Improving Yield and Fruit Quality of ‘Siyahoo’ Mandarin (Citrus reticulata) by Foliar Application of Nitrogen and Harvest Time

‘Siyahoo’ mandarin (Citrus reticulata) is one of the most important high-quality cultivars of citrus. The alternate bearing, especially in old trees, is one of the most important economic problems faced by this cultivar, which adversely affects the fruit quality. This study was carried out to examine the effects of the timing of nitrogen foliar application (mid-November, mid-December, and mid-January) as urea 0.5% and harvest time (the first time: concordant with the minimum commercial ratio of TSS/TA and the second time: 45 days after the first time) on improving the fruit yield and quality of ‘Siyahoo’ mandarin during five successive years from 2012 to 2017 using 36 trees. The results showed that the second harvest time (conventionally practiced) produced the highest yield compared to the first harvest time (for the lowest TSS/TA ratio). The highest yield was obtained in the second harvest time when nitrogen was sprayed in November. The significant interaction of harvest time and spray timing revealed the lower pH (~3) in the first harvest compared to the second one (~4). Nitrogen spraying in November and January yielded the highest (8-10) and lowest (<8) TSS/TA ratio, respectively. Although, the effect of the timing of nitrogen spraying on the fruit weight was not significant, spraying in January increased the fruit weight by 10% compared to the November spraying. Variations in the fruit diameter followed a similar pattern to variation in the fruit weight, which was due to their correlations. In conclusion, it is recommended to harvest the fruits after second nitrogen application, because the higher fruit yield and quality in terms of sweetness and flavor (TSS/TA ratio) are more acceptable.