To investigate the effects of split nitrogen topdressing under mulch-integrated drip irrigation combined with nitrogen fertilizer efficiency enhancers on peanut growth, yield, and nitrogen use efficiency, and to determine the optimal topdressing timing and the best combination of nitrogen fertilizer and inhibitors, a two-factor split-plot experiment was conducted using peanut cultivar Jinguan 1 as the test material. Compared with the no-nitrogen control (CK), the main plot factor was topdressing regime, with two treatments: two nitrogen topdressings applied at the flowering-pegging stage and pod-setting stage (T1), and three nitrogen topdressings applied at the flowering-pegging stage, pod-setting stage, and pod-filling stage (T2). The subplot factor was inhibitor type, with four treatments: urea (N1), urea + the urease inhibitor NBPT (N2), urea + the nitrification inhibitor DMPP (N3), and urea + NBPT + DMPP (N4). The effects of these treatments on peanut growth, yield, quality, nitrogen use efficiency, leaf SPAD value, physiological traits of mature leaves, and soil nitrogen supply capacity were systematically evaluated. The results showed that, compared with T2, T1 was more effective in improving peanut growth and physiological characteristics, significantly increasing biomass, yield, and quality, enhancing leaf SPAD values and antioxidant enzyme activities in mature leaves, reducing CAT content and the O2? production rate in leaves, increasing partial factor productivity, agronomic efficiency, and the contribution rate of nitrogen fertilizer by 10%-18%, 26%-45%, and 12%-24%, respectively, and significantly improving soil nitrogen supply capacity. Under the same number of topdressings, compared with N1, the addition of NBPT inhibited soil urease activity, whereas the addition of DMPP inhibited the activities of soil nitrate reductase and nitrite reductase. Among all treatments, N3 showed the best overall performance, significantly increasing plant height and dry matter accumulation, enhancing photosynthetic capacity and soil nitrogen supply capacity, and increasing yield per plant by 30%-32%. The highest yield per plant was obtained under T1N3. In conclusion, under mulch-integrated drip irrigation, the combined application of nitrogen fertilizer and the nitrification inhibitor DMPP at the flowering-pegging and pod-setting stages significantly promoted peanut growth. This treatment optimized the activities of soil nitrogen metabolism enzymes, improved soil nitrogen supply capacity, enhanced leaf physiological performance, increased photosynthetic capacity, delayed leaf senescence, and ultimately improved peanut yield, quality, and nitrogen use efficiency. As the optimal treatment under the present experimental conditions, it provides a scientific basis for efficient nitrogen management in peanut production.
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