Almond tree response to a change in wetted soil volume under drip irrigation

Under localized irrigation, even when applying non-limiting amounts of water, there could be transpiration (T) limitations due to a limited wetted soil volume. To study under field conditions how drip-irrigated almond trees responded to a change in wetted soil volume, two treatments were established in summer 2012 in a drip irrigated almond orchard in Cordoba, Spain. One treatment ("Large volume") was initially irrigated with micro-sprinklers (MS) to wet the entire ground surface, and then reverted to drip irrigation, while other was always kept under drip irrigation ("Small volume"). Continuous monitoring of T and measurements of soil moisture content, tree water status and trunk growth were carried out. Even though trees in both treatments were supplied with sufficient water, the MS application induced an increase in T and an improvement in water status in "Large volume" relative to "Small volume". A reduction in the hydraulic resistance of the tree was also detected in "Large volume", as well as an enhancement in canopy conductance and tree growth. We concluded that there are situations in the field where almond tree transpiration is limited by an insufficient wetted soil volume, even when supplied with adequate water, due to a high hydraulic resistance during times of high evaporative demand.