Objective To investigate the effects of local root water stress and nitrogen form on physiological characteristics and nitrogen utilization of rice seedlings.

Methods In this experiment, we used indica conventional rice Meixiangzhan No. 2, indica two-line hybrid rice Shenliangyou 7278, and indica three-line hybrid rice Taifengyou 208 as test materials, and set up three kinds of water conditions, namely, non-water stress (CK), localized root water stress (PRD), and total root water stress (PEG), and three kinds of nitrogen forms, namely, ammonium nitrogen (N) and nitrate nitrogen (N) in the ratios of 100∶0 (A₁₀₀/N₀), 50∶50 (A₅₀/N₅₀), and 0∶100 (A₀/N₁₀₀), a total of nine treatments, to study the effects of different water and nitrogen conditions on the physiological characteristics, nitrogen utilization, and nitrogen metabolism-related enzyme activities of different varieties of indica rice.

Results Moisture stress (PRD/PEG) inhibited plant height, leaf area, fresh mass, and dry mass of all three indica rice seedlings, but PRD treatments were all higher than PEG treatments and were not significantly different from CK, and plant height and dry mass of rice seedlings under synergistic treatments of nitrogen form and moisture stress were greatest under PRD+A₅₀/N₅₀; PRD did not have any unfavorable effect on chlorophyll content of rice; PRD and Nitrogen form synergistic treatment significantly increased the nitrogen utilization of three varieties of indica rice, the leaf total nitrogen content of Meixiangzhan No.2 and Taifengyou 208 under PRD+A₅₀/N₅₀ treatment increased by 9.6% and 7.2%, respectively, compared with PEG treatment; the nitrate reductase activities of Meixiangzhan No. 2, Shenliangyou 7278 and Taifengyou 208 were the greatest under PRD+A₀/N₁₀₀ treatment, which increased by 6.9%, 19.8% and 8.0%, respectively, compared with CK.

Conclusion Localized root zone water stress treatment enhances nitrogen uptake and transport without compromising rice growth. Rice growth is optimal when ammonium and nitrate nitrogen are applied in a 50∶50 ratio, which also mitigates adverse effects of water stress. The combined application of localized root zone water stress and a 50∶50 ammonium-to-nitrate nitrogen ratio enables reduced irrigation water use without compromising rice growth while improving nitrogen use efficiency. This approach achieves efficient irrigation and enhances nitrogen fertilizer performance.