Alleviation of Alternate Bearing in Satsuma Mandarin by Use of Nitrogen Management and Application of Pruning in East of Mazandaran Province

In order to investigate and reduce the alternate bearing in Satsuma mandarin (Citrus unshiu), an experiment was conducted in a randomized complete block design of 6 treatments and 5 replications and for a duration of 4 years. Treatments included: 1. Control (optimal application of mineral nutrients as based on leaf analysis and yield); 2. Autumn nitrogen application; 3. Spring pruning; 4. Summer urea spraying; 5. Winter urea spraying; 6. Urea spraying along with autumn nitrogen application, as well as spring pruning. Results obtained for the first year revealed that the highest yield belonged to treatment 6 with 274 kg of fruit per tree, while control yielding 214 kg per tree. During the second year, the highest yield was also obtained from treatment 6, i.e. 198 kg per tree compared with 65 kg in control. During the third year of the experiment which was an "off year", the highest yield was obtained in treatment 3 with 232 kg/ tree as compared with 84 kg in control. During the forth year being an "on year", the highest yield came from control with an average of 307 kg per tree. The total yields in different treatments during the four years of experiment were then compared. Results indicated that, alternate bearing cycle was alleviated as compared with the trees in control. However, in treatment 6, the alternate bearing cycle was almost disappeared with the total yield reaching an acceptable level during all the four years. The index of alternate bearing was calculated for all the treatments with the results indicating that treatment 6 bore the lowest while control had the highest index among all the treatments. So, as observed for treatment 6 (urea spraying with autumn nitrogen application and spring pruning) in which alternate bearing got almost balanced with an increase in total annual yield of acceptable level, this treatment could be considered as an economical, and profitable practices in citrus gardens in north of Iran.