Precision boron management improves cottonseed kernel yield by regulating sucrose metabolism during the critical kernel-filling window

Boron deficiency is a major yield-limiting factor in intensive cotton ( Gossypium hirsutum L.) production. However, the physiological mechanisms and the critical periods for boron regulation of cotton seed kernel biomass remain unclear, hindering precise nutrient management. This study aimed to (i) identify the key boron-regulated window for cottonseed kernel biomass accumulation, (ii) establish the critical kernel boron concentration during this period, and (iii) elucidate the underlying sucrose metabolic mechanisms. A three-year field experiment was conducted on two contrasting soils with three boron application rates. Dynamics of kernel biomass, tissue boron concentration, carbohydrate profiles, as well as the activities and gene expression of key enzymes involved in sucrose metabolism and glycolysis were monitored during kernel development. The results identified a critical boron-regulation window at 11.7–24.4 days post-anthesis, during which boron supply modulated yield primarily by affecting the accumulation rate. The critical kernel boron concentrations for optimal biomass were 53.5–80.5 mg·kg −1 . Adequate boron supply improved sucrose transport, optimized sucrose metabolism, and stimulated glycolytic flux, thereby directing carbon toward storage compounds and increasing kernel biomass. These findings provide a physiology-informed strategy for precision boron management to improve cottonseed yield and supporting sustainable production. • The key boron-regulated window for cottonseed kernel biomass accumulation was identified at 11.7–24.4 days post-anthesis; • The critical kernel boron concentration range of 53.5–80.5 mg·kg −1 was defined for optimal biomass during this window; • Adequate boron supply improved sucrose import, stimulated glycolytic flux, and ultimately increased biomass in kernels.