The WSU Wheat Beat Podcast: Soil Carbon Sequestration at Cook Agronomy Farm with Dr. Claire Phillips.

Authors: Phillips, Claire

Submitted to: Meeting Abstract
Publication Type: Other
Publication Acceptance Date: 3/27/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: The USDA-ARS Northwest Sustainable Agroecosystems Research Unit has monitored soil carbon changes since 1998 in a long-term no-till trial at Cook Agronomy Farm near Pullman, Washington. Over the initial decade following no-till adoption the site gained carbon in the top foot, but lost carbon between 1 and 5 feet soil depth. Over the next 7 years those initial gains in near-surface carbon were almost entirely lost. We believe this was a result of changing the planting implement in 2008 from a double-disk opener to a higher disturbance hoe-type opener. The site also continued to lose carbon below 1 foot, so that after 17 years the site lost an overall 5.8 tons carbon per acre in the top 5 ft. Incubation experiments have confirmed our expectation that the carbon in the subsoil can be readily re-activated and decomposed when placed in a favorable environment for decomposition. A commonly-used GHG calculator, COMET-FARM, did not capture the nuances of different types of no-till drills and therefore over-estimated the carbon sequestration benefits of no-till for this location.

Technical Abstract: It is not known how SOC accumulation on hillslopes changes following adoption of erosion control measures such as no-till. Our objective was to characterize SOC change (0 to 1.53 m) following no-till adoption within a 37 ha field with steep slopes and rolling topography, typical of the Palouse region in eastern Washington. A systematic, non-aligned grid of 180 geo-referenced sample locations was established at the Cook Agronomy Farm LTAR site near Pullman, WA. Baseline soil cores were collected in 1998 and repeat sampling occurred 10 and 17 years later. Overall, no-till adoption initially increased SOC stocks in the soil surface (0 – 30 cm) across both eroded and depositional settings. However, SOC stocks subsequently declined after 2008, following a change in planting implement to one that created more inversion tillage. Surface SOC (0 – 30 cm) declined over 17 years by -3.3 Mg ha-1 (SD 7.7) and subsurface (30-153 cm) SOC stocks declined by -9.7 Mg ha-1 (SD 19.9). The vulnerability of deep SOC to loss was also indicated by laboratory incubations, which showed that a larger fraction of the SOC in deep soil was vulnerable to decomposition. The stock of SOC that was readily mineralized in incubations was 51% larger for 30-153 cm than for 0-30 cm depth. While no-till adoption provided effective erosion control, it did not prevent SOC losses at a field scale. Finally, we estimated that the minimum sampling density needed for accurately monitoring SOC change was about 1 sample per hectare.