Hi, all, Much prefer Adam's post on garden joys and good eating, but this kind of tire exchange is one of the invaluable contributions of this list.
I'd like to pass along information on old tires in the garden from a USDA agronomist who has focused on composting and soils, Dr. Rufus Chaney. Seems like a good reliable place to start. Before his remarks, a couple of comments - The product I'm most concerned about is shredded tire 'mulch', as opposed to using whole tires as planters. Part of the problem is aesthetic - the 'mulch' stinks and gets sticky in hot weather. Sometimes, you see it advocated for playground use. Our car-intoxicated culture generates a huge number of old tires. Figuring out an environmentally sound method of dealing with them is a high priority. This foul smelling 'mulch' ain't on my list. My thought is that old tires are best re-integrated into pavement and, maybe, as 'frames' for inexpensive structures (Michael Reynold's 'Earthships'). 'Whole tire' planters probably are not much of a short-term risk, especially if painted with a tough non-toxic paint and/or lined with plastic (don't forget drain holes!), because of their relatively low surface area in contact with soil and microbes. But I still don't use 'em. I don't like the way they look, and, long-term, anything in the rubber will end up in your soil, as Dr. Chaney says. I completely agree that tires are especially inappropriate (and impractical) as compost containers. In two words - no, thanks. Here are Dr. Cheney's comments (from the SARE website, Sustainable Agriculture Research and Education, www.sare.org. Damn fine outfit.). It is in response to a post about recycled tires and their ag uses: >As you can see below, Pat Millner sent me a copy of the questions and responses about tires. I have been part of the USDA composting team since 1973, and studied metals in soils and food-chain from any source. Tires normally have 0.5-2% Zn. Most rubber items have this much Zn. In many situations, when rubber was used in plant growth media, or burned tires residues were on soils, Zn killed plants. There is an interaction between soil or medium pH and Zn toxicity. At a reasonable rate of application, rubber would be a high grade Zn fertilizer over time because the Zn in rubber is purified, with very low Cd concentrations. I have cited a number of papers over the years about Zn phytotoxicity from rubber, but not conducted research on this myself. This Spring, I attended a meeting in NC where one speaker noted that farmers had heard from one another that if you put a tire around a tree stump and started it afire, it aided in buring the stump to the ground. But when they tried to grow Zn sensitive crops, even at neutral pH, Zn killed peanuts and some other species. Because of the numerous adverse effects of rubber-Zn, I have advised against using rubber in any composting, or in any potting medium, and casual dispersal of rubber on agricultural or garden soils. If you need references, please write back. This topic was first reported in the early 1970s, and then re-done in the 1990s by people who didn't search literature. A nice demonstration of negative effects of rubber in potting media was recently reported from Australia by Handreck, I think in Commun. Soil Sci. Plant Analysis. Rufus Rufus L. Chaney Environmental Chemistry Lab USDA-Agricultural Research Service Bldg. 007, BARC-West Beltsville, MD 20705 Phone: 301-504-8324 Fax: 301-504-5048 On Wed, 5 Mar 1997 [EMAIL PROTECTED] wrote: > ---------- Forwarded message ---------- > Date: Wed, 5 Mar 1997 10:07:02 -0600 (CST) > Subject: Re: tires > > I'm sorry that I cannot cite the original reference--I cannot > remember it, and I don't have time to look it up, but... > the study was done with tires that were to be "landfilled" > in ponds. Dumped. > > Anyway, the upshot of the research was that tires without metal > belts were "stable," without any apparently harmful contaminants > or breakdown products leaching into water. However, tires with > exposed metal belts (ruptured, blown, whatever) leached trace > amounts of heavy metals into water. > > It was research conducted in the US. I agree that tires are being recycled in many ways. But use in the root zone has caused severe Zn phytotoxicity in numerous locations. Ash from tires is a toxic material, and barren soils (some declared hazardous sites) resulted where huge piles of tires burned (one in Washington State several years ago). I am not familiar with any aspect of the breaking of the surface of the rubber which was involved. Over time, rubber is biodegraded, and the constituents of the rubber become part of the soil. Rubber also contains considerable sulfide, which will acidify the soil making the Zn more phytotoxic. The higher the surface area of the rubber in the soil, the greater the transfer of Zn from the tire to the soil root zone. But whether you start with large chunks or small chunks of rubber, eventually between microbial and photodegradation, the matrix is lost and the Zn become under the control of the soil chemical processes. If acidic, plants are killed. I have a paper on Zn phytotoxicity in the book "Zinc in Soils and Plants", edited by Robson, 1993. > > Used tires are being recycled in many ways-road beds, building materials for > > houses, fuels for kilns, erosion stablization, shredding to improve turf field > > drainage. > > > > But---What about food production? Creating raised beds out of used tires and > > growing vegetable crops. Tires around soil as a raised bed garden has been used by many people. I have not heard of problems from that, but the surface area in contact with soil is small. In the short term, it may be little problem. But eventually the rubber degrades, Zn gets in the soil, and if the soil pH is 6 or below, uptake may be too much. Again, the higher the surface area, the more rapid the release of Zn and toxicity observation. > > What are any possible problems with this (e.g., heavy metals, xenobiotics)? > > Current thought is that tires are stable, with the only problems being in > > rodent and insect populations increasing. any ideas?? "Stable" is relative. Over time, microbes biodegrade rubber as a good source of energy. Toxicity to plants from ground rubber used as a mulch or a component or potting media, or burned tire residues in soils, have killed a wide range of plant species.< ______________________________________________________ The American Community Gardening Association listserve is only one of ACGA's services to community gardeners. To learn more about the ACGA and to find out how to join, please go to http://www.communitygarden.org To post an e-mail to the list: [EMAIL PROTECTED] To subscribe, unsubscribe or change your subscription: https://secure.mallorn.com/mailman/listinfo/community_garden
