Biochar Combined with Organic and Inorganic Fertilizers Promoted the Rapeseed Growth and Improved the Soil Quality in Purple Soil

Abstract Background Biochar is one kind of organic matter that can be added into soil as a soil amendment to improve its quality. To study the effect of biochar addition combined with organic and inorganic fertilizers on growth and fertility and microbial community in purple soil, a completely randomized block design was designed with three levels of biochar [B0: no biochar, B1: low-rate biochar (35 t/ha) , B2: high-rate biochar (50 t/ha)]; two levels of inorganic fertilizers [F1: low-rate inorganic fertilizer (30 kg/ha N, 87.5 kg/ha P2O5 and 60 kg/ha K2O); F2: high-rate inorganic fertilizer (60 kg/ha N, 175 kg/ha P2O5 and 120 kg/ha K2O)]; and two levels of organic fertilizers [M1: no organic fertilizer; M2: with organic fertilizer (4.5 t/ha)]. Results With the application of biochar, the plant height and stem diameter of rapeseed were increased by 6.15%-9.80% and 16.37%-20.11%, respectively. The photosynthetic capacity increased by 20.25% to 35.83%, and the yield increased by 16.40% to 19.11%, respectively. It also promoted the absorption and utilization of nitrogen, phosphorus and potassium by rapeseed to varying degrees. At the same time, the combined application of biochar and organic and inorganic fertilizers could improve soil pH, nitrogen, phosphorus and potassium content and soil microbial community richness: The pH of B1F2M1 increased 0.41 compared with the control, the nitrogen, phosphorus and potassium content in the soil increased by 103.95%, 117.88% and 99.05%, respectively. Meanwhile, soil microbial community richness was also improved. Conclusions Our research showed that biochar could promote the growth and development of rapeseed, and the combined application of biochar with organic and inorganic fertilizers could improve soil fertility and increase microbial diversity. Low-rate biochar combined with organic fertilizer and low-rate inorganic fertilizer was the most suitable application mode in rapeseed production in purple soil area of Southwest China.