Study of soil nitrogen cycling processes based on the 15N isotope tracking technique in the black soil areas

Abstract

In recent years, biochar has been widely used for soil improvement, but there has been some variation in its effectiveness; the mechanism of regulating nutrient cycling in soil is unclear due to different soil textures and physicochemical properties of biochar. Therefore, in this paper, the effects of different tillage patterns and biochar gradients on the nitrogen use efficiency (NUE) and soil nitrogen fixation capacity of soybean were monitored in a phased manner by field trials using 15N isotope tracer technology. The results of the study showed that (1) biochar increases the soil's nitrogen fixation capacity by improving the structural stability of the soil. Total nitrogen (TN) content of the soil increased by 42% after deep ploughing (DP) application of 500 kg/acre of biochar. (2) Biochar improved the nitrogen use efficiency of soybean plants and increased soybean yield. Compared to that of shallow tillage (SP), deep tillage application of 500 kg/acre of biochar increased the nitrogen use efficiency of soybean by 0.62–3.45%. 15N isotope tracking technology showed that soybean plants with deep tillage application of 500 kg/acre of biochar had the highest 15N content at flowering stage; compared to no biochar application, the 15N content of root, stem and leaf fractions increased by 65.4–86.9%. (3) Biochar increased soil CO2 emission fluxes, reduced soil CH4 emission fluxes and soil N2O emission fluxes, with better GHG emission reduction under DP treatment. The regulation model of deep ploughing application of 500kg/acre of biochar provides a reference and guiding meaning for future soil fertility maintenance and farmland soil tillage in black soil areas.