International Water & Irrigation

26 An autonomous irrigation controller, based on soil water tensionmeasurement was developed. The controller allocates the required quantity of water at the correct time without human intervention. The functioning of the controller for improved irrigation efficiency was tested in a tomato irrigation experiment. The experiment was carried out on winter grown tomato cv. Ikram in a polyethylene-covered greenhouse in the southern coastal region of Israel. The three treatments tested included a control based on current irrigation recommendation and two treatments, -8 kPa and -15 kPa threshold tension irrigation. Soil water tension was monitored every 15 minutes and uploaded to a server for visual inspection and data analysis. Irrigation was by drippers applying a continuous and uniform concentration of fertilizers to all treatments. Data collected included records of irrigation timing and volume of water applied, total and marketable yield, number of fruit clusters, non-marketable fruit (due to split, small, green, rotten, and blossom end rot) and fruit shelf life. At the end of the experiment the soil was sampled for salinity and water content measurement. The results showed that the autonomous irrigationmaintained the pre-set threshold tension steadily. Compared to the control treatment the threshold tensions of -8 kPa and -15 kPa saved 12%and 24%of water and fertilizers, respectively. Water use efficiency increased from 42.7 kg fruit/m3 of water in the control to 46.8 kg/m3 and 55.6 kg/m3 in the -8 and -15 kPa treatments, respectively. There were no significant differences between treatments in total yield (247 - 257 T/ ha), marketable yield (224 - 243 T/ha) and the shelf life of the fruit. The blossom-end rot infection was 0.4%, 0.8% and 1.3% of total yield in the control, -8 kPa and - 15 kPa treatments, respectively. The highest tension differed significantly from the control. Soil salinity was low, without difference between treatments. The salinity profile and root excavation indicated that the main root system was a in the 0-45 cm layer. Soil water content in the 0-90 cm depth was highest in the control and lowest in the -15 kPa treatment. The tomato irrigation experiments demonstrated the availability of an autonomous irrigation system whereby the timing and irrigation volume applied is dictated by the plants that best integrate the environmental conditions, the plant canopy size and the soil water availability. Materials and Methods. The tomato cv Ikram (cluster bearing fruit) irrigation experiment was carried out in a polyethylene- covered greenhouse in an experimental station located in the southern coastal plain of Israel (104m elevation, 31.271164 ; 34.392005). The irrigation water supply was a mix of desalinized and well water (EC 0.3-0.45 dS/m, pH 7-7.5). The experimental lay out was a randomized block with 3 replicates of 3 treatments: a control (Israel Extension Service protocol) and 2 autonomous irrigation tensiometers initiating irrigation at soil water tension thresholds of -8 kPa and -15 kPa (Tevatronic LTD, patented). The tensiometers were positioned 10 cm from a dripper at a depth of 15 cm and programed to terminate the irrigation when water percolated to a depth of 15 cm. A single tensiometer was used for each treatment. The total area of each treatment was 54 m3 . Planting was in the local soil (87% sand, 7% silt, and 6% clay) in flat beds of double rows. The distance Autonomous irrigation is enabled by soil water tension control The tomato irrigation experiments demonstrated the availability of an autonomous irrigation system whereby the timing and irrigation volume applied is dictated by the plants that best integrate the environmental conditions, the plant canopy size and the soil water availability. Dr. Mollie Sacks* * SHAHAM, The Agriculture Extension Service, Ministry of Agriculture, Israel