[Effects of Biochar and Soil Conditioner on Coastal Barren Saline-alkali Soil]

This study aimed to quantify the biological improvement and availability from a soil amendment substance for barren severe saline-alkali soils. A field experiment was conducted to apply biochar (B) and soil conditioner (C) rich in humic substances to pioneer crops and oil sunflower planted in the coastal barren severe saline-alkali area of the North China Low Plain. The six treatments included single or combined application of two-level biochar rates (0 and 1.25 kg·m^-2) and three-level soil conditioner rates (0, 0.83, and 1.66 kg·m^-2) at the start of the experiment. Soil samples were collected at 30 cm per layer and sampling from 0 to 90 cm after the oil was collected. The results revealed that the application of biochar increased the saline concentration of the 0-30 cm and 60-90 cm soil layers, whereas the soil conditioner significantly decreased the saline concentration of the 0-30 cm soil layers. Neither biochar nor conditioner showed a significant impact on soil pH. Biochar exhibited varying impacts on soil nutrients, that is, significantly inhibiting soil nitrification, which resulted in soil NO₃^--N decreasing while NH₄⁺-N increased significantly, along with no significant impact on soil organic matter content (SOM) in the 0-90 cm soil profile. The application of soil conditioner exerted positive effects on improving SOM in the 0-30 cm layer and NO₃^--N in the 0-90 cm soil depth when the conditioner rate was at 1.66 kg·m^-2. Either the sole application or the co-application of biomass and conditioner, along with their interaction, exhibited an increasing trend for the NH₄⁺-N, available phosphorus (Olsen-P), and available potassium (K_ex) contents, also seen in the 0-90 cm soil profile, although the increase effect for the three nutrients was primarily attributed to biochar. Soil conditioner was more effective in increasing SOM and reducing saline in the 0-30 cm soil layer. The application of a higher amount of conditioner accelerated soil nitrification, whereas biochar was applied essentially as a nitrification inhibitor. Therefore, the co-application of biochar with soil conditioner would be an effective practice for improving soil fertility, preventing soil nitrification, and deterring nitrate leaching, as well as reducing saline for topsoil, which would be a basis for developing soil amendments to control saline and a fertile soil environment for pioneer crops planted in coastal barren severe saline-alkali areas.