Brent Holtz 2017-06-28 00:27:48
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. Almond growers are concerned that whole-orchard recycling will deny valuable nutrients to the second-generation trees because of the high carbon-to-nitrogen ratio that could result when the previous orchard’s debris is incorporated into the soil—or that the woody debris may be so large that it interferes with normal soil preparation and orchard management practices. The effects of woody soil amendments on replant disease and pathogens have yet to be determined, but several studies have reported that increased soil organic matter can increase microbial diversity and reduce soilborne diseases. If whole-orchard recycling does not take valuable nutrients from the new trees and does not worsen replant disease or interfere with harvest, then growers would be more likely to adopt grinding and incorporating as an alternative to removing and burning the woody debris from their orchards, especially if advantages to soil health and nutrition can be demonstrated. Recycling versus burning University of California farm advisor David Doll, USDA plant pathologist Greg Browne, and I undertook a project at the UC Kearney Research and Extension center to compare grinding of whole trees with burning as a means of orchard removal. In 2008, an experimental stone fruit orchard on Nemaguard rootstock was used in a randomized block experiment with two main treatments: whole-tree grinding and incorporation into the soil with the Slasher, a 50-ton rock crusher and rototiller produced by IronWolf Manufacturing, versus tree pushing, burning, and spreading the ash. The second-generation almond trees were planted in February 2009. We examined second-generation tree growth, replant disease, soil nitrogen-to-carbon ratio, soil organic matter, soil-plant nutrition, and the soil water-holding capacity between treatments. The whole-tree grinding of the old trees, which produced about 30 tons of debris per acre, did not stunt the growth of replanted almond trees after eight growing seasons. Ultimately, greater yields, significantly more soil nutrients (including calcium, manganese, iron, magnesium, boron, nitrate, potassium, and copper), and higher electrical conductivity, organic matter, total carbon, and organic carbon were measured in the grind treatment plots when compared to the burn treatment plots. Soil pH was significantly lower in the grind treatment plots. Leaf petiole analysis revealed higher nutrient content (nitrogen, potassium, phosphorus, manganese, and iron) and less sodium and magnesium in trees growing in the grind treatment plots compared to the burn treatment plots, proving that the increased organic matter did not stunt the replanted trees. The increased organic matter appears to either reduce the sodium available for tree uptake or improve the soil-leaching efficiency. Replant disease was not observed in this trial. Measurement of leaf stem water potential during the 2015 harvest indicated that the trees in the grind plots were less stressed by temporary water deficits. Furthermore, bud failure severity was lower for trees in the grind plots than in the burn plots. If we had included debris removal in this comparison, we would have observed an even greater contrast between the grind and burn treatments, as spreading and incorporation of the ash after burning also had a positive effect on tree nutrition. Based on the encouraging results of our research, some growers have adopted grinding or chipping and soil incorporation as an alternative to transporting their orchard debris to a co-generation plant. We estimate that approximately 1,500 acres of orchards were ground and incorporated in 2015 and nearly 12,000 acres in 2016. Several new trials were established in 2016 to further examine two different methods of whole-orchard recycling. A trial at AgriLand, a full-service farm management company in Chowchilla, Calif., compares a Morbark horizontal chipper, where the chips have to be spread on the orchard floor in a separate process, with the Slasher, which grinds trees and roots in place—as compared to the standard method of orchard removal for energy co-generation. There are pros and cons with both methods of whole-orchard recycling, which this trial has allowed us to examine. The Slasher versus the chipper We expected that the carbon footprint would be much smaller for the Slasher than for a horizontal chipper or tub grinder because the Slasher performs two tasks with one machine. It travels forward to grind the trees and then travels backward to incorporate the debris into the soil. Removing an orchard with a horizontal chipper or tub grinder requires an excavator to uproot the trees, transporting the trees to the grinder, grinding or chipping the trees, spreading the chips on the ground, and then disking or tilling to incorporate the chips into the soil. However, the Slasher only ground and incorporated about two acres of trees per day, while the horizontal chipper could process up to 15 acres per day. The chips still needed to be spread on the orchard floor and disked in, but most growers can easily perform those tasks. For example, Randy Fondse of G&F Agricultural Services, Inc., in Ripon, Calif., purchased two Kuhn & Knight spreaders that were modified to spread wood chips on the orchard floor during orchard removal. Using these spreaders at AgriLand, Fondse was able to spread wood chips on the orchard floor at the same rate at which they were produced by the chipper, which was 68 tons per acre. In two other orchard recycling trials at Wonderful Orchards in Shafter, Calif., the wood chips averaged 40 and 65 tons per acre on the orchard floor. The Slasher also produces rather large chunks of wood, which are concentrated in a ten-foot-wide strip down the tree row, while the row middles are left relatively clear. Growers may have difficulty with these large chunks of wood if they are performing laser leveling or land scraping. In our initial trial, we had no problems ripping the soil after the Slasher. The ripper shank did not pull out the large chunks of wood left behind by the Slasher. In fact, the ripper operator noted that the Slasher also ground the large roots near the soil surface, which the ripper shank usually pulls up. In contrast, tub grinders produce much smaller chips that can be spread evenly on the orchard floor, typically one or two inches deep, and growers can easily disk or till these wood chips into the soil with their own equipment. Samples of the wood chips were analyzed for their nutrient contents, which averaged 0.31% nitrogen, 0.20% potassium, 0.60% calcium, and 50% carbon. Returning 64 tons of wood chips to the soil per acre provides 396 pounds of nitrogen, 768 pounds of calcium, 256 pounds of potassium, and 64,000 pounds of carbon per acre. These nutrients will not be immediately available to the next-generation orchard. Instead, as the woody material decomposes and organic matter accumulates, the nutrients will be released gradually and naturally. In two other replant trials in Kern County, Calif., whole-orchard recycling with a tub grinder is being compared to soil fumigation treatments that include spot fumigation, strip fumigation, and a non-fumigated control. Anaerobic soil dis-infestation treatments will also be examined, comparing ground rice hulls with ground almond hulls and shells. There will be six replications of 18 trees per treatment combination, arranged in a randomized complete block design for statistical analysis. This is the most extensive orchard trial I have ever witnessed or participated in! The orchard was planted to second-generation almond trees this past winter. Recognition and future research In the meantime, Amelie Gaudin (an agroecologist at UC Davis), Andreas Westphal (a nematologist at UC Riverside), Elias Marvinney (a post-doctoral scientist at UC Davis), Mohammad Yaghmour (UC Farm Advisor for Kern County), Mae Culumber (UC Farm Advisor for Fresno County), and Phoebe Gordon (UC Farm Advisor for Madera County) have joined our research team. We hope to determine if additional organic matter will increase the water-holding capacity of the soil as well as the ability of the soil to bind nitrogen, pesticides, and fertilizers that would otherwise leach out of the soil profile. The Accelerated Innovation Management (AIM) program of the Almond Board of California, which emphasizes stewardship of resources, sustainability, and production efficiency, recently funded the whole-orchard recycling project. Our specific objectives are to compare whole-orchard recycling with conventional orchard residue removal and burning in a co-generation facility to (1) refine the life cycle assessment (LCA) model for the evaluation of carbon dynamics, (2) quantify the physical, chemical, and biological soil properties that result from whole-orchard recycling, and (3) assess the effects on the growth, health, nutrition, and water use of the replanted orchard. In 2016, the California Department of Food and Agriculture and the Almond Board of California ranked increasing soil organic matter as a funding priority, and they funded our project just as world leaders were making capture of carbon in the soil a formal part of the United Nations Climate Change Conference agreement in Paris. We hope that this project will demonstrate the success of whole-orchard recycling and provide scientific evidence to support legislation that allows growers to receive carbon credits for recycling their orchards into the soil. These carbon credits would encourage sustainable agriculture and help compensate growers for the expenses they incur when adopting whole-orchard recycling. Brent Holtz, County Director and Farm Advisor, University of California Cooperative Extension in San Joaquin County, Stockton, Calif., USA, firstname.lastname@example.org. VisualChallenge7 is coming! Ag and Bio Engineering Beyond the Words To once again celebrate the visual aspects of the ABE profession, Resource magazine announces its seventh annual Visual Challenge—an opportunity to show those outside the field: “This is what we do.” Your entry can convey the beauty and meaning of your work, your research, your ASABE activities, or your professional experience as you pursue daily tasks or distant travel. Submit your original photography or illustration as an e-mail attachment in JPG format, 300 dpi or higher, to Sue Mitrovich (email@example.com). Enter “VisualChallenge7” in the subject line of your message, and include your full name, professional affiliation, contact information, and a descriptive caption for your entry. If necessary, include a source credit and an assurance that permission has been granted to submit, and possibly reprint, your entry. Multiple entries are welcome. The deadline for entries is October 2, 2017. The winning entries will be selected by Resource staff and published in the January/February 2018 issue. We look forward to your vision of ABE that goes beyond the words! Check out the winning entries from previous years at www.asabe.org/VisualChallenge.
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