Water-harvesting designs for fruit tree production in dry environments

• All designs increased the amount of water received in the target area (tree basin).
• The high slope treatment (15%) resulted in more runoff-water harvesting, especially during smaller storms.
• Water harvesting increased soil moisture content during important growth periods in the winter, spring, and early summer.
• The maximum net amount of water harvested (minus rainfall) could reach 722 l for the most effective treatment.
• Trees with deeper soil profiles stored more water.

Water scarcity and increasing demand coupled with climate change require maximizing the use of available resources. Water harvesting (WH) systems are currently being used in many areas to sustain crops and increase water productivity. This study investigated the effect of three treatments (S15: 50-m2 catchment area with 15% slope, S8: 50-m2 catchment area with 8% slope, and L8: 70-m2 catchment area with 8% slope) on the amount of water harvested in tree basin for young olive (Olea europaea L.) trees from November 2002 to July 2003. Soil moisture was monitored weekly during the rainy season and bi-weekly afterwards. To determine moisture changes in the catchment and target areas and amount of water harvested (in liters) for each tree, volumetric soil moisture content was measured at three or four points along the slope using a neutron probe down to a maximum depth of 120 cm, as soil depth allowed.WH structures increased soil moisture content in the rootzone compared to the catchment area. The rainfall threshold for runoff generation was less than 15 mm. Land slope was more important than micro-catchment size for increasing the amount of water harvested. Compared to the 8% slope, the 15% slope resulted in larger harvested amounts for small storms, but the two were comparable when storms were large. The large micro-catchment size resulted in higher amounts of harvested water only in the presence of storms greater than 26 mm. After adding the amounts lost by evapotranspiration, the net amount of water harvested in the tree basin of each tree for the 2002–2003 rainy season reached 722 and 688 l (or 361 and 344 mm) for treatments S15 and S8, respectively. Deeper soil profiles (i.e., >90 cm) were important to ensure longer storage periods. By early July, soil moisture content in the tree basin for treatments S15, L8 and S8 was still higher by 38, 13, and 5% respectively, than the levels recorded at the onset of the experiment. WH increased soil moisture content during the spring and early summer, a critical period for olive production.