Abstract: A pot experiment was conducted to study the coupling effects of watering and nitrogen fertilization on the growth and irrigation water use efficiency (WUEi) of Jatropha curcas. Three watering levels (W₁, 15.3 mm; W₂, 25.5 mm; W₃, 40.7 mm) and three nitrogen fertilization levels (N₁, 0 g·kg^-1; N₂, 0.3 g·kg^-1; N₃， 0.6 g·kg^-1) were designed. As compared with those in treatment W₃, the plant height, stem diameter, leaf area, and total dry mass in treatments W₁ and W₂ decreased significantly by 61% and 34%, 57% and 35%, 46% and 32%, and 49% and 35%, respectively, and the rootshoot ratio in treatment W₂ reached the maximum. In nitrogen fertilization treatments, the maximum values of plant height and leaf area appeared in treatment N₂, but the stem diameter and root-shoot ratio decreased with the increasing nitrogen fertilization level. As compared to treatment W₃N₃, treatment W₂N₂ (which saved the irrigation water and nitrogen fertilizer by 38% and 50%, respectively) decreased the plant height, stem diameter, and total dry mass by 12%, 21%, and 12%, and increased the root-shoot ratio and leaf area significantly by 48% and 16%, respectively, and decreased the transpiration significantly by 21%, 15% and 12% at the days 2, 3, and 4 after watering, respectively, leading to the WUEi of J. curcas increased significantly by 40%.

Key words: direct-seeding cotton after wheat harvest, nitrogen application rate, nitrogen uptake and utilization, yield.