Organic Fertilizer Substitution Promoted the Organic Carbon Sequestration in Calcareous Fluvisol: A Study Based on Acid Hydrolysis and Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR)

Abstract

ABSTRACT This study aimed to elucidate the mechanism of substituting organic fertilizer for mineral fertilizer to increase calcareous fluvisol soil organic carbon. Four years of soil culture experiments were conducted, wheat yield, soil nutrients, soil organic carbon (SOC) and SOC fractions were measured and the compositional changes of SOC was analyzed by attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy. Treatments included applying no fertilizer (CK), mineral N and P fertilizers (CF) and organic fertilizers to replace 6% (OF6), 12% (OF12), 18% (OF18) and 24% (OF24) of N and P under the same nutrient conditions. The results showed that the OF24 treatment was the best among the treatments employed. Compared with CF, wheat yield, SOC, microbial biomass carbon (MBC), labile fraction 1 (LOC1) and recalcitrant fraction (ROC) of OF24 increased by 10.4%, 24.4%, 66.3%, 43.2% and 30.7%, however, the labile fraction 2 (LOC2) decreased by 16.8%. ATR-FTIR results showed that the relative absorption intensity of OF24 treatment at 1,000 cm−1 band is lower than CK and CF treatment, other bands are higher than CK and CF treatment. Overall, OF24 treatment not only significantly increased wheat yield, but also increased the content of LOC1 and MBC. The increase of MBC can improve the soil microbial environment and promote the decomposition of LOC2, while also accelerate the turnover rate of soil carbon and then show the increase of ROC content and improve the proportion of the recalcitrant carbon pool.