Effects of foliar fertilization of biostimulants obtained from sewage sludge on olive yield

Abstract

The objective of this study was to investigate the effect of foliar fertilization of two biostimulants (BS1 and BS2) obtained from sewage sludge by fermentative processes using Bacillus licheniformis during four consecutive seasons in an olive tree crop applied at a dose of 6 L ha-1 divided into three applications (before flowering, beginning of flowering and fruit set). BS2 had a higher number of low molecular weight peptides the BS1. The contents of macro and micronutrients in leaves, photosynthetic pigments and olive yield were higher in plants fertilized with BS2 than BS1. With respect to the control treatment and for the 2017 and 2019 seasons, the olive yield increased by 20–22% in plants fertilized with BS2 and by 28–29% for the plants foliar fertilized with the BS1. For the 2018 and 2020 seasons, the olive yield increased by 35–36% in the plants fertilized with the BS1 and by 42–43% for the plants fertilized with the BS2. These results suggest that the foliar use of these biostimulants, that contain a higher number of low molecular weight peptides, could be of great interest to farmers as regards improving olive crop yield.