There is very little information about the performance of field-grown young olive trees during prolonged droughts. The latter is however a frequent occurrence in runoff irrigated orchards. A two-year study was carried out in the Israeli Negev Desert. Eight year-old olive trees (Olea europaea. L, cv. Barnea) were subject to a prolonged drying out period during each of two consecutive years. During the first year the plots in which the trees were growing were artificially flooded to a depth of 1.5 m and during the second year the drying out period followed a natural flood event that wetted the soil to a depth of 4-5 m.  Three plots with nine trees in each plot were selected within the olive orchard. Soil water content (SWC) to a depth of 5 m, and root development down to the depth of 2 m were measured in eleven access tubes in each plot using a neutron probe and eleven minirhizotron tubes. The access tubes were located in one of the quadrants of each of the central trees. Sap flux was measured using the Granier heat dissipation probe technique. During the first year one probe was inserted in each tree and during the second year two additional probes were inserted, in such a way that each of them spanned one third of the trunks circumference. One of the probes was always in the direction in which the neutron tubes were inserted. After soil wetting, the soil was covered with a plastic sheet to prevent soil evaporation. Sap flux density values varied with sensor position and good correlation was obtained when the sap fluxes obtained by the sensor that was closest to the neutron probe quadrant were correlated to the total soil water uptake. Correlations between sensors were good but the slopes were significantly different from each other. 

In a second experiment, the effects of Photoselective netting on the development of the above and below parts of 4-year-old orange orchard was examined. Photoselective netting is well-known for filtering the intercepted solar radiation affecting light quality. While its effects on above-ground of plants have been well investigated, the root system was neglected. Here, we evaluated the effects of photoselective netting on root growth and plant development. Minirhizotron and ingrowth cores were applied in a field experiment, performed in a 4-year-old orange orchard grown under three different photoselective net treatments (red, pearl, yellow) and an un-netted control treatment. Our observations confirmed the significant positive effect of photoselective nets on photosynthesis rate, vegetative growth and fruit yield. Trees grown in the pearl plot developed evenly distributed root system along the observation tubes while trees in control, red and yellow plots had a major part of roots concentrated at different depth ranges of 60-80, 100-120, and 120-140 cm, respectively. Photoselective nets showed a strong impact on shoot-root interaction and proved equally successful in promoting rapid establishment and early high-fruit yield in young citrus trees. However, at long-term effect, yellow net might outperform because it could enable plants to develop deeper root systems, which will uptake water and nutrients more efficiently in semi-arid areas with sandy soil.