An article authored by Anna Jones recently appeared in the U.S. online 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) 2,500 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 Department of Natural Resources (DNR) CAFO rules, 25 percent of that can be expected to evaporate from the pit, thus reducing the total nitrogen (N) to 54,750 pounds.
Another 2 percent can be expected to be lost during application if it is injected (more than three-fourths 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 rate 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.
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 that “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 the DNR that he had the potential of producing 322 corn bushels per acre on his field. While the average 2018 Iowa corn yield was 204 bu/ac, 322 is not unheard of. It’s possible. Marshall County was number one 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 that 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 MMPs 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.
(1.) Stanford, G., 1966. Nitrogen requirements of crops for maximum yield. Agricultural anhydrous ammonia technology and use, (agriculturalanh), pp.237-257.
(2.) 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 analysis, 18(5), pp.495-513.
(3.) Camberato, J., 2012. A historical perspective on nitrogen fertilizer rate recommendations for corn in Indiana (1953-2011). Purdue Extension.
Dr. Christopher S. Jones is a research engineer in the IIHR—Hydroscience and Engineering at the University of Iowa. His research interests include water quality and agriculture, water monitoring and nutrient and sediment transport. This article is republished by permission from Jones’ website.