This field experiment was conducted in order to evaluate the effects of day and night time irrigation -DT, NT- on tomato growth, yield and water use efficiency -WUE- at Meteorological Organization of Agricultural Faculty in Ferdowsi University of Mashhad, Iran. The investigation was carried out in three treatments and three replications in two irrigation timings, including one during the day and one at night on randomized plot design. Soil moisture, temperature and EC were measured at a distance of 30 cm from the drippers by data logger REC-P55. These parameters were recorded prior to and after irrigation. Irrigation was applied using tape drip system with drippers spaced every 30 cm. The discharge of the drippers was 2 l/h and the pressure was 0.5 bars. Drip tape instances in each block were considered to be 0.75 m. Three fixed irrigation regimes through the whole crop cycle in both DT and NT at I1 -100%-, I2 -75%- and I3 -50%- of the maximum irrigation water requirement -Iw- were used. The DT water used volume by I1, I2 and I3 was 17.2, 4.1 and 6.2% higher than the NT correspondent volume, respectively. Tomato yield measured for DT treatments was 7.88, 6.19 and 19.44 kg lower than NT treatments. The results revealed that NT treatments impression on tomato yield and WUE were not significant. Delivering irrigation at night may help reduce the water used volume and root-zone soil temperature, while increased water use efficiency up to 10% compared to DT irrigation which may translate to improved plant growth. Proper irrigation timing together with efficient water management can help in obtaining a high amount of tomato yield.

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