Objective The aims were to solve the problems of acid, heavy texture and low nutrient contents in red soil in Yunnan province, the growth of potato and soil condition were optimized by adding substrate soil and biochar, in order to provide a theoretical basis for the efficient planting and soil improvement.

Method The pot experiment method was used, with the test potato variety being 'Dian Shu 23'. Pure red soil (CKR) was used as the control. Five treatments were set up: red soil to substrate soil ratio of 1 : 1 (RZ1), 2 : 1 (RZ2), 3 : 1 (RZ3), adding 40 t hm⁻² of biochar (RT40), and 80 t hm⁻² of biochar (RT80). The changes in potato growth indicators and soil physicochemical properties were observed.

Result Research indicates that adding substrate soil and biochar enhanced potato plant height, stem thickness, yield and photosynthetic parameters, with a yield increase ranging from 15.51% to 196.82%. Compared to the pure red soil control, the sand particle size in the soil treated with substrate soil and biochar increased by 14.82% to 54.13%, while the clay particle size decreased by 0.04% to 7.47%. The water retention capacity and porosity of the soil were significantly enhanced by 3.37% to 68.91% and 5.30% to 18.12%, respectively. Additionally, the available phosphorus, availabe potassium nutrients, organic matter contents in the soil were all improved. Correlation analysis revealed a significant positive correlation between soil water retention capacity and nutrient levels. Principal component analysis showed that the first three principal components accounted for 98.388% of the total variance, with RZ1 (3.54), RZ2 (0.77) and RT80 (0.34) ranking as the top three treatments.

Conclusion Both substrate soil and biochar can promote the growth of potato plants and improve the physical and chemical properties of soil in the potato planting system in red soil area, and achieve a significant increase in yield. The optimal ratio of red soil to substrate soil is 1 : 1.