الملخص الإنجليزي
During summer cropping seasons (May-September) in Oman embient air temperature normally exceeds 40°C as a result of which there is increase in nutrient solution temperatures in hydroponic systems leading to decreased crop production. This study was conducted to improve yield potential and quality of cucumber (Cucumis Sativa L.) through improving root zone temperature (RZT) to improve nutrient uptake, growth and development during three cropping periods, viz. Summer (June-August), Fall (September-November) and Spring (February-May) for two years- 2016/2017 and 2017/2018 in the greenhouse at Directorate General of Agriculture and Livestock Research at Rumais in the Wilayat Barka Oman. The plants were grown in perlite medium of root-zone cooled temperatures of 22°CE1, 25°C+1, 28°C+1 treatments respectively besides the control (33°C+2). The results indicated that the crop at root-zone temperatures of 22°C+1 and 25°C+1 showed superior performance in terms of plant height, leaf number/plant, chlorophyll content, leaf area , fruit number/m2, yield, fresh and dry weight (g) shoot and root with significant differences between the treatments in all three cropping periods. Higher fruit yield was produced with cooled RZT-22°C+and cooled RZT-25°CE1 (4.4-8.7 ton/gh) as compared to the uncooled RZT-33°C+1 (2.8-6.5 ton/gh) during all three cropping periods in both the years. The plants at cooled RZTs responded positively and significantly (p<0.05) in the uptake of all nutrient elements in leaves, fruits, shoots and roots in comparison with uncooled RZT in all cropping periods in both years. Quality attributes like fruit length, diameter and total soluble solid percentages did not show any significant differences between the treatments in all cropping periods. Further, cooling of nutrient solution temperature was found influencing positively the levels of dissolved oxygen in the fresh and drained nutrient solutions in all cropping periods. Significant (p<0.05) differences between the treatments were observed in oxygen consumption by the plants (roots) of cucumber in all cropping periods. High levels of oxygen consumption were recorded with plants of cooled RZTs in all the cropping periods. All growth and production and quality attributes were positively influenced and greatly expressed by cooled root-zone temperature under the root-zone of cucumber with increased dissolved oxygen levels in nutrient solution. Regarding Cost Benefit Analysis the results indicate that all the four cooling nutrient temperature yields positive returns (benefits) above variable and total costs for the two years of this experiment. Cooling nutrient temperature (22°C+1) yields higher returns than the other treatments followed by treatment (25°C+1), (28°C+1) compaed to control (33°C+2). This study found that cooling of root-zone temperature that facilitates availability of optimum aeration (oxygen levels) in nutrient solution is essential and could be of significance for boosting cucumber yield as observed during high temperature growing periods in summer (May-September) in Oman.
