Objective  The aim of this study was to explore the effects of biochar application on the growth and physiological characteristics of cucumber (Cucumis sativus L.) under salt stress.

  Method  Pot experiments were conducted using the greenhouse cultivar ‘Cuilong’. Peanut shell biochar with mass ratios of 0% (B0), 3% (B3) and 5% (B5) was added to the cultivation substrate (peat∶vermiculite = 2∶1) with or without 150 mmol L⁻¹ NaCl, respectively. The cucumber growth, yield, fruit quality, antioxidant enzyme activity and leaf mineral nutrient content were investigated.

  Result  Results showed that biochar application could significantly improve the salt tolerance of cucumber. Under NaCl stress, the plant height, maximum single leaf area, yield and ascorbic acid content of cucumber treated with B5 were significantly higher than those without biochar treatment, and the nitrate content of cucumber fruit treated with B3 and B5 was significantly lower than that of the control under both non-salt stressed and salt stressed treatments. The cucumber yields of B5 treatment in the spring and autumn cultivation experiments were 2.97 times and 2.57 times than those of the control treatment under salt stress, respectively. Higher levels of antioxidant enzyme activity were observed in biochar-treated cucumber leaves under salt stress. The activities of SOD and POD in cucumber leaves of B5 treatment were significantly higher compared with those in the control, while the content of MDA was significantly lower. Under salt stress, the contents of N and K⁺ in the top leaves of biochar-treated cucumber were significantly higher compared with those in the control, while the contents of P, Na⁺, Ca²⁺ and Mg²⁺ were significantly lower. In the bottom leaves, the change of the nutrient elements content was related to the biochar application rates, except for the Na⁺ content which was significantly higher in the bottom leaves than that of the control.

  Conclusion  Appropriate biochar application to the substrate can alleviate the salt stress of cucumber, evidenced by enhanced growth performance, antioxidant enzyme activities, and higher N and K⁺ accumulation coupled with lower Na⁺ accumulation in the top leaves. The application of 5% biochar is recommended for substrate amendment to alleviate the salt stress in greenhouse cucumber production.