Effect of foliar- and soil-applied boron in deciduous fruit orchards 1: apple and pear

Abstract

Between autumn 1996 and May 1998 a variety of boron (B) treatments were applied to mature apple and pear trees on soils containing 0.3 to 0.5 mg B kg−1. Average mid-season apple leaf B levels in the B treatments were higher than in the controls, by 5.0% in 1997 and 7.9% in 1998. Corresponding increases in pear leaf B levels were 1.5% and 3.9%. Increases in fruit B contents were comparatively large: 31% and 33% in apple, 77% and 46% in pear. Increased leaf and fruit B levels were most consistently promoted by four early-season sprays, each containing about 20 g B 100 I−1 followed by one 41.6 g B 100 I−1 spray in autumn. Apple and pear leaf and fruit B levels were not affected by treatments in which one B spray was applied in spring. Treatments in which a single spring B spray was followed by one B spray in autumn increased pear leaf and fruit B in 1997 but had no effect on apple. Apple and pear leaf and fruit B levels did not increase in response to increases in the B content of the autumn spray. Applications of B to the soil had no effect on leaf and fruit B levels unless they were accompanied by four early season sprays, each containing about 20 g B 100 I−1. In both apple and pear, the 0.02 M CaCI2 extractable soil B levels correlated better with the levels of B in the fruit, than in the leaves. Leaf and fruit B levels correlated in pear, but not apple. Boron sprays, and soil B applications, had no effect on the number of seeds in apple and pear fruit.