Deep soil flipping increases carbon stocks of New Zealand grasslands.

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.

Effects of climate change on the delivery of soil-mediated ecosystem services within the primary sector in temperate ecosystems: a review and New Zealand case study.

Future human well-being under climate change depends on the ongoing delivery of food, fibre and wood from the land-based primary sector. The ability to deliver these provisioning services depends on soil-based ecosystem services (e.g. carbon, nutrient and water cycling and storage), yet we lack an in-depth understanding of the likely response of soil-based ecosystem services to climate change. We review the current knowledge on this topic for temperate ecosystems, focusing on mechanisms that are likely to underpin differences in climate change responses between four primary sector systems: cropping, intensive grazing, extensive grazing and plantation forestry. We then illustrate how our findings can be applied to assess service delivery under climate change in a specific region, using New Zealand as an example system. Differences in the climate change responses of carbon and nutrient-related services between systems will largely be driven by whether they are reliant on externally added or internally cycled nutrients, the extent to which plant communities could influence responses, and variation in vulnerability to erosion. The ability of soils to regulate water under climate change will mostly be driven by changes in rainfall, but can be influenced by different primary sector systems' vulnerability to soil water repellency and differences in evapotranspiration rates. These changes in regulating services resulted in different potentials for increased biomass production across systems, with intensively managed systems being the most likely to benefit from climate change. Quantitative prediction of net effects of climate change on soil ecosystem services remains a challenge, in part due to knowledge gaps, but also due to the complex interactions between different aspects of climate change. Despite this challenge, it is critical to gain the information required to make such predictions as robust as possible given the fundamental role of soils in supporting human well-being.