Optimization of appropriate boron fertilization application range for two cotton (Gossypium hirsutum L.) varieties in boron-deficient soils

Abstract Background Boron (B) constitutes a critical yield constraint in global cotton production. Although B application plays a vital role in cotton yield, research gaps persist regarding cultivar-specific B requirements, vertical canopy dynamics, and precision management protocols in B-deficient agroecosystems. Results In this study, we investigated the effects of B application rates on yield variation and spatial variation across two varieties at three locations. In Yancheng, applying 2.5 kg·hm−2 of boron resulted in yield increases of 14.7%–25.9%, and in Xinghua, applying 2.0 kg·hm−2 of boron achieved yield increases of 17.30%–20.58%. The optimal B application rates determined by quadratic function fitting were 1.90–2.36 kg·hm−2 of boron for CCRI 425 and 2.05–2.36 kg·hm−2 for Siza 3. Vertical canopy analysis revealed that the middle canopy (FB5–8), contributing 48.2% of total yield, responded significantly to B application rates. Conclusions Cultivar-tailored B application within 1.90–2.36 kg·hm−2 reconciles yield maximization. The boll number, especially those in the middle canopy, responded significantly to B application rates and was the main factor contributing to differences in yield formation. These findings underscore the necessity of location- and cultivar-specific B management.