You know those United Way posters with a thermometer showing progress toward a fundraising goal?  The image above is my attempt at a similarly easy-to-understand progress meter for the Iowa Nutrient Reduction Strategy (INRS).  Based on changes to farming practices in the decade since the Iowa Nutrient Reduction Strategy was released, we should have met our goal for phosphorus but have only reduced nitrogen losses by 2%, not enough to undo the increases of the previous decade.  These are best-case scenarios which do not account for manure, legacy sediment and nutrients, and interactions between practices.

Iowa State University is responsible for tracking the progress of the INRS, and has created a set of data dashboards covering dollars spent, minds changed, conservation practices on the land, and water quality trends in the rivers.  These were updated in May of 2024.  There is no top-line summary of where we stand relative to our goals, but wasn’t hard to make one.  I just added up the numbers in a pair of tables labelled “change in modeled nitrogen/phosphorus load for practices since the baseline period.”

Baselines, Goals and Timelines

The timeline requires some explanation.  The INRS was released in 2013, but the baseline period is 1980-1996.  That’s because the Hypoxia Action Task Force was formed in 1997.  The task force set a goal of reducing the size of the dead zone in Gulf to 5000 square kilometers (1,930 square miles).  The target date for meeting that goal has been pushed back several times.  Despite several dry years, the five-year average extent of the dead zone is still twice as big as the target.  Last year it measured 6,705 square miles, larger than Connecticut or Hawaii.

To meet the goals for shrinking the dead zone, each state would need to reduce the amount of nitrogen and phosphorus lost down the Mississippi River by 45%.  The Iowa Department of Natural Resources determined that mandatory upgrades for 102 municipal wastewater treatment systems and 28 industrial facilities could reduce state’s overall nitrogen load by 4% and phosphorus load by 16%.  The remaining 41% reduction in nitrogen load and 29% reduction in phosphorus load would need to come from controlling non-point sources of pollution like agricultural runoff.

Iowa State University was tasked with answering the question: “based on what we know about the performance of various conservation practices, how would it be possible to achieve these goals?”  The answer was “only with a combination of practices, and only if every farm uses at least one of them.”  This research began in 2010, using data about land use and farming practices from the previous five years (2006-2010), so the load reduction scenarios are relative to that “benchmark” period.  The researchers later issued a supplemental report to compare the benchmark period to the baseline.  Phosphorus went down due to changes in tillage but nitrogen went up due to an increase in corn and soybean acres and an increase in fertilizer application rates.

Using the information in ISU’s reports and dashboards, I’ve attempted to summarize our progress relative to both the baseline period (before the formation of the Hypoxia Action Task Force) and the benchmark period (before work began on the Iowa Nutrient Reduction Strategy).

Modeling vs. Monitoring

As I said, these are best-case scenarios.  While we can certainly expect a big reduction in phosphorus pollution from the growth of no-till and cover crops, ultimately, the only way to be sure that water quality is improving in our rivers is to test it!  If there’s a discrepancy between what you expect (a big reduction in phosphorus load) and what you measure (no clear trend in flow-weighted, five-year-moving-average phosphorus loads) that’s a sign that you left something important out of the spreadsheet!  The most likely suspects are legacy sediment in the river valleys and livestock manure.

On the other hand, if your water quality data is incomplete or inconclusive or just hard to explain, it’s worth stepping back and asking yourself: “how big a reduction in nitrogen can I reasonably expect, based on the conservation practices installed so far?”  If the answer is “1 or 2 percent,” there’s no need to wait for the results of a long-term study to acknowledge that your strategy isn’t working.

I remember doing that kind of reality check in 2019 for the Ioway Creek Watershed Management Authority, at the end of a four-year demonstration project.  I did not enjoy being the bearer of bad news then, and I’m not enjoying it now.  I remember how much work my colleagues put into those field days, and the ingenuity and vision displayed by the farmers who hosted them.  I was there when the woodchips were poured into the first bioreactor in Boone County.  So I totally understand the impulse to brag that Iowa now has 300 bioreactors, 3.8 million acres of cover crops, and 10.2 million acres of no-till.  Many people worked hard to achieve those numbers!  It is real progress!  It’s kept nutrients and sediment out the water!  It proves that there are many farmers who care about soil and water and are doing something about it!  But it doesn’t prove that the Iowa Nutrient Reduction Strategy is working.  For nitrogen, it definitely isn’t.

Conservation efforts have been partially offset by increased fertilizer use

I knew that we needed a lot more cover crops, wetlands, and saturated buffers to reach our nitrogen goal.  Iowa Environmental Council has made this point with infographics.  What I didn’t realize was the extent to which increases in fertilizer application rates have offset the hard-won gains that we’ve achieved so far. 

Nutrient rate management was supposed to be the low-hanging fruit the Iowa Nutrient Reduction Strategy.  At the time the INRS was written, the Maximum Return to Nitrogen (the point at which the yield bump from an additional pound of fertilizer doesn’t generate enough revenue to cover the costs) was 133 lbs/acre for corn in rotation and 190 lbs/acre for continuous corn.  Reducing rates from 150 lbs/acre for corn in rotation and 201 lbs/acre seemed like an easy way to reduce nitrogen in the rivers by 10% while actually saving farmers money.  Win-win!  Instead, rates for corn in rotation averaged 173 pounds/acre for the past several years, which would raise nitrate levels in tile water by (roughly) 23%!  Rates for continuous corn went down just a tiny bit, to 199 lbs/acre.  What happened?

Several of the authors of the INRS science assessment just co-authored a new paper in Nature Communications which provides an answer.  133 lbs/acre was economically optimal under outdated assumptions about corn genetics and yield response, fertilizer and corn prices, and precipitation.  Factoring all that in, the optimal rate for corn in rotation actually rose to 187 pounds/acre in 2020, leaving no opportunity for a win-win.  Farmers are acting in their rational economic self-interest and applying as much nitrogen as is required to get good crop yields after a heavy spring rain.  (Huge caveat: this doesn’t factor in manure).  The researchers acknowledged that this is bad for water quality, as measured by a growing gap between the economically optimal rate and an “environmentally optimal rate” with some externalities priced in.  Another way to say that: the fraction of agribusiness profits which come at the expense of other industries (i.e. commercial fishing in the Gulf, tourism for communities on polluted lakes) and the public (i.e. utility bills for customers of the Des Moines Waterworks, hospital bills for cancer patients) has been growing. 

The companion piece to this paper is a new calculator.  N-FACT uses data from on-farm nitrogen rate trials to factor in location, planting date, residual soil nitrogen, fertilizer price, and your best guess about corn prices and rainfall to provide a customized economically optimal nitrogen rate.  The research that went into it is very impressive, and gave me a new appreciation all the factors that can influence agronomists’ recommendations and farmers’ decisions.  I hope it will lead to reduced nitrogen losses by helping farmers improve their forecasting, but unless you’re doing a split application and soil or corn stalk testing, it seems like there’s still a lot uncertainty.  Your optimal rate may vary by 40 pounds/acre depending on whether we get a wet spring or a dry spring.  That’s why I’m more excited about Practical Farmers of Iowa N Rate Protection Program, which directly addresses uncertainty and risk.

What we really need is a calculator to answer the following questions about the Iowa Nutrient Reduction Strategy:

• How much voluntary conservation will it take to offset future profit-driven changes in the industry?
• How soon can we expect to see meaningful reductions in nitrate in our rivers and drinking water?
• How many people will get preventable cancers in the meantime?
• How long is the public going to put up with this before we demand a change in strategy?

What do I mean by “a change in strategy?”  Making policy recommendations isn’t our wheelhouse, but if you’re looking for ideas, you might start with this 2020 op-ed by Matt Liebman, Silvia Secchi, Chris Jones, and Neil Hamilton, or this 2022 report by the Iowa Environmental Council.