271 Olive Root Growth Observed by Field Rhizotron S. Polverigiani, E.M. Lodolini and D. Neri Department of Environment and Crop Science Polytechnics University of Marche Via Brecce Bianche 60131, Ancona Italy Keywords: root plasticity, root mortality, root turnover, soil moisture Abstract The olive (Olea europaea L.) is characterized by high drought tolerance and its roots show high transmigration capability and adaptability to changing conditions. Root growth is affected by the environment as is the functional specialization of each root structure. A quantity based analysis gives just a partial notion of the complexity of the process which allows the olive to be so adaptable. An experiment using rhizotrones was carried out that allowed sequential root growth, distribution, differentiation and mortality to be directly observed. Four olive trees were selected and a glass window for each tree (0.8 m deep by 1.3 m wide) was placed underground, 0.5 m away from the trunk in September 2007. Bi-weekly observations throughout the growing season made it possible to identify root growing rate and morphological changes. Based on their morphology roots observed have been divided into two different clusters <0.2 mm very fine (VF) roots, and >0.2 mm fine (F) roots. At no point during the observation period (from September 2007 to September 2008) did root growth stop, including winter months. The two clusters of roots behaved in a different way during the season. VF root growth peaked in February and F root growth from April to May. In both cases root growth drastically weakened from June to August with a faster reduction of VF roots. Root mortality was very low during the winter accelerating in May, likely influenced by an increase in temperatures. Root mortality slowed down deeper in the soil where moisture and temperature changes were not as high. All the presented results seem to be applicable to modern oliviculture, in high density orchard management, to obtain better control of the development of the whole plant and to reduce costs. INTRODUCTION Studies within a controlled environment show clear relationships between fine root dynamics and temperature, water and nutrient availability (Bevington and Castle, 1985; Kaspar and Bland, 1992). However, elucidating a relationship between fine root dynamics and environmental variables is more difficult working under field conditions where environmental variables interact in a complex way (Tierney et al., 2003). Root Growth and Differentiation Root movement is controlled by resource availability and climatic conditions but it also has to cope with inner balances and allelopatic interactions. Understanding environmental factors and source-sink relationships controlling roots growth is critical to understanding how plants may adapt to a changing climate and it also is essential in setting efficient agricultural management of woody crops. In planning agronomic interventions it is very important to control root development and self-competition without compromising their nutrient absorption efficiency. Attempts to isolate factors which control the timing and magnitude of root elongation in trees have been a subject of research for decades. Many have asserted that environmental variables, particularly soil temperature and soil water potential, exert primary control over the timing of root growth (Burke and Raynal, 1995). In a temperate environment temperature conditions, effects are mainly visible at the beginning of the growing season (Joslin et al., 2001) at the end of a rest period as it is Proc. VI th IS on Olive Growing Eds.: E.M. Sampaio and A.C. Pinheiro Acta Hort. 949, ISHS 2012