Late season mineral foliar application improves nutritional reserves and flowering of kiwifruit

Proper management of late season mineral nutrition in kiwifruit orchards is necessary to maintain sufficient carbohydrate and mineral reserves for efficient growth and yield in the following season. The present study was conducted in order to investigate the influence of urea (0.25%, 0.5% and 1%), zinc sulfate (1000, 1500 and 2000 mg l−1) and boric acid (500, 1000 and 1500 mg l−1) foliar application, both alone and combined, on physiological and biochemical characteristics and mineral nutrients concentration in leaf and bud tissues and, flowering of kiwifruit cv Hayward in Guilan, Iran during two years. In order to determine the best application time in late season, foliar application was applied at three different times: September 17, October7 and October 28. Leaf and bud samples were collected three weeks after the last foliar application. Although combined foliar application of urea (1%), zinc sulfate (2000 mg l−1) and boric acid (1500 mg l−1) significantly increased leaves chlorophyll concentration and boron, zinc, soluble carbohydrate and starch content of leaf and bud tissues in the fall, however this consistent elevation in almost all measured parameters was not found in other experimental fertilization treatments compared to control vines. Likewise, bud break, and flowering shoot percentage, and total number of flowers and abnormal flowers percentage was significantly improved in the following growth season by urea (1%), zinc sulfate (2000 mg l−1) and boric acid (1500 mg l−1) treatment in comparison with control group. There were no significant differences among the treated and non-treated vines regarding shoots growth, leaf abscission and the beginning of winter rest of the kiwifruit vines. Considering all measured parameters, we conclude October 28 was the best spraying time. These results suggest that urea (1%), zinc sulfate (2000 mg l−1) and boric acid (1500 mg l−1) treatment on October 28 can be used as a proper way to improve mineral and carbohydrate reserves of kiwifruit orchards to use in next growing season.