Boron Deficiency in Chestnut - Effect of Boron Application on Nut Yield and Quality

Although B deficiency in chestnuts (Castanea sativa Mill.) has been identified in Portugal and B fertilisation was carried in chestnuts, the post-treatment evaluations have not been made to date. So the objective of this trial was to confirm the B deficiency and to quantify the effect of application of B to the soil on nut yield and quality. In October 2006, a fertiliser trial was established in a 15-year-old orchard in a very acid soil. A basic fertilisation was carried out in 16 trees and two levels of sodium tetraborate (Granubor, 14.6% B) were applied to eight trees: control (B0) and 100 g of Granubor per tree (B1). Samples of chestnut leaves were collected and analysed for macro-and micronutrients. Nut productivity and some nut quality parameters were evaluated, including the chemical composition of the kernel (soluble sugars, starch, total fiber, crude protein and crude fat) in 2007, and dry matter, caliber and fruit damage in 2007 and 2008. Boron fertilisation of chestnuts significantly increased nut production: in the first year, 8 kg and 14 kg per tree, respectively in the B0 and B1 and, in the second year, 4 kg and 17 kg per tree, respectively in the B0 and B1. No significant differences were found in dry matter, caliber, nut damage and chemical composition of the kernel in the first year, but in the second year lower fruit damage by chestnut tortrix (p<0.0089) was observed. Foliar analyses exhibit low B concentrations in B0 (8 mg kg(-1)) in both years, while the concentration in B1 were in average 61 mg kg(-1) in the first year, and 34 mg kg(-1) in the second year. The results suggest the need to monitor the nutrient status of chestnut orchards or more frequent of B application than usual practice.