APPLICATION EFFICIENCY OF MICRO-SPRINKLER IRRIGATION OF ALMOND TREES

Micro-sprinklers are becoming a preferred irrigation method for water application in orchards. However, there is relatively little data avai lable to support a particular irrigation scheduling method. The object ive of this study is to quantify the components of the water balance o f an almond tree under micro-sprinkler irrigation. For that purpose, a n experimental plot around an almond tree with an area of 2.0 m X 2.0 m without vegetation, representing about one quarter of the wetted are a of the micro-sprinkler was instrumented with neutron access tubes, t ensiometers and catch cans. Twenty-five access tubes with catch cans w ere distributed in a square grid of 0.5 m X 0.5 m, to a depth of 0.9 m . Eight pairs of tensiometers were installed at depths of 0.825 and 0. 975 m within the experimental plot. During a 7-day period in August, 1 995 the plot was sprinkler-irrigated on three days, and water applicat ion rates and uniformity coefficients were calculated for each irrigat ion event. Neutron probe readings at 15 cm depth increments and tensio meter readings were taken 4 to 6 times daily. Results showed large eva poration losses during and immediately after the irrigations. Evaporat ion losses of the wetted area was estimated to be between 2 and 4 mm/i rrigation event. Consequently, application efficiencies were only 73-7 9%, the wetting of the root zone was limited to the 0-30 cm depth inte rval only, the soil profile was depleted of soil water, and daily crop coefficient values at days between irrigation events were between 0.6 and 0.8. The study recommends irrigation in the evening and night hou rs, thereby largely eliminating the evaporation losses that occur duri ng daytime irrigation hours. (C) 1997 Elsevier Science B.V.