Potential and limitations of soil organic carbon sequestration in croplands: the role of sustainable fertility management

Abstract

Poor land and soil management practices are associated with widespread severe degradation in global agricultural systems. Urgent attention to judicious land use and prudent soil/crop/water management is required to restore degraded soils and improve the environment (Lal 2019a). Maintaining or enhancing the SOC stocks is one of the most critical interventions to fight against climate change, soil degradation and ensuring the sustainability of agriculture. The global soil organic carbon (SOC) contents are 677 Pg to 0.3 m, 993 Pg to 0.5 m and 1,505 Pg to 1 m depth. Thus, ~55% of the SOC in the top 1 m soil depth is below 0.3 m depth. However, the average SOC stocks are relatively lower in agroecosystems than in natural ecosystems due to lower biomass production, biomass removal/harvest, and land management practices such as tillage that increase the loss of SOC. The low carbon stocks place croplands as high priority areas for SOC sequestration. The strategy of enhancing SOC sequestration for climate and food security was adopted at COP21 in Paris in November 2015 under the program “4 per Thousand” (https://www.4p1000.org/). The goal is to sequester SOC in soils of the world at the rate of 0.4% per year to 0.4 m depth. The AAA (Adapting African Agriculture) (https://www.aaainitiative.org/) initiative proposed at COP22 in Marrakech is complementary to the “4 per Thousand” as both initiatives aim to enhance SOC stock in agricultural systems. Although the goal of sequestering C in croplands appears straightforward, it faces several challenges and tradeoffs that need to be considered. This report aims to review and synthesize the current scientific evidence on the potential of various crop, soil and nutrient management practices to enhance soil C sequestration in different regions. This report highlighted the need for more research to provide policy-makers and farmers with the evidence base that will encourage them to adopt SOC-enhancing practices. Current evidence is clear that a site-specific nutrient management using a combination of mineral and organic fertilizers, combined with other techniques, can deliver optimal results for farmers and for food security.