Chips from old trees renourish the soil for new ones
ByBob Johnson The end of the productive life of a block of almonds offers a unique oppor- tunity to use the old trees to make one last contribution to the health of the soil before replanting. University of California studies show the feasibility of chipping the old trees, incorporating the chips into the soil and taking a year off before replanting. “It’s a once-in-a-30-year opportunity to add organic matter to your soil,” said Brent Holtz, UC Cooperative Extension farm advisor in San Joaquin County. “Pruningmight be 1,000 to 2,000 pounds an acre, but it’s not like the 60 tons you can get from recycling.” Holtz has been a leading researcher of chipping and keeping first annual pruningmaterial in the orchard. Inmore recent years, he has suggested adding chipping and keeping entire blocks of trees that are due for replacement. He appeared at the Nickels Soil Lab Annual Field Day in Arbuckle as grow- ers looked over an area of the research orchard where old, unproduct i ve trees were removed and chipped in December 2016. They were incorpo- rated into the soil before replanting in the spring of 2019. “The trees are looking great,” Holtz said, standing near rows of nonpareil and
estimates 50,000 acres of old trees are being replaced every year. Holtz recommends taking a year off between incorporating the old trees into the soil and replanting to give the soil microbes time to break down the wood chips—so they do not interfere with or- chard operations. When the 20 acres of old trees at the Nickels site were first removed and chipped, the resulting piles of wood were imposing. “There were three piles of wood chips that were three or four stories tall,” Holtz said. “But spread out, it was an inch or two.” After waiting well over a year, the new block was planted in nonpareil almonds and the pol linator variety Carmel at a three-to-one ratio. The pause appears to have helped make the new orchard workable. “One of the things people worry about is the chips getting in the way,” he said. “There is more on the ground here from cover crops and weeds than the chips.” In addition to needing time and fu- migation to rid the ground of diseases and nematodes, the new trees also re- quire supplemental fertilizer because otherwise the carbon in the chips can tie up nitrogen and starve the trees. “The chips are 50% carbon, so we need more nitrogen at first,” said Holtz, who has studied how much addition- al nitrogen the new trees need. “We probably need to put on more than 30 pounds, but we probably don’t need to put on 100 pounds.” “Trials show that between 30 and 60 pounds is right,” Holtz added. “I think around 45 pounds, but no more than 1 ounce of nitrogen per tree at a time.” He advised applying the nitrogen ear- lier rather than later to feed themicrobes that break down the chips and also break down whatever was living on or in that old wood. Although it is too early to assess the yield of the trees planted in the chip-en- riched ground at Nickels, the early growth of the trees is promising. Plots were divided into those fumigat- ed or not and between those receiving 25 tons or 52 tons of chips an acre or no chips at all. “To date, tree growth is generally good across this orchard,” Holtz said. “Fumigation did improve tree growth as measured by trunk cross-sectional area. Tree growth in the two different chip rates was greater than in the no- chip treatments. But there was no dif- ference in trunk area between 25 or 52 tons of chips per acre.” The difference in size between the fastest and slowest growing among these young trees is just 10%, as measured by trunk size. ( Bo b J o hn s o n i s a r e p o r t e r i n Sacramento. He may be contacted at bjohn11135@gmail.com.)
University of California Cooperative Extension farm advisor Brent Holtz speaks about whole or- chard recycling during a seminar at the Nickels Soil Lab in Colusa County.
Carmel pollinator almonds planted at Nickels after the old block was recycled. “I think one of the things that helped is that the trees were taken out in 2017 and theydidn’t put thenewtrees inuntil 2019.” The i nc o r po r a t i on o f ma s s i v e amounts of organic material benefits the soil, the environment and the next generation of trees, Holtz said.
“It improves water-holding capac- ity, infiltration and yield,” Holtz said. “Showing how long the carbon stays in the ground gets this qualified as a healthy soils practice.” Although recycling an entire orchard by chipping the wood and incorporat- ing the chips into the soil can work, the challenge is in the details. The decision to remove in 2016 a 20- acre orchard planted a quarter century earlier at the Arbuckle site gave research- ers a chance for an in-depth study of re- cycling into the ground and impacts on soil quality and growth and productivity of the next trees. The fate of those old trees has be- come agronomically and environmen- tallymore important than ever, as many orchards planted near the beginning of the almond boom are due for replace- ment. The Almond Board of California
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