| The Shixia longan variely was employed as the plant materials in the field experiment. The plants were treated with different concentration of KClO3 and of KClO3 to PP333 by soil drenched and root-inserted. The effects of the off-season floral induction of longan, and the redations between nitrate reductase activity, C/N, nutrient elements and the flower-bud formation of longan were studied. The results showed as follows:1. Both treatments with KClO3 and the solution of KClO3to PP333 could induce the plants to blossom. The result of the treatments by soil drenched was more effective; than those by root-inserved. The heading rate of the L treatment was higher than the rates of else treatments obviously. The heading period of all treatments concentrated on a period of time relatively. The flower clusters of plants in off-season were small in shape, rare in branch , intense in space and the male-female ratio was close to that of spring flower cluster. The result showed that the quality of flower cluster in off-season was different as compared with spring flower cluster.2. After treatment, the nitrate reductase activity decreased generally. It began to increase before the flower-bud appearing , and gradually came to peak at flower cluster growing stage, but decreased then and gradually came to a low tide at early blossoming stage. These results indicated that the increasing of the nitrate reductase activity stimulated flower-bud to pass during physiological and moephological differentiation stage. The decreasing of nitrate reductase activity and the increasing of ammoniacal nitrogen content stimulated the plants to blossom. The vary of nitrate nitrogen content was positively correlated to the vary of nitrate reductase activity.3. The; contents of soluble sugar and starch increased and the nitrogen content decreased. The lowest nitrogen content was found while the flower-bud appeared. The high soluble sugar content at early stage supplied enough nutrition for the need of flower-bud differentiating. During heading period the soluble sugar content began to decrease and then the contents of soluble sugar and starch increased gradually until to surpass that of control. The contents of them decreased again after blossoming, but the contents still were higher than that of control. For the treatments both A and L, the contents of soluble sugar and starch were higher than those of else treatments and their ratios of C/N were also higher as compared with those of other treatments. To most of treatments, their ratios of C/N were lov/er than that of control in total. That showed the high contents of soluble sugar and starch increased the heading rate and the heading plant rate. All those results indicated that the high ratio of C/N was not theunique decided factor of flower-bud formation.4. After treatment,the contents of K, Ca, Mg, Cu, Fe, Mn and B decreased in leaves, but promoted plant to absorb P and Cl. The K content was decreased during heading and blossoming periods. It began to increase after blossoming. The K content at early blossoming stage was higher than that of control and the result was opposed at late blossoming stage. The Ca content was lower than that of control at early blossoming stage and the result was opposed at late blossoming stage. At late blossoming stage the Mg content decreased gradually and was lower than that of control in the end. The high contents of Cu, Mn and B benefited to heading. The contents of Cu, Zn, Fe, Mn and B decreased after blossoming. The highest Cl content was recorded at heading stage. The Cl content was positively correlated with the concentration but no correlation with blossoming. The result showed the effect of Cl on the off-season blossom of longan was still not clear.
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