Impact of whole orchard recycling on greenhouse gas emissions, soil carbon storage, and almond productivity in a replanted orchard

Authors: CULUMBER, MAE - University Of California - Cooperative Extension Service; Gao, Suduan; Poret-Peterson, Amisha; Thao, Touyee; ZUBER, CAMERON - University Of California - Cooperative Extension Service; CAMARENA-ONOFRE, DIANA - Cooperative Extension Merced County; Perez-Sandoval, Julio; Hendratna, Aileen; HOLTZ, BRENT - University Of California - Cooperative Extension Service

Submitted to: Agriculture, Ecosystems & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2025
Publication Date: 4/8/2025
Citation: Culumber, M., Gao, S., Poret-Peterson, A.T., Thao, T., Zuber, C., Camarena-Onofre, D., Perez-Sandoval, J.C., Hendratna, A., Holtz, B. 2025. Impact of whole orchard recycling on greenhouse gas emissions, soil carbon storage, and almond productivity in a replanted orchard. Agriculture, Ecosystems & Environment. 389:109664. https://doi.org/10.1016/j.agee.2025.109664.
DOI: https://doi.org/10.1016/j.agee.2025.109664

Interpretive Summary: Whole orchard recycling (WOR) is the practice of grinding and incorporating whole trees into soil during orchard removal, which has shown to be a more sustainable method for disposing large amounts of biomass. WOR has quickly become a common practice in California orchards due to the ban of agricultural burning, with few other disposal alternatives. Some challenges remain in irrigation and nutrient management due to limited knowledge on the dynamics of woodchips breakdown over time and the impact on soil, crop, and the environment including contributions to greenhouse gas (GHG) emissions. This study monitored soil properties, tree performance, and GHG emissions for four years following WOR in comparison with no woodchips incorporated control (CTL). Results show that half of the wood biomass was lost with about half remaining after four years and projected that 6.6% would remain after 20 years. Soil C stock after WOR increased by 1 metric ton per hectare greater than CTL in the first four years. Although the nitrous oxide emission factor from WOR was significantly higher than CTL for the first two seasons, there were no differences thereafter. Almond trees in WOR plots were 32% larger than the CTL after the first season of growth, although no yield differences resulted for the first two nut-bearing years (average 1439 kg per hectare). Further, the replanted almond orchard following WOR did not show significant increase in global warming potential from CTL. This study quantified the overall benefits of WOR in improving soil, crop, and environment at a N fertilization rate that was not much higher than current rate in most orchards. No compromise in nut yield was observed, a major concern for growers. The findings from this research provide very useful information to assist management decision-making in replanted orchards after WOR and the information may also benefit multiple perennial crop industries.

Technical Abstract: A four-year study was conducted to characterize the impact of incorporating a high rate of recycled woodchips (approximately 134 dry weight metric tons (mt) ha-1 or 61.6 mt carbon (C) ha-1) on carbon dioxide (CO2) and nitrous oxide (N2O) greenhouse gas (GHG) emissions, soil C storage, and almond productivity in orchards replanted after whole orchard recycling (WOR). Throughout the trial, WOR treatments had higher CO2 emissions than control (CTL) plots. The highest CO2 flux was in the first season (~27% C loss) but declined by 43% in the second year and 80% in year three and four. Average daily CO2 emissions from the WOR and CTL plots was fitted to a summation of two first-order equations to estimate WOR C biomass decomposition and retention over time. Cumulative C loss after four years was 31.6 mt C ha-1 leaving 49% or 29.9 mt C ha-1 biomass remaining. Continued projections show 4.05 mt C ha-1 (6.6%) would remain after 20 years. Soil C stock analysis predicted 1.09 mt C ha-1 of this remaining biomass entered the < 2 mm soil fraction after four years. Soil N2O-N emissions increased across both WOR and CTL plot treatments during the four-year monitoring period in parallel with a 53 to 161 kg N ha-1 increase in fertilizer rate during the four-year period. The total N2O-N emission factor (EF%) was greater (p< 0.0222) in WOR 1.65 ± 0.28 than in CTL plots 0.85 ± 0.28 in the first orchard growing season but the differences diminished in the third and fourth year. These findings highlight the importance of identifying strategies to limit N2O emissions during the first seasons in recycled orchards. Almond trees planted after WOR were 32% larger than the CTL after the first season of growth and remained statistically larger than CTL during the study period, however no differences in yield were observed in the early bearing years. No significant difference was found in global warming potential (GWP) between WOR and the CTL treatments averaging 0.34 ± 0.03 CO2eq kg-1 almond kernel kg-1, suggesting that WOR did not increase GWP of almond production despite higher overall GHG emissions in the first two years of establishment.