Widespread soil acidification due to atmospheric acid deposition and agricultural fertilization may greatly accelerate soil carbonate dissolution and CO2 release. However, to date, few studies have addressed these processes. Here, we use meta-analysis and nationwide-survey datasets to investigate changes in the soil inorganic carbon (SIC) stocks in China. We observe an overall decrease in the SIC stocks in topsoil (0-30 cm) (11.33 g C m–2 yr–1) during the 1980 s and 2010 s. The total SIC stocks have decreased by approximately 8.99 ± 2.24% (1.37 ± 0.37 Pg C). The average SIC losses across China (0.046 Pg C yr–1) and in cropland (0.016 Pg C yr–1) account for approximately 17.6–24.0% of the terrestrial C sink and 57.1% of the soil organic carbon sink in cropland, respectively. Nitrogen deposition and climate change have profound influences on SIC cycling. We estimate that approximately 19.12–19.47% of the SIC stocks will be further lost by 2100. The consumption of SIC may offset a large portion of the global efforts aimed at ecosystem carbon sequestration, which emphasizes the importance of better understanding the indirect coupling mechanisms of nitrogen and carbon cycling and of effective countermeasures to minimize SIC loss.
Biochar has attracted global attention because of its widespread application to improve soil quality and enhance soil productivity. Five types of biochar were prepared from peanut shells at 200–600°C by slow pyrolysis, and their physicochemical properties were investigated. Biochar was produced at 300 and 400°C, PBC300 and PBC400, respectively. The two forms of biochar were evaluated as soil amendments with an incubation and a pot experiment in a soil that had become acidified because of excessive use of nitrogen (N) fertilizers. The PBC300 and PBC400 additions significantly decreased the soil bulk density and increased the pH, cation exchange capacity (CEC) and soil organic matter (SOM) content. Both types of biochar significantly decreased NH4+‐N and NO3−‐N contents as a result of N immobilization, reduced nitrification because of the enhanced microbial activity (determined by the fluorescein diacetate method) and reduced the abundance of ammonia‐oxidizing bacteria (AOB). The growth of maize (Zea mays L.) was stimulated and, compared with the unamended soil, the biomass increased by 15.2–32.7% following the addition of PBC300 or PBC400. Maize root morphology (e.g. length and tips) and the properties of the rhizosphere soil (e.g. CEC and pH) were improved by the addition of biochar, leading to enhance N bioavailability by decreasing NAE (N accumulation efficiency) and increasing NUE (N utilization efficiency). In general, the ameliorating effects of PBC400 on the acidic soil were superior to those of PBC300. These results indicate that producing a specific type of biochar based on pyrolytic temperature might be an alternative strategy for selecting the most appropriate biochar for a specific soil.
Highlights
Biochar was selected for an acidic soil based on the pyrolytic temperature.
Biochar decreased the soil bulk density and increased the soil pH, CEC and SOM.
Biochar slowed nitrification by decreasing the abundance of ammonia‐oxidizing bacteria (AOB).
Adding biochar stimulated maize growth and improved N bioavailability.
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