Effects of brackish water irrigation and biochar application on fertility, enzyme activity, and winter wheat yield in coastal saline-alkali soils

Soil salinization is a common form of land degradation in coastal regions. The Yellow River Delta is a typical coastal saline-alkali soils distribution region, with saline-alkali soils accounting for nearly half of the total area of the region. In view of the lack of fresh water in the region, the use of brackish water and biochar made from agricultural waste to improve coastal saline-alkali soils has a good application prospect, but there are fewer studies on this at present. To explore water conservation, fertilization, and yield enhancement solutions appropriate for saline-alkali soils in the Yellow River Delta region, this study focused on investigating the impact of biochar addition on the fertility, enzyme activity, and winter wheat yield in saline-alkali soils under brackish water irrigation conditions. The research was conducted through outdoor potting experiments, utilizing a local moderately saline-alkali soil as the subject of study. The study design established three different irrigation water mineralization levels (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. The research findings indicated that brackish water irrigation adversely affected soil fertility and soil alkaline phosphatase activity and soil sucrase activity but increased soil urease activity and soil peroxidase activity. In contrast, biochar application improved soil fertility and enzyme activities. The soil fertility and enzyme activities of K2Y10 treatment was higher than that of CK (fresh water, no biochar application) except for soil total nitrogen, which increased by 5.5%-71.2%. While brackish water irrigation decreased winter wheat yield. Biochar application increased winter wheat yield, with the K2Y10 treatment showing the highest yield under brackish water irrigation conditions, and increased by 17.7% compared to CK. In conclusion, the study recommends a combination of water-saving measures, fertilizer cultivation, and yield increase strategies to improve saline-alkali soils in the Yellow River Delta region effectively. Specifically, irrigating with 2 g L-1 brackish water and application 10 t ha-1 of CB demonstrated greater efficacy in addressing the challenges of saline-alkali soils in the region.