Background Zhongjie Farm is located in Huanghua city, Hebei province. The soil in this area is mostly salinized soil. The soil structure is poor, the nutrient is poor, and the soluble salt content is high, which is not conducive to the development of local agroforestry. In order to solve the problem of high salinity and salinity of coastal saline-alkali soil, the surface soil (0-20 cm) of Zhongjie Farm was selected, and the indoor leaching and desalination test method was adopted to investigate the effects of biochar and garden waste compost on leaching and desalting of coastal saline-alkali soil.

Methods Biochar and garden waste compost were treated according to different mass ratios (0% as CK treatment, 2% biochar as B treatment, 5% garden waste compost as G treatment, 2% biocharplus 5% garden waste compost as BG treatment). Using deionized water as a water source, intermittent irrigation was used to simulate natural rainfall. The Electrical condunctivity (EC) value, pH value and concentration of water-soluble ions (Na⁺, Cl^-, SO₄^2- and HCO₃^-) of the leaching solution after 6 times of leaching were detected. In addition, after the leaching, the EC value of the soil, the pH values of Na⁺, Ca²⁺, Mg²⁺, Cl^- and SO₄^2- were detected Dual-indicator neutralization titration method for CO₃^2- and HCO₃^-, silver nitrate titration method-Moore method for Cl^-, EDTA titration method for Ca²⁺ and Mg²⁺, indirect EDTA complexometric titration for SO₄^2-, and flame photometry for K⁺ and Na⁺. Sodium adsorption ratio (SAR) value was calculated.

Results 1) During the leaching and desalting process, the pH of the solution from B treatment decreased from 8.28 to 8.37, and the pH of the G treatment increased from 7.67 to 8.24. The pH change trend of CK and BG treatments was close to a gradual upward trend. The EC values of each group showed a downward trend and gradually became stable. 2) The concentrations of Na⁺, Cl^- and SO₄^2- in the leaching solution showed a decreasing trend, and the decreasing rates of B, G and BG treatments were significantly greater than those in CK treatment. The content of HCO₃^- increased and then remained stable. The trend of G treatment and CK treatment was similar, but the increment was small, and the change of biochar treatment (B and BG) was small. 3) There was a significant difference in the pH value of the soil after leaching under different treatments. The order of pH value was B>CK>BG>G, and the pH of G treatment was the most obvious in 8.45.4) Compared with CK, the EC value of the soil after leaching decreased from 0.41 mS/cm to 0.20-0.27 mS/cm, the SAR(sodium absorption ration)value decreased from 3.28 to 1.19-2.03, and the Cl^- content decreased from 0.30 g/kg to 0.13-0.19 g/kg; The EC value, SAR value and Cl^- content of BG treatment were the most obvious, which were 0.20 mS/cm, 1.19 and 0.13 g/kg, respectively. The decrease of SO₄^2- content in B treatment was 0.06 g/kg.

Conclusions Adding biochar and garden waste compost to the coastal saline-alkali soil can not only significantly improve salt washing efficiency, but also reduce soil EC value and SAR. And it can reduce the content of Na⁺, the content of Cl^-, and the total salt content in the soil. The mixed application effect of the two materials is better than that of sole application, and the addition of garden waste compost reduces the alkalization phenomenon of the coastal saline-alkali soil during leaching and desalination.