Feasibility of 4 per 1000 initiative analyzed from national scale assessment of SOC sequestration by conservation tillage practices

Sequestration of atmospheric CO2 into long-term soil organic carbon (SOC) storage is necessary for sustainable food production and climate change mitigation. The numerous field studies demonstrated the positive effect of conservation tillage on SOC stock, but the effects significantly differ depending on environmental conditions. Thus, the process-based SOC dynamic model conjugating with a site-specific environmental database is necessary to assess the potential of conservation tillage adequately. In this study, we aim to evaluate the conservation tillage effect on SOC stock of South Korean agricultural land. To assess the conservation tillage effect, we used the RothC model and newly developed tillage rate modifiers (TRMs), multipliers for the decomposition rate constants. Briefly, TRMs were parameterized with 210 field observations of the middle-latitude area, which thoroughly reflected the variance of the conservation tillage effect stemming from soil properties. We ran the RothC model under two scenarios with different application areas of conservation tillage: 1) conventional tillage practice is applied to 100% current cropland area, and 2) conservation tillage is applied to its maximum attainable area, which is estimated from the national statistics on crop type. As a national scale simulation result, the 0.21Tg of C can be sequestered in the soil yearly under the second conservation tillage scenario, meaning 13% of the 2050 emission reduction target of the Korean agricultural sector can be achieved by conservation tillage adoption. The 0.21 Tg of C is equivalent to 0.066% of total SOC stock in South Korea, which is 16.4% of 4 per 1000. Thus, for the practical achievement of 4 per 1000 in South Korea, it is necessary to adopt multiple sustainable soil managements more than conservation tillage, including green manure and biochar.