International Water & Irrigation

32 causes of soil and root density variability are eliminated. Furthermore, the position close to the dripper at a shallow soil layer enables response in real time to maintain a pre-set tension threshold without restricting the wetting of deeper soil layers. It was found that the combination of shallow monitoring, active promotion of root growth and effective irrigation depth control eliminates the need to use replicate measurements of soil tension. The soil water tension was recorded every 15mand uploaded to a server on the internet for visual monitoring and analyzing the irrigation data (Fig 2 and 3) . The irrigation controller maintained successfully the pre-set soil water tensions. Minor overshoots above the pre-set tension lasting 15 - 120 minutes were the results of the time it takes the water to percolate and reach the tensiometer. A few cases of more severe overshoots, up to -69 kPa, were caused by electricity failure. These overshoots had no effect on the growth and yield of the tomato. The tension controlled irrigation saved water (Fig 4) and fertilizers (Table 2) while maintaining total and marketable yield equal to the control (Table 3) . As a result the water use efficiency increased from 42.7 kg fruit/m3 of water in the control to 46.8 kg/m3 in the -8 kPa treatment (9.6%) and 55.6 kg/m3 in the -15 kPa treatment (30.2%). With the exception of blossom-end rot, there were no differences between treatments in the non-marketable fruit (Table 3). Tomato fruit can be affected up to 50% with blossom-end rot when deficit irrigation is used and the Ikram cultivar used in this study is known to be a sensitive cultivar to blossom-end rot. The tension controlled deficit irrigation caused only a slight increase in blossom-end rot. The tomato irrigation experiments demonstrated the availability of an irrigation system whereby the timing and irrigation volume applied is dictated by the plant in real time and carried out autonomously, without human intervention. ■ Fig. 6. Salinity profile measured when experiment terminatedFig. 7. Soil water content measured when experiment terminated. Fig. 7. Soil water content measured when experiment terminated Fig 8. The correlation between soil matric potential and photosynthesis in soil-less potted fig (Klein 2006)