Nitrogen fertilizer combined with DPC+ chemical topping agent can improve cotton yield by enhancing antioxidant enzyme activity and improving the endogenous hormone balance

Nitrogen fertilizer and fortified DPC (DPC+) chemical topping agent management is essential for replacing manual topping and achieving simplified cotton cultivation. However, the response of cotton physiological characteristics to the interaction between nitrogen fertilizer and DPC+ and the relationship between this interaction and yield remain unclear. A 2-year field experiment was conducted to investigate the effects of nitrogen rates (N1, 150; N2, 300; N3, 450 kg ha−1) and DPC+ doses (D1, 450; D2, 750; D3, 1050 mL ha−1) and D0 (manual topping) on antioxidant enzymes, endogenous hormone content and balance, reproductive organ dry matter (RODM) and yield. N1D1, N2D2, and N3D3 significantly improved the RODM and yield, with N2D2 having 3.5 − 37.1% higher RODM levels than N1D1 and N2D2. At the N1 level, D1 decreased malondialdehyde (MDA) content by 4.1 − 35.6% compared to D0, D2 and D3, and increased catalase (CAT) activity and abscisic acid (ABA) content by 69.7% and 34.2% than D0, respectively. At the N2 level, D2 decreased the MDA content by 16.1 − 51.9% and increased peroxidase and CAT activity and ABA and gibberellic acid contents by 12.7 − 355.7% compared to D0, D1, and D3. Furthermore, D2 decreased indole-3-acetic acid (IAA) content and IAA/ABA by 12.1% and 30.5% in boll opening but increased trans-zeatin-riboside (ZR) content by 25.5% compared to D0. At the N3 level, D3 increased ZR/ABA by 20.1% compared to D0. Overall, the interactions between appropriate nitrogen levels and DPC+ doses can increase cotton yield by enhancing antioxidant enzyme activity and promoting endogenous hormone homeostasis, with N2D2 performing best.