CONTROL OF ROOT SIZE AND ROOT ENVIRONMENT OF FRUIT-TREES FOR OPTIMAL FRUIT PRODUCTION

Recent development in technologies of irrigation and fertilization enable us to control root size and environment under field conditions. Low volume irrigation and fertilization affects root size and rate of rootlets production and consequently vegetative and reproductive processes of whole plants. The mechanisms involved seem to include growth regulators production at the root apexes and their translocation to the shoots. Field experiments in a few species of deciduous trees and citrus, showed that root systems are very flexible and can adjust to low volume irrigation irrespective of age or size of the trees or stage of development. Root restriction under field conditions was found to cause precocity, increase productivity and reduce the size of the trees. A greater number of trees per unit land can be grown without reducing light penetration which is the most important factor affecting physiological processes controlling fruit bud differentiation, such as assimilate translocation, photosynthetic efficiency fruit composition, size and coloration. Control of root environment in terms of soil matric potential, mineral concentration and aeration can also be achieved by irrigating and fertilizing at the rate of consumptive use. A non uniform distribution of water and minerals was found to exist when a point source irrigation such as drip was used. Nevertheless, a highly efficient uptake of water and minerals were found under conditions of an almost continuous supply of water and minerals by drip irrigation systems. Results of various studies show that this phenomenon may be attributed to transfer of water, minerals and air among individual roots of a root system subjected to gradients of water, minerals, and oxygen concentrations. A computer controlled automated irrigation and fertilization system which consists of soil matric potential sensors located in the main root zone was developed. This system provides means for controlling the size of the root system as well as the root environment. An increase in yields and in fruit quality was obtained in a few fruit trees species during field experiments.