Optimal Matching of Spring Soybean Varieties and Sowing Dates in Rapeseed Stubble of Southwest China: A Multidimensional Evaluation

In the rapeseed‐soybean rotation system of Southwest China, spring soybean yield and quality are constrained by poor varietal adaptation to rapeseed stubble and imprecise sowing dates. A two‐factor (variety × sowing date) randomized block experiment was conducted in Dianjiang, Chongqing, in 2025. Thirty spring soybean varieties were evaluated under four sowing dates (May 10, May 20, May 30, and June 10). A multidimensional evaluation system integrating agronomic traits, growth, stress resistance, yield components, and grain quality was established. This study aimed to evaluate the effects of different sowing dates on growth, yield, and quality parameters, to examine the interaction between crop varieties and sowing dates, and to identify optimal variety–sowing date combinations that maximize yield, improve quality, and enhance stress resistance. Results showed variety and sowing date had highly significant effects ( p < 0.01) on growth, yield, and quality, with a significant interaction ( p < 0.05). Principal component evaluation identified DHX3, QH34, and DHX9 as most suitable, with T2 (May 20) as the optimal sowing date. Under T2, DHX3, QH34, and DHX9 achieved yields of 2762.5, 2675.0, and 2525.0 kg·ha −1 , respectively, with excellent quality and stress resistance. Compared to the control, DHX3 and QH34 under T2 increased yield by 232.3% and 205.3%, respectively. Average population yield under T2 was 1782.5 kg·ha −1 , 13.9%, 25.1%, and 23.6% higher than under T1, T3, and T4, respectively. T2 coordinated a growth duration of 102–108 days, avoiding local meteorological disasters. Delayed sowing shortened growth duration and reduced yield and quality markedly. The combinations ‘DHX3 × T2’ and ‘QH34 × T2’ were identified as optimal cultivation strategies. This study provides a quantitative basis for variety selection and precision cultivation in regional rapeseed‐soybean rotation systems, though further validation across diverse agro‐ecological conditions is recommended.