Yellow River alluvial sandy soil suffers from poor structural stability and low fertility, constraining soybean productivity. We hypothesised that co-applying straw return with an organic–inorganic composite would modify Fe–Al oxide fractions, promote water-stable macroaggregate formation, and thereby improve soybean physiological performance and yield components, with the ternary combination outperforming single or binary regimes. A soil-column experiment was conducted at Shandong Agricultural University Experimental Station, Tai’an, China, using a completely randomised design (n = 3) with six treatments: straw-only control (CK), organic fertiliser (JO), biochar (JB), organic fertiliser+attapulgite (JOA), biochar+attapulgite (JBA), and organic fertiliser+biochar+attapulgite (JOBA). Compared with CK, JOBA increased water-stable macroaggregates (>0.25 mm) by 268.82%, mean weight diameter by 89.88%, and decreased soil bulk density by 19.97%; it also increased catalase activity by 35.74%, pods per plant by 110.34%, seeds per plant by 128.57%, and 100-seed weight by 60.82%. The JOBA showed the greatest overall improvement, reflecting complementary functions among amendments. However, these findings were obtained in a controlled short-term column experiment; field validation and even long-term evaluation are required.