Effect of biochar addition on water–salt distribution and growth of winter wheat in coastal saline-alkali soils under brackish water irrigation

To investigate water-saving and yield-enhancing improvement programmes suitable for saline-alkali soils in the Yellow River Delta region, this study conducted outdoor pot experiments utilizing local moderately saline-alkali soils as research subjects. The primary focus was to examine the impact of biochar addition on water and salt distribution in saline-alkali soils and its effect on winter wheat growth under brackish water irrigation conditions. The study design established three different irrigation water mineral concentrations (0, 2 and 4 g L⁻¹) during the research. Two types of biochar, wheat straw biochar (WB) and corn straw biochar (CB), were used with four different applications (0, 5, 10 and 20 t ha⁻¹). There were 21 treatments; each replicated three times. These findings demonstrated that brackish water irrigation and biochar application contributed to a notable increase in soil water content (SWC), with increases ranging from 12.8 to 83.9% across treatments. Using brackish water for irrigation increases soil salt content (SSC) and exacerbates soil salinization. However, the application of biochar counteracts this effect by reducing soil salinity and mitigating the degree of salinization. Treatments applying biochar mostly increased SSC, but proper application had a salinity-reducing effect, reducing SSC by up to 15.2%. And biochar reduced the soil sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP), mitigating the adverse effects of high salinity on winter wheat. Finally, the application of biochar promoted the growth of winter wheat and increased yield, with the treatment applying 10 t ha⁻¹ of CB (K₂Y₁₀) producing the greatest yield under brackish water irrigation conditions and increased by 18% compared with the treatment without biochar (CK₀). In summary, considering the aspects of water conservation, salt reduction and yield increase, the most effective saline land improvement programme for this region involved using 2 g L⁻¹ brackish water for irrigation in combination with applying K₂Y₁₀. This approach balances addressing soil salinity, enhancing water conservation and maximizing crop yields.