Weather whiplash

Weather whiplash

cover crops near Nevada
Nice looking rye cover crop near Nevada, IA
November 2020

A big thank you to farmers who planted cover crops after this challenging year. Cover crops will hold soil and nutrients in place through the winter and early spring. That could be especially important this year.

After a drought, nitrogen that might normally have been taken up by a high-yielding crop or flushed away by rainfall remains in the soil. That leftover nitrogen could be available for next year’s crop, but only if:

A) we have a dry spring, or

B) farmers have made use of practices like cover crops or nitrification inhibitors that prevent nitrogen losses during the fallow season.

A wet year in 2013 following a dry year in 2012 (dark blue) caused nitrate concentrations in many central iowa streams to jump as much as 10 mg/L higher than usual (red). Figure from Van Metre et al. 2008

A drought in 2012 following by a wet spring in 2013 led to nitrate concentrations in excess of 20 mg/L in many rivers in Central Iowa. If we have a wet spring in 2021, we could see this happen again. As one scientific paper put it, “weather whiplash drives deterioration of water quality.”

“Weather whiplash” can also help explain the long-term trends I’ve been seeing in the South Skunk River and its tributaries: a decline in nitrate concentrations from 2005-2012, a big jump in 2013, and another decline over the past 7 years. I’ll walk you through my analysis.

Explaining nitrate concentrations in the South Skunk River

Technical details, feel free to skip: This data was collected by the City of Ames just upstream of wastewater treatment plant. The City has monitored the South Skunk River above and below its wastewater treatment plant almost every week since 2003! Flow is measured continuously at a few miles upstream USGS gage near S. 16th St. I’ve summarized nitrate concentrations and streamflow by season (Jan-Mar, Apr-Jun, Jul-Sep, Oct-Dec). At each step of the way, I apply a linear regression equation and graph the model residuals. Taken together, these three factors explain 59% of the variation. The effects of “weather whiplash” may extend beyond one year, since nitrate from some parts of the field may travel more slowly to streams via groundwater.

In a given quarter, nitrate concentrations in the South Skunk can be up to 10 mg/L higher than the long-term average, or as much as 10 mg/L lower. The following graphs show how much variation is left to explain after correcting for current weather, last year’s weather, and season.

Nitrate in the South Skunk is again declining after a sudden increase in 2013.
Low-flow conditions in 2011-2013 explain unusually low nitrate concentrations.
Wet springs following dry years explain unusually high nitrate concentrations.
Seasonal patterns explain some of the remaining variation.
  1. The lowest nitrate concentrations can be explained by streamflow: when the weather is dry and tiles aren’t flowing, nitrate levels in rivers taper off to the background levels seen in groundwater.
  2. The highest nitrate concentrations can be explained by weather over the previous 12 months: a wet period following a dry period will flush out nitrate that’s accumulated in the soil.
  3. After that, there’s still a seasonal pattern independent of rainfall: nitrogen is most susceptible to loss in spring when soils are bare and microbial activity picks up (April-June) and least susceptible when the maturing crop is using up the available nitrogen (July-Sept).
  4. Can some of the remaining pattern be explained by greater adoption of conservation practices in the watershed in the past 5 years? We hope so, but let’s see what happens next spring!

Too close to call

Too close to call

Disclaimer: This article is not about politics. PRI is a non-partisan organization and does not want to get drawn into a discussion about the election. My intent here is to use an example that’s fresh in our minds to illustrate a challenge for progress tracking in water quality.

Polls are not always accurate. If you didn’t know that before November of 2020, you do now.

There are plenty of parallels with water, so if you’re looking to water quality monitoring to tell you whether or not conservation efforts in your watershed or your state are succeeding, read on.

Bottom line: Short-term water quality trends are usually too close to call.

Quinnipiac University can’t talk to every eligible voter in Florida, so they surveyed 1,657 people the week before the election.

Similarly, it’s not practical to test water quality in a stream 365 days a year, so we often make do with just 12 days a year. There are sensors that can test nitrate or turbidity continuously during the ice-free months, but they’re not cheap.

The voting patterns of those 1,657 people won’t be perfectly representative of Florida. How close do they expect to be? Based on the sample size, Quinnipiac calculates a margin of error: in this case 2.4 percentage points. Talking to more people would reduce the margin of error, but not enough to be worth the cost. In this case, Biden’s lead appears to be outside the margin of error.

Support for candidatePoint estimate95% confidence interval
Biden47%44.6% to 49.4%
Trump42%39.6% to 44.4%

Similarly, the 12 days we test water quality won’t be perfectly representative of the year. How close can we expect to be? We can calculate a margin of error (here, the 95% confidence interval) around our water quality average. Did phosphorus decline in 2019? Too close to call!

Phosphorus in South Skunk RiverPoint estimate95% confidence interval
2019 average0.30 mg/L0.20 mg/L to 0.40 mg/L
2018 average0.36 mg/L0.26 mg/L to 0.46 mg/L

Oops! This poll missed the mark, and by more than the margin of error. Trump actually won Florida with 51.2 percent of the vote. Well, some errors are unavoidable. If sampling error were completely random, we’d expect about 5% of polls to miss by more than the margin of error. That’s what “95% confidence” means. However, according to a new study of 1,400 polls from presidential primaries and general elections, 40% of polls conducted a week before the election missed the mark by that much.

That’s because sampling error isn’t all random. People who ultimately voted one way may have been less likely to appear on the list of phone numbers, less willing to respond, less likely to say what they truly intended, or were more likely to have changed their mind in the final week. And then there’s undecided voters, who don’t always split evenly between candidates. Any of these things can skew the results. Pollsters try to correct for some of these things by weighting various demographic groups, but it doesn’t always work. For “margin of error” to mean what we think it means, according to Kotak and Moore, it would need to be at least two times wider.

Similarly, if monthly samples are not collected on a fixed day of the month, you might underestimate phosphorus or sediment load by planning your week to avoid getting wet, and over-estimate it by going out of your way to capture a sample during a storm. This challenge is well understood in environmental science and there are sampling strategies and equipment to get around it.

What’s not widely appreciated is just how big purely random sampling errors can be. I’ve read the literature and run my own numbers. Even with a 3 years of sampling, you’re lucky to get below a 20 percent margin of error. The problem is more severe for phosphorus and sediment (which move with runoff and vary a lot within a month) than nitrate (which moves with groundwater and drainage water, and is less variable).

Knowing this can help us set realistic expectations. As much as we’d like to know whether conservation efforts on the land are translating into improvements in water quality in the river, we’re not going to be able to tell the difference between a modest improvement and no improvement unless we sample often enough or long enough to bring down the margin of error. Figuring out whether this is worth doing, how to sustain it, and what other things we can learn from water monitoring has been the task of PRI and our partners around Story County working on a ten-year monitoring plan.

A final note. Have some sympathy for pollsters and scientists who are doing their best to base their findings on data, acknowledge the uncertainty in their conclusions, and strive to be less wrong. There are plenty of people on both sides of the aisle who confidently make predictions based on anecdotes, are wrong more often than not, and never admit it. 😉

Fall 2020 Water Quality Snapshot finds sensitive critters

Fall 2020 Water Quality Snapshot finds sensitive critters

Thirteen volunteers braved the cold on October 24 to test water quality in Squaw Creek, the South Skunk River, and their tributaries. For some, this was their 14th Fall Water Quality Snapshot. For others it was their first time doing stream monitoring. What we found defies easy categorization.

Update: The name “Squaw Creek” was officially changed to “Ioway Creek” in February of 2021, to be more respectful to native peoples. Over the next year, expect to see some changes to the names of the Squaw Creek Watershed Coalition and other groups that have formed to protect the creek, as well as maps and signs.

volunteers collecting invertebrates in Squaw Creek with a kick-net
Volunteers Diane Birt, Paul Readhead, Liz Calhoun, and Rick Dietz take turns brushing off rocks to capture bugs in our net. The water was freezing!

By some indicators, water quality in Squaw Creek was good. Since I wasn’t sure how many creeks would be flowing when I planned this event, I added bug collection to the agenda to keep us busy. Excuse me. Benthic macroinvertebrate sampling. We were pleased to find tiny stoneflies and mayflies. They’re good fish food, ask any fly fisherman! Excuse me. An important part of the aquatic food web. These insects also act as a sort of canary in the coal mine. They need water with a lot of dissolved oxygen so will be rare or missing in streams with too much pollution, murky water, or not much in the way of habitat.

Fun fact: while the adult mayfly is notorious for living only 24 hours, the juvenile form (naiad) lives in the stream for several years. If you’re curious what adult mayflies and stoneflies look like, I found some photos from our neighbors in Missouri.

Vials containing tiny mayflies and stoneflies

By some indicators, water quality in Squaw Creek and it’s tributaries was bad. As in, there’s poop in the water. Excuse me, fecal indicator bacteria. This month, E. coli bacteria in Squaw Creek continued to exceed the primary contact recreation standard, and College Creek jumped above secondary contact standard. I wondered if this spike might be due to accumulated… debris… being washed out of the storm sewers and off the landscape by the 1.25 inch rain we received Thursday and Friday, but the lab samples were actually collected on Wednesday Oct 21, so I’m not sure. Anyway, covid-19 is not the only reason I bring hand sanitizer to these events!

By some indicators, water quality was unusually dry this fall. Nitrate was too low to detect at 13 of 16 sites we tested. Under wetter conditions, as we had this spring or last fall, nitrate in these same streams was higher and differences due to landuse or conservation practices in the watershed become more apparent.

SiteWatershedFall 2020Spring 2020Fall 2019
Squaw Creek @ Duff AveRural and urban0105
Bluestem Creek @150th StRural2105
Glacial Creek @ U AveRural (with a constructed wetland)022
College Creek @ UniversityUrban022
Nitrate-N concentrations, in mg/L

Water quality is rarely all good news or all bad news. Citizen science can us a more complete picture.

Thanks to all our intrepid volunteers!

E. coli in context

E. coli in context

Edited 2020-10-16 to clarify a few sections, add references as links, and correct statements about trends. It has gotten worse

People swim, paddle, and wade in Iowa lakes and rivers. I’ve seen a lot of that this summer. We’d like those waters to be clean enough that it doesn’t pose a health risk. But see enough E. coli data, and it’s tempting to give up. There’s raccoons in the storm sewers, and geese on the lakeshore, and livestock on the farms, so therefore there will be poop in the rivers and lakes. How on earth would you ever figure out where it’s coming from, let alone improve the situation? I’ve said this once or twice, and I’ve heard it from experts I’ve consulted.

So hat tip to Chris Jones for putting our numbers into context. I love context! Let me add some more! (Check out his blog post to for some excellent background on what this bacteria is, and why we measure it).

It’s bad, and don’t blame the geese

cow in a stream
Cow in an Iowa stream. Photo credit: Rick Dietz

I was inspired by Chris’s graph, which compares E. coli in the Raccoon and Des Moines Rivers in Des Moines to the Mississippi River in Minneapolis. That river has plenty of geese and raccoons, as I can attest to from having lived in the Twin Cities. So clearly there’s some additional sources of fecal contamination in these Iowa waters that we could do something about, if we had the will.

graph by Chris Jones. Raccoon River in Des Moines exceeds the standard 50%, while Mississippi in Minneapolis exceeds 10% of time
Figure by Chris Jones. Percent of samples collected from 2010-2020 during recreational season that exceeded 235 CFU/100mL.

It’s very bad some places, fine in others

I love this metric: percent of days in the recreation season that E. coli exceeded the standard. Nobody knows what a geometric mean is, or how many samples you need before you can apply it. This is a simpler way of acknowledging that sometimes there will be poop in waters where people wade or swim (say because there are racoons in the storm sewers and it just rained) but we’d like that to be less often. Using my new powers of R scripting, I computed this metric for every water body in an Iowa DNR database that had at least 50 E. coli samples during April-Oct of 2010-2020, and when I couldn’t fit 160 bars on a graph, I pulled out an arbitrary selection to give you a sense of the range.

As I feared, the South Skunk River below Ames is even worse than the Racoon River, exceeding the standard 75% of the time, as are several rivers in central, western, and northeastern Iowa. As Chris mentioned, E. coli is lower downstream of reservoirs, which allow sediment to settle and light to disinfect. Some of the cleanest waters aren’t on here because DNR rarely finds anything, and thus has scaled back testing. This includes destination spots like Okoboji Lake, and my favorite local beach, the former gravel pit at Peterson Park, which is mostly groundwater fed.

It hasn’t gotten worse, has it?

I have fond childhood memories of wading and canoeing and fishing in Iowa rivers and lakes, including the South Skunk River. How bad was it then? I don’t know. I do have data from 2000-2004, when I was an ISU student hauling trash out of the river and planting willow stakes with Jim Colbert’s “Skunk River Navy.” At that time, the South Skunk upstream of Ames met (today’s) primary contact recreation standard, but started to exceed it in 2006. The South Skunk River downstream of Ames and below the confluence with Squaw Creek has exceeded the standard in every year it’s been measured, but was twice as high the last two years as it was in 2000-2004.

Here I’m using the geometric mean for April-October and the 126 CFU/100 mL standard that applies to it, since I already had that calculated. Apologies if you have trouble keeping track of the various standards.

The DNR was monitoring the South Skunk upstream of Ames at Riverside Drive for a special project, which ended in 2014. However, we’ve been monitoring that site and several others in Story County this year. So far, it’s higher there than it was in 2000-2004, barely meeting the standard, but I have one more month left in the “recreational season.” Every other site we monitored (that didn’t dry up this summer) was 2 to 9 times higher than the standard.

Confession: I am unwilling to give up playing in rivers or deny that experience to my kids because of a fecal bacteria problem that seems unlikely to be addressed. As a whitewater paddler, I’ve always been willing to take some risks to enjoy nature, and am not sure how the risk of waterborne illnesses compares to the more obvious risks of drowning and injury. I now make sure to pack hand sanitizer on river outings, and try to keep my head out of the water, but hey, sometimes your boat tips over and that’s part of the fun!

Can you keep your head above water?

Primary contact recreation uses “involve full body immersion… such as swimming and water skiing.” The same standard applies to smaller creeks “where children’s activities are common, like wading or playing in the water.” Small kids tend to splash and put their hands in their mouths. Water designated for secondary contact recreational uses, “such as fishing and shoreline activities” have a less stringent single sample E. coli criteria of 2,880 CFU/100mL. The South Skunk River exceeds the secondary contact standard less than 10% of the time, so if fishing is all you’re doing, you can worry less.

Graph comparing streams to secondary contact standard

Wait, can I do that? Apply secondary contact criteria to a water body designated for primary use? The DNR doesn’t, even when it would make sense. Long Dick Creek is on the Impaired Waters List for E. coli levels above 235 but below 2,880. In reality, it’s too small to float a canoe and has no public access. If this decision affected anyone’s permit, someone would have asked for an assessment to rebut the presumptive designated use, but it doesn’t, so it will remain on the Impaired Waters List for the foreseeable future, last in line for a cleanup plan (TMDL). This underscores a frustrating truth about the Impaired Waters List and the broader Clean Water Act. It was set up to regulate point source polluters like wastewater treatment plants and industry. It’s not a very good framework for educating the public about risks, or for cleaning up waters affected by other (non-point) sources of pollution.

How risky is manure?

Which brings us to risk. Not only is it hard for most people to evaluate risks when they have the numbers, we don’t have numbers that are relevant for Iowa.

What does EPA mean by “protective of human health” when considering E. coli and contact recreation in a lake or stream, where immersion and ingestion of the water is likely? In this case, a threshold of 235 CFU/100ml (or a geometric mean of 126) would be expected to produce illness in no more than 36 people in 1000 (i.e. 3.6%). So meeting the standard does not equate to zero risk.

Chris Jones, “Dream On

I’ll have to dig up the references, but as I recall, these risk calculations were based on epidemiological studies of GI infections at swimming beaches that were sometimes affected by human waste. Part of the debate in the scientific literature is whether those same rates risks apply when the source of E. coli is animal waste.

It’s a question of relatedness. Assuming there’s poop in the water and assuming you swallowed some water, and assuming the animal in question was sick, you’re less likely to contract an illness from poultry and geese manure than swine manure, which is less risky than cow manure, which is less risky than untreated human waste. On the other hand, here’s some research linking pathogens in central Iowa streams to swine manure.

Also, a single threshold is not that helpful for evaluating risks in the many waters that don’t meet the standard. If E. coli a stream is 10 times the standard, is my risk ten times as high? Probably not. Twice as high? The original EPA studies are no help here because not only is the risk model hard to interpret (I’ve tried), the numbers we have here in Iowa are well outside the range used to calibrate the model!

What are we gonna do about it?

As part of Story County’s 10-year Monitoring Plan, we’ve been monitoring E. coli in several local streams. Our partners at ISU, Story County, and City of Ames will be exploring the use of optical brighteners to track down wastewater discharge. We know there are some bad septic systems and aging sewer pipes contributing to high E. coli levels in the South Skunk River and Squaw Creek, and since those pose a higher health risk and are perhaps easier to address than livestock manure, that’s where we’ll start. But I’ve love it if we could talk about manure too, without it being seen as controversial.

I appreciate that Chris Jones brought up E. coli. Amid all the talk about nutrients, we often lose sight of another pollutant whose impact is easier to see locally.

Prairie Rivers of Iowa and Story County Officials are Organizing County-Wide Water Quality Monitoring Effort

Prairie Rivers of Iowa and Story County Officials are Organizing County-Wide Water Quality Monitoring Effort

Story County leaders are beginning to develop a ten-year water quality monitoring program for the county.  The program will be the first of its kind in Iowa in which a county, its jurisdictions and supporting organizations have worked together to create such a planning document.  The Ames based nonprofit Prairie Rivers of Iowa has organized and is facilitating the effort with planning team representing members from Story County, City of Ames, City of Gilbert, City of Huxley, City of Nevada, Leopold Center for Sustainable Agriculture, Izaak Walton League and the Story County Community Foundation.

According to City of Ames Municipal Engineer Tracy Warner Peterson, “Much more can be achieved as we work in collaboration rather than have all of the weight on one organization’s shoulders. The vast knowledge of team members through the collaboration brings together so much more potential than if we were each independently working to improve water quality.”

South Skunk River in Ames, Iowa
The team is focusing on establishing a ten-year plan to create a pathway for data collection for use towards education and guiding water quality improvements throughout the county. “It’s pretty clear that the quality of our water effects our quality of life – we drink it, we are made of it, we recreate in it, we count on it for production of our food, for green lawns and for trees which clean our air, and so much more,” relates Story County Conservation Director Mike Cox,  “Therefore we want to understand our water quality so we can make improvements where needed”.

A primary goal for the plan’s creation includes supporting the quality of life in Story County by aligning water quality monitoring efforts with recreational, environmental education and watershed improvement projects. Secondly, the team plans to provide residents with tools to understand water quality concerns and solutions while actively participating in citizen science to improve local streams and lakes. “As water quality information becomes more available, land owners/residents in the watershed can then learn what we are each able to do to reduce nutrients thereby improving water quality that results in healthier habitat and enhanced recreational opportunities in our communities,” states Peterson.

Creeks run through many of the county’s public lands, city parks and backyards. They can be full of fish or lifeless, clear or muddy and choked with algae, safe for kids to play in or full of pollutants depending on the water quality as runoff enters the watershed.

NRCS photo
Many area farmers and developers are implementing conservation practices that address water quality problems.  The team plans to celebrate the progress taking place and identify new areas where conservation practices can be most effective.
Even the smallest creeks and drainage ditches can influence water quality downstream. Bacteria ending up in the South Skunk River affects the use of the newly dedicated water trail while nitrogen, phosphorus and algae blooms winding down to the Gulf of Mexico contribute to the “dead zone” where water holds too little oxygen to sustain marine life.
State agencies only have resources to monitor the biggest rivers like the South Skunk River and Story County’s most heavily used beaches like Hickory Grove Lake. Only a small amount is known about backyard creeks without the efforts of volunteers.  Ballard Creek in Huxley, West Indian Creek in Nevada and Minerva Creek in Zearing have rarely been tested.
The Squaw Creek Watershed Coalition, along with local volunteers, have been monitoring Squaw Creek and its tributaries for over ten years. Some initial findings suggest that many creeks in the watershed have elevated levels of nitrate and E. coli bacteria. That data led to a watershed plan and grant-funded project that Prairie Rivers of Iowa and partners used to help farmers install water quality conservation practices like a denitrifying bioreactor, 3532 acres of cover crops and 3719 acres of no-till practices.  
Volunteers testing water quality in the South Skunk Watershed in Story County.
The development of a ten-year water quality monitoring program for the county addresses the need for continued water-quality monitoring of Squaw Creek, its tributaries other streams in the county. It will raise awareness, guide improvements and track the progress towards conservation efforts. Prairie Rivers of Iowa will continue to organize water quality monitoring events, share monthly lab tests and develop educational materials.
Peterson concludes, “Through collecting and analyzing water quality data throughout Story County, we are able to make more informed decisions, including financial priorities, regulations, and improvements to the land.  By changing, we can improve water quality to enhance habitat, reduce flooding, create natural areas that are flourishing with potential to explore and enjoy more recreational opportunities.

5 ways to get more conservation bang for our buck

5 ways to get more conservation bang for our buck


On any field in Iowa, cover crops will improve soil health, sequester carbon, and prevent nutrients from washing down to the Gulf of Mexico.  There are at least six situations where cover crops can add to the farmer’s bottom line, but in other situations, or to help encourage farmers to make that initial investment and get through the troubleshooting stage that comes with any new practice, public cost sharing can make a difference.  Most taxpayers I talk to are quite willing to pay farmers who are employing conservation practices for the ecosystem services they provide.  But we either can’t afford to or aren’t willing to invest at the scale needed to achieve universal adoption of cover crops and other conservation practices, and that means we have to make some decision about where to invest first, so as to get the most nutrient reduction (and hopefully carbon sequestration, soil protection, flood reduction, and other benefits) for our buck.

Most of those discussions are way above my pay grade.  I suppose the legislators who draft the federal farm bill and the NRCS bureaucracy set payment rates and application scoring criteria for EQIP and other cost share programs.  Iowa’s Water Resource Coordinating Council picked priority watersheds that can get special funding.


Planning at the local level can also influence where conservation investments are made.  However, it’s not always clear what influence a Watershed Management Authority actually has over where 1000 acres of cover crops gets planted, or why it’s better to plant them in one part of a county rather than another.  Same goes for other conservation practices.  Here are 5 possibilities.

1. Plant cover crops where they can protect a local lake or water supply


Algae in pond

In addition to Gulf Hypoxia, phosphorus that washes off the land is causing algae blooms in many of Iowa’s lakes.  Overnight, these algae blooms can use up the oxygen that fish and other aquatic critters need to breathe.  Some kinds of cyanobacteria can produce toxins that can harm people and pets.  Algae blooms are nuisance for those who would like to swim, fish, boat, or water-ski in those waters.  We can address two problems at once if those 1000 acres of cover crops are planted in the watershed of Hickory Grove Lake, Saylorville Lake or other water bodies suffering from an excess of green.

In addition to Gulf Hypoxia, nitrogen that washes off Iowa farmland can cause a problem for cities that pull their water from a river, or from wells close to and influenced by a river.  The Des Moines Waterworks and the Raccoon River watershed have rightly gotten a lot of attention, but other cities in other watersheds (like Boone, on the Des Moines River) also are dealing with high nitrate in their source water.  Cover crops in the right watersheds can help protect those water supplies.

Nitrogen and phosphorus can also cause algae blooms in creeks and rivers, but the science is more complicated than in lakes, and not often done.  For example, while the Squaw Creek Watershed Management Plan demonstrates that nitrogen and phosphorus levels in the creek are high, it does not make the case that meeting our nutrient reduction goals will protect drinking water, improve fisheries, make for safer recreation in Squaw Creek.  Maybe that’s a safe assumption, but I honestly don’t know.

2. Plant cover crops where they can reduce the most nitrogen

Here’s a map of nitrogen load by HUC-12 watershed in Story County, based on landcover.  This kind of model would be handy if you wanted to guess which stream has higher nitrate levels at its outlet.  If I plant 1000 acres of cover crops south of McCallsburg (in the “Drainage Ditch 81” hydrologic unit) will I get more nitrogen reduction than if I plant them west of Ames (in the Squaw Creek-Worrell Creek hydrologic unit)?  Nope.  The pounds/acre estimate here is for the whole watershed, and it’s based purely on landcover in that watershed.  Unlike the larger watershed, a field west of Ames wouldn’t be 20% developed, it’d be 100% agriculture, so with this model we can’t assume it’d be different than a field anywhere else in the county.   More sophisticated computer models like SWAT or SPARROW incorporate things like soils, slope, and county-level fertilizer sales as well as landcover, but it’s hard to tell which of those things is driving the results.

Other models like the Nutrient Tracking Tool are field scale, and can be used for this kind of prioritization.  Running through some quick scenarios, I estimated that cover crops on a tile-drained field in the Squaw Creek watershed could prevent 9 lbs/acre of nitrogen loss each year, versus 3 lbs/acre in an undrained field in the watershed.  Computer models can be helpful, if we’re clear about their purpose and limitations.

3. Plant cover crops where they can reduce the most phosphorus and sediment

Cover crops have gotten more traction in hilly southern Iowa, where soil erosion is a more visible problem and no-till is common.  From a standpoint of tons of soil erosion prevented, or pounds of phosphorus loss avoided, it makes sense to plant on fields with steep slopes and erodible soils.  Models like RUSLE can be helpful for this.

4.  Plant cover crops where their water quality benefits can best be measured

1000 acres of cover crops will make a bigger splash in a small watershed than in a big one.  A small change in water quality is difficult to detect.  Just like a poll that talks to a small number of people has a margin of error, a water testing program that samples only 12 or 24 days out of the year will have some uncertainty attached to the results.   I’ll be talking more about “minimum detectable change” in future posts, but suffice to say that margin of error is usually closer to 10 or 20 percent than 1 or 2 percent.  That means we need to give some thought to where conservation practices will be located relative to long-term water monitoring sites if we hope to document their effects with water monitoring.

Location of monitoring sites in Story County, and agency monitoringRow-cropped acres in watershedExpected N and P reduction at monitoring station from 1000 acres of cover crops in watershed
CREP wetland inflow (Conservation Learning Labs)1,27023.62 %
Walnut Creek @ 530th Ave, near Kelly (USDA)3,7567.99%
Onion Creek @ Reactor Woods, Ames (ISU)10,1042.96%
E. Indian Creek @ S27 (SCC/PRI/Ames)63,8520.47%
Squaw Creek @ Moore Park (IIHR)99,9190.30 %
Squaw Creek @ Lincoln Way (SCC/PRI/Ames)107,7750.27%
South Skunk River @ Riverside Drive (DNR)162,7180.18%
South Skunk River @ 280th St, Story County (DNR)297,5470.10%

5. Plant cover crops where it is most cost-effective for the producer

We do some of this unintentionally.  A farmer who can figure out how cover crops will make financial sense for their operation–cutting a pass for weed control or loosening compaction, providing forage for cattle, or protecting yields in wet or dry years–is more likely to sign up when the cost share being offered is $25-$35/acre.  Those that think they will lose money will pass until we offer better incentives–for example, Maryland was paying up to $90/acre and has gotten more takers.

This is also the idea behind “precision conservation” promoted by Land O’Lakes and other retailers.  With precision yield monitoring, conservation practices like wetlands, prairie strips, or buffers can be placed so as to minimize lost revenue.  Poorly draining or steep parts of a field might actually cost more to plant, till, and fertilize than it generates in revenue, so farmers could install conservation practices and even come out ahead.

That’s 5 ways to get more conservation bang for our buck.  Let’s be more clear about which of these we’re hoping to achieve when we do watershed planning, and more creative about how we support good stewardship.

Does this make sense?  Are there other ways to be more cost-effective with conservation?  Leave a comment!