SPATIAL AND TEMPORAL DISTRIBUTION OF SOIL-WATER BALANCE FOR A DRIP-IRRIGATED ALMOND TREE

Relatively little information is available on the spatial distribution of soil water under drip irrigation, and how it is affected by root d istribution, emitter placement and irrigation amounts. We hypothesize that variables such as emitter position relative to the active roots a s well as irrigation amount and frequency will affect the soil water r egime in general, and specifically the spatial and temporal changes in soil water content as controlled by root water uptake and leaching. A better understanding of these interrelationships will provide alterna tive means for proper and efficient drip irrigation water management p ractices. Moreover, the present study will provide an extensive databa se which can serve as input for analytical or numerical modelling of d rip-irrigated trees. We present the results of a field study in which the soil water regime of a surface drip irrigated almond tree is inves tigated. The experimental site (6.6 m x 4.8 m) was intensively instrum ented with tensiometers and neutron probe access tubes to infer the th ree-dimensional distribution of soil water and root water uptake durin g the irrigation season. Drainage fluxes were estimated from measured hydraulic head gradients and hydraulic conductivity data. Unsaturated hydraulic conductivity were determined from in situ measurements by th e instantaneous profile method, and in the laboratory using the multi- step outflow method. The water balance results showed that the applied water was not sufficient to match the actual tree water use by evapot ranspiration, causing soil water depletion around the tree as the irri gation season progressed. Moreover, soil water content data demonstrat ed temporal changes in the water uptake patterns. The temporal occurre nce of leaching justifies the need for soil water measurements in the scheduling and design of drip irrigation systems. (C) 1997 Elsevier Sc ience B.V.