Effect of soil permanent grass cover on growth, yield and water status of rainfed olive trees in Sicily

Abstract

The study was carried out in an olive grove located along the hills of northern Sicily where soil had been managed for decades by chemical weeding. Starting in 2008, one portion of the grove was left non-weeded, and the permanent grass cover was managed by mowing 2-3 times per year in winter and spring. In 2011, 2012 and 2013, yield, average drupe weight, percentage of drupe black color (veraison), trunk circumference, shoot elongation, and leaf relative water content (RWC) were determined on 34 adult trees of the cultivar 'Biancolilla' with uniform size and age. In 2013, soil organic matter content and leaf nutrient concentrations were also determined in the two portions of the grove. As expected, permanent grass cover increased soil organic matter especially in May and in the first 15 cm of soil. Regardless of the year, soil management did not affect yield, drupe weight, yield efficiency, and RWC. In early June 2013, shoot elongation was reduced by permanent grass cover. The percentage of black color was consistently higher in drupes of trees under permanent grass cover than in those of trees under chemical weeding, indicating an advanced degree of maturation in the permanent grass cover trees. In December 2013, leaf N was lower in trees under permanent grass cover than in trees under chemical weeding. Under the environmental conditions of this study, permanent grass cover induced no competition for water between olive trees and grasses. It appears tree vegetative growth was reduced by permanent grass cover due to N limitation along with greater sink strength of fruits over shoots.