Efficient cotton population photosynthetic production synergistically increases seedcotton yield and fiber quality through straw incorporation with appropriate nitrogen fertilization in wheat-cotton rotation system

•Straw incorporation with 150 kg N ha−1 had the most cotton yield and fiber quality.•Cotton square and boll during the efficient photo-thermal period were measured.•Improved canopy photosynthetic capacity contributed to cotton square and boll.•Straw incorporation optimized photosynthate allocation in cotton boll.•Straw incorporation with a 30% reduction from 150 kg N ha−1 was recommended.