Spatial and temporal distribution of root water uptake of an almond tree under microsprinkler irrigation

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The spatial and temporal pattern of root water uptake in partially wetted soil was studied in the root zone of a 6-year-old microsprinkler-irrigated almond tree. The water balance of about one quarter of the root zone's wetted soil volume (2.0×2.0×0.9 m3) was determined by catch cans, neutron probe and tensiometer measurements. Twenty-five neutron probe access tubes with catch cans were distributed in a square grid of 50 cm spacing. Eight pairs of tensiometers were installed at depths of 82.5 and 97.5 cm in a regular pattern between the access tubes. Neutron probe readings at 15 cm depth increments and tensiometer readings were taken at time intervals of 4–24 h. The rate of soil water depletion was calculated and used to estimate the spatial and temporal distributions of root water uptake. Soil water dynamics was studied in two stages: (1) during a week of conventional irrigation management with three irrigation events; and (2) during a period of 16 days without irrigation, after the monitored soil volume was thoroughly moistened so that soil water was easily available everywhere, initially. The zones of maximum root water uptake were the same for both stages in periods of high local rates of water application. After water applications, root water uptake occurred initially near the tree trunk and then progressed towards the root system periphery, thereby changing locations of maximum root water uptake and shifting to root zone regions with minimum soil water stress.

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