الفهرس 
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Abstract
SUMMARY AND CONCLUSION
This study was carried out to investigate the effect of irrigation with saline water and foliar sprayings of potassium silicate on growth, yield and chemical composition of grain sorghum (Sorghum bicolor L. Moench cv. Dorado) and barley (Hordeum vulgare L. cv. Giza 123) plants in the two successive seasons of 2018 and 2019.
Two pot experiments were carried out during the two successive seasons of 2018 and 2019. Trials took place in the experimental farm of the Botany Department, Faculty of Agriculture, Ain Shams University, Shoubra El-kheima, Qalyubia Governorate, Egypt
Four concentrations of salinity at 0, 50, 100 and 150 mM of NaCl were used. Pure sodium chloride was dissolved in tap water to prepare the concentrations.
Three concentrations of foliar sprayings of potassium silicate were used at 0, 1 and 2 mM. In sorghum plants, spraying of potassium silicate was done after 15, 30 and 60 days from sowing seeds. While in barley plants, it was sprayed after 20, 50 and 80 days from sowing seeds.
Treatments were arranged in a completely randomized block design with three replicates, each replicate represented by 120 pots in each experiment.
Vegetative characteristics were recorded, i.e., plant height, fresh and dry weights of the plants, leaf area/plant and leaf area index. In addition, photosynthetic pigments such as Chl a and Chl b were estimated. Moreover, the leaf water status, osmolytes such as proline and sugars were assayed. Further, the oxidative stress was measured in form of H2O2. On the other hand, the antioxidant capacity was estimated as scavenging ROS by DPPH, also antioxidant enzymes, i.e., APX, CAT and POX were assayed.
Furthermore, chemical analysis for the plant were done to assay Na, K and Si percentages in the plant. Moreover, proline and chlorophyll and carotenes contents in the leaves were estimated.
Finally, the yield/plant and the weight of the spikes and panicle were recorded in the both plant species.
The obtained results could be summarized as follows:
1. Effect of irrigation by saline water
Salinity negatively affected the vegetative growth of the grain sorghum and barley plants. As the salinity concentration increased, the values of the vegetative growth parameters decreased. The lowest significant values of plant height, fresh and dry weights of the plants, leaf area/plant and leaf area index were obtained at the application of saline water at 150 mM. While, the highest significant values of the aforementioned parameters were obtained by the treatment of non-saline irrigation water (control treatment) in both seasons for the both plants. In addition, the photosynthetic pigments have the same trend of the vegetative parameters The Chl a and Chl b decreased as the salinity level increased. However, the lowest values were obtained at 100 mM of NaCl in sorghum plants. While for the Chl a/b ratio, the highest values were obtained at 100 mM of NaCl in both of grain sorghum and barley plants.
Concerning the leaf water status, the relative water content percentage was decreased by increasing the salinity concentration in grain sorghum and barley crops. The lowest values of relative water content % were obtained by the application of NaCl at 150 mM.
Respecting the osmolytes content, H2O2 and antioxidant enzymes, i.e. APX, CAT and POX. As the salinity concentration increased, the values of the aforementioned characters increased. Also, the highest values were obtained at the application of 150 mM of NaCl in both seasons at grain sorghum and barley plants.
Concerning the minerals content, increasing the salinity level decreased in K and Si percentages, however it increased Na percentage in both seasons at grain sorghum and barley plants. The application of saline irrigation water at the high levels (100 and 150 mM) showed the highest percentages of Na and the lowest significant percentages of K and Si.
With respect to yield attributes, increasing the salinity concentration decreased the yield attributes, i.e. grain yield/plant, panicle weight and spike weight for grain sorghum and barley plants.
2. Effect of potassium silicate foliar spraying
Obviously, results showed that potassium silicate enhanced the vegetative growth characteristics of the grain sorghum and barley plants. Potassium silicate foliar spraying at 1 and 2 mM showed the highest significant values of the vegetative growth parameters, i.e plant height, fresh and dry weights of the plants, leaf area/plant and leaf area index. While the lowest significant ones were obtained by the application of potassium silicate at 0 mM (Control).
As for the chlorophyll pigments, the application of potassium silicate at 1 and 2 mM significantly enhanced the Chl a and Chl b as compared to control treatment in grain sorghum and barley plants.
Regard the leaf water status, the relative water content percentage significantly increased by the foliar spraying of potassium silicate at 1 and 2 mM in grain sorghum and barley crops as compared to the control treatment of potassium silicate.
With respect for osmolytes content and antioxidant capacity, the application of potassium silicate at 1 and 2 mM not only enhanced the proline and sugars but also the scavenging ROS as indicated by DPPH (antioxidant activity) and the antioxidant enzymes, i.e. APX, CAT and POX as compared to control treatment in grain sorghum and barley.
On the other hand, the H2O2 (oxidative stress) was decreased by application of potassium silicate at 1 and 2 mM as compared to the control treatment at grain sorghum and barley plants.
Concerning the minerals content, the application of potassium silicate at 1 and 2 mM enhanced the K and Si percentages, while it decreased the Na % in grain sorghum and barley plants.
Clearly, the potassium silicate application enhanced the yield attributes, the foliar spraying of potassium silicate at 1 and 2 mM increased the grain yield/plant, panicle weight and spike weight for grain sorghum and barley plants.
3. Effect of interaction between salinity and salicylic acid foliar spraying
The application of potassium silicate alleviates the harmful effects of salinity on plants. Under each salinity concentration, the application of potassium silicate at 1 and 2 mM enhanced the vegetative growth parameters, chlorophyll pigments, relative water content percentage, the contents of proline and sugars, antioxidant capacity in term of scavenging ROS as indicated by DPPH (antioxidant activity) and the antioxidant enzymes, i.e. APX, CAT and POX as compared to control treatments. Under all salinity concentrations in grain sorghum and barley plants, the highest values of the H2O2 (oxidative stress) were obtained at the control treatment of potassium silicate.
Respecting the minerals content, under each of salinity concentrations, the application of potassium silicate at 1 and 2 mM significantly enhanced the K and Si percentages, while it decreased the Na % in grain sorghum and barley plants.
In regard to yield attributes, the application of potassium silicate at 1 and 2 mM under each salinity concentration significantly increased the grain yield/plant, panicle weight and spike weight for grain sorghum and barley plants.
In conclusion, this study demonstrated that the salinity concentrations decreased the vegetative growth parameters, relative water content percentage, the contents of proline, sugars and photosynthetic pigments in leaves. Also, it decreased the percentages of K and Si while increased Na, oxidative stress (H2O2) and yield attributes. While the application of potassium silicate foliar sprayings at 1 and 2 mM alleviates the negative effects of salinity on grain sorghum and barley plants under the same salinity concentrations. This study recommends to apply foliar sprayings of potassium silicate at 1 mM on grain sorghum and 2 mM to barley plants watered by saline water under sandy soil condition to obtain the highest yield/plant.