Effects of foliar application of urea and boric acid on growth characteristics and yield of "Poost Kaghazi" walnut trees (Juglans regia L.)

Mineral nutrition of walnut trees (Juglans regia L.) via foliar application is one of the most important techniques to improve the fruit quality and quantity. Therefore, foliar application of urea and boric acid on growth characteristics, fruitset and yield of "Poost Kaghazi" walnut trees. Was studied the experiment was carried out in bud swell stage as a randomized complete block design with seven treatments and four replications. Treatments were, urea (at 0, 0.5 and 1 %), boric acid (at 0, 2000 and 4000 ppm) and combined treatments of urea and boric acid. Results showed that urea at 1% and boric acid at 4000 ppm improved the growth characteristics, fruit set and yield, therefore, the yield was increased to 174 g dry-wieght per shoot. Also, the combined treatment of urea and boric acid increased the amount of photosynthetic pigments, reduced sugars and total protein. The results of leaf analysis showed that the combined treatment of urea 1% and boric acid 4000 ppm increased the leaf nitrogen concentration to 1.9 % and boron concentration to 65.6 ppm compared to control trees (1.1% nitrogen and 26.2 ppm boron). It was also found that the combined treatment of urea 1% and boric acid 4000 ppm was the most effective in improving the quality and quantity of walnut crop. According to the results, we can suggest that combined treatments of urea and boric acid may improve the yield and growth characteristics of "Poost Kaghazi" walnut trees.