Autonomous irrigation of Olive

Transcription

1 Olive trees are rain-fed or irrigated. The fruit is pickled or extracted for oil. We carried out a detailed autonomous irrigation experiment of Manzanilo for 6 years and gained experience irrigating autonomously 58 ha of commercial orchards with saline water (3 5 dsm) Autonomous irrigation of Olive The frequency and volume of autonomous irrigation is a function of the threshold tension chosen for irrigation, the evaporative demand, the available soil water, the plant parameters (i.e. leaf area) and the irrigation lay out. The integration of all these parameters are manifested in the soil water tension sensed by the plant. Under the condition prevailing in the coastal plain in Israel the irrigation frequency and volume increases gradually as evaporative demand throughout the growing season increases, from the end of the winter rains throughout the long and dry growing season. The following picture is a sample of the irrigation frequency and soil water tension of Manazanilo olive drip irrigated autonomously at -1 and -2 kpa in July and August, when the evaporative demand peaks out:

2 Cantibar Cantibar July Cantibar Cantibar August

3 Irrigation frequency and volume was greater at -1 kpa compared to -2 kpa. The irrigation frequency increased from once a day to twice a day in -1 kpa and from once every 2-4 days to daily irrigation in -2 kpa, from the beginning of July until the end of August. In the on year the cumulative annual autonomous drip irrigation of Manzanilo in the coastal plain in Israel reached 149 mm and 346 mm in -1 kpa and -2 kpa threshold irrigations, respectively. Compared to the recommended irrigation (6 mm) the autonomous irrigation saved 75% and 42% water in -1 kpa and -2 kpa threshold irrigations, respectively. The Fruit size was greatest when irrigated at a threshold tension of -1 kpa. Irrigation at a tension of -2 kpa reduced fruit size 12%, increased fruit dry weight 13%, increased oil content 11% and oil yield 7%. Neutron scattering measurements showed a negative gradient of soil water content with depth, all through the growing season. The soil water content declined gradually from the end of the rainy season (end of March), in all soil layers. After 4 months of irrigation (end of July) the water content leveled off in all soil layers (-18 cm). The negative gradient with depth indicated that the high irrigation efficiency was achieved by controlling soil percolation. The soil water content of the -2 kpa irrigation was less than the -1 kpa irrigation. Autonomous sub surface drip irrigation of a commercial olive orchard was irrigated in 217 in the Negev of Israel ( , ) with saline water at a tension of -25 kpa ( Barnea ) and -22 kpa ( Picual ). A plot of Barnea irrigated according to the commercial practice served as a control. The commercial plot was irrigated 682 m3/ha. The autonomous irrigation of Barnea and Picual saved 12.7% and 17.7% water, respectively. The following is the soil water tension of the 3 plots:

4 Barnea Autonomous /4 11/5 1/6 22/6 13/7 3/8 24/8 14/9 5/1 26/1 Barnea Comercial /4 11/5 1/6 22/6 13/7 3/8 24/8 14/9 5/1 26/1 - Picual Autonomous /4 11/5 1/6 22/6 13/7 3/8 24/8 14/9 5/1 26/1 Date 217 The tension of the commercial Barnea plot fluctuated -8 cnetibar while the autonomous Barnea plot -7 centibar and the autonomous Picual plot -3 centibar. The actual soil tension exceeds the threshold tension set in autonomous irrigation for several reasons: An overshoot of several centibars is expected because the tension continuous rising after the irrigation command is sent until the water reach the tensiometer in the soil. The rise in tension in the autonomous Barnea was greater than expected, caused by practical constrains of unavailable water when the threshold tension was reached. The delay in irrigation however was compensated by an increase in the irrigation volume once the irrigation was initiated:

5 Irrigation (m 3 / ha) and Tension (centibar) Irrigation Tension pre-irrigation 2 2/7/17 22/7/17 24/7/17 26/7/17 28/7/17 3/7/17 1/8/17 Date R 2 =.916 Contrary to the autonomous Barnea the soil water tension of the Picual did not exceed the set tension beyond a few centibars, as expected. The different response of the Picual can be explained by cultivar difference. It has been shown by Tugendhaft et al. (216, Scientia Horticulturae 199: ) that the the Picual maintains higher stomatal conductance and lower mid-day leaf water potential compared to the Barnea under water stress. The Barnea is a cultivar that was selected for intensive cultivation while the Picual is a rain fed cultivar.