DEFICIT IRRIGATION OF THE OLIVIER Olea europeae CORRELATIVE RELATIONSHIPS: PARAMETERS OF GROWTH, DEVELOPMENT, PRODUCTION AND WATER

Abstract

This paper summarizes the work carried out in Tunisia on olive trees during the period going from 1998 to 2013, in order to study the water relations and the factors of variations with regard to the variety pote ntial. This latest was studied in a preliminary work in which the agronomic, physiological and eco-physiological behavior was analyzed for many olive cultivars growing in the sites of the low valley of Medjerda (North), at Sfax (South-East) and at Nabeul (north-East). Herein, the most relevant relations are presented. Results showed that the tree height is a determining factor in the development of the other parts of the olive tree. It is positively and linearly correlated to the canopy (r =0.96) and trunk (r=0.94) diameters and is highly affected by maximum and minimum temperatures, the climatic demand and the level of water recovery (P+I/ETc ). The lowest correlative coefficients are obtained during the years when water was missing. Trunk development is cor related to the soil cover level, itself correlated to the surface of soil explored by roots (r=0.94); equilibrium is reached after the 3 th year of cultivation. Canopy development is correlated to olive production (r=0.45), maximum yield is given for P+I/ET c of 1.4. However, yield evolves inversely to fruit size. When water is used for fruit enlargement, the final tonnage evolves towards the downside. Fruit growth is correlated to shoot elongation (r=0.89), but the fruit water use efficiency remains highly dependent on soil cover. High values of WUE fruit are obtained when fruit increases during stages 1 and 2 are 50% and 25-30%, respectively. Such increases are obtained when the tree has enough carbohydrates‟ reserves. The Chétoui variety shows a greater effectiveness of the use of assimilate resource (2.59 fruits/cm 2 of leaf) in comparison to Picholine and Manzanilla. The number of fruits and their size depend on the specific leaf area, which is correlated to the soil and leaf water content, itself correlate d to the midday leaf water potential Ψ feuille by a highly significant positive linear function at 20%ETc. The increase in irrigation water supply to 50%ET c results in a decline of production of varieties Picholine, Coratina Chétoui and Manzanilla. The vari ety Chemlali gives maximum output for an average seasonal intake of 400 mm. To conclude, vegetative and productive parameters are inter related, and any intervention to increase soil cover to 15 -17% improves production, its maximum is observed for a water supply of 200 mm/season.