Deep soil flipping increases carbon stocks of high productive pastures on New Zealand’s West Coast Marcus Schiedung1, 2, Beare M.H.3, Tregurtha C. 3, Don A.1 1Thünen
Institute of Climate-Smart Agriculture, Braunschweig, Germany 2Technical University of Braunschweig Institute of Geoecology, Germany 3Plant and Food Research Institute, Lincoln, New Zealand
Contact: Marcus Schiedung E-Mail:
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Introduction
Conclusions
Soils are the largest terrestrial carbon (C) reservoir and sequestration of soil organic carbon (SOC) is accepted to significantly off-set global atmospheric carbon dioxide emissions. Especially subsoils have a large sequestration potential due to an increased saturation deficit and a high ability for SOC stabilisation. Soil melioration by flipping (deep full inversion to 1-3 m depth, Fig. 3) has been used in New Zealand to break iron pans of highly podzolized soils (Fig. 1) in order to enable high productive pasture management. In this study, a chronosequence of 20 years and re-sampling were used to determine changes in SOC stocks (0-150 cm depth) through topsoil burial and the creation of “new” topsoils following flipping.
1.5 Mg SOC ha-1 a-1 accumulated in upper 0-15 cm over 20 years. “New” topsoils will accumulate SOC for further 25 years. Burial preserved 160 Mg SOC ha-1 in flipped subsoils. FIG. 1: Un-flipped Pakihi soil (a) and a soil flipped 3 years ago (b) at Cape Foulwind on New Zealand‘s West Coast.
SOC stock changes by flipping due to: → Burial of topsoils → Creation of “new” topsoils
Total SOC stocks increased significantly by 179 Mg SOC ha-1 following flipping.
Results and Discussion
FIG. 4: SOC stocks in 0-15 cm following 1-20 years of flipping of samples taken in 2017 (triangles and circles) and in 2005/2007 (black dots) by Thomas et al. (2007). FIG. 2: SOC stocks of un-flipped and flipped topsoils (0-30 cm), subsoils (30-150 cm) and total soils (0-150 cm) with standard error as whiskers and significance by lettering.
FIG. 3: Flipping in action at Cape Foulwind on the West Coast of New Zealands’s South Island.
SOC stocks and accumulation
SOC degradability and stability
o Total SOC stocks (0-150 cm) were increased by 69 ± 15 % (179 ± 40 Mg SOC ha-1) following 20 years of flipping (Fig. 2).
o Relative contribution of SOC fractions in flipped topsoils developed towards un-flipped fraction composition.
o Topsoils accumulated 1.2-1.8 Mg SOC ha-1 a-1 in 0-15 cm after 20 years of flipping (Fig. 4).
o Labile SOC in buried topsoils contributed to 16-30 % of total SOC and was less biodegradable than labile topsoil SOC.
o “New” topsoil SOC stocks were 36 ± 5 % lower after 20 years of flipping than un-flipped topsoils, indicating further 16-25 years of SOC accumulation.
o C:N ratios indicated a preservation of former vegetation for >150 years in subsoils.
Estimated C balance o Topsoil burial resulted in one-time sequestration of 160 ± 14 Mg SOC ha-1 in subsoils.
o 34 % of C sequestered through flipping were emitted after 20 years of high productive pasture (Fig. 5).
o Flipped subsoils contained two-thirds of total SOC.
o Theoretically, 1-2 % of New Zealand’s total emissions from agriculture over 20 years could be compensated when all pasture land on the West Coast would be flipped.
o Subsoil SOC was preserved since flipping with no decrease in SOC stocks over time.
FIG. 5: Estimated carbon balance with SOC sequestration following flipping (negative fluxes) and GHG emissions associated with flipping and 20 years of high productive pasture management (positive fluxes). Material and Methods o High productive dairy pastoral soils flipped between 3-20 years ago were sampled at Cape Foulwind, New Zealand, to 150 cm depth. o Re-sampling of topsoils (0-15 cm) sampled 10-12 years ago by Thomas et al. (2007). o Minimum equilibrium soil mass was used for SOC stock comparison. o Linear mixed effect models were used to determine differences in SOC stocks. o SOC degradability and stability estimation with incubation (72 h) and SOC fractionation. o A C balance was calculated according to IPCC guidelines with default and New Zealand specific emission factors. Reference: Thomas et al. (2007), Proceeding of New Zealand Grassland Association 69
