Four-years after whole orchard recycling; effects on soil ecosystem services in young almond orchard

Authors: Thao, Touyee; Gao, Suduan; CULUMBER, CATHERINE - University Of California Agriculture And Natural Resources (UCANR); Poret-Peterson, Amisha; Perez-Sandoval, Julio; HOLTZ, BRENT - University Of California Agriculture And Natural Resources (UCANR)

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2026
Publication Date: 4/26/2026
Citation: Thao, T., Gao, S., Culumber, C.M., Poret-Peterson, A.T., Perez-Sandoval, J.C., Holtz, B.A. 2026. Four-years after whole orchard recycling; effects on soil ecosystem services in young almond orchard. Soil Science Society of America Journal. 25,e70099. https://doi.org/10.1002/vzj2.70099.
DOI: https://doi.org/10.1002/vzj2.70099

Interpretive Summary: Whole orchard recycling (WOR) is an approach to managing large quantity of on-farm biomass during orchard turnover. Yet, the long-term impact of incorporating large amount of woody material to soil is still unclear. In this study, we evaluated the potential benefits of soil amended with recycled woodchips in a four-year-old replanted almond orchard. We monitored its effect on soil gas emissions (e.g. CO2, N2O, and CH4) and influence on soil carbon (C), nitrogen (N), and nitrate (NO3-) leaching, during the fifth and sixth years. We observed that by year six, soil CO2 emissions from WOR and control became similar, suggesting mineralization of woodchips had been substantially reduced. Likewise, no difference in soil N2O and CH4 emissions were observed across soil treatments in both years. However, soil C, total N, and NO3- were substantially greater in WOR plots compared to control in year six. No difference in NO3- leaching potential was detected between WOR and control. Overall, four years after WOR conversion, a positive effect on soil ecosystem services was observed. Findings from this research are important knowledge to California agriculture as perennial cropping systems (e.g. almond and pistachio) hold significant economic value, with traditional biomass management such as open burning banned under regulation (S.B. 705).

Technical Abstract: In California, assessing the long-term effects and potential ecosystem services provided by soil amended with large quantities of recycled woodchip is essential knowledge to farmers, researchers, and regulatory agencies regarding management of orchard biomass. In this study, we evaluated the impacts of whole orchard recycling (WOR) on soil ecosystem services in a four-year-old replanted almond orchard, during the 2023 (fifth) and 2024 (sixth) years. Assessed ecosystem services include regulating soil gas emissions, e.g. carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4), and influence on soil carbon (C), nitrogen (N), and nitrate (NO3-) leaching. Field measurements were made from WOR and unamended control plots subjected to low and median N fertilization rates (Low-N and Median-N). Soil was collected in 2024 for soil NO3-, organic C, and total N analysis. Soil NO3- leaching was determined annually using buried resins trap. Cumulative CO2 emissions were observed to be significantly higher in WOR than control across N subregions in 2023 (p < 0.05), but not in 2024 suggesting a substantial reduced in emissions by year sixth from WOR. CO2 emissions from orchard berm were statistically higher than alleyway, regardless of soil treatments and N rates in both seasons (p < 0.05). N2O emissions were similar between WOR and control treatments and are mainly driven by N fertilization. CH4 emissions were negligible for all treatments in the orchard. At the top 0'15 cm berm soil, organic C and total N in WOR plots (1.38% and 1042 mg kg-1) were statistically greater than control (0.88% and 617 mg kg-1). No significant difference in soil NO3- leaching was detected in both seasons. Overall, a positive effect on soil ecosystem services was observed four years after WOR and replanting.