Effects of Different Nitrogen Application Rates on Growth, Photosynthetic Characteristics, Yield, and Nitrogen Use Efficiency of Zizania latifolia

To promote the growth, photosynthetic capacity, yield and nitrogen use efficiency (NUE) of Zizania latifolia, optimizing the amount of nitrogen (N) fertilization applied is critical. We investigated the effects of different nitrogen application rates on the growth, development, photosynthetic characteristics, yield components and nitrogen partial factor productivity (NPFP) of Z. latifolia. The experiment was conducted under field conditions using five rates of N application (N1 = 196, N2 = 266, N3 = 336, N4 = 406, and N5 = 476 kg N ha−1). The results showed that increasing N application significantly enhanced plant height and tiller number, whereas leaf length and width were less responsive. Photosynthetic performance and yield increased initially and subsequently declined at the highest N treatment. The N4 treatment achieved the highest yield of 19.24 t ha−1 and the highest maximum net photosynthetic rate (25.5 μmol m−2 s−1). NPFP gradually decreased as N application increased, demonstrating diminishing returns under excessive N supply. The present study demonstrated that N application rate significantly modulated the growth, photosynthetic performance, yield formation, and NUE of Z. latifolia. Nitrogen addition improves plant growth and photosynthesis within an optimal range; further N increases fail to bring proportional yield gains and reduce NUE. The results provide a practical reference for developing more efficient and sustainable N management strategies for Z. latifolia production.