Influence of nitrogen source on physiology, yield and fruit quality of young apricot trees

Abstract

The objective of this two-year study was to assess the effect of N source on plant physiology, yield and fruit quality of apricot (Prunus armeniaca ‘Mogador’) trees. Parameters evaluated included: gas exchange [photosynthesis (Pn), transpiration (E), and stomatal conductance (gs)], chlorophyll content index (SPAD), leaf nutrient concentrations, fruit yield, total soluble solids (°Brix), acidity, sugar content (fructose, glucose, and sucrose), fruit color coordinates (L*, a*, b*), firmness, and radical scavenging activity. Trees were subjected to two N sources: ammonium nitrate [NH₄⁺/NO₃^-(4/6)] applied as N-P₂O₅-K₂O (18-18-18) and ammonium (NH₄⁺) applied as urea, with an annual application of 150 g N tree⁻¹. In both years, apricot trees fertilized with NH₄⁺/NO₃^- showed higher SPAD, macronutrient (N, P, K) concentrations, fruit yield and number than those treated with NH₄⁺. However, Pn, gs and E were similar for the two N treatments (NH₄⁺/NO₃^-, NH₄⁺). Comparing with NH₄⁺, trees supplied with NH₄⁺/NO₃^- exhibited an increase of 34% in total soluble sugars, 39% in firmness, 7% in scavenging capacity, 14% in fructose content, 31% in glucose content, 38% in sucrose content, 64% in the a* value, and 8% in the b* value. Sugar content (fructose, glucose, and sucrose), color coordinates, and firmness are the main contributors of fruit sweetness, sensory quality, and consumer or preference satisfaction. Since high marketable fruit yield is the main determinant for income returns by apricot producers, and considering that application of NH₄⁺/NO₃^- (4/6) significantly increased fruit yield and sensory quality components, this N source should be preferred over NH₄ source for commercial apricot production.

Keywords:

• ammonium nitrate
• fruit color
• leaf nutrient
• photosynthesis
• sugars
• urea
• yield

Acknowledgements

This study was funded by the Deanship of Scientific Research at The University of Jordan. We also thank Hashem Al-Hajaj, Hanadi Sawalha, Tala Assaf, and Hana Al-shakabna for their assistance in the fruit quality measurements.

Conflict of interest

No conflict of interest was reported by the authors.