Published on July 28th, 2009 | by Steve Savage


Followup to “An Inconvenient Truth about Composting”

Compost pile


My earlier blog about greenhouse gas emissions from composting generated a lot of good discussion so I am writing to respond.

  • Yes, composting is certainly better than some outcomes like food scraps going into a garbage dump which does not do anything to capture the methane
  • Yes, an anaerobic digester would be a very good thing to use for most waste streams.  A recent example is what was done at Gill’s Onions
  • Many wastes can also be put through a fast-pyrolysis process to form syngas and biochar.  This is another way to get at the carbon-neutral energy that is in the manure or other waste
  • Greenhouse gas emissions are not the only metric that matters as was pointed out, but manures in particular are undesirable fertilizers based on multiple other metrics as well: tendency to leach more nitrates because of extended release, more nitrous oxide emissions for the same reason, and excess levels of phosphorus relative to nitrogen leading to water pollution
  • Compost is indeed a very good way to build soil carbon and that is a super important thing to do for true sustainable farming, but there are other ways to accomplish that that don’t have the greenhouse gas issues.  One is the use of biochar.  The other is to practice no-till farming and grow cover crops which I describe in another post.
  • There may be ways of composting that don’t emit as much methane, but I’ve seen far more theoretical arguments that way with no actual measurements taken.  As a microbiologist I have a hard time imagining how you could avoid having some anaerobic conditions in a big pile of manure.  Starting from 14 times as much carbon equivalents as synthetic nitrogen, the process would have to be vastly improved to be acceptable
  • Un-composted manure has similar drawbacks as a fertilizer.  When it is stored for later use on a farm, at least 1-2 percent of its total methane potential gets released even with very good manure management practices
  • Chicken manure is more attractive to farmers as a nitrogen source because the levels are higher, but there is every reason to believe it would generate methane in storage and during composting if someone bothered to measure it

Tags: , , , , , , , , ,

About the Author

Born in Denver, now living near San Diego. Agricultural scientist for 30+ years with a Ph.D. in Plant Pathology. Have worked for Colorado State University, DuPont and Mycogen and for the last 13 years consulting for all sorts or companies, universities and grower groups. Experience in biological control, natural products, synthetic chemicals, genetics, GMOs and agronomic practices. Have given multiple invited talks on the interaction between agriculture and climate change (both ways)

  • Rich

    Seriously, you propose biochar as an environmentally friendlier solution to composting? And you believe biochar is carbon neutral by its proponents’ claims that carbon emitted during pyrolysis is supposedly offset by carbon absorbed by new plant growth created by using biochar as a soil amendment, yet you won’t accept the same carbon sequestration and offset associated with amending soil with compost. In fact, that value would be higher than biochars as sequestration occurs with compost amended soil within the soil as well as with the plants that grow in it (and an additional offset value for reduced fertilizer and pesticide use required for healthier plants). What exactly are you trying to prove with these posts? I’m not trying to be a smart aleck when I say this. I just really don’t get what your thrust is her. And how do using uncomposted manures as a fertilizer relate to your argument that petroleum-based fertilizers have a smaller carbon footprint than large-scale composting? Rather than simply trying to defend your last post, why don’t you spend more than a day researching these issues and write again when you understand the larger picture better. Your allegations now as they stand do not make rational nor scientific sense and you’re misleading readers into thinking pirolysis and petro-chemicals associated with conventional farming are somehow better environmental choices than cyclical organic resource management methods such as direct land application and composting.

  • Brendan

    Rich, where are your facts? You seem to assume a lot more than Steve. Too many of us blindly assume that because something is labeled “green” it does not have negative impact and is significantly better than any alternative. Steve is running his hypothesis through a scientific method and he backs his points with facts. What is wrong if we determine that pyrolysis and petro-chemicals are better for the environment than composting? In the end, it only matters what is the right thing for the environment not that we just default to what we label as “green”. The Earth does not care how we label what we do just that the impact is less.

    We are living in complex times and answers to challenging problems are not always straightforward. Let’s open our minds to alternative thinking, compare the alternatives using facts and resist making conclusions on “feelings”. Maybe we find that our limited time and budgets are better spent on wind energy than composting. So be it, in the end, our grandchildren will measure our efforts based on impact not on the labels we use for our practices.

    Challenge Steve, please, but let’s use facts and not assume that the “natural” way is always the “right” way.

  • mary c anderson

    Can you please define for me your definition of manure? Coming from a farm i know that “manure” has many different forms ie- cow poop alone is manure, in a stall barn, cow poop, urine and bedding (straw or shavings) mixed is manure, in large industrial dairys manure is cow poop and urine collected and stored in an anaerobic enviromnent is called manure, lastly cows in a grazing situation manure is only the cow poop not mixed with urine because cow usually will walk 15 to 20 feet between manures and urination–but it’s still called manure. now if you look at each type of “manure” it’s different structural and chemical make ups because of what takes place when we (as humans) mix those various compounds together….
    So back to the original question-what is your definition of manure and nutrient wise what does it look like (NPK micros, pH, etc)?

    mary c

  • Rich

    First I should say I’m a composting consultant with almost 20 years of experience in the business.

    I’ve dedicated half of my life and my entire professional career to composting because I believe it’s the most economically, socially, and environmentally beneficial way to handle discarded organic residuals (for life cycle analysis studies see Dr. Jeffrey Morris of Sound Resource Management’s work), a material that comprises half or more of what we’ve historically (let’s say since at least WWII anyway) buried in a hole in the ground with lots of other perfectly good resources.

    There are two primary flaws in Dr. Savage’s assumptions:

    Firstly, that compost is typically created for sale as a fertilizer. It is not, but rather primarily marketed to build the physical structure of a soil (tilth) and improve its microbiology. Compost has a multitude of other benefits as well, thoroughly researched and documented by the scientific community for minimizing erosion and run-off of synthetic pesticides and fertilizers into surface waters, reducing irrigation demands by improving the moisture-holding capacity of soil (further lowering the carbon footprint of the farm using it), and reducing greenhouse gas emissions by providing a dual-edged carbon sink: the amended, high organic soil itself and the healthier plants that grow in it (Google Dr. Sally Brown University of Washington to see an easy-to-understand PowerPoint).

    Compost is rarely sold for its NPK value because it has so little, and it’s not regarded by the agricultural industry as a fertilizer nor regulated by our government as such. So to compare the emissions that result from producing enough compost to provide a hundred pounds of nitrogen for an acre of crop to the emissions that occur to make the same hundred pounds of synthetic nitrogen is an unfair argument but the very basis of Dr. Savage’s argument.

    This is like contending that the carbon footprint of bicycles is many times that of a tractor trailer because it would take 500 bikes to pull and carry the same load as the truck, and there were much fewer emissions associated with manufacturing a single truck than 500 bicycles. Like Dr. Savage’s argument, a stretch, but could okay if you knew nothing about bicycles and didn’t know they don’t have the torque or capacity and aren’t typically used to haul heavy loads of products and materials around.

    Secondly, it’s true there haven’t been many studies looking at the emissions emanating from compost piles, which doesn’t prove high emissions exist any more than it proves that they don’t. Dr. Savage bases his belief methane is generated from large-scale composting by two studies that even the California EPA and Integrated Waste Management Board agree used emission levels from composting activity atypical of industry practices. Dr. Savage is then left to make his own assumption: “As a microbiologist I have a hard time imagining how you could avoid having some anaerobic conditions in a big pile of manure. Starting from 14 times as much carbon equivalents as synthetic nitrogen, the process would have to be vastly improved to be acceptable.”

    Improved from what? A big pile of manure is hardly a professionally managed composting facility and another entirely unfair, unscientific comparison. And there’s that baseline 14 times number again based on using something for a fertilizer that wasn’t designed to be a fertilizer!

    Agreed, there may be pockets of methane and even some nitrous oxide emanating from large-scale composting, but there are plenty of BMPs to minimize or eliminate them (See Fatih Büyüksönmez’s work at SDSU).

    The last thing a large-scale facility operator wants is their process to go anaerobic, even in pockets. The resultant odors and longer residence time for the material jeopardize the facility’s regulatory status and profit margin. Hence, a professionally run facility is constantly striving to keep producing compost aerobically (sans methane and other gases) and efficiently.

    I’m open to any fair arguments against composting and for other technologies, but I’ve yet to hear any. And since the value of compost was first discovered at the same time humans began realizing they could grow things in it, about 10,000 years ago during the Neolithic Age, nobody has come up with anything better.

Back to Top ↑