Nitrification inhibitor 3,4-dimethylpyrazole phosphate alleviates the dissolution of soil inorganic carbon caused by nitrogen fertilization

In carbonate soils, soil inorganic carbon (SIC) dissolves and releases CO2 due to exogenous application of nitrogen fertilizer, which makes the soil an important carbon source. Application of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is likely to be an effective measure to alleviate SIC dissolution. A 5-year field experiment was conducted to observe SIC dynamics under three treatments: No N fertilizer (CK), N fertilizer (NF), and N fertilizer combined with DMPP (N + NI). Soil samples were collected from 0 to 20, 20-40, 40-60, 60-80, and 80-100 cm in depth, and soil organic carbon (SOC), SIC, total carbon (TC), total nitrogen (TN), and carbon isotope composition (delta C-13) of the soil were analyzed. The proportion of pedogenic carbonate (PIC) in SIC was estimated using an isotopic mass balance equation. Results showed that: (1) compared with the application of N only, DMPP had no significant effect on SOC content and delta C-13(SOC) in the 0-100 cm soil profile; (2) the application of N fertilizer significantly reduced the SIC content by 10.0 gkg(-1) (58.3 %) in the 0-80 cm soil profile. In the 0-20, 20-40, and 60-80 cm soil layers, the SIC content was reduced by 2.9, 1.9, and 3.8 gkg(-1), respectively. However, the SIC content significantly increased by 3.2 gkg(-1) (58.9 %) in the 80-100 cm soil layer. DMPP application significantly increased the SIC content in the 0-20 and 20-40 cm soil layers by 1.3 gkg(-1) (50.9 %) and 1.2 gkg(-1) (48.2 %), respectively; (3) DMPP combined with N significantly alleviated PIC dissolution in the 0-40 cm soil layers and increased PIC stock in 0-100 cm soil by 6.2 Mgha(-1) (64.6 %). Applying DMPP to farmland soil containing carbonate significantly alleviated the dissolution of N fertilizer on PIC, which may decrease CO2 emissions in the field.