الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
SUMMARY AND CONCLUSION
A field experiment was carried out during the two growing seasons of 2020 and 2021 at the Experimental Vegetable Farm of the Horticulture Department (30° 06ʹ 46ʺ N, 31°14ʹ 37ʺ E), Faculty of Agriculture, Ain Shams University, Qalyubia Governorate, Egypt. The study investigates the effects of cobalt, selenium, and silicon on the growth, yield, and quality of lettuce cv. Limor plants.
Ten foliar-application treatments; including cobalt sulphate at concentrations of 100, 200, and 300 μM, sodium selenite at concentrations of 10, 20, and 30 μM, and sodium silicate at concentrations of 0.5, 1, and 2 mM plus distilled water, which served as a control treatment, were applied on lettuce plants. The treatments were arranged in a completely randomized block design with three replicates. The treatments were applied as foliar applications twice; 21 and 28 days after transplanting.
Vegetative characteristics were recorded, i.e., head diameter, leaf surface area, number of leaves/head, fresh and dry weights of vegetative growth. Also, chemical analysis of the plant leaves was done to assay N, P, K, Ca, Mg, S, Co, Se, and Si percentages as well as nitrates and nitrites in the leaves. Ultimately, chlorophyll, soluble sugars, free amino acids in leaves were determined.
The obtained results could be summarized as follows:
- Spraying lettuce plants with cobalt at 200 μM, selenium at 20 μM, or silicon at 2 mM showed the highest significant values of head diameter, while foliar application of silicon at 2 mM gave the highest number of leaves per head. Cobalt at 100 μM, selenium at 10 μM, or silicon at 1 or 2 mM revealed the highest significant values of total leaf area.
- The highest significant fresh weights of heads were obtained from spraying with cobalt at 100 μM, selenium at 20 μM, or silicon at 2 mM without significant differences between them, while selenium at 20 μM, or silicon at 2 mM gave the highest significant values of dry weights of heads.
- Cobalt at 100 μM, selenium at 20 μM, or silicon at 2 mM gave the highest nitrogen content without significant differences, while cobalt at 100 μM, selenium at 10 μM, or silicon at 2 mM gave the highest significant values of phosphorus content. In the same manner, spraying lettuce plants with selenium at 20 μM or silicon at 2 mM resulted in significant increases in leaf magnesium content, while supplementing with silicon at 1 or 2 mM significantly improved calcium content in the leaves. In addition, it was found that selenium at any concentration significantly improved sulfur content. Meanwhile, foliar treatments did not affect the potassium content in the leaves.
- Spraying lettuce plants with cobalt, selenium, or silicon resulted in significant accumulations of the same sprayed element in the. Increasing the applied element resulted in increasing the leaf content of that element.
- Foliar applications of cobalt, selenium, or silicon enhanced chlorophyll a and total chlorophyll as compared to the control treatment in both seasons. However, there was no considerable effect of all foliar treatments on chlorophyll b content in the leaves. The highest significant values of the aforementioned attributes were obtained with cobalt at 100 μM, selenium at 20 μM, or silicon at 2 mM in both growing seasons. On the contrary, the control treatment showed the lowest significant values in both growing seasons.
- spraying lettuce plants with cobalt, selenium, or silicon improved the content of total soluble sugars and amino acids in the leaves in both seasons. Cobalt at 100 μM, selenium at 20 μM, or silicon at 2 mM significantly increased the total soluble sugars and free amino acids, as well as cobalt at 200 μM for free amino acids in both growing seasons.
- There were insignificant variations between all foliar applications of these beneficial elements and control treatment for nitrate and nitrite content in the leaves.
- It was found that the first two principal components accounted for 52.5 and 13.8% of the variations for PC1 and PC2, respectively. The cumulative proportion of the variation approached 66.3% of the total variance. All evaluated traits, except for potassium, cobalt, selenium, nitrate, and nitrite contents in the leaves, were positively associated with cobalt of 100 and 200 μM, selenium of 20 μM, and silicon of 1 and 2 mM treatments. The control treatment was positioned on the negative range which means that it gave the lowest values of all tested parameters compared with the foliar applications of the used elements.
It can be concluded that using beneficial elements such as cobalt, selenium, and silicon as foliar applications on lettuce plants cv. Limor can improve the vegetative growth, yield, quality, and nutritional value of lettuce heads. Providing cobalt at 100 μM, selenium at 20 μM or silicon at 2 mM as foliar sprayings not only improves the vegetative growth and yield of lettuce plants but also raises the nutritional quality of the heads by fortifying the content of these elements. Furthermore, farmers can increase the productivity of lettuce cv. Limor by 14-16% with the recommended concentrations of these beneficial elements under Qalubia Governorate conditions, Egypt.