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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.

SUBMITTER: Schiedung M

PROVIDER: S-EPMC6850463 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Rain-fed pastoral systems are tightly connected to meteorological conditions. It is, therefore, likely that climate change, including changing atmospheric CO2 concentration, temperature, precipitation and patterns of climate extremes, will greatly affect pastoral systems. However, exact impacts on the productivity and carbon dynamics of these systems are still poorly understood, particularly over longtime scales. The present study assesses the potential effects of future climatic conditions on productivity and soil organic carbon (SOC) stocks of mowed and rotationally grazed grasslands in France. We used the CenW ecosystem model to simulate carbon, water, and nitrogen cycles in response to changes in environmental drivers and management practices. We first evaluated model responses to individual changes in each key meteorological variable to get better insights into the role and importance of each individual variable. Then, we used 3 sets of meteorological variables corresponding to 3 Representative Concentration Pathways (RCP 2.6, RCP 4.5 and RCP 8.5) for long-term model runs from 1975 to 2100. Finally, we used the same three RCPs to analyze the responses of modelled grasslands to extreme climate events. We found that increasing temperature slightly increased grasslands productivities but strongly reduced SOC stocks. A reduction in precipitation led to reductions of biomass and milk production but increased SOC. Conversely, doubling CO2 concentration strongly increased biomass and milk production and marginally reduced SOC. These SOC trends were unexpected. They arose because both increasing precipitation and CO2 increased photosynthetic carbon gain, but they had an even greater effect on the proportion of biomass that could be grazed. The amount of carbon remaining on site and able to contribute to SOC formation was actually reduced under both higher precipitation and CO2. The simulations under the three RCPs indicated that grassland productivity was increased, but that required higher N fertilizer application rates and also led to substantial SOC losses. We thus conclude that, while milk productivity may continue at current rates under climate change, or even increase slightly, there could be some soil C losses over the 21st century. In addition, under the highest-emission scenario, the increasing importance of extreme climate conditions (heat waves and droughts) might render conditions at our site in some years as unsuitable for milk production. It highlights the importance of tailoring farming practices to achieve the dual goals of maintaining agricultural production while safeguarding soil C stocks.

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Deep soil flipping increases carbon stocks of New Zealand grasslands.

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