The effect of N, Zn and B fall spray on increasing their storage and availability in peach trees

Due to low efficiency of chemical fertilizers and high nitrogen demand for fruit trees at the first stage of growth, early spring growth, flowering and fruit set in fruit trees is heavily dependent on tree N reserves. Therefore, this experiment was performed to investigate the possibility of urea, zinc sulfate and boron uptake, as well as transmission of these materials from leaves to storage organs and from storage tissues to new developing tissues, in autumn foliar application. On the other hand, nitrogen application in early spring is more often devoted to the vegetative growth of the branches, while nitrogen uptake at the end of the season goes more to the storage organs such as root bark and tree trunks.

The experiment was conducted in a randomized complete block design with seven treatments and four replications for three years on 56 trees with the same age and size trees in the east of Mazandaran. The treatments included: 1. Control, 2. Urea (10 g.l-1), 3. Urea (10 g.l-1) + Zinc sulfate (5 g.i-1), 4. Urea (10 g.l-1) + Zinc sulfate (5 g.l-1) + Boric acid (4 g.l-1), 5. Urea (15 g.l-1) + Zinc sulfate (5 g.l-1) + Boric acid (4 g.l-1), 6. Urea (20 g.l-1) + Zinc sulfate (5 g.l-1) + Boric acid (4 g.l-1), 7. Urea (25 g.l-1) + Zinc sulfate (5 g.l-1) + Boric acid (4 g.l-1).

Urea foliar application increased the nitrogen concentration of leaves in autumn and also increased the concentration of nitrogen in bark and wood in various organs. Foliar application of zinc sulfate and boric acid also increased the concentration of zinc and boron in the leaves. Measuring the concentration of nitrogen, zinc and boron in the leaf tissue of young shoots in the spring showed that in foliar spraying treatments, the nitrogen concentration of young leaves increased compared to the control. Measurement of nitrogen concentration in leaves of young shoots, bark and wood of annual shoots as well as flower and flower buds showed that foliar spraying treatments had a significant effect on nitrogen concentration of bark and wood of these shoots. Thus, the nitrogen concentration increased from 0.53% in the control treatment to 0.92% in the treatment 25 gl-1 urea + 5 gl-1 zinc sulfate + 4 gl-1 boric acid.

According to the results of this experiment, in order to increase the storage of nitrogen, increase the fruit set, and reduce the flower and fruitlets drops, it is strongly recommended to do foliar application of urea at 20 to 25 gl-1 + zinc sulfate at 5 gl-1 + boric acid at 4 gl-1 in autumn, when 10 to 15 percent of the leaves are yellow.