1 - Global carbon cycle and methods for estimating soil carbon: general concepts

Abstract

Soil is a three-dimensional heterogenous body having spatial and temporal variability. Depending on the scale considered for SOC estimation, the degree of heterogeneity varies significantly. Land use, type and number of tillage operations, and plant diversity have a major role in soil heterogeneity at plot scale. The dynamic nature of natural and anthropogenic activities in response to carbon dioxide (CO2) is a mystery as the magnitude of CO2 from each of these sources is unknown. Prediction of global carbon (C) pools is an area of interest in national and international policies for accounting and reviewing C sequestration, removals, and emissions status in different land uses and forestry sectors. Arrhenius first concluded that the carbon dioxide (CO2) emission from fossil fuel combustion is directly linked with global climate change. Worldwide, various research studies on SOC are carried out with relevance to climate change and C sequestration but still there is limited knowledge on SOC baselines, potential changes, and detection of SOC losses and gains from vulnerable hotspots and land use. Although global SOC estimates already exist, there is high variability in data reported by different authors mainly due to diversity in soil sampling and methodologies followed. A baseline of SOC stock can be measured by physical soil sampling and analysis or by use of models. The key challenge in this job is to deal with high spatial variability of SOC associated with soil biogeochemistry, soil types, and vegetation. Hence, the method chosen for determination of baseline should be robust and have high reproducibility. Despite recent scientific advancement, the estimates of global soil C are insufficient or not available for many regions. Therefore, a comprehensive understanding of global C pools and SOC sequestration and estimation is required, which will be applicable at all scale to formulate solutions in reducing CO2 flux from soil that is consistent from both scientific and policy perception.