Continuous wheat-cotton residue incorporation combined with potassium fertilizer improved cotton root production capacity and constructed an optimized photosynthate distribution structure for high seedcotton yield

In order to strengthen the cognition on synergy between crop residue incorporation and K, a continuous positioning experiment was carried out in 2020 and 2021. Four crop residue incorporation (CK, residue removal, WR, CR, and WR+CR, denoted wheat, cotton, and wheat and cotton residue incorporation) and three K rates (0, 150, and 225 kg K2O ha-1, denoted as K0, K150, and K225, respectively) were set. Compared with CK-K0, WR+CR-K150 increased seed cotton yield by 30.2% which reached the yield level of CK-K225. Taking the maximum theoretical seed cotton yield under CK as target yield, WR+CR, WR, and CR could achieve the same yield level with 59%-62%, 41%-49%, and 35%-43% less K fertilizer, respectively. Higher load capacity of root (LCR), boll loading of root (BLR) and lower root-shoot ratio (R/S) were observed at the boll-opening stage under the combined condition. When R/S, LCR and BLR were 0.12 g g-1, 4.00 g g-1 and 1.12 boll g-1, cotton could achieve maximum theoretical yield. 13C labeling result showed that WR+CR-K150 increased reproductive organ distribution proportion by 30.5% on average as compared with CK-K0. Thus, WR+CR-K150 can increase seed cotton yield by improving cotton root production capacity and increasing the photosynthate distribution proportion in reproductive organ.