Abstract
The main objective of this work was to analyze the microclimate generated inside a low tunnel (floating row cover) installed in an Almería-type greenhouse. Low tunnels are commonly used in the open field to protect plants against insect attack and to improve the production of muskmelon and strawberry. Floating row covers can also be used inside greenhouses during the first few weeks after the transplantation of muskmelon and watermelon crops in spring-summer cycles. This work was carried out during the first weeks of a watermelon culture (Citrullus lanatus Thunb.) growing with a polyethylene row cover inside an Almería-type greenhouse (2115 m2). Air temperature and humidity, plant temperature and soil temperature and humidity were measured in the greenhouse inside and outside the row covers. During the three days of measurement, all greenhouse vent openings were closed. The use of the low tunnels increased average air temperature around plants from 24.0 ± 9.0 °C to 26.9 ± 9.7 °C. A maximum difference in air temperature of about 5.9 °C was observed at noon. The average daily temperature of the crop was 28.2 ± 11.8 °C inside the row cover and 24.6 ± 8.9 °C without it. Similarly, the absolute humidity of air was clearly higher inside the low tunnel (0.0201 ± 0.0098 g/g) than around the plant rows without floating cover (0.0131 ± 0.0048 g/g). The soil temperature was also higher inside the low tunnel compared to the area without this second plastic cover. The effect of the tunnel decreased with depth, with average temperature differences of 1.2 ± 0.5 °C on the soil surface and 0.6 ± 0.5 °C at 20 cm depth.
Highlights
IntroductionLow tunnels (floating row cover) are small arched metal structures, covered with plastic film that provides protection to crops in their early stages of development [1,2,3,4]
Low tunnels are small arched metal structures, covered with plastic film that provides protection to crops in their early stages of development [1,2,3,4]
The presence of the low tunnel could be expected to significantly affect net radiation levels measured at 2 m in height above the crop, but no such significant differences have been observed between the two areas of the test, being slightly lower in the area without the low tunnel (Table 2)
Summary
Low tunnels (floating row cover) are small arched metal structures, covered with plastic film that provides protection to crops in their early stages of development [1,2,3,4]. The low tunnels protect against frost [17,18] They are usually used in outdoor crops [1], they can be used in crops inside greenhouses to give extra protection in the early stages of cultivation. Only 6% of the greenhouses of the province of Almería (Spain) used low tunnel to protect horticultural crops at the early stages of growth [7]. The leaves touch the plastic, and it is necessary to remove the low tunnel. These low tunnels allow increasing the air temperature surrounding the seedlings by decreasing energy losses by infrared radiation at night. Placing them above heating pipes allows great energy savings by greatly limiting heat losses by convection to the rest of the greenhouse [7]
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