Effect of Postharvest Sprays of Boron and Urea on Yield and Fruit Quality of Apple Trees

ABSTRACT

The objective of the experiment was to examine the effect of postharvest sprays of boron (B) and urea on apple tree yield and fruit quality. The study was conducted during 2002–2003 at a commercial orchard in central Poland on mature ‘Jonagold’ apple trees/M.26 planted on a sandy loam soil with low B status. All experimental trees received soil-applied nitrogen (N) at a rate of 50 kg ha^?1 at bud break. The following spray treatments were performed: (1) postharvest B spray three to four weeks before leaf abscission at a rate of 1.2 kg ha^?1; (2) postharvest urea-N spray at the same time as B spraying at a rate of 18.4 kg ha^?1; and (3) combined B spray with urea at the same time and at the same rates as in the combination of treatments (1) and (2). Trees not sprayed with B and urea served as a control. The results showed that all spray treatments damaged leaves, but only postharvest urea spray and combined B spray with urea caused defoliation. Postharvest B spray with/without urea improved flower B status, fruit set, and tree yield. However, the efficiency of combined B spray with urea in improving reproductive growth was lower than that of foliar B application without the addition of urea. Postharvest sprays of B and urea had no effect o n blushing, flesh firmness, or soluble solids concentration of apple fruit. These results indicated that under B-deficiency conditions, postharvest B sprays are successful in improving reproductive growth and should be recommended without the addition of urea. It is suggested that combined B sprays with urea may be applied in the autumn to apple trees with limited soil B and N availability.