International Water & Irrigation
28 irrigation. Salinity was measured on soil samples leached with a volume of water twice their weight. Soil water content was measured by weight loss after 24 h of drying at 105 oC and converted to volumetric water content. Roots of a single plant in each replicate was exposed for qualitative inspection by washing off the soil from one side of the plant into a 60 cm deep trench located 40 cm parallel to the row. Temperature, relative humidity, global radiation and Penman-Monteith evapotranspiration were measured outside the greenhouse on the site of the experimental station (meteo-tech.co.il ). Statistical analysis was carried out by JMP. Results Environment: The experiment was carried out on winter cultivation of tomato when global radiation and temperatures in the region are at minimum (Fig 1) . The prevailing winter temperature in the region enables cultivation in polyethylene- covered greenhouses without heating. Radiation outdoor in the winter months was ca. 60% compared to the radiation at the end of the experiment in mid May and evapotranspiration ca. 2 mm compared to 6 mm. Irrigation The control treatment was irrigated in months October - February every other day and gradually at increasing frequencies thereafter (Table 1) . The irrigation frequency of the soil water tension treatments was consistency less than that of the control but inconsistent between the -8 kPa and -15 kPa treatments. The soil water tension of the -8 kPa and -15 kPa treatments was maintained at the pre-set tension with minor exceptions (Fig 2 and 3) . An overshoot of 2-3 kPa, lasting 15-120 min, is the result of the elapsed time it takes the water to percolate and reach the tensiometer located in the soil after the initiation of the irrigation. The irrigation frequencies of the soil water tension treatments decreased to a minimum in mid winter (January) and increased considerably when radiation, temperature and evapotranspiration rose (April - May). Cumulative irrigation was 6000 m3/ha, 5310m3/ha and 4570 m3/ha in the control, -8 kPa and -15 kPa treatments, respectively (Fig 4) . Water saved was 12% and 24% in the -8 kPa and -15 kPa treatments, respectively. Except in November, tension control treatments irrigated less than the control all through the growing season and the -15 kPa treatment equally or less than the -8 kPa treatment (fig 5) . Reduced irrigation by soil water tension control was greatest in the mid-winter months when evapotranspiration was at its minimum. Fertilization : Fertilizer was continuously applied at the same concentration to all treatments. The total applied was therefore proportional to the irrigation volume. A total nitrogen of 594 kg/ha, 511 kg/ha and 448 kg/ha was applied to the control, -8 kPa and -15 kPa treatments, respectively (Table 2) . The saving of all other nutrients was the same. Yield and shelf-life : Total yield was 257 T/ha, 249 T/ha and 254 T/ha in the control, -8 kPa and -15 kPa treatments, respectively (Table 3) . The respective marketable yields were 91%, 90% and 96% of total yield. There were no Fig. 1. Environmental data in the experimental site for the period 1/9/2015-31/5/2016 Table 1. Number of irrigations Month Control - 8 kPa - 15 kPa October 2015 (21 days) 10 11 12 November 2015 15 17 14 December 2015 16 14 10 January 2016 10 8 7 February 2016 15 13 13 March 2016 21 13 15 April 2016 28 17 25 May 2016 (22 days) 22 16 15 Table 2. Fertilizer input Fertilizer Control -8 kPa - 15 kPa N (kg/ha) 594 511 448 P (kg/ha) 356 307 269 K (kg/ha) 950 817 717 Mg (kg/ha) 59 51 45 Fe (g/ha) 3369 2819 2573 Mn (g/ha) 1683 1408 1286 Zn (g/ha) 842 704 643 Cu (g/ha) 123 103 94 Mo (g/ha) 90 75 69
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