Orchard Productivity

Nuts on an almond tree — Nuts in a Nonpareil/Aldrich orchard on Atlas rootstock, planted in 2015 on a recycled orchard block. Kruppa Farms, Winton, CA, 3/21/19.

How does WOR impact orchard productivity?

Many factors of production are important for generating good yields from almond orchards after WOR, and the grower must consider the potential tradeoffs of inputs like water and fertilizers with expected kernel yields. UC research on the long-term effects of WOR over a period of 9 years suggests that WOR may allow growers to maintain or increase yields under typical nitrogen and irrigation regimes.

Initial results also suggest that second-generation orchards planted following WOR require a greater input of nitrogen fertilizer in their first season to counteract N immobilization to decompose woodchips and reduced shoot growth, but thereafter trees “catch up” to achieve the expected growth rate and do not require additional fertilizer in subsequent years. Another study in 2004 showed that, without any nitrogen fertilizer, almond trees grown in barrels with wood-chip-amended soils exceeded the growth rate and leaf petiole nutrient levels of trees grown in non-amended soils by the third year after planting (Holtz and Caesar-TonThat, 2004). These results suggest a potential for growers who incorporate wood chips into their orchard soils to reduce fertilizer inputs after the first year without sacrificing tree health or development.

WOR Effects on Almond Yields

Almond yield (+ up to 20%)

WOR Effects on Nitrogen Requirements

Nitrogen fertilizer requirement in first year after replanting (+100% or more)

WOR Effects on Water Use Efficiency

Water use efficiency (+20%)

Results: Kearney Agricultural Research and Extension Center

These results are from a long-term trial assessing effects of whole orchard recycling over nine years

Water Use Efficiency

Research at Kearney found an increase in irrigation water use efficiency in WOR plots compared to the control treatment.

Almond kernel yield under two different irrigation scenarios was shown to be greater in WOR plots compared to the control (push and burn) treatment. In 2017 this research found a statistically significant increase in yield (and water use efficiency) of 20% under regular (100% ET) irrigation. A smaller increase was observed in a deficit (80% ET) irrigation treatment, although this finding is not statistically significant.

Almond kernel yield comparison between regular and deficit irrigation — Almond kernel yield was 20 percent greater in whole orchard recycled plots under regular irrigation. Asterisk (*) indicates a statistically significant finding (*p ≤ 0.05*).

Almond Yield

Table A shows an annual comparison of kernel yields at regular (100% ET) irrigation in the WOR and control treatments at Kearney for years 2011 through 2017 (years three through nine following the orchard turnover). Yields are greater in the WOR plots for all years, with the difference peaking in year six.

**Table A**. Comparison of yields in WOR and control treatments at Kearney for years three through nine following orchard turnover.
Year	Whole orchard recycling (lbs/acre)	Burned (lbs/acre)	Difference (lbs/acre)
2011	1,007.3	925.0	82.3
2012	1,618.4	1,533.1	85.3
2013	2,100.6	1,853.1	247.5
2014	2,829.5	2,331.1	498.4
2015	1,599.6	1,427.1	172.5
2016	1,603.2	1,504.6	98.6
2017	2,674.1	2,355.8	318.3
Total	13,432.7	11,929.8	1,502.9

Results: Nitrogen Use In a Private Orchard in Parlier, CA

Almond tree showing improved shoot growth — Figure 2 Shoot growth improved quickly with nitrogen application

Almond tree showing stunted shoot growth — Figure 1 Reduced shoot growth on a tree not supplemented with nitrogen during the first year after previous orchard was recycled

A previous study by Merced County UCCE Farm Advisor David Doll determined that first-year almond trees grew best when given 25-35 lbs N per acre in the first growing season, with applications spread out to apply no more than one ounce of actual N per tree per application.

However, this may not be enough under WOR, where 40-60 tons of wood chips, containing 15-30 tons of organic carbon, are incorporated into the soil. Observations of trees planted after WOR in Manteca and Parlier suggested that the high carbon-to-nitrogen ratio in the woodchip and soils following incorporation was likely causing immobilization of nitrogen resulting in poor shoot growth.

Initial research results in Parlier suggest that a larger application of nitrogen fertilizer (50-70 lbs N per acre) in the orchard’s first year can make up for this deficit in soil nitrogen. Trees responded quickly to a hand-application of 15-15-15 granular fertilizer at a rate of 0.8 ounces per tree (Figures 1 and 2), and by the second year, trees in the WOR trial had achieved growth rates comparable to those in non-WOR plots without the addition of further nitrogen fertilizer.

These results suggest that growers undertaking WOR may need to consider nitrogen use when assessing overall orchard productivity. Although this research suggests an increase in nitrogen use is necessary in the first year, the increased costs associated with recycling and more N input in the first year may well be returned by the lack of need to use fertilizer in subsequent years and by increases in water use efficiency and almond kernel yields.