الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
A field experiment was carried out during 2017 and 2018 seasons at the Agronomy Department Experimental Farm, Agriculture Faculty, Assiut University to study the effect of foliar spray time by different zinc oxide nanoparticles (ZnO NPs) concentrations on production of maize. The experiment was laid out in randomized complete block design (RCBD) using strip plot arrangement with three replications. Zinc oxide nanoparticles concentrations (control (tap water) 100, 200 and 300 ppm) and were allocated horizontally, while, application time (8-10 leaves, tasseling and grain filling stages) were arranged vertically. Each Experimental unit area was 10.5 m2. White single cross Hybrid (S.C.128) grains were hand sown on 6th and 11 June in the first and second seasons, respectively. Grains were sown in rows 80 cm apart with hills spaced 25 cm. Plants were thinned after complete emergence before the first irrigation leaving one plant per hill. Maize plants were sprayed by the certain concentration of ZnO NPs at the mentioned stages. The preceding winter crop was wheat in both seasons. All other cultural practices recommended for maize crop were done in both seasons. The obtained results can be summarized asfollows:
1- Plantheight (cm)
The exhibited data reveal that the tested zinc nanoparticles concentrations had a non-significant effect on maize plant height in both seasons. While, the applications time had a significant influence on plant height in the first season only. Zinc oxide application at tasseling stage surpassedtheothersapplicationstimeinthisrespectandrecordedthe tallest maize plants (218.81 and 207.25 cm in the two respective seasons). In addition, the interaction between ZnO NPs concentrations and applications time failed to be significant at 5 % level of probability on maize plant height in the two growing seasons. Whatever, the highest mean value of plant height in the first season (223.77 cm) was registered from maize plants which were sprayed by 100 ppm of ZnO NPS concentration at tasseling stage. While, the highest mean value of plant height in the second season (211.00 cm) was registered from maize plants which were sprayed by water (without ZnO NPs) at grain fillingstage.
2- Number of leavesplant-1
It is clear from the obtained data that the applications time had a significant influence on number of leaves per plant in the second season only. The highest mean value of leaves number per plant (12.41) was recorded from maize plants which were sprayed at tasseling stage. interaction between zinc oxide nanoparticles concentration and applications time had a significant effect on number of leaves plant of maize in the first season only. Thus, the highest mean value of leaves number plant (12.85 leaf/ plant) was recorded from maize plants which were sprayed by 100 ppm ZnO NPS at 8-10 leavesstage.
3- Leaf area index(LAI)
The obtained data show that the applications time had a significant influence on leaf area index in the first season only. The maximum LAI mean value in first season (3.51) zinc oxide application at 8-10 leaves stage. interaction between zinc oxide nanoparticles concentration and applications time had a significant effect on LAI trait in the first season only. Thus, the maximum LAI mean value in the first season (4.25) was registered from maize plants which were sprayed by 200 ppm zinc oxide nanoparticles at early growth stage (8-10 leaves stage).
4- Stem diameter (cm)
Illustrated data show that the interaction between ZnO NPs concentrations and applications time in this respect failed to be significant at 5 % level of probability in the two growing seasons. Whatever, the mean values of stem diameter trait (1.58 and 1.42 cm in the first and second seasons, respectively) were obtained from maize plants which were sprayed by tap water (control) at 8-10 leaves stage in the first season, and sprayed by tap water at grain filling stage in the second season.
5- Ear length(cm)
The exhibited data focus that the interaction between studied zinc nanoparticles concentrations and applications time in this respect failed to be significant at 5 % level of probability in the two growing seasons. Whatever, the highest ear length mean value (18.06 cm in the first season) was recorded from maize plants which were sprayed by 100 ppm zinc oxide nanoparticles at tasseling stage while, the corresponding value in the second season (18.88 cm) was achieved from maize plants which were sprayed by 100 ppm zinc oxide nanoparticles at 8-10 leaves stage.
6- Ear diameter (cm)
The obtained data reveal that the interaction between studied zinc nanoparticles concentrations and applications time in this respect failed to be significant at 5 % level of probability in the two growing seasons. Whatever, the highest ear diameter mean value (4.28 cm in the first season) was recorded from maize plants which were sprayed by tap water (control) at 8-10 leaves stage while, the corresponding mean value in the second season (4.23 cm) was achieved from maize plants which were sprayed by 200 ppm zinc oxide nanoparticles at 8-10 leaves stage.
7- Number of rowsear-1
The obtained data show that the interaction between studied zinc nanoparticles concentrations and applications time in this respect failed to be significant at 5 % level of probability in the two growing seasons. Whatever, the highest number of rows ear-1 mean value (14.30 row ear-1 in the first season) was recorded from maize plants which were sprayed by tap water (control) at grain filling stage while, the corresponding mean value in the second season (13.10 row ear-1) was achieved from maize plants which were sprayed by 100 ppm zinc oxide nanoparticles at 8-10 leaves or grain filling stages.
8- Grains numberrows-1
The exhibited data show that the studied zinc application time had number of grains per row of maize the second season ,the highest mean value of grains per row (38.23)was recorded from maize plant which were received zinc oxide nanoparticles at 8-10 leaves stage. Interaction between studied zinc nanoparticles concentration and applications time in this respect failed to be significant at 5 % level of probability in the two growing seasons. Whatever, the highest number of grains row-1 mean value (35.40 grain row-1 in the first season) was recorded from maize plants which were sprayed by 100 ppm of zinc oxide nanoparticles (ZnO NPs) at tasseling stage while, the corresponding mean value in the second season (39.40 grain row -1) was achieved from maize plants which were sprayed by 100 ppm zinc oxide nanoparticles or tap water at 8-10 leaves stage.
9- Seed index(g)
The data exhibited reveal that the interaction between studied zinc nanoparticles concentrations and applications time in this respect failed to be significant at 5 % level of probability in the two growing seasons. Whatever, the highest seed index means values (35.22 and 33.75 g in the two respective seasons) were recorded from maize plants which were sprayed by tap water (control) at tasseling stage and 8-10 leaves stage.
10- Grains weight plant-1 (g)
The obtained data reveal that the application time of zinc oxide nanoparticles had a significant effect on grime weight per plant trait in the first season only. Interaction between studied zinc nanoparticles concentrations and application time in this respect failed to be significant at 5 % level of probability in the two growing seasons. Whatever, the highest grains weight plant-1 mean value in the first season (146.36 g ) was recorded from maize plants which were sprayed by 300 ppm of zinc oxide nanoparticles (ZnO NPs) at tasseling stage while, the corresponding mean value in the second season (146.77 g) was achieved from maize plants which were sprayed by 100 ppm zinc oxide nanoparticles at 8-10 leaves stage.
11- Grains yield fed.-1(Kg)
The obtained data illustrated that the application time of zinc oxide nanoparticles had a significant effect on grime weight per plant trait in the two seasons. Interaction between studied zinc nanoparticles concentrations and applications time in this respect failed to be significant at 5 % level of probability in the two growing seasons. Whatever, the highest grain yield fed.-1 mean value in the first season (3090.00 kg ) was recorded from maize plants which were sprayed by 100 ppm of zinc oxide nanoparticles (ZnO NPs) at tasseling stage while, the corresponding mean value in the second season (3846.00 kg) was achieved from maize plants which were sprayed by 200 ppm zinc oxide nanoparticles at 8-10 leaves stage.