Interactive responses to water deficits and crop load in olive (olea europaea L., cv. Morisca) I. – Growth and water relations

To characterize the interactions between variable water supply and crop load on vegetative growth and water relations of an olive orchard (cv. Morisca) planted in 1998 at 417 trees ha−1, two different experiments were conducted over a six-year period (2002–2007) in Badajoz, Southwest of Spain. Experiment 1, assessed the responses during the early years of the orchard (2002–2004) using four irrigation treatments that applied fractions of the estimated crop evapotranspiration (ETc) (125%, 100%, 75% and 0%) and three crop load levels (100%, 50% and 0% of fruit removal, termed off, medium and on treatments). Experiment 2, assessed the response of more mature trees (2005–2007) to three irrigation treatments (115%, 100%, and 60% of ETc) and the natural crop load which were off, on, and medium in 2005, 2006 and 2007, respectively. Although vegetative growth was mainly affected by the level of water supply, crop load also influenced vegetative parameters, especially the interaction between high loads and water deficit. Trunk growth was more sensitive to water deficits than ground cover, and at the branch scale, water deficits reduced branch length and node numbers but only reduced internode length in on trees. Water relations were more affected by the level of water supply than by crop load. Nevertheless, the presence of fruits affected olive tree water status and, particularly, increased the stomatal conductance of on trees during late summer and early fall under all levels of water supply. Interactions between water stress and crop load levels were not very strong, and were more evident in mature than in young olive trees.