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

• Published in: Global change biology 2021-05, Vol.27 (10), p.1998-2010
• Main Authors: Lawrence‐Smith, Erin J., Curtin, Denis, Beare, Mike H., McNally, Sam R., Kelliher, Frank M., Calvelo Pereira, Roberto, Hedley, Mike J.
• Format: Article
• Language: English
• Subjects: Agricultural land; Agriculture; Burying; Carbon - analysis; Carbon capture and storage; Carbon Sequestration; deep soil carbon; Emissions; Farm buildings; full inversion tillage; grassland renovation; Grasslands; Greenhouse gases; negative emission practice; New Zealand; offset greenhouse gas emissions; Pasture; pasture renewal; Renewal; Seeding; Soil; soil carbon sequestration; Soils; Stocks; Subsoils; Tillage; Topsoil
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.15561

As soils under permanent pasture and grasslands have large topsoil carbon (C) stocks, the scope to sequester additional C may be limited. However, because C in pasture/grassland soils declines with depth, there may be potential to sequester additional C in the subsoil. Data from 247 continuous pasture sites in New Zealand (representing five major soil Orders and ~80% of the grassland area) showed that, on average, the 0.15–0.30 m layer contained 25–34 t ha−1 less C than the top 0.15 m. High‐production grazed pastures require periodic renewal (re‐seeding) every 7–14 years to maintain productivity. Our objective was to assess whether a one‐time pasture renewal, involving full inversion tillage (FIT) to a depth of 0.30 m, has potential to increase C storage by burying C‐rich topsoil and bringing low‐C subsoil to the surface where C inputs from pasture production are greatest. Data from the 247 pasture sites were used to model changes in C stocks following FIT pasture renewal by predicting (1) the C accumulation in the new 0–0.15 m layer and (2) the decomposition of buried‐C in the new 0.15–0.30 m layer. In the 20 years following FIT pasture renewal, soil C was predicted to increase by an average of 7.3–10.3 (Sedimentary soils) and 9.6–12.7 t C ha−1 (Allophanic soils), depending on the assumptions applied. Adoption of FIT for pasture renewal across all suitable soils (2.0–2.6 M ha) in New Zealand was predicted to sequester ~20–36 Mt C, sufficient to offset 9.6–17.5% of the country's cumulative greenhouse gas emissions from agriculture over 20 years at the current rate of emissions. Given that grasslands account for ~70% of global agricultural land, FIT renewal of pastures or grassland could offer a significant opportunity to sequester soil C and offset greenhouse gas emissions. Soil organic C (SOC) stocks in permanent pastures and grasslands tend to be strongly stratified, being high near the surface and declining with depth. A one‐time use of full inversion tillage during pasture renewal (FIT‐PR) could increase SOC storage by burying C‐rich topsoil and bringing low‐C subsoil to the surface where C inputs from pasture are greatest. Data from New Zealand permanent pasture soils indicate the potential for FIT‐PR to increase average SOC stocks (over 20 years) in allophanic (9.6–12.7 t C ha−1) and sedimentary (7.3–10.3 t C ha−1) soils, with the amount sequestered related to pre‐renewal SOC stratification ratio.