Effects of biochar from populus alba × populus berolinensis and pinus sylvestris var. mongolica application on soil physicochemical properties

This study examined the effects of biochar produced from forestry waste (Populus alba×P. berolinensis and Pinus sylvestris var. mongolica branches and leaves) on soil physicochemical properties through a 60-day static incubation experiment under varying pyrolysis temperatures (300, 500, and 700 °C) and application rates (1%, 3%, and 5% (w/w)). Results indicated that biochar application enhanced soil available potassium content and pH to different extents. Notably, the most pronounced effect was observed with a 5% application rate of Populus alba×P. berolinensis leaves biochar pyrolyzed at 700 °C, which increased available potassium by 266.39% and pH by 9.82% compared to the control. At a 5% application rate, biochar produced from Populus alba×P. berolinensis leaves pyrolyzed at 300 °C increased soil ammonium nitrogen content by 49.27% and available phosphorus content by 141.68% compared to the control. Furthermore, biochar improved soil organic Matter content, water content, and aggregation. Specifically, the most significant increases were seen with a 5% application rate of Populus alba×P. berolinensis branch biochar pyrolyzed at 300 °C, raising organic Matter by 320.03% and water content by 30.61% compared to the control. Regarding soil aggregate distribution, a 5% application rate of Pinus sylvestris var. mongolica branch biochar pyrolyzed at 300 °C significantly increased the macroaggregate fraction while reducing microaggregates and silt-clay fractions. In conclusion, the application of forestry waste-derived biochar demonstrates potential for improving soil physicochemical properties, with pyrolysis temperature, feedstock source, and application rate all significantly influencing these improvement effects.