Abstract
Optimum cool root zone temperature positively influences the production of greenhouse vegetables grown during summer/high temperature period under hydroponics system. Hence, the effect of root-zone temperature was investigated on the growth, yield and nutrient uptake of cucumber (Cucumis sativus L.) plants grown in pots filled with perlite medium under recirculating hydroponic system in greenhouse during summer period (June-August) in two consecutive years 2016/2017 and 2017/2018 using three cooling treatments-T1 (22 ºC), T2 (25 ºC) and T3 (28 ºC) and non-cooled treatment T4 (33 ºC) as control in Randomized Complete Design (RCD). All the treatments received the same nutrient concentrations. Significant (p < 0.05) differences were observed for all the characters viz. plant height, leaf number/m2, chlorophyll content, leaf area (cm2), fruit number /m2, yield (t/gh), fresh (g) and dry matter weight (g) of shoot and root at all cooled root-zone temperatures as compared to control in both the years. Plants at cooled root-zone temperature (RZT) of 22 ºC gave high number of fruits/m2 to the extent of 180 in 2016/2017 and 220 in 2017/2018 followed by that at 25 ºC (167, 221) and 28 ºC (178, 143) as compared to those in control (33 ºC) (101,133) in both the years. Similarly, highest fruit yields were found at cooled RZT of 22 ºC (5.0 t/gh) and 28 ºC (4.7 t/gh) in the first year and 22 ºC (6.1 t/gh) and 25 ºC (6.0 t/gh) in the second year. The plants at cooled RZT responded positively and significantly (p < 0.05) in the uptake of all nutrient elements in shoots and roots in comparison with those at non-cooled RZT in both years.
Highlights
While the air temperature is one of the most important environmental elements for the altering secondary metabolism in the plants for production (Kaplan et al, 2004; Zobayed et al, 2005; Ramakrishna & Ravishankar, 2011), the temperature at the root-zone influences the growth and chemical composition of many plants (Adebooye et al, 2010; Malik et al, 2013; Yan et al, 2013; Sakamoto & Suzuki, 2015a, 2015b)
The highest plant height was found at cooled root-zone temperature of 22 oC to the extent of 173.4 cm followed by 170.3 cm at cooled root-zone temperature of 28 oC whereas the lowest plant height was found at 33 oC (141cm) in 2016/2017 (p > 0.05)
Differences in response of cucumber plants from two years in plant height at different root-zone temperatures at different stages of growth of the crop were similar to the study of Moon et al (2007) where it was observed that during summer the growth rate of the stem of cucumber at both temperatures had been linear for a long time in contrast to the exponential growth found in winter while in autumn and spring the growth rate at 25 oC was linear
Summary
While the air temperature is one of the most important environmental elements for the altering secondary metabolism in the plants for production (Kaplan et al, 2004; Zobayed et al, 2005; Ramakrishna & Ravishankar, 2011), the temperature at the root-zone influences the growth and chemical composition of many plants (Adebooye et al, 2010; Malik et al, 2013; Yan et al, 2013; Sakamoto & Suzuki, 2015a, 2015b). One of the characteristics of hydroponic cultivation is its ability to control the temperature of the nutrient solution around the root system using heaters or cooling spirals, to increase or decrease the temperature, respectively. In the hot summers, the root-zone temperature of hydroponic systems often exceeds 30 oC. The root-zone temperature can often reach 35 oC when the air temperature is 38 oC. This was strongly found to suppress the plant growth process and reduce uptake of water and nutrients (Mozafar et al, 1993; Marschner et al, 1996; Stoltzfus et al, 1998). Several studies on different species have shown that plant growth is greatly jas.ccsenet.org
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