped. Dr. Hall shared with me the early results of his research on this region, which shows that farmed depressions (former prairie potholes) can potentially contribute 3 to 4 times more nitrates to water (on a per acre basis) than the adjacent uplands. Additionally, Dr. Hall’s findings indicate these poorly drained potholes contribute a disproportionate quantity of greenhouse gases, to our atmosphere, in the form of nitrous oxide.
These depressions start with a 3-fold level of extractable soil nitrate over the adjacent uplands even at peak growing times. Dr. Hall says this condition is even further amplified, when the excess water stunted or completely drown out the crop. There is little or no vegetation left to utilize the available nitrogen.
Now, if only we could prevent against the negative effects of poorly drained depressional areas, like we do for influenza. Could we prevent nitrate leaching or reduce greenhouse gasses with an effective, innocuous, simple and inexpensive conservation practices? What if we inoculated the cropped prairie pothole regions with precision conservation, year after year, after year? Would it make a difference?
Unfortunately, scientists do not yet have enough data to recommend a precision conservation solution, analogous to a flu shot; which likely precludes a one-size-fits-all solution. Instead, farm-specific situations will be critical to consider when trying to mitigate the effects of cropping pothole regions. But Dr. Hall is encouraged and speaks about current research that will help us understand how to better treat these areas. He suggests at least 4 possible solutions:
- Conservation tillage: Improve soil structure to achieve better infiltration of water.
- Improve drainage of upland wetlands and offset impacts with downstream restored or constructed wetlands at tile outlets.
- Return to natural wetlands conditions (CRP or other perennial vegetation mixes).
- Plant Flood-tolerant crops, including vegetation for use as biomass energy feedstocks.
Solution #1: Conservation tillage to improve soil structure thereby increase water infiltration.
If the crop is stressed or drowns out from saturated or flooded conditions, less nitrogen is removed from the system dramatically increasing the likelihood of leaching or denitrification.
Pros:
- In theory, increased soil health will lead to less saturated conditions; creating a healthier environment for the crop. The healthier crop will better utilize the available nitrogen. When less nitrogen is available less nitrogen will leach or be emitted as nitrous oxide.
Cons:
- Our tiling systems in the Des Moines lobe is undersized. If a large percentage of farmers go to conservation tillage, improving infiltration, it will only further overload the tile system somewhere else, just transferring the problem. There may be no positive net gain from this strategy.
Solution #2: Improve drainage of upland wetlands and offset impacts with downstream (CREP) wetlands.
The tile drainage in most prairie potholes is under-designed. Like Solution #1 if we can create a healthier environment for our crops, those crops can utilize the available nitrogen in a more efficient manner. This could lead to less nitrogen leaching and denitrification. To mitigate the effects of increase tiling downstream (CREP) wetlands could be developed.
Pros:
- Better drainage of prairie potholes will likely lead to better yields and better profitability for the farmer.
- Less stressed crops will lead to better nitrogen utilization.
- On a per pound basis, of nitrogen removal, downstream (CREP) wetlands may be the most cost-effective practice we have in our toolbox. Likely, it is significantly cheaper to install a few downstream wetlands vs. restoring numerous upland prairie potholes.
- These downstream CREP wetlands often reduce the pressure on the upstream tiling systems, creating a circular effect of better draining the upland prairie potholes.
- These downstream (CREP) wetlands provide significant wildlife habitat.
Cons:
- The initial out-of-pock costs for developing these downstream (CREP) wetlands are very expensive. The typical downstream (CREP) wetland requires an average of 45 acres. At $10,000/acre, these wetlands require nearly $1/2 million of upfront investment. Annually, it doesn’t take many of these wetlands to drain an entire conservation budget.
- The downstream (CREP) wetlands require specific landscape conditions. These wetlands cannot be built just anywhere. Finding the combination of a willing landowner and the out-of-pocket cost can be challenging.
Solution #3: Return prairie potholes to natural wetlands conditions
Pros:
- If the crops are being stressed or drown out, then returning these potholes to native conditions could reduce the loss of nitrogen.
- Farmers will not apply commercial nitrogen to these areas.
- Depending on the specific site, it may be more cost effective to not farm these areas.
- These areas will significantly add to wildlife habitat.
Cons:
- When these prairie potholes are returned to wetlands, they are hard to farm around. If they are dry enough, likely the farmer will drive through them enough severely stunting or killing the vegetation.
- It is unlikely farmers will give up cropland without some type of incentive program like CRP. And if these incentive programs are not permanent (CRP is typically 10 to 15 years) then this will not be a permanent solution.
- And if the prairie pothole (and surrounding area) is saturated, and not flooded, the wetlands might continue to emit greenhouse gasses, albeit at a lesser rate, regardless of the vegetation.
- In most cases these prairie potholes are in flat topographies. Inundating these potholes may cause adjacent farmland, a bit higher on the landscape, to become saturated. This again will lead to stressed or drown out crops adjacent to the wetland just moving the problem of leaching and denitrification further upland.
Solution #4: Plant and harvest flood-tolerant crops and use the vegetation for biomass energy feedstocks
Pros:
- Most of us desire renewable biofuels. The planting of a flood tolerant crop that can be used as a cellulosic (or combustion) energy source holds great promise.
Cons:
- The economics of cellulosic vegetation is largely unproven.
- Developing a third crop is far more difficult that it appears. Harvesting vegetation in saturated or flooded conditions will require completely new planting and harvesting equipment.
- This is a long-term strategy with great promise and plenty of opportunity to fail.
Just because it is difficult…
If we are going to solve our water quality issues it is clear, we need to focus on these areas that contribute disproportionate levels of pollution. If these poorly drained depressional areas are contributing 3 to 4 times more nitrogen to our water and air, than the adjacent uplands, we simply cannot ignore them. However, in my conversations with Dr. Hall, all potential solutions have substantial associated costs and trade-offs. We have not yet identified the simple and effective flu shot. For now, our best recommendation will depend on the site-specific conditions.
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Not to be too cynical but where was your voice 2001 when GPS yield monitors first provided objective data on the economics of farming prairie potholes. A proposal to make potholes eligible for CRP was developed and taken through the county and state USDA review processes. It was approved and sent on to Washington for inclusion in the CRP payments program where it was promptly hijacked by the “ducks” people for duck habitat. To my knowledge, it was not supported by a single individual or ag organization in Iowa (or ISU for that matter). A farmer survey showed that if the set aside boundaries were set up correctly (to account for equipment widths and pothole contours), farmer acceptance would be near 100%. An associated implementation project sought funding for and identified specific techniques for defining optimized cover crops, down slope movement of nutrient rich soil into potholes, controlling water release into open tile line intakes (to minimize sediment/phosphorous) commonly found in prairie potholes, and more.
Interesting point about the ducks people. So did more harm than good.
So, if farmers can use GPS yield monitors to provide objective data on the economics of farming prairie potholes, and these potholes are not cost-effective to farm, why do we need a government program to pay farmers not to farm them?
According to the latest Iowa CREP report, https://iowaagriculture.gov/sites/default/files/water_resources/2017%20annual%20report%20062118%20correction.pdf
the ratio of CREP wetland plus buffer area to protected watershed area is about 3%. The cost needs to be evaluated on that basis (area protected and nitrate removed). The average wetland plus buffer area was 39 acres in that report. The buffer area was three times the wetland pool area averaged across the 86 reported wetlands. In some topographies, that could be reduced. The wetlands can also reduce the peak flows in streams, reducing the amount of streambank erosion and channel widening we are seeing in Minnesota.
Les, thank your for pointing out this information. I absolutely agree that CREP wetlands are an excellent practice for many reasons, including wildlife habitat, downstream flooding, nitrogen removal, reducing upstream and downstream pressure on tile lines, and increased farmer acceptance. The only downside is the upfront cost is considerable. I am not sure how we overcome that.
As of now, Iowa’s seasonal cropfield wetlands provide important habitat for migrating shorebirds. And those long-distance-migration shorebirds need all the help they can get, because around the world, their populations are crashing.
https://www.nytimes.com/interactive/2018/04/27/opinion/shorebirds-extinction-climate-change.html
I’ve talked with a shorebird expert at ISU. Shorebirds are not so able to use big deep CREP-type wetlands. So replacing many small shallow wetlands with fewer bigger much-deeper tile-outlet permanent wetlands could be problematic for shorebirds.
Even some good habitat projects can have adverse shorebird impacts. In Story County, one poorly-drained wet farmland area that used to be excellent migrating shorebird habitat stopped being so good for some kinds of shorebirds when it was acquired as a public area and became covered with tall permanent vegetation. It’s wonderful wildlife habitat now for many bird species, but ironically, for some shorebirds, it’s not as good as it used to be.
I’ve learned that on my own land. I own a small restored prairie-wetland complex with four small wetlands ranging from deep to shallow, set in diverse tallgrass prairie. It has hundreds of migrating ducks, geese, and other waterfowl in the spring and fall. But if I want to see migrating spring shorebirds, there are far more of them on area cropfields that have shallow temporary flooded wetlands.
I don’t know what the answers are. As this “flu” post points out, there are various options for partially-drained depressional areas, and there are upsides and downsides to all of them. Maybe there are ways to accommodate shorebirds while at the same time helping farmers and helping to reduce the nitrogen and greenhouse gas problems. Fire management might help. Other measures might help.
What I do strongly believe is that if public money is going to be used to help solve the problems caused by partially drained depressional areas, not making things worse for shorebirds should be one of the priority goals. It should be just as important as the other goals.
It would be great if migrating shorebirds could actually be helped. But at least, if public money is used, the shorebird situation in Iowa should not be made worse. Apart from the other reasons, adding more species to threatened and endangered lists is an unhappy prospect for everyone.
Cindy, I fully agree with you on shorebirds. This summer/fall my brother Stan (who is one of Iowa’s best wildlife photographers) spent many, many hours sitting at one these flooded potholes with the sole purpose of taking photos of waterfowl/shorebirds. He was able to capture some outstanding pictures from one drowned out pothole 3 miles outside of Carroll. However as you indicate, it is difficult to have your cake and eat it to. I do not know of any research that allows us to preserve these mud flats for shorebirds while at the same time control nitrogen leaching and greenhouse gas emissions from these same areas. For now I am not sure how we balance the two. It is hard to tell farmers to reduce their impact on water quality and greenhouse gas emission while at the some time we tell them to preserve and protect areas that are causing a disproportionate amount of these pollutants. It sounds like a need for more research.
Dr. Hall reminded me that this research is still early. Maybe more research will lead him to a different conclusion. I will ask both Stan and Dr. Hall to comment.
I spent a lot of time photographing birds at the site mentioned above. I cannot speak definitively regarding the quality of habitat but can say there were quite a few bird species that used this seasonal wetland (made seasonal by partial drainage). If left alone, this farmed wetland would have a lot of native wetland vegetation growing in it. The mudflats used by shorebirds are only made possible by the yearly deep fall tillage, followed by spring tillage. This suppresses growth of the wetland species. The corn drowns out most every year, thereby leaving nominal residue. The result is the exposure of dark black soil loved by shorebirds. These mudflats could be mimicked in CRP or WRP fields, IF USDA regulations were altered, allowing for deep tillage along the edge of the wetland. I am guessing there are not too many landowners who would care enough about shorebirds to go out and till these edges though.
As with any practice (especially those that do not have complicated management involved), there are trade-offs. Not every practice that improves water quality will improve wildlife habitat and vise versa. And, not every species of wildlife will respond positively to the same practice. The early research indicates that these mudflats (saturated areas) contribute a disproportionate amount to nitrogen loss. Keeping these areas black may benefit shorebirds but this is detrimental to other wetland species.
I guess this speaks to the need for a multitude of practices from which we can select. Each landowner can select the practice/s that help them meet their goals. There is no sliver bullet that meets all needs.
Thanks Stan for you comment. There are always trade-offs to be made. It is what complicates resource management.
Tom, Nice piece. There is always one more detail. One feature of the Des Moines-Lobe I felt was unique was the soils formed around these potholes. The harps series had a very high pH. The soils lower in the pothole, such as Okoboji had very high organic matter levels. Do these, if at all, unique chemical and phycological levels affect the nitrate runoff levels? Are there management considerations because of these features?
Second question seeing more development on the drainage in these depressions. The old original pre thirties standard was a prairie drainage coefficient of 1/4″ per acre. This was increased to 3/8″ for upland loams as much as one or two inch drainage for the landlocked potholes. While most of the pre-1985 drained areas are now fully improved, what does science tell us of nitrate deliver rates?
Dave, good questions. I will have to think about these and maybe do a little research.
Agreed, these soil differences could be really key. The high organic matter content of the Okoboji soils relative to upslope series (Clarion, Nicollet) suggests that N mineralization rates may also be greater in these depressions, as noted below by Dr. Jaynes. Our preliminary data are consistent with this idea–potential N mineralization tends to be greatest in the depressional soils.
The question about drainage intensity is really interesting. If increased drainage rates significantly decreased crop mortality in periodically flooded depressions, we might expect decreased nitrate export given the capacity for greater N uptake in crop biomass. You could make the case for other scenarios, however, and we need more information in this area.
Again, thank you Dr. Hall. There is certainly a lot of interest int this topic. I hope we can keep the readers up-to-date as your research continues.
There is one other partial solution that you missed and that is to not to apply N fertilizer in potholes when growing corn. Our research showed that when potholes do not drown out they are usually the highest yielding areas of the field. But the most economical N fertilizer rate to apply in those years was 0. Because of their high organic carbon levels, deep soils, and large capacities to mineralize N, no additional N is needed. Thus, in the years when they do flood out at least no commercial N will be lost.
Dan, thanks for your perspective. I would be interested in Dr. Hall’s input on the amount of impact this may have.
Great point, we addressed this briefly in the webinar that Tom has commented on above. In addition to the high N mineralization rates characteristic of these depressional soils, they also receive a subsidy of nitrate from upslope soil (nitrate moves downhill in surface and shallow subsurface flow). Variable rate N application, with reduced or no N application to depressions, might be a useful place to start from a management perspective.
Dr. Hall, thank you for this information.