Effects of the combined application of biochar and humic substances on the improvement of saline cropland in the Yellow River Delta of China

Soil salinization has become a global environmental problem with the potential to cause serious land degradation. Thus, improving salt‐affected soils and enhancing the nutrient utilization efficiency of saline farmlands through scientific and effective measures are urgent scientific problems. In this study, a 2‐year field experiment was conducted to evaluate the effects of different soil amendments and their combinations on the dynamics of soil salinity, soil nutrients, and crop yield in a moderately salinized soil (EC1:5 of 0.78 dS m−1 and total salt content of 3.06 g kg−1). Nine soil treatments were implemented: biochar (B), lignocellulose (L), humic acid (H), fulvic acid (F), biochar + humic acid (B + H), biochar + fulvic acid (B + F), lignocellulose + humic acid (L + H), lignocellulose + fulvic acid (L + F), and control (CK). The results demonstrated that the application of F led to a certain reduction on the contents of soil salt, Na+, and Cl− among the soils amended with a single amendment application. The combined application of B and F or H could increase the soil desalination rate and increase the mineral N and Olsen‐P concentrations at a soil depth of 0–20 cm, which improved the grain yield, biological yield, N recovery efficiency (REN), N agronomic efficiency (AEN), N partial factor productivity (PFPN), P agronomic efficiency (AEP), and P partial factor productivity (PFPP). Although the single application of L led to decreases in the grain yield, biological yield, REN, AEN, PFPN, REP, AEP, PFPP, and P physiological efficiency (PEP), the combined application of L and F had superior effects on enhancing the winter wheat grain yield and accumulative nutrient use efficiency. In conclusion, the combined application of B and F or H is recommended to ameliorate salt‐affected soils and improve nutrient availability.