Alon, H., MOP Darom, Besor Experimental Station, Mobile Post 485400, Israel
In southeastern Spain, one of the main areas for growing tomatoes in greenhouses, tomato seedlings transplanting usually takes place at the end of July or August, when air temperatures can exceed 40°C at midday. In this area, substrate cultivation is a common practice and the seedlings are initially placed in small blocks of rock wool or coconut fiber, where the volume of substrate is very limited. Under these conditions, a high temperature of the irrigation solution could cause the appearance of fungal diseases that cause the death of the plant or delays in growth. Some manufacturers of irrigation systems indicate that the use of white pipes can reduce the temperature of the water up to 8°C even though there have not been found scientific studies in the bibliography that confirm such claims. From April to December 2018, an experiment in a greenhouse located in Murcia was carried out to check if there would be variations in the temperature of the nutrient solution when using a white pipe compared to a conventional black one. Water solution temperatures were determined continuously using type T thermocouples placed inside the irrigation pipe with anti-drainage emitters. In April, with watering scheduled at 12:00 pm and mean temperatures inside the greenhouse of 30°C, differences of up to 10° were found 3 min after irrigation started (33°C inside black pipe vs. 23°C inside the white one). However, in August, when the mean temperature inside the greenhouse was 35.5°C, with 5-min irrigations scheduled at 2-h intervals from 8 am to 5 pm, the maximum water temperature differences found were 2.3°C. The results demonstrate that the use of the plastic pipe color can significantly affect the irrigation water temperature within a greenhouse farming system. © 2020 International Society for Horticultural Science.
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