The effects of various drip fertigated water quantities on hydroponically cultivated Cucumis sativa L.
The effects of various water quantities were assessed on Cucumber (Cucumis sativa L.) grown hydroponically in the greenhouse. The objectives of the study were to evaluate influence of water quantities on: i) photosynthesis and chlorophyll content of Cucumis sativa L.; ii) the nutrient uptake in Cucumis sativa L. iii) flavonoid and anthocyanin metabolism in Cucumis sativa L. and iv) growth and yield in Cucumis sativa L. The treatments included 8 various water regimes (2l/h, 4l/h, 6l/h, 8l/h, 10l/h, 12l/h, 14l/h and 16l/h. The plants received water five times a day, making it 10, 20, 30, 40, 50, 60, 70, and 80 litres per day. Results showed that generally the Photosynthetic rate (A), intercellular CO2 concentration (Ci) and stomata conductance (gs) and the transpiration rate of the cucumber plants were significantly increased by increasing water quantities compared with lower water quantities. Additionally, there were significant improvements in leaf colour in weeks 2, 3, 4, 5, 6, 7 and 8. Overall, the foliage colour was improved as water supply was increased. The greener leaves were documented in treatments supplied with higher water doses. Additionally, the chlorophyll content of cucumber plants was increased significantly with varying water quantities. The highest chlorophyll contents were found in plants treated with 16l/h. The fresh and dry weights of roots, leaves and stems were significantly (P≤0.001) influenced by different water quantities supplied to Cucumis sativa L. The largest quantity of fresh roots was recorded in the control treatment (2l/h) in comparison with all other treatments. However, the best growth with regard to fresh and dry weights of leaves and stems were recorded by supplying the water quantities ranging from 10-16l/h. Altering water supply significantly (P≤0.001) affected the uptake of nitrogen, phosphorous, potassium, calcium, sodium, copper, zinc, aluminium and iron in roots of Cucumis sativa L. Irregular results were recorded in the uptake of these nutrients in the roots. However, leaf uptake of N, P, K, Ca, magnesium, sulphur, Cu, Zn, manganese, boron, and Al responded significantly (P≤0.001) to the different water quantities. The best result for each was observed at quantities involving 16l/h. In stems of cucumber water quantities significantly (P≤0.001) affected the uptake of N, P, K, Ca, Mg, Na, S, Cu, Zn, Mn and B. The highest uptake of N, P, Ca, Mg and S were found at the maximum supply of water (16l/h) compared with the control (2l/h). Sodium uptake showed irregular patterns, whereas K and Zinc uptake peaked at 14l/h. The data from this study showed that flavonoid metabolism was not significantly affected by the different water quantities supplied to cucumber plants. However, the anthocyanin content in roots, leaves, and stem was significantly influenced by water levels. The lowest water quantity (2-6l/h) significantly increased the levels of anthocyanins in all tissues tested. Increasing water quantities significantly decreased the anthocynanin metabolism in all tissues. Plant height displayed significant differences with water quantities from weeks 1-8. In week 1, the plant height was superior at supplying 4l/h in comparison with other treatments. In week 2 and 5 irregular trends were detected. At weeks 3 and 4, plants supplied with 8-12l/h displayed superior plant height performance. At weeks 7-8, significant and optimal results were observed at water quantities ranging from 4-16l/h compared with the control treatment. Water quantities significantly (P≤0.001) affected the number of leaves per plant from weeks 2-8. Irregular results were displayed in weeks 2 and 3. At weeks 4 and 5, the highest numbers of leaves were in water quantities of 12l/h and 10l/h, respectively. Generally, leaf numbers increased with increasing water levels from weeks 6-8. Plant vigour was significantly affected by the alteration of water quantities at weeks 1, 2, 4, 5, 6, 7 and 8. At weeks 1 and 4, more vigorous plants were found in the treatments that received from 10-16 l/h. At weeks 2 and 5, optimal results were found at treatments that received from 6-14l/h. At weeks 6, 7 and 8, the most vigorous plants were found at the highest water quantity of 16l/h. With fruit length, fruit width, rind colour, fruit quality (marketable fruit) and weight, results from the harvest done in the first, second and third week showed that water quantities significantly influenced these parameters. Optimal results were reported when the plants were supplied with water ranging between 14-16l/h. During harvesting at week 4, the fruit length, width, rind colour, were of marketable quality at 16l/h. Generally, the plants that received highest amount of water (16l/h) had the highest cucumber yields compared with all other treatments. Higher water quantities in this study resulted in increased physiological responses such as photosynthesis and nutrient uptake which resulted in the higher fruit yields. In water-limited environments, results from this study could assist growers with reasonable cucumber yields while saving water for other farm uses.