In regions with sandy soil texture and water scarcity, it is little to know the coupling effect of deficit irrigation with fertilization on soybean growth. The three combined effects of deficit irrigation (DI) and nitrogen fertilization (NF) on the leaf-level physiological and morphological parameters were identified. Irrigation was started once soil water content (SWC) was below 60% (T1), 50% (T2), 40% (T3), or 70% (CK) of field capacity (FC), respectively; meanwhile, 54 kg N ha(-1) (T1), 67.5 kg N ha(-1) (T2), or 81 kg N ha(-1) (T3) was assigned at the beginning of the blooming stage. The results showed that the net photosynthetic rate (P-N) and leaf water use efficiency (LWUE) was highest in T3. The leaf area (LA), plant height (SH), and leaf fresh mass (LFM) of T1, T3 increased by 32.69%, 16.05%, 29.10%, 14.93%, 62.49%, 71.43%, respectively, in comparison to CK. Relative water content (RWC, including leaf and pod) was lower in T1, T3 than in CK significantly, which was negative linear relationship with leaf water potential (psi(w)), and decreased continuously across growth stage. Ultimately, the average pod dry mass (PDM) in T3, T1 was up to 1.93g, 1.85g, CK just was 0.26g. Our results suggested that combination of 324mm irrigation and 54 kg N ha(-1) optimally elevated VG, and 81mm water combining with 81 kg N ha(-1) coupling most favoured RG and dry matter accumulation (DM) in comparison to single 405mm irrigation, maximizing the use efficiency of water, nitrogen and increasing vegetative growth (VG) and reproductive growth (RG).
