Ground cover and dynamic of weeds after the introduction of herbicides as soil management system in a rainfed olive orchard.
Results of the percentage of ground cover by weeds and the dynamic of the vegetation are presented after the introduction of herbicides as soil management strategies in a rainfed olive orchard. The field experiment was carried out in Mirandela, NE Portugal. The soil management treatments included: conventional tillage; post-emergence herbicide (glyphosate); and post-emergence plus residual herbicide (diuron+glyphosate+terb utilazine). The ground cover percentage and the botanical composition of vegetation were monitored since 2002 to 2007 from the pointquadrat method. Both the herbicide formulations killed efficiently the vegetation in a single annual application. The ground cover percentages in conventional tillage, prior to the first tillage event, varied between 50 to 80% beneath the trees and between 30 to 60% in the open space. The ground cover percentages in April, in the treatment of glyphosate, were in the range of 60 to 90% and 40 to 50% beneath the trees and between rows, respectively. In the residual herbicide plot the ground cover percentages were always very low. The soil of the glyphosate plot was covered with vegetation over all the year. In autumn/spring the soil was covered with green weeds and in the summer with a mulching of the dead material. In the glyphosate plot the dynamic of species was high. One year after the first application of herbicide, Ornithopus compressus appeared as the most abundant species. Thereafter, acquired relevance species with short growing cycles which seeds mature before April (e.g. Mibora minima, Logfia gallica) and other that produce a high number of seeds easily spread by wind (e.g. Hypochaeris radicata, Conyza canadensis) and which seeds proceeded from surrounding untilled fields and rural-tracks or from individual plants that escaped to the herbicide control.