Controlled-release Nitrogen Fertilizers for Improving Yield and Fruit Quality of Young Apricot Trees

The objective of this two-year field study was to assess the effects of controlled-nitrogen (N) fertilizers releasing speed and rates on tree morphology, physiology, yield and fruit quality of apricot (Prunus armeniaca cv. Mogador). In this study, four different releasing speed (conventional: < 1 month, controlled-release: 3, 6 and 9 months) and three N rates (56, 75, and 150 kg ha(-1) which is equivalent to 75%, 100% and 200% of recommended rates, respectively) were used. Parameters evaluated included: gas exchange (photosynthesis, transpiration, and stomatal conductance), chlorophyll content index, leaf and soil N concentration, fruit yield and quality component [total soluble solids, sugar content, fruit color coordinates (L*, a*, b*), firmness, and radical scavenging activity]. The physiology and fruit quality of apricot trees responses to 6-month controlled-release fertilizer was comparable to the conventional. In both growing seasons (2019-2020), gas exchange, soil and leaf N concentration and fruit quality components from the 6-month controlled-release fertilizer were similar or higher (never lower) than conventional. Interestingly, the 6-month controlled-release fertilizer had higher yield than conventional in 2020. This study revealed that the response of apricot trees to controlled-release N fertilizers was significant after two years of application. Higher N rate (150 kg ha(-1)) significantly increased fruit yield and reduced sucrose content compared to 75 kg N ha(-1) in both years. In 2019, high N rate (150 kg ha(-1)) reduced fruit redness coordinate (a*) which is considered a visual guide for consumers to select ripen fruits. Overall, this study highlighted the usefulness of using controlled-release fertilizer as an alternative "less waste " N source. The long-term use of controlled-release fertilizers hold promise for increasing apricot production and reducing environmental contamination.