Whole-Orchard Recycling Can Sequester Carbon and Improve Soil Fertility

Abstract.

Before air quality restrictions were implemented, orchard removal meant pushing trees over and burning them. More recently, old orchards were uprooted and ground with a tub grinder or wood chipper, and the woody debris was hauled to a co-generation plant, which burned the debris to generate electricity. A small percentage of the wood waste was also sold for use as mulch. However, many biomass co-generation plants have closed throughout California, and the remaining plants have reduced the amount of wood debris they will accept and reduced the price they will pay. Tree fruit growers who need to remove old trees need an alternative method of disposing of the resulting debris. Whole-orchard recycling, which involves grinding and soil incorporation of whole trees, could be a sustainable method of tree removal that would enhance both air and soil quality. When trees are ground with a tub grinder and the woody debris is burned in a co-generation plant, the stored carbon and nutrients in the wood are lost from the orchard system. With whole-orchard recycling, the soil is amended with the woody debris. We hypothesize that the amended soil can sequester carbon and provide increased soil organic matter, increased soil fertility, increased water retention, and reduced emission of greenhouse gases.