Effects of controlled-release urea on morphological characteristics and physiological traits of rice seedlings

In order to determine the appropriate amount of controlled release urea(CRU)and the best application method, the mechanism of controlledrelease urea on enhancing the nitrogen use efficiency were investigated by conducting the experiment of the rice seeds and total CRU particles onetime contacted application methods during the beginning of rice nursery stage. The results showed that the rice seeds fertilized by coexistence placement of a large amount of CRU particles germinated without any damage, and the rice seedlings grow very well with the CRU application rate of 800 g/box and 1000 g/box. With these two application rate，the best placement position the CRU particles was just below the rice seeds in which the CRU particles and the seeds contacted each other during the rice seed germination and the seedling growth. With these two application rate，the POD，CAT and AsAPOD enzyme activity of the rice seedling leaves were higher and the content of MDA was lower than that of conventional urea treatment，which were propitious to the rice seedlings growth. However，when the CRU application rate was 1200 g/box，the POD、CAT and AsA-POD enzyme activity were lower and also the content of MDA was higher than that of conventional urea treatment，which would retard the growth of rice seedlings. The IAA content in the rice seedling leaves was increased with the increase of CRU application rate and the IAA content was increased sharply when the CRU application rate was increased to 1200 g/box. In addition, the high ABA content induced by deficiency or superabundant of the nitrogen in the leaves would retard the growth of the rice seedlings.