Effect of Biochar on Seed Germination and Seedling Growth of Robinia pseudoacacia L. In Karst Calcareous Soils

Biochar is predicted to improve soil properties and facilitate plant growth, yet few studies verify such an effect on seed germination and seedling growth in karst calcareous soils. We evaluated the effect of rice husk and woodchip biochar at varying application rates (1%, 2% and 5% by weight) on seed germination and seedling growth of Robinia pseudoacacia L. in calcareous soils by a 240-day glasshouse pot experiment. The germination rate of Robinia pseudoacacia L. seeds in biochar-treated soils reached a peak on day 3, 2 days faster than the control. The shoot and root biomass of seedlings were significantly increased by adding 1% and 2% biochar. With increasing levels of biochar, the root to shoot ratio decreased sharply, which was related to the increased soil capillary water and nutrient supply (i.e., P and K). We found soil capillary water-holding capacity was significantly correlated with seed germination rate and shoot dry weight. The shoot dry weight was also significantly correlated with soil available-P. The studies indicated the addition of 1-2% biochar had a significantly positive impact on seed germination, shoot and root growth of Robinia pseudoacacia L. in karst calcareous soils during 240 days of biochar-soil incubation.