Abstract: The optimum fertilizer requirements of N, P, K were studied quantitatively for common jujube trees (Zizypus jujuba) by using the method of threefactor regressive opcimum design. An effector model between the amount of N, P, K fertilizer and the yield of jujube trees has been established, by which the optimum fertilization scheme, the main effector and intereffector of various fertilizers, and margining yield effector have been approached. Meanwhile, the diagnosis of nitrogen nutrition was studied; and inquired into the influence of nitrogen nutrient status on jujube trees growth, fruitage, and fruit quality, in which the ranges of the critical value for nitrogen nutrition diagnosis has been determined.

Key words: Zizyphus jujuba, Yield, N, P, K, Nutritional diagnosis