Abstract: Rice, most widely cultivated in China, consumes much more water and nitrogen than other crops. While keeping the current rice yield, to increase the use efficiency of water and nitrogen by means of water saving irrigation and reasonable nitrogen application is of great importance to sustainable agricultural development. To a certain degree, nitrogen cooperates significantly with water. Reasonable water use will increase the absorption of one or more types of nutrients, and vice versa. However, researches on effects of water use on nutrients uptake have been mainly focused on the upland crops. Recent studies show that the ecological adaptability of rice is so strong that its growth and output will not be affected so much when supplied with a moderate amount of water. Therefore, a considerable amount of water can be saved by cultivating rice using non-full irrigation methods and even upland cultivation. Different from the flooded irrigation, non-full irrigation or upland cultivation can significantly increase soil oxidation and nitrate concentration of soil solution. Nitrate becomes an important nitrogen source for rice growth thereafter. Although there are some researches concerning the effects of nitrogen form and water stress on crop growth and water use situation, very few work has been done on rice up till now. In this paper, water culture experiments，treated with or without PEG at 50 g L^-1, were conducted to study the effects of different NH₄⁺-N/NO₃^--N ratios (75/25, 50/50, 25/75) on some water physiological characteristics of rice. Items observed in the experiment included the concentrations of NO₃^-, Ca²⁺, and Mg²⁺ in leaf, conductance of leaf lixivium, relative water content and critical saturation deficiency of leaves, and leaf water potential of rice seedlings. The results showed that under simulated water stress condition more NO3--N was absorbed by Guanglin Xiangjing rice seedlings treated with low NH₄⁺-N/NO₃^--N. Conductance of leaf lixivium was reduced by the decrease of NH₄⁺-N/NO₃^--N ratio. When NH₄⁺-N/NO₃^--N ratio reached 25/75 lower leaf lixvium conductance was observed in rice seedlings treated with simulating water stress than that without water stress. Under none water stress conditions, the conductance of leaf lixivium increased with the decrease of NH₄⁺-N/ NO₃^--N ratio. Water stress decreased the relative leaf water content and increased the critical saturation deficiency when treated with higher NH₄⁺-N/NO₃^--N ratio. However, water stress didn’t show any significant effect on relative water content and critical saturation deficiency of leaves treated with lower NH₄⁺-N/NO₃^--N ratio (25/75). Therefore, nitrogen supply with low NH₄⁺-N/NO₃^--N ratio (25/75) was able to prevent leaf water potential decreasing caused by simulating water stress. In general, high ratio of NO₃^--N supply could reduce the negative effects of water stress on rice water-physiological response.

Key words: Simulating water stress, Rice, Water-physiological response