Pedosphere 36(5): 1119--1132, 2026
ISSN 1002-0160/CN 32-1315/P
©2026 Soil Science Society of China
Published by Elsevier B.V. and Science Press
| Assessing deep soil carbon stocks in California nut orchards: Insights and opportunities for climate mitigation |
Alexia COOPER1 , Jeffrey BORUM2, Rebecca RYALS3 |
1 Environmental Systems Graduate Group, University of California, Merced, Merced CA 95343 (USA);
2 East Stanislaus Resource Conservation District, Modesto CA 95358 (USA);
3 Department of Life and Environmental Sciences, University of California, Merced, Merced CA 95343 (USA) |
| Corresponding Author:Alexia COOPER |
| ABSTRACT |
| Orchard soils in California's Central Valley represent a large but poorly characterized pool of soil carbon (C), and understanding the magnitude and drivers of that pool is essential for evaluating the C sequestration potential of soil health practices such as compost application and cover cropping. Yet few studies have systematically quantified soil C stocks to depth across multiple orchard types, management regimes, and soil conditions in this region. This study comprehensively assessed soil C stocks by the equivalent soil mass (ESM) and fixed depth (FD) methods within conventionally managed orchard systems in the Central Valley of California, investigating the factors influencing soil C stocks across different sites and soil depths. Across orchards of almond, pistachio, peach, and walnut, we observed a significant range in cumulative soil C stocks to 100 cm depth, with values spanning from 55 ±5.2 to 109 ±11.6 Mg C ha-1, underscoring the influences of specific site conditions and management practices. Both ESM and FD methods were revealed to be reliable in estimating cumulative soil C stocks. We suggest the use of ESM for long-term monitoring efforts in environments prone to bulk density changes, especially in surface soils, where there was a significant difference between the two methods. We highlighted the importance of deep soil sampling, as limiting sampling to just surface soils (0–30 cm) would have underestimated orchard soil C stocks by 60%. Our study identified soil type as the most dominant factor affecting soil C stocks in orchards, followed by orchard type and irrigation method. The depleted condition of orchard soils underscored their potential for C sequestration if soil health practices were adopted. Growers aiming to enhance C storage should first prioritize practices that build soil organic matter (SOM), such as compost and cover crops, particularly in low-C soils. As organic matter accumulates, management should shift toward strategies that minimize C losses to sustain long-term soil C retention and resilience. |
| Key Words: deep soil sampling,management practices,orchard system,organic matter,soil carbon storage,soil health |
| Citation: Cooper A, Borum J, Ryals R. 2026. Assessing deep soil carbon stocks in California nut orchards: Insights and opportunities for climate mitigation. Pedosphere. 36(5): 1119-1132. |
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