Combined Urea Humate and Wood Vinegar Treatment Enhances Wheat–Maize Rotation System Yields and Nitrogen Utilization Efficiency Through Improving the Quality of Saline–Alkali Soils

Abstract

We aimed to investigate the effect of combining urea humate and wood vinegar on the improvement of saline soils and the yield of wheat and maize. The following seven treatments were designed and conducted for 2 years, a no nitrogen fertilizer (CK) treatment, and a further six treatments consisting of a combination of three rates of urea humate (H0: no urea humate; H1: 50% urea humate; H2: 100% urea humate) and two rates of wood vinegar as a foliar fertilizer (W0: no wood vinegar; W1: 90 L ha−1 wood vinegar). The results indicated that the wood vinegar treatment increased wheat yields by 12.4–44.3% and maize yields by 6.8–13.7% and that 100% urea humate application increased wheat yields by 8.1–38.0% and maize yields by 3.5–9.7%. Furthermore, nitrogen use efficiency was significantly improved with the combined application of humic acid urea and wood vinegar. Compared with the no urea humate treatment (H0), at the end of the 2-year field trial, microbial biomass carbon and nitrogen increased by 9.8–24.9% and 18.1–29.2%, respectively, urease activity decreased by 16.6–25.0%, and mineral nitrogen (NH4+-N and NO3--N) content increased in the 0–40 cm soil layer. Collectively, our findings thus indicate that the combined application of urea humate and wood vinegar can increase the yields and nitrogen fertilizer utilization of rotation wheat and maize, although the extent of these increases differed according to the amount of urea humate input.