Abstract: This study explored the effects of biochar addition and ryegrass growth on the nutrient distribution in yellow soil in Karst area, of Bozhou County, Guizhou Province, China. The experiment was conducted over a period of 45 days with twelve treatments, including a bare land control (CK), only planting of ryegrass (R), only addition of biochar at various rates (BLB₁, BLB₃, BLB₅, BLB₇, BLB₉; subscripts indicate % biochar added to soil weight∶weight), and ryegrass planting together with addition of biochar at various rates (RB₁, RB₃, RB₅, RB₇, RB₉). The soil organic matter (SOM), pH, total phosphorus (TP), available phosphorus (AP), total potassium (TK) and available potassium (AK) were tested after 45 days. The results indicated that the treatments BLB and RB were the most effective way to increase the content of all nutrients. The rate of biochar addition was significantly positively correlated with the content of all nutrients (P<0.01), and the smallest correlation coefficient was 0.78. The R treatment was the treatment in which the content of SOM, TP, TK and AP were decreased, as the nutrient consumption of ryegrass was higher than the nutrient return to the soil. Compared with BLB treatments, RB treatments decreased the nutrient except the 7% treatment. However, considering the optimum pH value for ryegrass growth and the soil erosion situation in Karst area, the treatment RB₇ can be recommended because it both improved the soil nutrient status and texture in this yellow soil. This study provided scientific data comparing options for ameliorating the nutrient limitations of nutrients in Karst region yellow soil.

Key words: biochar, ryegrass, yellow soil, nutrient, soil improvement