CO2 emission and source partitioning from carbonate and non-carbonate soils during incubation
Section snippets
INTRODUCTION
Soil is the largest carbon (C) pool on the earth, with an organic carbon (OC) stock of 1 550 Pg and an inorganic carbon (IC) stock of 950 Pg (Lal, 2007). In arid and semi-arid regions, which occupy a total land area of 4.9 × 107 km2 (Lardner et al., 2015), the soil inorganic carbon (SIC) stock is approximately 10 times greater than that of soil organic carbon (SOC) (Schlesinger, 1982). The SIC and SOC pools play a significant role in global C sequestration (Lal, 2009). Because SIC significantly
Incubation experiment
Two types of soils, carbonate and non-carbonate soils, were used for this experiment. The carbonate-rich soil was collected in Shanxi Province in northwestern China (34°17′59.317″ N, 108°04′9.384″ E), at the southern edge of the Loess Plateau. This region is in a warm temperate zone with a semi-humid and semi-arid climate and an average annual temperature and precipitation of 13 °C and 600–650 mm, respectively. The soil is classified as Eum-Orthic Anthrosol in Chinese Soil Taxonomy, equivalent
Soil C contents, pH and δ13C values
The C contents, δ13C values, and pH differed significantly between Hapludult (non-carbonate soil) and Haplustalf (carbonate-rich soil) (Table I). The pH of Hapludult (7.2 ± 0.2) was significantly lower than that of Haplustalf (7.8 ± 0.2). The TC content of Hapludult was 10.3 ± 0.1 g kg-1, of which 99% was SOC. In contrast, the TC content of Haplustalf was 17.1 ± 0.1 g kg-1, comprising about 50% SOC and 50% SIC. The δ13C value of TC (δ13CTC, −20.6‰ ± 0.1‰) in Hapludult was significantly lower
CONCLUSIONS
Both alkali trap and gas sampling methods can be used to quantify CO2 emissions from soils in incubation studies. For the carbonate soil, the alkali trap method may overestimate the CO2 emissions due to decreasing CO2 pressure within the incubation jar, while the direct gas sampling method may underestimate CO2 emissions. It was found that longer sampling intervals resulted in greater differences in measured CO2 values between the two gas collection methods. Interference from ambient air was a
ACKNOWLEDGEMENTS
This work was supported by the National Key Research and Development Program of China (No. 2016YFD0201200) and the National Natural Science Foundation of China (Nos. 31370527, 31261140367, and 30870414). The first author would like to acknowledge the Chinese Scholarship Council (No. 201706350210) for the support of the work.
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2022, GeodermaCitation Excerpt :The topsoil SIC loss (0.61 Mg C ha−1 y−1) in this reclaimed arable land in Germany exceeds values measured for carbonate-containing agricultural soils in China; although, China is recognized as a country with high N fertilizer application rates (Potter et al., 2010) that are at least 2–3 times those in Germany (Löw et al., 2021). We speculate that there are two main reasons for this: (1) the SIC content in the arable soil in our study was twice that at the beginning of restoration in Chinese carbonate soils (∼6–8 g C kg−1 soil) (Bughio et al., 2015; Bughio et al., 2017; Zhao et al., 2022); and (2) in the arid and semi-arid regions of China, part of the CO2 produced after carbonate decomposition will be bound again in the form of PIC (Bughio et al., 2015; Entry et al., 2004; Sahrawat, 2003). However, in our study, almost all of the carbonate present in the surface soil of the reclaimed arable land was decomposed to CO2 and released to the atmosphere.