Objective To investigate the soil physicochemical properties and fruit quality in gonggan (Citrus reticulata ‘Gonggan’) orchards, and clarify the relationships between soil physicochemical properties and fruit quality indicators, aiming to provide a scientific basis for nutrient regulation and fertilization strategies in these orchards.

Method Ten representative orchards were selected in Deqing County, Guangdong Province. Soil physicochemical properties and fruit quality indicators were measured, respectively. Multivariate analysis methods, including correlation analysis, regression analysis, and linear programming, were applied to identify the primary soil nutrient factors those influence fruit quality. The ranges of soil indicators for the optimal fruit quality were determined based on linear programming equations. The fruit qualities of 10 sample orchards were comprehensively ranked by using the entropy weight TOPSIS method.

Result The soil in gonggan orchards was generally acidic. The medium elements such as Ca and Mg were predominantly deficient, whereas soil organic matter was generally abundant, and microelements such as Fe and Cu were at appropriate or abundant levels. Correlation analysis result indicated that fruit transverse diameter was significantly and positively correlated with soil exchangeable Mg content; Titratable acid content was significantly and positively correlated with soil organic matter, total N contents, and cation exchange capacity; Ascorbic acid content was significantly and negatively correlated with exchangeable Na, Ca, and Mg contents. Multivariate linear regression analysis result demonstrated that the key soil factors affecting the quality of gonggan fruit quality included pH as well as total N, alkali-hydrolyzable N, exchangeable Ca, exchangeable Mg, available Mn, available Cu, and available B contents. Comprehensive evaluation using the entropy-weighted TOPSIS method indicated that the overall fruit quality from the Huilong Town production area was relatively superior, while Lijia Farm exhibited the optimal fruit quality. When the quality of gonggan is best, the theoretical optimal ranges of soil physicochemical property indicators were: pH 5.5–6.5, total N content 1.40–1.50 g·kg⁻¹, alkali-hydrolyzable N content 200 mg·kg⁻¹, exchangeable Ca content 1 000 mg·kg⁻¹, exchangeable Mg content 100 mg·kg⁻¹, available Mn content 5 mg·kg⁻¹, available Cu content 1 mg·kg⁻¹, and available B content 0.50 mg·kg⁻¹.

Conclusion Soil management in Deqing gonggan orchards shall focus on the application of alkaline fertilisers to mitigate soil acidification, and optimize the supply of N, Ca, and Mg.