Relationship between K15NO3 application period and 15N enrichment of apricot blossoms and developing fruit.

The relationship was assessed between the period of K¹⁵ NO₃ application and the level of ¹⁵N in the blossoms of ‘Royal’ apricot (Prunus armen iaca L.). Late summer applications of K¹⁵NO, resulted in a 34 fold greater ¹⁵N enrichment of apricot blossoms the following year than K¹⁵NO₃ applied during the dormant period. In contrast, ¹⁵N enrichment was 60% higher in vegetative shoots 30 days after anthesis when K¹⁵NO₃ was applied during the dormant period as occurred following summer applications. Thus, fertilizer nitrogen applied in summer may support the early development of fruit to a greater extent than nitrogen applied during the dormant period. When K¹⁵NO₃ was applied in Jan, ¹⁵N accumulation in reproductive organs occurred after anthesis and corresponded with the period of shoot elongation and leaf expansion. It appears that fertilizer N must be absorbed prior to leaf fall to reach reproductive organs during anthesis.