Grower's Guide to WOR

Whole orchard recycling: An orchard removal method that can boost yields and lower water use in the replanted orchard.

Recently recycled orchard
A recently recycled almond orchard in Denair, CA, on 10/17/2018. Potted trees were planted in April 2018.

 

Burning restrictions and power plant closures are leaving growers in need of solutions for disposing of their old trees in an economical and environmentally friendly way.

 

Whole orchard recycling (WOR) is one solution to this challenge. It involves:

  • on-site grinding or chipping of whole trees during orchard removal;

  • incorporation of the chips or grindings into the topsoil before replanting.

Common questions about WOR

To see a full list of common questions and answers, visit our FAQs page.

  • Will whole-orchard recycling perpetuate diseases in the orchard? Should I still recycle my orchard if I have disease problems?
  • Research on this topic is just beginning, but there is good reason to believe that most almond diseases will not be transmitted by recycled wood. There are several exceptions: we do not currently recommend recycling orchards that are infested with Armillaria, Ganoderma, or crown gall. See our Tree Health page for more information.
  • Do I need to apply extra nitrogen in the first year after replanting? If so, how much and for how long?
  • Yes, extra nitrogen is essential to avoid stunting of the replant orchard. Based on our field trials so far, we recommend doubling N applications in the first year after replanting, from 3-4 ounces of N per tree (50-70 lbs N per acre) to 6-8 ounces of N per tree (100-140 lbs N per acre). This extra N should be started early and applied gradually. Extra N application in the second year is often unnecessary but can be done if needed.
  • How quickly do the chips break down? Will they still be there at the first harvest, and if so, will they cause any problems?
  • The longevity of wood chips in the orchard depends on the chip size, the total amount of chips, whether they were pre-treated to speed decomposition, and the depth to which they were incorporated. Some recycled orchards have almost no chips visible at planting time, while others still have visible chips several years later. Fortunately, very few growers and hullers/shellers have reported problems with wood chips contaminating the first harvest.

 

Nutrient Use and WOR

Growers who do whole orchard recycling may need to apply fertilizer nitrogen at greater rates than what is normally recommended for trees in their first leaf.

 

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, but as the woody material decomposes and soil organic matter increases, the stored nutrients will be released gradually and naturally.

Second leaf trees
Second-leaf replanted orchard on recycled block (Denair, CA, 2/28/2019)

While the large amounts of organic material added to the soil by WOR has many benefits (see box above) it can create an imbalance in the ratio of carbon to nitrogen in the soil, which can lower the availability of nitrogen from fertilizers in the newly planted orchard.


Brent Holtz, UCCE County Director and Farm Advisor of San Joaquin County recommends:

  • growers apply at least 6-8 ounces of actual nitrogen per tree (50-70 lbs N/ acre) in the first year of tree growth following whole orchard recycling. After the first year of tree growth, growers can return to typically recommended rates of fertilizer nitrogen application;

  • nitrogen should be applied early in the season;

  • nitrogen applications should be spread out so that no more than one ounce of actual nitrogen is applied per tree per application in the first year of tree growth.

Cost considerations with WOR

WOR requires some upfront costs and different practices than other orchard disposal methods (see table below).

 

However, with burning restrictions and with biomass power plants paying less and less for wood chips, costs to the grower of implementing WOR are comparing increasingly favorably with hauling chips to a power plant, particularly when long-term yield and water saving benefits are considered. See our Cost Guide for more details.

Land preparation task

Scenario 1: Burn

Scenario 2: Grind and haul

Scenario 3: Grind and recycle

1. Pulling trees $200-$300/acre $200-$300/acre $200-$300/acre
2a. Grinding trees Not done $500-$700/acre $500-$700/acre
2b. Burning with permit $400-$500/acre Not done Not done
3. Spreading chips Not done Not done $125-$400/acre
4. Deep ripping $300-$700/acre $300-$700/acre $300-$700/acre
5. Discing $50-$80 (for 2x) $50-$80 (for 2x) $50-$160 (for 2-4x)
6. Plowing (optional) Not standard Not standard $0-$50/acre
COST DIFFERENCE Baseline + $0-$200/acre + $125-$810/acre

 

After the above land preparation expenses, growers can follow their usual practices of soil fumigation, making berms and floating, planting trees, and installing an irrigation system (none of which vary due to WOR).

We have observed about a 1,000-pound kernel increase per acre from almond trees growing where the previous orchard was recycled after 8 seasons in our original trial at Kearney Agricultural Research and Extension Center. If this trend turns out to be widely applicable to other recycled orchards, it would pay back the additional costs of orchard recycling within the first few harvests. Water savings of 10% or more are also possible according to our preliminary data.



Spreading chips
Spreading chips with a modified manure spreader (Denair, CA, 10/17/18)