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Posted on October 3rd, 2019

An article authored by Anna Jones recently appeared in the U.S. on-line version of The Guardian about Iowa and our struggle with nitrate pollution. One thing in particular about the article caught my eye and it was the description of a Marshall County farmer’s management of hog manure. He and his brother borrowed $1.5 million to build two hog confinements with a third still under construction. Ten thousand weaned pigs (18 days old) are raised in the two buildings and one brother “finishes” (hogs fed until they reach market weight) 2500 hogs at the site.

In a process governed by Iowa “law”, manure is stored in an 800,000 gallon pit beneath the confinement which is emptied once per year and applied to a 200 acre corn field.

Please permit me a few moments to take deep dive into this pit.

According to the most recent nutrient budget created by the Iowa Geological Survey, those hogs will produce 73,000 pounds of nitrogen. Per Iowa DNR CAFO rules, 25% of that can be expected to evaporate from the pit, thus reducing the total nitrogen (N) to 54,750 pounds. Another 2% can be expected to be lost during application if it is injected (more than ¾ of Iowa hog farmers inject manure with the rest applying to the surface). This further reduces the amount to 53,655 pounds. Applied to 200 acres, that effective N application rate is 268 pounds per acre, about double the ISU recommended rate for corn grown after soybean and about 1.4 times the recommended for corn following corn.

Why do our “laws” permit this over-application of nutrient?

The technical reason is because the rules written in Iowa Code Chapter 65 Animal Feeding Operations are based on a strategy for nitrogen management known as “Yield Goal” or “1.2 Rule,” first advocated by the University of Illinois agronomist George Stanford in 1966, before we had a Gulf of Mexico Dead Zone and the world’s largest nitrate removal facility at the Des Moines Water Works. It works like this: if you think the corn yield potential of your field is 200 bushels per acre, then multiply 200 by 1.2 to get the pounds of N you will need, which in this example would be 240 lbs/ac.

University of Illinois agronomist George Stanford, 1916-1981. Image Credit: American Society of Agronomy.

This is how manure management plans (MMPs) work in Iowa.

Manure management plans are not protective of water quality.

The easy-to-understand ‘1.2’ formula quickly and unfortunately became the conventional wisdom in agriculture and the environmental wreckage it has wrought is nearly incalculable. In his first published paper on the subject, Stanford made a statement almost unheard of for a scientist: “Future progress (in agriculture) demands that less empirical means be developed for predicting and meeting the N needs of crops” (1).

In other words, if you’re growing corn, don’t bother yourself with a bunch of stupid evidence.

We have known since at least 1987 that this approach to nitrogen management is flawed (2). A more recent paper (3) stated “yield-goal based N recommendations are not useful” when deciding how much nitrogen to apply.

In the example from the Guardian article, the Marshall County farmer must have demonstrated to DNR that he had the potential of producing 223 corn bushels per acre on his field. While the average 2018 Iowa corn yield was 204 bu/ac, 223 is very possible. Marshall County was #1 in 2018 with an average of 226 bu/ac.

The problem we have is that a field does not always or even commonly reach its yield potential (bugs, disease, rainfall etc.). In those circumstances, excess nitrogen is lost to the environment and the public shoulders the burden for the environmental consequences.  Your tax dollars are paying for conservation practices that help trap these excess nutrients on a small subset of farms.

So you might ask yourself why industry advocates tenaciously defend this manure management approach here in Iowa.

The answers are obvious. If we enlarge the area required for manure application by reducing the allowable application rate, not only do we increase hauling costs for the manure, we also in effect constrict the expansion of the hog production industry. In fact, some counties and watersheds are now so nutrient-rich as a result of intense livestock production, you would have to remove confinements and/or restrict sales of commercial fertilizer to get inputs aligned with crop needs. And to repeat, your tax dollars are paying for conservation practices that help trap excess nutrients, in effect enlarging the area into which the industry can expand.

Remember this when people tell you they want to double Iowa’s hog population.

And as bad as this story sounds up to this point, it gets worse. We have nearly non-existent enforcement of manure management plans. Fields get included in multiple MMPs, which is not illegal, but our DNR allows farmers to work it out between themselves on who gets to apply where in such situations. The growth of the industry has far outpaced DNR’s ability to monitor and regulate it.

And this last shoe drops with a thunder: we still sell almost as much commercial fertilizer in areas that are livestock-dense as in areas that aren’t.

Thus we’ve had a return of nutrient-fed algae blooms in places like Lake Darling, which was restored only six years ago at taxpayer expense ($16 million). Is it any wonder we have water quality problems?

Tragedies abound in the story of hog industry expansion. One is that farmers filling out their paperwork and following their MMP understandably think ‘it’s all good.’ And why wouldn’t they? Our government has given them license to think that.

It’s not ‘all good’, at least when it comes to our water.

  • Stanford, G., 1966. Nitrogen requirements of crops for maximum yield. Agricultural anhydrous ammonia technology and use, (agriculturalanh), pp.237-257.
  • Fox, R.H. and Piekielek, W.P., 1987. Yield response to N fertilizer and N fertilizer use efficiency in no‐tillage and plow‐tillage corn. Communications in soil science and plant analysis18(5), pp.495-513.
  • Camberato, J., 2012. A historical perspective on nitrogen fertilizer rate recommendations for corn in Indiana (1953-2011). Purdue Extension.
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8 Responses

  1. Lorraine May says:

    Would you please add me to your distribution list? Jen Terry was kind enough to forward one of your blogs.

  2. Good one! In our study (Jackson, Keeney and Gilbert 2000) not only could MMPs use the 1.2 lbs N per bushel of expected yield, but also expect 10% better yield than their county average or five-year average (whichever was greater, of course). And they were allowed to throw out 1993 from that 50 year average, which was a terrible year for everyone.
    On a landscape scale, this is madness.

    • cjones says:

      Thanks for reading Laura. That 2000 paper is a great one and it’s a travesty things havent changed all that much in the intervening 19 years.

  3. Dennis Goemaat says:

    Another great article. Have you tried to get a regular column in the Gazette/Register where this information can be shared across the state? It would be great if you could submit this for reprinting in the paper. Keep up the good work.

  4. Sarah says:

    Folks, the New Internationalist Magazine has named Iowa Farmers, upstream from the Gulf, as THE majority polluters of and THE cause for the dead zone!

    And yet, they shrug and keep building!
    Proving BOTH greed and ignorance!

  5. John Norwood says:


    Great topic. Each year, we have to dispose of manure from 50 million hogs. Manure is 95% water and little did I know when leading a feasibility study for a manure coop concept back in 2004 with support from state and federal grant funds we won through a competitive process. Drum roll. Manure is perishable!

    That is, the methane potential in the manure breaks down as the manure sits in the pit and degrades through methanogenesis. For many confinements, the manure pit lies under slatted floors in the barn. If it weren’t for powerful fans exhausting the toxic gas the animals in the barn would die of asphyxiation. In fact, one of the most dangerous times in the barn occurs when the hogs are sent to market and thecmanure is pumped out. Because of settling, it needs to be stirred. This stirring can cause the release of deadly H2S and methane. With an electrical short, barns have been known to explode. Workers occasionally die.

    What I’d like to see is a systems based approach for capturing the methane potential at the barn level using some sort of distributed anaerobic digestion technology that can kill pathogens, stabilize the nitrogen, create a higher quality manure derivative, capture the methane which is 21x the impact of CO2 in terms of its global warming potential, and dramatically reduce the odor (associated with the poor biological breakdown process).

    We’d need a public financing system to incent this not unlike what it took to get solar and wind off the ground.

    What is the methane potential of our 50 million hog annuity stream? We ought to figure that out and what it’s worth to society and producers to capture that gas! It may be more cost effective than other forms of carbon capture with a host of additional benefits.

    Thanks for yet another great piece!

    John Norwood
    Commissioner, Polk County Soil and Water

  6. Bob Havens says:

    Thanks for the nitrogen accounting. Separation distance from residence rules, Master Matrix passing score, manure application rates allowed, all converge at 10,000 pigs per square mile. The P index threshold of 10 will not be exceeded for over one hundred years. Yes, there are plus 10% factors in corn yields, nitrogen content reduction in manure if the pigs are owned by a specific company (I have the letters from the DNR stating this) and get this: a 30% discount of phosphorous content when calculating the P index for the field (this is in the instructions for filling out the forms). The goal is 10,000 pigs per acre and they will defend anything that encroaches on this number.

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