Effect of Slow-Release Urea on Yield and Quality of Euryale ferox

Slow-release urea, as an environmentally friendly fertiliser, can provide a continuous and uniform supply of nutrients needed by the crop, reduce the amount and frequency of fertiliser application, and promote the uptake and utilisation of nitrogen in crops. The production of <i>E. ferox</i> is often dominated by the application of quick-acting fertilisers, resulting in serious problems of over-fertilisation, inappropriate periods of fertilisation, eutrophication of soil and water due to fertilisation, and difficulties in applying fertilisers. Therefore, in this study, different amounts (CK, T1, T2, T3, T4, T5) of SRU (Slow-release Urea) were first applied, and T3 (18.8 kg·667 m^-2) was found to significantly improve both yield and quality. Further, it was found that under different SRU (CK, S1, S2, S3, S4) application period treatments, application of 18.8 kg·667 m^-2 at AFP20 (S2) period significantly increased the yield and quality of <i>E. ferox</i>. In the seed kernels of <i>E. ferox</i>, the total yield, soluble sugar content, total starch, and flavonoid content increased significantly by 10.35%, 36.40%, 5.91%, and 22.80%, respectively, compared with CK. In addition, the expression of key sugar transporter genes (<i>EfSWEETs</i>), flavonoid synthesis-related genes (<i>EfPAL</i>, <i>EfDFR</i>, etc.), and starch synthesis-related enzyme activities (SBE, SSS, GBSS) were significantly increased. By exploring the quantity of application and application period of SRU, this study was carried out to investigate the in-depth effect of SRU on the growth and development of <i>E. ferox</i> and to provide technical references for the increase in <i>E. ferox</i> yield, the improvement in <i>E. ferox</i> quality, and the simplification of fertiliser application.