Carbon accumulation in arid croplands of northwest China: pedogenic carbonate exceeding organic carbon

Abstract

Soil carbonate (SIC) exceeds organic carbon (SOC) greatly in arid lands, thus may be important for carbon sequestration. However, field data for quantifying carbonate accumulation have been lacking. This study aims to improve our understanding of SIC dynamics and its role in carbon sequestration. We analyzed two datasets of SOC and SIC and their 13C compositions , one with over 100 soil samples collected recently from various land uses in the Yanqi Basin, Xinjiang, and the other with 18 archived soil samples from a long-term experiment (LTE) in Pingliang, Gansu. The data from the Yanqi Basin showed that SOC had a significant relationship with SIC and pedogenic carbonate (PIC); converting shrub land to cropland increased PIC stock by 5.2 kg C m−2, which was 3.6 times of that in SOC stock. The data from the LTE showed greater accumulation of PIC (21–49 g C m−2 year−1) than SOC (10–39 g C m−2 year−1) over 0–20 cm. Our study points out that intensive cropping in the arid and semi-arid regions leads to an increase in both SOC and PIC. Increasing SOC through straw organic amendments enhances PIC accumulation in the arid cropland of northwestern China.

Dynamics of soil organic and inorganic carbon in the cropland of upper Yellow River Delta, China

“…also found that the slope reached 1.9 (over 0–100 cm) in Yanqi Basin’s cropland that had access to groundwater (containing high level of Ca 2+ /Mg 2+ )15. These findings imply that increasing SOC in alkaline soil can lead to an increase of SIC in subsoil if there is no limitations of calcium (and magnesium)7.…”

“…On the other hand, a positive relationship between SIC and SOC was found in the Badan Jaran Desert, Gansu (over 0–30 cm)16 and in the Yanqi Basin, Xinjiang (over 0–100 cm)8. The negative relationship may only exist in surface layer where CO 2 production is high due to root respiration and decomposition of SOC, which creates acidic conditions, thus leads to dissolution of soil carbonate; the positive relationship may be more common in high pH soils and without Ca/Mg limitation7.…”

“…Earlier analyses showed a negative relationship between SIC stock and SOC stock in northern China19. However, a recent study demonstrated that there was a strong positive correlation between SIC and SOC in the Yanqi Basin, northwest China7. Positive relationship was also reported for the soils of Canada20 and the USA21.…”

“…On the other hand, an increase in soil CO 2 or a decrease in soil pH would drive the reaction (2) to the left. Therefore, acidic conditions could lead to dissolution of carbonate, causing a decrease in SIC stock, whereas alkaline environment would benefit the formation of carbonate7. However, there are limited studies assessing how these environmental conditions regulate SIC dynamics.…”

Spatial distribution and sources of organic carbon in the surface sediment of Bosten Lake, China

“…Nevski), were responsible for terrestrial plant's contribution. Based on our recent studies conducted in the Yanqi Basin (Wang et al, 2015;Zhang, 2013), C : N ratio was 22.1 ± 9.9 and 10 ± 1.8, and δ 13 C org value was −26.4 ± 1.2 and −23.6 ± 1.3 ‰ for the native plants and surface soils around the lake, respectively. We used the values as the end-members for the mixing model.…”