ROOT DISTRIBUTION UNDER TRICKLE IRRIGATION - FACTORS AFFECTING DISTRIBUTION AND COMPARISON AMONG METHODS OF DETERMINATION

Four methods were used to characterize root distribution under drip (trickle) irrigation:root weight, cation exchange capacity (CEC), uptake of Rb-86, and the line intersect method. Trickle irrigated tomato (Lycopersicon esculentum Mill. var. Naama) and peanut (Arachis hvpogeae L. var. shulamit) plants were grown on sandy soil (Typic Torripsamment) and their roots were used for the study. The four methods showed that most of the roots are concentrated close to the emitter. A linear correlation was found between root weight and the uptake of Rb-86. This indicated that although roots near the emitter seem to be relatively old, the uptake activity is also concentrated there. Furthermore, it is apparent that the effect of the limited root distribution is even more pronounced when using CEC as an indicator for fine roots or surface area, than when using weight as an indicator. It was therefore concluded that all criteria emphasized the restricted distribution of roots as well as their activity in the wetted volume of soil beneath the emitter. When saline water was applied, more roots were found in the leached soil volume than in the saline part of the trickle irrigated hemisphere. In the fresh water irrigated soil, the roots extended also to the periphery of the wetted volume.