Evaluation of the potential for nine established and emerging interventions to reduce soil carbon losses and increase stocks in grazing systems: A case study for Aotearoa New Zealand

This article reviews nine soil carbon interventions to reduce soil carbon losses or increase stocks in grazing management systems, using their potential application in Aotearoa New Zealand (A-NZ) as a case study. The interventions are classified into three strategies: (1) increasing carbon inputs through deep-rooting and diverse species grasslands, reducing forage cropping and deferred grazing management; (2) increasing protection of carbon stocks by water table management on organic soils, reducing cropping on organic soils, full inversion tillage grassland renewal, the addition of clay minerals and enhanced rock weathering and (3) the adoption of integrated systems including establishing tree clusters into grasslands and agroforestry. We estimated the land area where these interventions could realistically be implemented in A-NZ and assessed their potential impact on mitigating national overall agricultural greenhouse gas emissions. The potential impact of each intervention ranged from <1% to 2.5% of national agricultural greenhouse gas emissions over 20 years. However, confidence in these approaches is hindered by a lack of research data where these approaches have been tested for different soil types and conditions. Notably, water table management, which reduces carbon loss from organic soils, was the only intervention that could achieve moderate, short- and long-term impacts with a confidence level assessed as 'likely'. We conclude that reducing further soil carbon losses and achieving modest increases in soil carbon stocks are possible but will require economic and political incentives that encourage the integration of multiple interventions at the farm scale.