Effect of Soil Management on Olive Yield and Nutritional Status of Trees in Rainfed Orchards

Studies on the effect of groundcover treatments on perennial tree crops have been common in recent decades. However, few have included leaf analysis as an aid to understand the effects of groundcover treatments on tree crop growth and yield, in particular in rainfed olive orchards. Field experiments took place in northeast Portugal, over the course of eight consecutive years, in two commercial orchards selected on the basis of their contrasting situation regarding the floor-management system before the trial started. An orchard located in Bragan a, currently managed as a sheep-walk, received the following treatments: sheep-walk (SW), where the natural vegetation was managed with a flock of sheep; mechanical cultivation (MC), which consisted of two tillage trips per year in the spring; and glyphosate (Gly), where the herbicide was applied once during the first fortnight of April. Another orchard near Mirandela, currently managed by tillage, received the following treatments: mechanical cultivation (MC); glyphosate (Gly); and residual herbicide (RH), where an herbicide with a residual component was applied late in the winter. The trees that underwent Gly treatments produced the greatest tree crop growth and olive yield. The worst results were achieved with the SW and MC treatments in the Bragan a and Mirandela experiments, respectively. Leaf nitrogen (N) and boron (B) concentrations were significantly higher and lower, respectively, in the treatments that caused the higher and lower olive yields in both experiments. In the Mirandela orchard, where the leaf potassium (K) concentrations were close to the lower limit of the adequate range, the leaf K levels followed the pattern registered for N and B. The results showed a strong link between tree crop nutritional status and tree crop growth and olive yield. The groundcover treatments that facilitate nutrient absorption by olive trees yielded more crops.