Basic information has been obtained on the effects of the intensified fertilization and irrigation techniques used with existing carob trees, contributing to the protection of the environment and the sustainable exploitation of mediterranean ecosystem resources. The preplanting juvenile period and subsequent transplant stress has been reduced, leading to economic gains for the grower through reduced losses of young orchard stock. Both field and greenhouse experiments were carried out. Carob growth improvement was studied using different nitrate and ammonium concentrations. Evidence based on growth parameters and nitrogen content indicated 3 mM as the best nitrate concentration. The comparison of studies with different nitrogen sources showed that the ammonium ion stimulates carob growth, when ammonium concentrations are added between 0.5 and 3 mM. However, the best growth was obtained at 1.5 mM concentration. The study developed to evaluate the mycorrhizal status of Ceratonia siliqua L. in Portugal was able to prove the existence of arbuscular mycorrhizal (AM) fungi colonizing carob roots. No ectomycorrhizal association was found. Fertigation practices, both in mature and juvenile carob trees improved production but the results obtained are conflicting showing that the usual complexity of field experiments in crops is much more puzzling when we are dealing with no crop trees. The use of stable isotopes is very promising to promote understanding of the effect of irrigation on water use efficiency of the trees and also to evaluate the sources of water used by the trees. The total amount of nitrogen in the soil was not affected by nitrogen fertilization treatments. This means that independently of the amount of nitrogen added to the trees, there was no difference between treatments. High values of soil nitrogen were registered after fertigation but in autumn the values were similar to the control ones, without fertilization, and to the amount registered at the beginning of the experiment. Only soil organic matter seemed to be higher after 2 years of fertigation treatments.