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Iowa’s Real Population

Posted on March 14th, 2019
Hogs in a confinement facility.

These hogs are getting ready for market as they grow inside this Iowa swine finishing barn.

Iowa has around 3 million people, a total that has not changed much over the last 80-90 years. People are large animals, and as such our bodies produce a lot of waste. That being said, we produce much less waste than the animals that we eat. Take hogs, for example. A feeder pig is about the same size as a human being, but it excretes 3 times as much nitrogen (N), 5 times as much phosphorus (P), and 3.5 times as much solid matter (TS-total solids) (1). Some of this is because of the pig’s diet and some it is because modern hogs grow really, really fast (these things relate to each other, obviously). A pig weighs about 3 pounds at birth and about 250 pounds at slaughter a mere 6 months later, so it is gaining more than one pound per day. By comparison, a human infant gains a pound about every 20 days. There’s a reason we use the word “hog” metaphorically and pejoratively because they consume anything and everything in sight virtually non-stop, which is one reason why they make for a good food animal.

Everybody knows Iowa has a lot of livestock. If you’re like me, maybe you have heard from time to time that our state has enough animals to effectively be as populous as California, using one common example. As you will soon see, it’s bigger than that. Much bigger.

Exactly how many of each species that we have at any one time is a difficult thing to quantify for reasons I will not get into here. I’m going to present some watershed-by-watershed numbers for the following analysis and I do not claim that they are exact, but I have consulted with a couple of experts and I am confident they are in the ball park. Anyway, statewide, we have around 20-24 million hogs; 250,000 dairy cattle; 1.8 million beef cattle, 80 million laying chickens, and 4.7 million turkeys. I did not consider sheep, goats, horses, broiler chickens, deer or Canada geese.

When I apply the N, P and TS values of the waste from these animals, what would be the equivalent-sized human population that would generate such waste is staggering:

  • Iowa hogs: equivalent to 83.7 million people
  • Dairy cattle: 8.6 million people
  • Beef cattle: 25 million people
  • Laying chickens: 15 million people
  • Turkeys: 900,000 people

In total, these five species generate the waste equivalent to that produced by about 134 million people, which would place Iowa as the 10th most populous country in the world, right below Russia and right above Mexico. (Caveat: obviously Russia and Mexico have their own livestock that I am not counting.) And in terms of population density in the context of N, P and TS waste, Iowa would come close to the country of Bangladesh.

Managing the waste from these animals is possibly our state’s most challenging environmental problem. Of course we have a lot of cropland to apply this waste, but the time windows in which farmers have to do this in without damaging the crops with equipment are usually not large. Wet, cold and hot weather can all limit application. As a result, there are only a precious few weeks in a year when this Mt. Everest of waste can be applied to corn and soybean fields. And there can be no doubt that the sheer amount, and the logistical complications of hauling and handling it, have consequences for water quality (2). Watersheds with the highest density of livestock frequently have some of the highest stream nitrate concentrations (North Raccoon, Floyd, and Rock River watersheds, for example).

My colleague Dan Gilles, a Water Resources Engineer at the Iowa Flood Center, was able to derive the human population for all of Iowa’s HUC8 watersheds. Dan has been a great collaborator to work with and most days he could run circles around me. Anyway, our most populated watershed, the Middle Cedar, has 294,000 people. Even in that watershed, the human-equivalent livestock population (3.6 million) dwarfs that of actual people. I added the human population to this human-equivalent livestock population for each of Iowa’s HUC8 watersheds and this is illustrated below by relating it to a city or state that has a similar human population. I realize that most people will not know the population of many of these places, and the table that follows will help with that.

To finish up, I present this illustration not to make any value judgments on the livestock industry. Clearly it is an important part of our economy. I think we can and should, however, objectively and dispassionately ask ourselves how much we can accommodate while still being able to achieve our desired environmental outcomes. Denmark and the Netherlands both have livestock densities on the scale of Iowa. As a result, both of these countries have in the past suffered environmental consequences similar to our own, but, both country’s governments have intervened in more forceful ways than ours. I’m not saying this is good, bad, or in between, it’s just true. I think even industry advocates would say there is not much that limits further expansion in Iowa, except perhaps available land in certain areas of the state to apply the waste. Is it reasonable to think about what’s possible when trying to reconcile our desired environmental outcomes with the economic and regulatory considerations the industry wants? If we are going to be honest with ourselves, then I think the answer to that question is yes.

This map shows the human waste equivalent of the people, hogs, laying chickens, turkeys, and dairy and beef cattle the city or state that relates to it with its human population only. Reflected is an average of N, P and TS waste. Only the population of the city proper is reflected, not the overall metropolitan metro area.



Iowa HUC8 Watersheds and the number of Iowans that live in them.


Data table used to derive the maps above.


  2. Jones, C.S., Drake, C.W., Hruby, C.E., Schilling, K.E. and Wolter, C.F., 2018. Livestock manure driving stream nitrate. Ambio, pp.1-11.


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20 Responses

  1. Great social math making the point that Iowa’a 15,000 + CAFOs are too many. The other point you could make. Perhaps in a future blog, is that all the cities you identify have some sort or sanitary sewage system that controls harmful downstream chemicals and pathogens.

    • cjones says:

      Yes I did consider this point, and you are correct. Many municipal treatment works do little to remove N (although they do convert ammonia to nitrate), and for that reason I decided not go down that path with this installment. Thank you for your comments and for reading the blog.

    • Katrin says:

      be my guest. thanks for reading..

  2. John Congdon says:

    What are the different methods available for treating the waste before putting it into the fields? The lagoons don’t do much.

    I have a friend who worked for a few years with a dairy operation in north Texas to compost the waste and make bio-gas. However I don’t know the end results.

    • cjones says:

      There are technologies available that can digest the waste to make it more easily manageable and reduce the number of biological pathogens. I’m not sure how this affects the nutrient content but I suspect that it would reduce the N content. These types of methods are fairly common in Denmark and the Netherlands but uncommon in Iowa.

      Thank you for reading the essays.–Chris

  3. Reinstatement of Adam Lack’s USDA-NRCS Revised Universal Soil Loss Equation Version Three that educated farmers on proper drainage restrictions (which prevent Point Source Contamination) for application of CAFO liquid manure and Anhydrous Ammonia Nitrogen fertilizers. two very water soluble Nitrogen fertilizers that should not be applied on land increasingly flooded by our more frequent flooding, since the 1990’s.

    Furthering the support of our Designated National Wetland’s and with increasing the Corps of Engineer’s Protection of them and our Aquifer Recharge Area’s Sinkhole Drainage Protection with 404 Corps Permits and 401 DNR Permits being Strictly Enforced to protect our drinking water in Iowa and the US.

    Support the 2015 Waters of the US Rule! Don’t allow the increasing degradation of our US Source Waters to be so contaminated with the very water soluble Nitrogen fertilizers that we will not be able to safely treat or filter our U.S. Tap Water.

  4. Jim Ruebush says:

    Wow! That is an impressive study you did. It puts our challenges of waste management into a very real perspective. We have some major issues to grapple with when viewed this way.

    May I post a link to your article on my own blog? I want to share it with other Iowans.

  5. […] in August, North Carolina, the state that ranks second in swine, only had 9.4 million. And pigs, Jones explained on his blog, produce much more waste than […]

  6. Arline Pabon says:

    Hello, I think your blog might be having browser compatibility issues.
    When I look at your blog in Safari, it looks fine but when opening in Internet Explorer, it has some overlapping.
    I just wanted to give you a quick heads up!

    Other then that, very good blog!

  7. Iowa has around 3 million people, a total that has not changed much over the last 80-90 years.

    what the meaning of “has not changed much over the last 80-90 years?

    • cjones says:

      Iowa’s human population has been about the same for the last 80 to 90 years, and this is about 3 million people.

  8. […] in August, North Carolina, the state that ranks second in swine, only had 9.4 million. And pigs, Jones explained on his blog, produce much more waste than […]

  9. TAHA says:

    Thanks for sharing

  10. Mark Kane says:

    I am thankful to see these numbers. Facts are valuable and will be more valuable when the citizens of Iowa and the Legislature debate how much pollution of the state’s water is too much. Have you calculated how much manure one pig produces in its short life?

    • cjones says:

      thanks for reading Mark. Yes, the amount of waste and nutrients generated by a hog is an easily quantified number.

  11. […] massive amounts of manure, so much in fact, that University of Iowa research engineer Chris Jones estimates that Iowa, with a population of 3.2 million people—and 23 million hogs—produces more than twice […]

  12. […] amounts of manure, so much in fact, that University of Iowa research engineer Chris Jones estimates that Iowa, with a population of 3.2 million people—and 23 million hogs—produces […]

  13. […] been more than a year ago now that I wrote “Iowa’s Real Population”, which featured the map below. Considering all our livestock animals and the waste they excrete, […]

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