الفهرس 
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Abstract
Two field experiments were conducted out at the experimental farm,Faculty of Agriculture, Saba Basha, Alexandria University, Alexandria Governorate, Egypt, during the two seasons of 2018/2019 and 2019/2020 to study the effect of foliar application of different froms of silicon (Si) on some onion cultivars productivity and thrpis population under soil as affected by salts.A split plot design was used in the two field experiments, where the main plot was four onion varieties (Giza Red, Giza 20, Hybrid Red and Hybrid Yellow), while the sub plots was differnet silicon forms (water = control, nano silicon, silicon in tablets and silicon in powder form) in both seasons.Four varieties planted in the nurse by seeds on ridges at 29/9/2018 in the first season, and at 25/9/2019 in the second season, at rate of 5 kg seeds/fed and after 70 days transplanted at in experimental Field.Four varieties were transplanted on December 15th and December 10th in 2018 and 2019 seasons, respectively. The experimental plot size was (3.5 m long and 3 m Width). Recommended doses of nitrogen, phosphorus and potassium fertilizers were added at the rate of 90 kg N, 45 kg P2O5 and 48 kg KO2/fed., all other cultural practices for onion production in clay soil in Alexandria conditions were followed according Ministry of Agriculture and Land Reclamation.The important results summarized as followed:- The results obtained showed the significant effect of silicon forms on total chlorophyll content, plant height (cm), fresh weight (g/plant), dry weight (g/plant), number of leaves/plant and leaf length (cm), bulb weight (g), bulb yield (t/fed), total soluble substances (TSS), K (%) and Si contents (mg/kg) of the four onion varieties in 2018/2019 and 2019/2020 seasons.- Respecting to the four onion varieties, results revealed that onion varieties differed in all the studied characters i.e. total chlorophyll content, plant height (cm), fresh weight (g/plant), dry weight (g/plant), number of leaves/plant and leaf length (cm), bulb yield (t/fed), total soluble substances (TSS), K (%) and Si contents (mg/kg) except bulb weight (g) in both seasons, whereas Giza Red variety the tallest plants and the highest mean values of total chlorophyll content, dry weight, bulb yield, TSS (%),K (%) and Si content, on the other hand Giza 20 recorded the highest values of dry weight, number of leaves/plant, and leaf length with no significant with Giza Red variety and Giza 20 variety as compared with the other two varieties hybrid Red and Yellow in both seasons.