Appropriate substitution of chemical fertilizer with organic fertilizer increases fresh-waxy maize yield by regulating source–sink relationships

To investigate the regulatory mechanism of replacing chemical fertilizer with organic fertilizer on fresh‑waxy maize yield and source–sink relationships, and to determine the optimal substitution rate, a field experiment was conducted in Wuwei, China, during 2024–2025. Five treatments were established: conventional fertilization (NPK) and four organic fertilizer substitution ratios of 10%, 20%, 30%, and 40% of chemical nitrogen (OF1–OF4). The characteristics of source, flow, and sink, as well as yield responses of fresh‑waxy maize, were systematically analyzed. The optimal substitution rate was determined using a multi-model comprehensive evaluation integrating TOPSIS, MFA, and GRA combined with Gaussian fitting. The results showed that the OF2 treatment delayed the decline of leaf area index after silking, prolonged the duration of high SPAD values, and enhanced the maximum source activity and initial biomass. It also increased the bleeding intensity and the transport efficiency of assimilates in the bleeding sap. Furthermore, this treatment significantly increased the maximum and average grain-filling rates, extended the grain-filling duration, and achieved synchronous enhancement of source capacity and sink growth while maintaining a stable source–sink ratio. Ultimately, the fresh grain yield in the OF2 treatment was significantly increased by 6.55%−6.60% compared with the NPK treatment. The PLS-PM model indicated that the yield improvement was primarily positively regulated by source capacity and sink growth. The multi-model analysis identified a theoretical optimal substitution rate of 16.33%, which achieves high fresh‑waxy maize yield and reduced chemical fertilizer application by optimizing source–sink balance. Therefore, a theoretical optimal organic fertilizer substitution rate of 16.33% can be recommended as a technical parameter for green and high-yield cultivation of fresh‑waxy maize in oasis irrigation regions.