Throwing away billions of dollars in pet manure

August 18, 2010

NOTE: Images in this archived article have been removed.

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Not until I was well into writing my new book, Holy Shit: Managing Manure To Save Mankind, which is about how to manage manure for soil enrichment, did I realize that cats, dogs and horses are a very significant source of valuable fertilizer that we are mostly throwing away. Or, as our friends’ cat, Django, indicates in the photo above, flushing it down the toilet. Until I got to know Django, my attention was focused on farm animal manure and human manure. I was really surprised to find out how much feces, urine, and litter that pets were adding to our overflowing waste stream, let alone realize that cats were learning how to use the flush toilet.

Instead of wringing hands over the problems of livestock manure, the non-farm sector of society might first want to take a closer look at its own problem: manure from pet cats, dogs, and recreational horses— animals that have little or nothing to do with putting food on anyone’s table. According to recent statistics, there are 73 million pet cats in the United States in addition to an equal number of feral cats roaming the alleys and fields (and killing millions of songbirds). There are some 68 million pet dogs and of course millions of strays out there doing beneficial work like killing my sheep. In addition there are some 9.5 million horses and the number is rising.

The numbers I use in Holy Shit to calculate the amount of manure flowing from these pets can only be approximations but they are based on the best statistics I could find. A horse weighing a thousand pounds produces about 20 tons of manure a year including bedding. So unless I can’t multiply any more, 20 X 9.5 million equals 190,000,000 tons of road apples. Pet dogs and cats together produce per year another five million tons of manure. All this waste is good, holy fertilizer. Dog and cat waste is particularly valuable because, compared to most manures, it is higher in phosphorus, the plant nutrient most difficult for organic farmers and gardeners to come by naturally.

Only a small fraction of this manure is being used for fertilizer however. Most of it is going to landfills or to sewage disposal plants as pet owners get rid of the manure by way of dumpster or toilet. Pet owners are supposed to pick up manure when they walk their dogs (which they then flush down the toilet or put in the garbage) but when I walk public park areas, I see droppings all over the place. And of course the urine, which is richer in nitrogen, phosphorus and potash than feces, just disappears into the public grass— or more often, the neighbor’s lawn.

This waste is particularly worrisome now because the cheaper sources of commercial fertilizer for farming are declining. Competing uses for natural gas, our biggest source of nitrogen fertilizer, is driving up prices. Potash deposits in Canada, our handiest source, are declining, and talk of opening up new mines in the rainforest does not sit well with the environmental community. Some specialized phosphorus fertilizers are very expensive. The day is coming when we must start thinking about scrupulously saving our wastes for fertilizer as humans have done, especially in Asia, for centuries.

Django is not going to appreciate this but, as I write in the book, the possible specter of 73 million cats perched on toilet bowls across the nation causes me to shudder. Doubtlessly training cats to go on the pot is rather clever and saves messing with litter boxes. But with the tiniest bit of effort, litter boxes can be dumped into compost piles instead of flushing them down the toilet. I wonder if cats will learn how to flush the pot too. Will they do like children do sometimes, and flush the toilet just out of boredom when master is not around? Or maybe flush master’s slippers down the pot? But whoever does the flushing, let us contemplate seventy three million toilets flushing ten times per day just from cat use. That would take something like 36.5 billion gallons of water. Every day! Now add on the incalculable number of flushes from human use and you have a demand that the experts say would be impossible to meet if the whole world lived like Americans.

What are we throwing away in money? In Holy Shit I use my own way to come up with a figure. You may agree or disagree. Experts say that ten tons of animal manure and bedding per year can adequately fertilize an acre of farmland. Therefore we have enough pet manure in this country to fertilize something like 20 million acres every year. If a farmer is paying out $100 an acre for commercial fertilizer (right now it’s lower than that, last year higher) we’re talking about a value for pet manure of something like two billion bucks. And the cost of throwing it away in the landfill or sewage treatment system is a whole lot more.


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Just out this week from Chelsea Green Publishing, White River Junction, Vermont

Gene Logsdon

Gene and Carol Logsdon have a small-scale experimental farm in Wyandot County, Ohio. Gene is the author of numerous books and magazine articles on farm-related issues, and believes sustainable pastoral farming is the solution for our stressed agricultural system.

Tags: Food