Abstract
High nutrient solution temperature stress around root-zone (rhizosphere) is a major factor limiting hydroponic crop growth due to change in dissolved oxygen (DO) levels in nutrient solution during the high-temperature seasons. This suggests that easier and economical control of root-zone temperature (RZT) could be an effective solution to the temperature stress for the crop plants in hydroponics. In this respect, the present investigation was undertaken to comprehend the influence of nutrient solution temperature on its oxygen level (ambient dissolved oxygen in feeding tank), growth, yield and quality of cucumber (Cucumis sativus L.) plants. The plants were cultivated in recirculating hydroponic system in a greenhouse with dimensions of 9 m wide × 30 m long and total area of 270 m2 during three cropping periods in Oman viz. summer (June-August), fall (September-November) and spring (February-May) in two consecutive years 2016/2017 and 2017/2018. Three cooling treatments were applied viz. T1 (22 ᵒC), T2 (25 ᵒC) and T3 (28 ᵒC) through cooling nutrient solution besides non-cooled treatment T4 (33 ᵒC) as control. The plants were grown in pots filled with perlite medium in randomized complete design (RCD) with four replications. All the treatments received the same nutrient concentrations. The results showed that cooling of nutrient solution temperature influenced positively the levels of DO in the fresh nutrient solution feeding tank and drain nutrient solution for all cropping periods in both the years. Significant (p < 0.05) differences between the treatments were observed in oxygen consumption by the roots of cucumber in the cropping periods in both the years. High levels of oxygen consumptions were recorded with cooled RZTs as compared to that of control-non-cooled RZT for all cropping periods in both the years. All growth, production and quality attributes were positively influenced and greatly expressed by cooled root-zone temperature in the root-zone of cucumber with increased DO levels in nutrient solution. This study revealed that availability of optimum aeration (oxygen levels) in nutrient solution through cooling of nutrient solution temperature could be of significance for boosting cucumber yield as observed during all the growing periods especially in summer in Oman.
Highlights
Among the factors affecting hydroponic production systems, the nutrient solution temperature is being considered as one of the most important determining factors of crop yield and quality (Muthir et al, 2018)
Summer cropping period in general in Oman and other Arabian Peninsula countries has temperature ranging from 38 oC to 49 oC with a relative humidity (RH) varying from-50 to 90%
Significant (p < 0.05) differences were observed in dissolved oxygen (DO) levels between nutrient solution temperatures (NST) at different times in both the years 2016/2017 and 2017/2018 for cucumber crop
Summary
Among the factors affecting hydroponic production systems, the nutrient solution temperature is being considered as one of the most important determining factors of crop yield and quality (Muthir et al, 2018). Vol 11, No 3; 2019 undertaken on the effect of nutrient solution temperatures and their effect on oxygen levels, uptake of nutrients, growth and yield of some vegetable crops grown in hydroponics systems. High solution temperature (35 °C) was found to affect in the short and long-term during growth period of the crop. In view of the above, the present investigation was carried out to know the effect of root-zone temperature on the dissolved oxygen level in the solution and on root and plant development, growth, yield and quality of cucumber
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