Inprovent of biochemical property of surface soil by combined application of biochar with nitrogen fertilizer

Objectives The objectives of this study were to investigate the influence of combined application of biochar with nitrogen (N) fertilizer on soil carbon and nitrogen, biological property and spring maize yield, to elucidate the changing rule of soil carbon (C) and N content and the biological character by combined application of biochar with N fertilizer, providing a scientific basis for reasonable fertilization, improving soil environment and increasing spring maize yield.

Methods Field experiments were conducted in the west (Baotou) and east (Tongliao) region of Inner Mongolia. There were four biochar rates as 0, 8, 16, 24 t/hm² (expressed as C₀, C₈, C₁₆, C₂₄, respectively) and three N rates of 0, 150, 300 kg/hm² (expressed as N₀, N₁₅₀, N₃₀₀, respectively). Soil C, N content, microbial biomass and enzyme activity of three soil layers (0–10 cm, 10–20 cm and 20–40 cm) and maize yield were tested at harvest.

Results Biochar and N fertilizer application significantly affected the organic carbon, C/N ratio, microorganism quantity and enzyme activity of 0–10 cm, 10–20 cm and 20–40 cm soil layers (P < 0.01), and their interaction was also significant in two experimental sites. With the increase of biochar application rate, organic C in three soil layers and total N in 0–10 cm and 10–20 cm soil layers were gradually increased in two sites. Applying biochar and N fertilizer could significantly improve microbial biomass C, microbial biomass N, sucrase activity, urease activity, catalase activity, total enzyme activity index in the three soil layers, and had the trend of increase first, then decrease with the increase of biochar and N application rates. The microbial biomass C, microbial biomass N and sucrose enzyme and urease activity in the 0–10 cm and 10–20 cm soil layers were significantly higher than those in the 20–40 cm soil layer. N fertilizer and biochar could significantly increase grain number per cob, 100-seed weight and the yield of spring maize in Baotou and Tongliao. The maximum yield of 15.51 t/hm² and 16.43 t/hm² in Baotou and Tongliao, respectively, was from the treatment of C₈N₁₅₀. According to the correlation analysis, spring maize yield was mainly related to the microbial biomass and enzyme activity in 0–10 cm and 10–20 cm soil layers.

Conclusions The appropriate rate of biochar combined with N fertilizer could increase the soil carbon and nitrogen reserves, microbial biomass and enzyme activity in Inner Mongolia, improve the soil micro-ecological environment, and finally increase the yield of spring maize. Combined application of biochar and N fertilizer could improve soil fertility and reduce chemical fertilizer input. From this experiment, the optimal combination was 8 t/hm² of biochar and 150 kg/hm² of N fertilizer.