Deep soil flipping increases carbon stocks of New Zealand grasslands

Abstract

Sequestration of soil organic carbon (SOC) has been recognized as an opportunity to off‐set global carbon dioxide (CO2) emissions. Flipping (full inversion to 1–3 m) is a practice used on New Zealand's South Island West Coast to eliminate water‐logging in highly podzolized sandy soils. Flipping results in burial of SOC formed in surface soil horizons into the subsoil and the transfer of subsoil material low in SOC to the “new” topsoil. The aims of this study were to quantify changes in the storage and stability of SOC over a 20‐year period following flipping of high‐productive pasture grassland. Topsoils (0–30 cm) from sites representing a chronosequence of flipping (3–20 years old) were sampled (2005/07) and re‐sampled (2017) to assess changes in topsoil carbon stocks. Deeper samples (30–150 cm) were also collected (2017) to evaluate the changes in stocks of SOC previously buried by flipping. Density fractionation was used to determine SOC stability in recent and buried topsoils. Total SOC stocks (0–150 cm) increased significantly by 69 ± 15% (179 ± 40 Mg SOC ha‐1) over 20 years following flipping. Topsoil burial caused a one‐time sequestration of 160 ± 14 Mg SOC ha‐1 (30–150 cm). The top 0–30 cm accumulated 3.6 Mg SOC ha‐1 year‐1. The chronosequence and re‐sampling revealed SOC accumulation rates of 1.2–1.8 Mg SOC ha‐1 year‐1 in the new surface soil (0–15 cm) and a SOC deficit of 36 ± 5% after 20 years. Flipped subsoils contained up to 32% labile SOC (compared to <1% in un‐flipped subsoils) thus buried SOC was preserved. This study confirms that burial of SOC and the exposure of SOC depleted subsoil results in an overall increase of SOC stocks of the whole soil profile and long‐term SOC preservation.

Full inversion tillage during pasture renewal to increase soil carbon storage: New Zealand as a case study

“…The formation of organo‐mineral complexes is widely believed to be the most important long‐term (decades to centuries) SOM stabilization mechanism (McNally et al, 2017; Rumpel et al, 2012; Schmidt et al, 2011; Wiesmeier et al, 2019). Enhanced stabilization of C is consistent with the relatively high rates of SOC accumulation (1.2–1.8 t C ha −1 year −1 ) that have been reported for low C surface soils (0–0.15 m) under continuous pasture production (up to 20 years) following a one‐time deep ploughing (Schiedung et al, 2019; Thomas et al, 2007).…”

Loss of soil organic carbon in Swiss long-term agricultural experiments over a wide range of management practices

“…However, the Swiss agricultural system is strongly dependent on subsidies and methods to improve SCS, could be promoted through payments. Deep ploughing, a method used to improve soil structure, has been shown to increase SOC stocks by very significant amounts (Alcantara et al, 2016(Alcantara et al, , 2017Schiedung et al, 2019). Nevertheless, to date, these studies remain the only ones we know of and thus the generality of this approach, as well as further ecological implications must be explored in more detail.…”

The climate benefit of carbon sequestration

“…Carbon management of ecosystems can maximize CS and/or CBS by not only increasing carbon inputs, but also by increasing the transit time of carbon. There are many ways in which the transit time of carbon can be increased -for instance, by increasing transfers of carbon to slow cycling pools such as the case of increasing wood harvest allocation to long-duration products (Schulze et al, 2019), or addition of biochar to soils, or by reducing cycling rates of organic matter such as the case of soil flipping (Schiedung et al, 2019). Independently of the management activity, CS and CBS can be powerful metrics to quantify their climate benefits, make comparisons among them, and compare against baselines or no-management scenarios.…”