June 21, 2007 | General

Environmental Benefits Of Compost Use

BioCycle June 2007, Vol. 48, No. 6, p. 19
Sally Brown

WHEN I’ve given talks about greenhouse gas accounting for composting, all of the people in the room who operate composting facilities or who have used compost are sure that the use of compost will result in very large reductions in greenhouse gas (GHG) emissions. Compost is so good for so many things, it must be good for this too. When, during the talk, I say that credits related to methane avoidance (preventing the compost feedstocks from emitting GHGs by composting rather than letting them decompose anaerobically in a landfill) are much greater than for final use of the compost, I see an audience looking at me like I’ve lost my mind as well as any credibility that I might have had. Methane avoidance may end up being the tool that forces the understanding of a wide range of benefits that compost can provide. But understanding the true value of compost involves using a broad and realistic mindset, not just considering methane avoidance.
Use of compost can be a terrific environmental practice. The key to understanding how good of a practice it can be is to evaluate it using realistic end use scenarios and multiple metrics. A holistic framework when evaluating the costs and benefits associated with using compost is really the only way to understand its true value. The U.S. Environmental Protection Agency evaluated the impact of compost production and use on GHGs. It is a well-intentioned analysis that makes use of modeling programs that are currently used for understanding soil carbon balances. The evaluation concludes that compost can have a minimal effect on GHGs, i.e., some emissions related to compost manufacture and some potential sequestration associated with end use. However, it also shows that the authors of the analysis and the models are not regular compost users. EPA based its analysis on compost use in corn fields in Iowa and Colorado, looking at application rates of 10 to 40 wet tons/acre. The “Century” model was employed to predict changes in total soil carbon even though the model had no provisions for external carbon inputs into a soil system. The authors found that adding compost to soil can result in small changes in total soil carbon, but admitted that they weren’t sure how stable the compost-added organic matter was or how long it would persist.
It is your atypical corn farmer that will use compost for his or her soils. For many years, large-scale farmers have depended on synthetic fertilizers and highly groomed fields to maximize yields. Compost for these farmers is something for the vegetable patch and is much too expensive for large-scale use. It is only when a farmer is really paying attention, by choice or by circumstance, that they will decide that compost is their best option.
Using compost restores soil health by building soil organic matter and tilth. In the process, it increases the soil’s ability to hold water. It restores a healthy microbial population to the soil, which can be key to fighting off soil-borne plant diseases. It helps restore high salt soils to productivity. A more complete analysis of the benefits associated with using compost would bring out these points. In fact, a recent analysis done by the Recycled Organics Unit (ROU) at the University of New South Wales has included these factors as well as GHG benefits in their analysis (http://www.recycledorganics.com/index.htm). In the study done by the ROU unit, compost use was centered on an area close to urban centers where intense cultivation has resulted in soil degradation. Instead of corn, the scientists included irrigated cotton and grape cultivation in their model. Both are high value, high input cropping systems where compost use would make sense. In addition to GHGs, sustainability was considered. The study recognized that returning organic resources back to the soil is essential to reverse land degradation and losses in productivity. Because of a broader perspective, a more realistic understanding of the value of compost was developed. The ability of compost to reduce irrigation water requirements, limit use of herbicides and synthetic fertilizers, limit erosion, decrease effects of high salinity, increase productivity and total soil carbon and improve soil structure were all recognized. Although there were GHG savings associated with some of these benefits, these paled in comparison to the larger scale environmental benefits.
An analysis of farming practices that focuses on sustainability – our ability to continue to demand so much of the soil -clearly shows the importance of organic amendments such as composts. Rattan Lal, a soil scientist, expert on carbon sequestration and president of the Soil Science Society of America, recently linked organic inputs with “long-term sustainable use of natural resources.”
In a nutshell, while understanding greenhouse gas impacts of our activities is essential to reduce our emission of these gases, global warming is not the only environmental crisis we face. Compost is one of the best tools available to maintaining soil productivity and reducing environmental degradation as a result of intensive agriculture. It is also a tool that we can make from material that we have treated as waste. By realizing the value of composts, we can start turning these wastes (aka feedstocks) into resources, keeping them out of landfills.
Sally Brown is a Research Associate Professor at the University of Washington in Seattle. Dr. Brown is a new member of BioCycle’s Editorial Board, and will be authoring this regular column on the connections of composting, organics recycling and renewable energy to climate change. Your comments and suggestions for future columns are welcome. Contact Dr. Brown, or Nora Goldstein, Executive Editor.

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