Soil as a source and/or sink for carbon

摘要

Carbon sink and source capacity of the soil is the most debated topic in recent decades to minimize carbon (C) release to the atmosphere. The ambiguity related to the sink capacity of the soil is yet to be resolved, resulting in continuous publications with various types of analysis to prove the hypothesis that 'soils are sink or source of carbon'. With this background the article by Dinakaran and Krishnayya makes an attempt to analyse the quantity of carbon in soil profiles of various land-use systems. However, there is no mention on the generic classification of soil types in each of these land-use systems as the particle size distribution appears to vary largely, which is a critical flaw in the manuscript. Arguably, looking at the dataset suggests that there appears to be variation in soil C content in different land-use systems with annual to perennial vegetation types. It makes sense to argue that interpretation cannot be drawn as soils are sinks for C rather than how vegetation types affect accretion of C in soils. The authors clearly fail to explain the discrepancies in the many fold increase of C values in aggregate size classes of the same soil depth. The C values were analysed taking data from tables 2 and 3 of the article. Table 2 presents C values in different depth layers, and table 3 presents C values in aggregate size classes of corresponding depth layers of the same soil sample, thus qualifying the comparability for each site. For instance, the dataset for site 1, depth 0-2 cm soil has a C value of 8.9 t/ha. Interestingly, pooled C value in the aggregates (coming from the same depth of 0-2 cm) is 34.6 t/ha, which is 3.8-fold higher than the C value in the same soil depth layer. There appear to be critical flaws in the dataset leading to speculative inference, which is clear in the authors' ambiguous explanation and lack of clarity in the concept. There appears to be a critical problem as to why the pooled C value in aggregates is many fold higher than that in the respective soil depth layer, which is not a possibility. Moreover, interpretation is not appropriate in the given case of comparison of land-use systems and vegetation types. The authors must address this issue so that readers will not be misrepresented about the concept of soil as a source and/or sink for C.