Effects of combined application of compound fertilizer and biochar on absorption and utilization of phosphorus by wheat

Unreasonable fertilization practices are still applied in agricultural production, resulting in reduced crop yields and wasting resources. Therefore, it is essential to optimize fertilization regimes to improve the nutrient absorption capacity of crops. However, the effects of combining nitrogen, phosphorus, and potassium (NPK) compound fertilizer with biochar on the uptake and utilization of phosphorus (P) by wheat and soil fertility remain poorly understood. Thus, we tested three biochar levels (0 quintal (q) ha^-1 (B1), 75 q ha^-1 (B2), and 150 q ha^-1(B3)) and four compound fertilizer levels (0 q ha^-1 (F1), 2.25 q ha ^-1(F2), 4.50 q ha^-1 (F3), and 6.75 q ha^-1 (F4)), and compared the effects of different experimental combinations across two years. The results showed that combined application could increase the wheat yield, soil P content, accumulated plant P, and P utilization efficiency. Among the different treatments, the wheat yields in both years were highest under B2F3, and the total soil P contents in the booting and flowering stages were also the highest. The soil available P contents in the jointing stage, booting stage, and flowering stage were highest under B3F3. The available P soil contents at maturity in both years were highest under B3F4. In addition, compared with B1F4, the accumulated plant P amounts in the booting and flowering stages were 17.6-77.3% and 17.0-87.3% higher, respectively, under B2F2, B2F3, B3F2, and B3F4 (P < 0.05). The accumulated plant P amounts in the maturity stage during the two years were highest under B2F3 (0.83 q ha^-1) and B3F3 (0.42 q ha^-1), respectively. Moreover, the partial factor productivity and agronomic use efficiency were significantly higher under B2F2, B2F3, B3F2, and B3F3 than B1F4. In summary, under the experimental conditions in this study, applying compound fertilizer at 4.50 q ha^-1 combined with biochar at 75 q ha^-1 is recommended as the optimal fertilization scheme.