Preliminary report on the effect of tire chips as a mulch and substrate component for blueberries

Disposal of scrap tires is a environmental and health problem since most landfills will not accept them, and they provide breeding sites for virus-carrying mosquitoes. In 1995 and 1996, tires cut into chips (about 75-150 mm size pieces) were tested as a mulch. Smaller tire chips (less than 32 mm)were tested as a container substrate component for blueberries. Mulching treatments were unmulched (control), pine bark nuggets (industry standard), tire chips, and milled yard waste. Mulching treatments were 10 cm deep x 91 cm wide centered on the row. Both rabbiteye and southern highbush blueberries were used in the experiment on nine sites. Mulching in July or Aug. did not increase plant growth the first growing season, but there was a trend toward increased plant growth on most sites. Mulching for 11 to 12 months significantly increased growth on two of eight sites and there was a trend toward increased growth on most other sites. Mulches greatly reduced peak soil temperatures and weed growth. Tire chips were nearly as effective as pine bark in reducing peak soil temperature in the root zone. On a hot day, mean afternoon temperature at the 5 cm soil level was reduced by about 8.8 degrees C by the pine bark and 8.3 degrees C by the tire chips compared to bare soil. Mulching with tire chips increased soil zinc levels, but not leaf zinc levels. There was no apparent phytotoxicity from mulching with tire chips during the course of the study. In an additional phytotoxicity experiment, plant growth was not significantly different for plants grown in 100% milled pine bark substrate versus a mix of 25% small tire pieces (less than 32 mm) and 75% milled pine bark substrate. Plant growth was significantly less for plants grown in 25% styrofoam "peanuts" and 75% milled pine bark substrate. Tire rubber contains about 1.2% zinc, so additional monitoring is needed.