Effect of Maize Straw-Derived Biochar on Calcareous Arable Soil Organic Carbon Mineralization Under the Condition of with or Without Nitrogen-Fertilizer Addition

The object of this study was to explore the effect of biochar on Loess Plateau calcareous arable soil organic carbon mineralization under the condition of with or without nitrogen-fertilizer addition. Maize straw-derived biochars were prepared at 400 and 800 degrees C (BC400 and BC800), respectively. After physicochemical property determination, biochars were thoroughly mixed with soil at the mass ratio of 1% and 2% respectively, and a control without biochar addition was also arranged. Each treatment was carried out with 6 replicates, half of which were subjected to nitrogen-fertilizer addition. After 1-week preincubation, 50-day indoor static soil incubation experiment was carried out consecutively. Results showed that compared with BC400, pH, carbon content, alkaline oxygen-containing functional group, and specific surface area of BC800 significantly increased, while dissolved organic carbon, nitrogen, hydrogen, oxygen contents, carboxyl, carbonyl, and acidic oxygen-containing functional group significantly decreased. In the treatments without nitrogen-fertilizer addition, maize straw-derived biochar inhibited CO(2)emission, especially for BC800-1% and BC800-2%. However, in the treatments with nitrogen-fertilizer addition, the biochar promoted CO(2)emission, especially for BC400-1% and BC400-2%. Moreover, the pyrolysis temperature of biochar preparation showed more crucial impact on CO(2)emission than its application rate. CO(2)emission was significantly correlated with total organic carbon/inorganic nitrogen (TOC/IN) and dissolved organic carbon/inorganic nitrogen (DOC/IN). However, DOC/IN explained the variance of CO(2)emission with a higher degree than TOC/IN. Carbon/nitrogen mass ratio was the key factor in controlling CO(2)emission from biochar-amended soil, and DOC/IN showed more significant effect on CO(2)emission than TOC/IN.