Mechanism of KOH-Modified Biochar Application Under Water-Saving and Nitrogen-Reducing Conditions to Inhibit Soybean Root Rot and Improve Quality And Efficiency

To elucidate the mechanism of modified biochar in inhibiting soybean root rot and improving its quality. The effects of 0 t·ha⁻¹ (CK), 15 t·ha⁻¹ (15BC; 15KBC), 30 t·ha⁻¹ (30BC; 30KBC) and 45 t·ha⁻¹ (45BC; 45KBC) of raw biochar (BC) and modified biochar (KBC) on the incidence of root rot, rhizosphere soil ecological environment and quality were studied. The improvement of soybean root rot by BC was very weak, and the application of 45 t·ha⁻¹ BC could reduce soybean root rot by about 7% only. Compared with the BC treatment, the disease index of 30KBC and 45KBC was 22.17% and 19.82% less than CK, respectively. High application rates of BC and KBC increased the aeration, bacterial abundance and diversity of soybean rhizosphere soil, and improved the proportion of soil nutrients. The 30KBC and 45KBC significantly increased the relative abundance of beneficial bacteria (Acidobacteria, Mortierellomycota, Pseudomonas, Chryseolinea, Lysobacter and Mortierella) and decreased that of pathogenic bacteria (Bacteroidetes, Ascomycota and Fusarium) in soil. Soybean quality indicators including oil content, K, P and protein content correspond to 30KBC. The biochar can improve soil physicochemical properties, reduce the relative abundance of pathogenic bacteria, and increase that of beneficial bacteria, thereby reducing root rot incidence and improving soybean quality. Under the condition of water saving and nitrogen reduction, 30KBC is the optimum. This study is significant for alleviating soybean continuous cropping obstacles, disease prevention and control, and improving soybean quality.