Views from Almond Professionals on Whole-Orchard Recycling
Amber Kerr,UC Sustainable Agriculture Research and Education Program (UC SAREP), Agricultural Sustainability Institute, University of California Davis
Sonja Brodt, UC Sustainable Agriculture Research and Education Program (UC SAREP), Agricultural Sustainability Institute, University of California Davis
Brent Holtz, University of California Cooperative Extension, San Joaquin County
Amelie Gaudin, Department of Plant Sciences, University of California Davis
Almond orchard removal in California’s Central Valley is more expensive and complicated than it used to be, due to closures of biomass energy plants and stricter regulations on open burning. In response, an increasing number of almond growers are trying whole-orchard recycling, the practice of chipping the old trees and incorporating the wood chips into the soil before replanting the new orchard. Research on whole-orchard recycling (WOR) began in 2009, but only in the last few years have enough growers tried the practice to give a clearer picture of its effectiveness in the real world. What do adopters and non-adopters think about WOR at this early point in its development?
Almond wood chips on the floor of a recycled orchard in Stanislaus County (2/2019), ready to be incorporated before the orchard is replanted. All photos by Amber Kerr.
Our team just completed a three-year field trial funded by the California Department of Food and Agriculture to investigate how whole-orchard recycling affects soil properties and tree growth. To guide the creation of outreach materials for our new website, and to prioritize future user-driven research, we conducted a series of surveys and interviews with almond professionals around the state. The results were informative in their own right, and we wanted to share them with a wider audience.
Survey and interview methods
We surveyed California almond professionals in two ways: (1) Paper surveys handed out at two WOR-focused field days in October 2018; (2) An online survey that was advertised via paper flyers at the December 2018 Almond Conference and via email to readers of West Coast Nut magazine. Here, we will present quantitative results from the online survey, which had similar outcomes but a larger sample size than the paper surveys.
We also conducted 30 phone and in-person interviews with survey respondents who voluntarily identified themselves for follow-up (along with other almond professionals known to have relevant expertise). Insights from those in-depth conversations are reported after the quantitative survey results.
A newly replanted orchard in Stanislaus County (2/2019) that was recycled in Fall 2018. Some wood chips are still visible on soil surface.
Online survey respondents
Our online survey received 125 valid responses, of whom the majority were WCN readers responding to an emailed survey link. They self-identified as 59% growers, 28% crop advisors or extension agents, 22% suppliers of farm products or services, 2% commodity board members, 2% researchers, and 13% other. (Each respondent could choose multiple categories if applicable, so percentages sum to more than 100%.)
Of these respondents, 27% had actually implemented whole-orchard recycling; 50% were familiar with how it worked but had never tried it; 18% had heard of it but did not know the details; and 6% had never heard of it before taking the survey. We note that WOR users are overrepresented in this survey; a random sample of almond growers and advisors would show much lower levels of experience with WOR. (Our best estimate, according to informed guesses from orchard removal companies and crop advisors who work with large numbers of growers, is that the current adoption rate of WOR ranges between 5% and 10% in the San Joaquin Valley, whereas it is close to 0% in the Sacramento Valley.)
Online survey results: Benefits
We first asked respondents (n = 125) to chose all possible benefits of whole-orchard recycling from a list of options, and then we asked them to identify what they thought was the main benefit. When asked to “choose all that apply,” respondents spread their answers nearly equally across all the options, ranging from carbon sequestration to yield increases. But when asked to name only the “most important benefit,” respondents clearly focused on two factors (Figure 1a): improving soil physical properties (chosen by 30%) and providing the most economical option to comply with air quality regulations (21%).
When we examined only the subset of respondents who had actually practiced WOR (n = 33), opinions shifted in an interesting way (Figure 1b). Economical compliance with air quality regulations was their number one perceived benefit of WOR (27%), followed by soil physical properties (21%). Not a single one of these WOR adopters thought that soil nutrient status was the main benefit, perhaps due to their experience with higher nitrogen demand in recycled orchards. Three adopters (9%) said that the practice had no major benefits, indicating that not everyone had a positive experience with WOR.
Most important benefit of whole-orchard recycling in almonds, according to online survey participants in December 2018. (Answers were mutually exclusive; respondents could only pick one.)
Online survey results: Drawbacks
Similarly to the benefit questions, we asked respondents to choose all perceived drawbacks of WOR from a list, and we then asked them to select the single most important drawback. Answers to the “choose all” question (not shown) had a similar breakdown to the “single most important” question. Opinions on the most important drawback are shown for all respondents (Figure 2a) and for WOR adopters only (Figure 2b).
Most important drawback of whole-orchard recycling in almonds, according to online survey participants in December 2018. (Answers were mutually exclusive; respondents could only pick one.)
The most notable difference between all respondents versus only adopters was how they perceived the issue of disease in the replanted orchard. Disease risk was the number one concern for respondents in general, but for respondents who had actually tried WOR, disease dropped to a fourth-place tie. Our data cannot clarify the direction of cause and effect (growers may be more likely to try WOR if they have no major disease concerns), but it does seem that WOR adopters have not generally noticed increases in disease so far.
Concerns about expense were common among all participants (22% named it as the top drawback). Among adopters, expense was an even bigger concern (27%) than among non- adopters. A variety of other drawbacks were consistently mentioned (woody debris; poor nitrogen status; lack of equipment; etc.), and only 4/33 adopters (12%) said that they had no major problems with WOR. This ranking of benefits and drawbacks helped us focus our in-depth interviews by phone and in person.
In depth interview results
We wanted to learn how growers and crop advisors overcame the stumbling blocks of whole-orchard recycling and whether they were on track to see its theoretical benefits. The headings below correspond to the most frequently-asked questions from the write-in sections of our surveys. We answer these questions to the best of our ability on the basis of our field research and interviews with almond professionals in January to March 2019.
These interviews comprised 30 practitioners (12 growers, 13 crop advisors, and 5 other professionals including nursery operators and almond processors).
Is WOR too expensive?
WOR has a higher upfront cost, but the extra cost depends on the baseline practice that it is being compared to. Where open burning of old orchards is still common and legal, that may still be the cheapest option, at least for now. WOR is similar in price to the grind-and-haul disposal method, except for the additional cost of spreading the chips (which our interviewees reported as being $125-$400 per acre). Subsequent land preparation (deep ripping, disking, leveling, floating; fumigating) is usually the same regardless of whether WOR is used, though some of our interviewees noted the need for more tillage and/or larger equipment to incorporate the chips properly.
Many interviewees mentioned that they would be more eager to try WOR if the additional cost could be offset by a subsidy. Although WOR is not yet eligible for CARB greenhouse gas offsets, nor is it yet on the list of funding-eligible NRCS EQIP practices, the San Joaquin Valley Air Pollution Control District now offers an incentive of $600 per acre for grinding and incorporating wood chips (helping to offset the cost compared to burning).
Does WOR perpetuate diseases?
Little empirical research has been done on this question. However, none of the growers and crop advisors in our interview sample who had done whole-orchard recycling (n = 13) had noticed any disease concerns in the replant orchard. Theory suggests that once the chips are dried and incorporated into the soil, they do not tend to harbor viable pathogens from above-ground parts of the tree (twigs, branches, flowers). Nor do wood chips from WOR appear to affect fumigation efficacy, according to our interviewees.
Expert opinion differs on which almond diseases are incompatible with WOR. Two diseases of special concern are Armillaria (oak root fungus) and Ganoderma adspersum (a virulent butt rot fungus found from Madera County south), because they are known to survive in dead wood. Although is no direct evidence that wood chips from these infected trees would increase disease pressure (beyond what already occurs from left-behind infected roots and soil), growers with heavy infestations of Armillaria or Ganoderma may want to err on the side of caution and dispose of old orchard wood offsite or by burning.
Research is also needed on whether crown gall (Agrobacterium tumefaciens) and band canker (Botryosphaeria sp.) can be transmitted via orchard recycling, as these pathogens may be able to persist in wood and/or soil. To reduce the risk of any disease organisms surviving the recycling process, we recommend grinding the wood with a 2” screen and letting the chips dry completely on the surface before incorporating them thoroughly.
What equipment is needed?
Most growers lack the specialized equipment (usually, horizontal grinders and modified manure spreaders) to carry out WOR themselves, so finding a trusted contractor is crucial. Because demand for orchard removal services exceeds supply, and because WOR is a new practice, there is a risk of poor quality control. Many WOR adopters reported frustration due to orchard removal companies arriving weeks
late, spreading the chips unevenly, and/or not incorporating the chips properly before they rushed off to the next job. A Stanislaus County grower reported that the first time “didn’t go very well” due to careless spreading, which left large wood chunks and uneven chip depth. She had to change contractors three times over the next three years and is now happy with the results.
For post-spreading land preparation, many interviewees reported good results from using a moldboard, Baker, or switch plow (in addition to deep ripping and stubble disking). Leaving the chips mostly in the top 4-6” of soil is not desirable, especially if the chip layer was more than 3-4” deep to begin with.
No chips are visible on the floor of this fifth-leaf Nonpareil / Aldrich orchard, which was planted on a recycled orchard block in 2015. (Merced County, CA, 3/2019)
How fast do the chips decompose?
Most growers practicing WOR have no problem obtaining a clean orchard floor in time for the first harvest in year 3 or year 4. “The chips disappear after one full season,” said a grower in Merced County who is on his 6th round of WOR. The few growers who did have problems with woody debris generally used a large screen size (>4”), had excessive amounts of wood (>60 tons/acre), and/or lacked adequate equipment to incorporate the chips below 4-6” depth.
Growers have achieved better decomposition rates by letting the chips dry on the soil surface first, treating the chips with fertilizer, manure, or irrigation before the new orchard is planted, and maintaining native vegetation or planted cover crops in between the tree rows. Many growers who started out trying a larger chip size (4-6”) say that next time they would spend the extra time and cost to obtain a smaller chip size (2-4”).
Will the replant orchard be stunted?
After some early setbacks with nitrogen-starved replant orchards, growers and researchers alike have learned that proactive extra fertilization is crucial for success following WOR. UC Cooperative Extension Advisors Brent Holtz and Mae Culumber summarized these findings in the 2/2019 issue of WCN. In a nutshell, they recommend 6-8 ounces of N per tree during the first year after WOR – a doubling of the standard amount. Our interviewees noted that the timing of this extra N is as important as the amount; the additional N demand kicks in surprisingly early, as soon as March. One WOR adopter in San Joaquin County made a habit of checking on the leaf color of his replant orchard daily, using a pair of binoculars from his kitchen window. “It was fairly time-consuming working out that nitrogen issue,” he said.
How does WOR benefit the soil and the trees?
Although it is too soon to generalize about yield increases under whole-orchard recycling, the original 2009 WOR trial at Kearney Ag Center has shown a consistent yield advantage of about 20% (215 kernel-lbs/acre) in the recycled plot compared to the burned control plot over the first seven bearing years. Only one of our interviewees had orchards that were of bearing age after WOR, so not enough farm-level data are available yet.
Data on soil physical properties is encouraging so far. The field trials in this experiment have shown that, over the first three years, WOR increases soil organic matter, water infiltration, soil microaggregate stability, and soil water-holding capacity, among other factors. We expect to see these effects translate into healthier, more water-efficient trees over the longer-term.
Acknowledgements and more information
Research on whole-orchard recycling is ongoing, and we want to hear from as many practitioners as possible. You can contact us via the new website orchardrecycling.ucdavis.edu, which also includes the latest research results, best-practice guidance, interviews with grower adopters, events, and publications.
PIs on this project were Amelie Gaudin (UC Davis), Brent Holtz (UCCE), Sonja Brodt (UC Davis), Greg Browne (USDA/ARS), and Andreas Westphal (UCR). We extend our sincere thanks to the 30 interviewees who gave so generously of their time, as well as to the 181 survey respondents who shared their thoughts for the benefit of the community.