Auftreten von Bormangel bei Citrus aurantium L. (Bitterorangen) am Kaspischen Meer (Iran)

Occurence of boron deficiency in Citrus aurantium L. (Bitter orange) at the Caspian Sea (Iran) In a Bitter orange plantation near the Caspian sea over a period of two years different amounts of boron were applied either as borax to the soil or as Solubor to the leaves. Without boron supply the fruits were misshapen, had a rough and thick peel and often brown spots in the pulp. Supply of 5 – 20 g B per tree prevented the occurence of these symptoms and increased both the fruit size and the proportion of the pulp. Without boron supply on fresh weight basis the proportion of pulp/peel was 1 : 1, 6 – 2, 0 as compared to 1 : 0, 6 – 0, 7 with boron supply. The effect of the different boron supply was well reflected in the boron content of the leaves and especially of the fruits. Borax increased the boron content of the plants more than Solubor. Conzidering both the low content of available boron in most of the soils of the Citrus area near the Caspian sea and the special ecological conditions (high pH values and low water content of the soils during fruit development) boron deficiency can be expected. The results of the experiment with Bitter oranges confirm that boron fertilizing is an important factor for plant production in this area.