الفهرس 
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Abstract
Four Azospirillum strains (As1, As2, As3 and As4) and three yeast isolates (A, B, and C) were isolated from rhizosphere soil of wheat plants growing on soil Experimental Farm of Soil and Water Department, Assiut University.
The Azospirillum strains were isolated using the Nitrogen Free Bromothymal Blue (Nfb) semi solid medium; and the Malt Extract Peptone Glucose agar medium (MEPG) for yeast isolation.
The morphological, cultural and physiological characteristics of the isolated Azospirillum strains were examined to variety their identity to these reported in Bergey’s Manual of Determinative Bacteriology (1994). Also, the nitrogen fixing capacities of the isolated strains were determined, by micro kjeldeh’s technique (Jackson, 1973), and ranged from 13.8 to 42.5 mg N2-fixed / g malic acid used, and the most active isolated strains in fixing N2 (As.2 and As.4) were chosen for microbial grain inoculation under field conditions.
The three isolated yeast strains were examined for morphological characteristics by light microscope, and their capacities of acid production were determined on three different media; and their abilities of solubilizing CaCO3 were tested on MEPG agar medium containing 0.5% CaCO3; and for solubilizing Ca(PO4)2, on Pikoviska agar medium. Yeast strain B. was selected for use in grain inoculation studies under field conditions because of its highest acid production and its ability of solubilizing calcium carbonate and calcium phosphate
Also, the early promotive stimulating effects of the selected Azospirillum strains (As2 and As4) and the yeast strain B were tested in Lab for their stimulation of wheat grain germination and early seedling growth, on Nfb agar medium in petri plate.
Field experiment on wheat, T. aestivum, cultivare Gemmiza 11 for testing response to different N-fertilization levels and microbial grain inoculations.
The field experiments were conducted on wheat cultivar Gemmiza 11 on winter seasons of (2018/19) and (2020/21), The planted wheat grains in the first season were obtained from Agronomy Dept., Assiut University. But, in the second season the planted Gemmiza 11 grains were purchased from Seed Bank of Ministry of Agriculture at Assiut, and the grains were found heavily dusted with fungicide, that necessicate washing them three times with tap water to remove the dusted fungicide before microbial grain inoculation or planting.
The two field experiments on wheat were conducted to test response of wheat growth and yield, to two factors: 1- different levels of nitrogen fertilization (60, 80, and 100 kg N/fad.) in season (2018/19) and response of (60 and 80 kg N/fad.) in season (2020/21), added in urea form (N 46%). 2-The effect of application of elemental sulfur to soil, and to the microbial inoculation treatments: Azospirillum, yeast, and to (sulfur+Azospirillum+ yeast), compared to untreated control.
The experimental design was randomized complete block design (RCBD) of the two tested factors:
1- The N-fertilization levels in main plots.
2- The untreated control, or sulfur application or microbial inoculation in the subplot, with four replications. The area of the subplot 1/400 fad. and the wheat grains were planted broadcast at a rate of 150 g/subplot, (60 kg /fad.).
Elemental powdered sulfur was added at rate of 500 g/subplot at surface soil and mixed well with surface soil before planting the grains.
Microbial inoculation of the grains was made by adding 15gm of the inoculated peat moss carrier to 150gm grains in polyethylene bag plus 2 ml of Arabic gum solution, and mixed well before broadcast planting the grains on surface of the soil.
Numbers of viable microbial cells/g of inoculated peat moss were determined before use for grain inoculation, for yeast by plate colony count on Malt extract peptone glucose agar medium (MEPG), whereas, by most probable number (MPN) for Azospirillum using Nfb semi solid medium
The results of plant samples at 80 days from sowing showed that no significant differences were recorded in vegetative growth of plants; fresh or dry weights, or no. of tillers/plant due to the tested N-fertilization Levels (60, 80, 100 kg N/fad. in first season; or to the tested N fertilization rates (60, 80 kg N/fad.) in second season (2020/21).
But, the microbial grain inoculation treatments (with Azospirillum or yeast) or soil S0 application resulted in significant increases in plant roots and shoots in both seasons, as well as in no. of tillers/plant in the first season (2018/19).
Also, microbial grain inoculations, particularly with yeast, and soil S0 application resulted in significant reductions soil pH at the 80 days sample.
At harvest, grain, straw and total yields obtained of wheat Gemmiza 11 in field experiment of (2020/21) were much higher than those obtained in season (2018/19).
Total yields obtained in season (2020/21) ranged from 13480.5 kg/fad. to 14848.7 kg/fad. whereas those obtained in season (2018/19) ranged from 8470.6 kg/fad. to 9881.9 kg/fad. in (2018/2019).
Also, the grain yields obtained in season (2020/21) ranged from 3660.6 to 4516. 3 kg/fad., and were much higher than those obtained in season (2018/19), ranged from 2633.5 to 3394,0 kg/fad. These differences in total and grain yields in the two growing seasons are probably due to variation in environmental condition prevailing during the winter season of wheat growth.
In both planting seasons, the highest significant grain and total yields of wheat, and highest P % in grains were obtained in the N-fertilization level of 80 kg N/fad.
Soil sulfur application in both season resulted in highest significant increases in grain, straw and total yields, as well as in N % in grains and total uptake and weight of 1000 grains.
Azospirillum grains inoculation resulted in both seasons in significant increases in grain and total yields, although the increases obtained in second season (2020/21) were much lower than these obtained by soil sulfur application.
Yeast grain inoculation in first field experiment of (2018/19) resulted in significant increases in grain and total yields obtained. But in second season (2020/21) yeast grain inoculation had no effect at all on wheat yields (grain, straw, or total).
The only recorded effect of yeast inoculation in second field experiment was the significant increase in P % in grains. These results may be attributed to washing of grain with tap water before microbial inoculation to remove the dusted seed coating fungicide. But, the remaining adsorbed fungicide in washed grains may have caused the failure of the inoculated yeast from growth and multiplication to dominate the microbial community around the washed grains, and thus did not result in significant improvements in plant growth or yields obtained.
The interactions between the tested N-fertilization levels and microbial grain inoculations, or soil sulfur application.
• In the first field experiment of season (2018/19), significant positive interactions were recorded between nitrogen fertilization, at any applied level, and Azospirillum or yeast grain inoculation or soil sulfur application alone or (S0+Azo+Y), that resulted in higher grain, straw and total yields of wheat, cultivar Gemmiza 11.
• Also, significant increases in N % in grains, and total uptake of N/fad. were recorded in the Azospirillum inoculation treatment at any N-fertilization level (60, 80, or 100 kg N/fad. highest increases in grain, straw and total yields of wheat were obtained by Azospirillum inoculation were obtained at 80 and 100 kg N-fertilization/fad.; with non-significant differences between them; and lowest with nitrogen application at 60 kg N/fad..
• But in the second field experiment of (2020/21), none of the grain inoculation treatments: Azospirillum, yeast, (alone or with S0) recorded significant interactions with N-fertilization at any level, or resulted in higher yields of grain, straw or total yields, or higher P % in grains, or total uptake of N or P kg/fad.
Only the sulfur application treatments (alone, or with Azo + y) recorded significant positive interactions with N-fertilization at any tested level.
The non-significant interactions of microbial grain inoculation with N-fertilization levels (60, 80kg N/ fad.) in this season are probably due to the small amount of fungicide remained adsorbed by the grains after washing with tap water, which could probably affect the multiplication and proliferation of the inoculated microbial strains and prevent them to from beneficial microbial communities around the germinated seeds.