Objectives  The aim was to clarify the responses of white gourd yield, quality and soil nitrogen (N) leaching to fertilizer-N reduction and biochar application, which can provide a theoretical basis for scientific application of N fertilizer and biochar for vegetable production in the Pearl River Delta Region.

  Methods  A 2-year field experiment was conducted in Sanshui District, Foshan City to observe the changes in white gourd yield, quality, N leaching and soil nutrients under 5 treatments, including control (Control), traditional fertilizer (100%N), 30% N reduction (70%N), 30% N reduction + biochar 10 t hm⁻² (70%N + BC10) and 30% N reduction + biochar 20 t hm⁻² (70%N + BC20).

  Results  Compared with 100%N treatment, the yield of white gourd under 70%N treatment was significantly reduced by 27.4% in 2019. Compared to the 70%N treatment, the white gourd yield increased by 18.2%-32.6% (2019) and 13.8%-46.3% (2020) in the 70%N + BC10 and 70%N + BC20 treatments and their yield levels were equal to N100% treatment, which indicated that biochar had a significant yield increasing effect on white gourd. Moreover, the number of white gourds, the weight per white gourd and the length of white gourd were all increased in the biochar amended treatments. Compared to the 70%N treatment, biochar application reduced the nitrite content and increased the vitamin C content, and improved the quality of white gourds. There was no significant effect on soluble solid, juice yield and total acidity, but the 70%N + BC20 treatment significantly reduced the total sugar content of white gourd in 2019. Therefore, the application of 10 t hm⁻² biochar could improve the quality of white gourd. Compared to 70%N, the nitrate content of leachate was reduced by an average of 8.6% and 7.2% in the 70%N + BC10 and 70%N + BC20 treatments in 2020, and the total N content of leachate also reduced by 4.3% in the 70%N + BC10 treatment. Under reduced N conditions, biochar application increased soil pH by 0.81-1.55 units and soil organic matter content by 4.0%-8.9%.

  Conclusions  Based on the results of a 2-year field plot experiment, the application of biochar significantly increased the yield of white gourd and farmers could obtain the yield equivalent to that of conventional N application under 30%N reduction. Application of biochar with 10 t hm⁻² improved the quality of white gourd. Meanwhile, the application of biochar improved the soil pH condition, increased organic matter content, and reduced N leaching losses.