Biochar distribution mode in soil affects the vegetative peanut growth, nitrogen uptake and nitrogen-fixing bacteria activity

Biochar plays an important role in agricultural production as it can improve soil fertility, promote nutrient adsorption and enhance plant growth. However, the distribution of biochar in the soil significantly impacts its application effect. In order to investigate the impact of non-uniform biochar distribution on soil nutrient uptake, root shape, peanut development, and the makeup of soil microbial communities, we carried out greenhouse peanut pot studies. This experiment followed a completely randomised design with four treatments, each with three replications. The four treatments were as follows: no biochar application (B0); concentrated biochar application near seeds (B1); relatively concentrated surface application of biochar (B2), and uniformly dispersed application of biochar (B3). The findings demonstrated that, compared to the no-biochar scenario, the aboveground and root nitrogen uptake was significantly (P < 0.05) improved by the B2 treatment, increasing by 42.79% and 51.39%, respectively, compared to the control group. Additionally, it reduced the concentrations of NO₃^–-N and NH₄⁺-N in the soil. The B2 treatment also significantly (P < 0.05) increased the net photosynthetic rate and aboveground dry matter weight, increasing by 196.85% and 53.96%, respectively, compared to the B0 treatment. The B1 and B3 treatments also demonstrated a higher promoting effect. The growth of the root system and the quantity of root nodules were promoted by the addition of biochar. The number of root nodules in the B2 treatment was 72.22% higher than that in the control group. In terms of microbial and bacterial communities, the addition of biochar increased the number of nitrogen-fixing bacteria to a certain extent, while the relative abundance of soil bacterial communities showed no significant differences. In general, the non-uniform distribution of biochar in the soil significantly affected peanuts' vegetative growth and developmental effects. The relatively concentrated surface application of biochar treatments contributes to improving plant nutrient uptake and root system development. This provides a more effective application method for agricultural personnel to apply biochar fertiliser in the future.