الفهرس 
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Abstract
V. SUMMARY
A field trial was carried out at the Experimental Farm of Sakha Agricultural Research Station, Kafr El-Sheikh Governorate, Egypt in the two successive seasons of 2006/2007 and 2007/2008 to study the influence of mineral nitrogen rate and bio-nitrogen fertilizer under three sowing dates on the yield, its components and juice quality of sugar beet crop.
Each sowing date included 9 treatments, which were the combinations between three mineral nitrogen fertilizer rates (30, 60 and 90 kg N/fed) and three sources of bio-N fertilizer (inoculation with Azospirillum, Bacillus N-fixers bacteria and untreated (control)).
Nitrogen fertilizer was applied as urea (46% N) in two equal doses, the first one after thinning (45 days from sowing) and the second one at one month later.
Sugar beet seed was inoculated by the examined bacteria through the following method: Seed of sugar beet variety Montebianco was mixed with a glue solution and the specific bacteria and left in unsunny place till be dried before sowing it.
The nine combinations of mineral nitrogen and bio-fertilizer source were arranged in randomized completely block design with three replications was used. Plot area was 17.5 m2, which consisted of 5 ridges of 7 m in length and 50 cm in width, with 20 cm distance between hills. A combined analysis for the three sowing dates over the two seasons was done.
At harvest (210 days from sowing), a sample of five plants was taken at random to determine the following characteristics:
a. Yield and its components:
1. Root length (cm).
2. Root diameter (cm).
3. Root fresh weight g/plant.
4. Top fresh weight g/plant
5. Root dry weight percentage/plant.
6. Top dry weight percentage/plant
At harvest four guarded rows were harvested, topped, cleaned and the following criteria were recorded:
7. Root yield (t/fed).
8. Top yield (t/fed).
9. Sugar yield (t/fed).
b. Juice quality:
10. Total soluble solids percentage.
11. Sucrose percentage.
12. Purity percentage.
c. Chemical constituents:
13. Nitrogen percentage in roots and tops.
14. Potassium and sodium percentages in roots and tops.
15. Nitrogen uptake of root (kg/fed).
16. Nitrogen uptake of tops (kg/fed).
17. Potassium uptake of root (kg/fed).
18. Potassium uptake of tops (kg/fed).
19. Sodium uptake of root (kg/fed).
20. Sodium uptake of tops (kg/fed).
Results could be summarized as follows:
1. Effect of season:
1. Results revealed that root length and diameter, fresh weight/plant and root dry matter were insignificantly affected, while top fresh weight and dry matter were significantly affected by the growing season at harvest.
2. Root, top and sugar yields were insignificantly affected by the growing season at harvest.
3. Purity percentage was significantly affected by the growing season, whereas, total soluble solids and sucrose percentages were not affected.
4. Percentages of nitrogen, potassium and sodium in roots and top, as well as nitrogen, potassium and sodium uptakes of root were not affected by the growing season, while the values of potassium and sodium uptakes of top were significantly affected by the growing season.
2. Effect of sowing date:
1. There was insignificant difference between sowing on 15th of September and 15th October in their effect on root diameter, fresh weight and top fresh weight/plant. While root length was significantly increased by sowing sugar beet on 15th of October, in the second season and the combined. The greatest values of root and top dry matter percentages were recorded in case of sowing beets on 15th of September, while delaying sowing dates from 15th September to 15th October reduced their values.
2. The earlier and middle sowing dates (15th September and 15th October) recorded better root yield/fed than that attained at the late one (15th November) in the two seasons and their combined analysis.
3. The early sowing date on 15th September had the greatest top yield/fed, while the late one (15th November) gave the lowest value of this trait, in both seasons and their combined analysis.
4. The highest sugar yield/fed was recorded with both early sowing dates (15th of September and October) without significant difference between them, in both seasons and their combined analysis.
5. The combined analysis of the two seasons showed that delaying sowing to 15th November attained a positive response in total soluble solids percentage, while the highest values of sucrose and purity percentages were recorded with the early sowing on 15th September.
6. Sugar beets sown earlier on the 15th of September contained the lowest nitrogen, potassium and sodium percentages, while the highest values were recorded with the latest sowing date on 15th November, in both seasons and their combined analysis.
7. In both seasons and their combined, nitrogen content in top decreased significantly and gradually by delaying planting date from 15th September to 15th October and to 15th November.
8. Differences in potassium and sodium contents in sugar beet top did not reach the 5 % level of significance in case of sowing sugar beet on 15th September and/or 15th October, in both seasons and their combined analysis.
9. Values of nitrogen uptake in root increased significantly with planting dates of 15th October followed by 15th September and 15th November, respectively, in both seasons and their combined analysis.
10. The lowest values of nitrogen, potassium and sodium uptakes in top were recorded by sowing sugar beet on 15th November. The difference between 15th October and 15th November reach to significance in their influence on these traits, in the two seasons and their combined analysis.
11. The effect of the interaction between sowing date and season was insignificantly on the most criteria, except purity percentage, nitrogen concentration of root and nitrogen uptake of top.
3. Effect of mineral nitrogen fertilizer rate:
1. In both seasons and their combined, increasing nitrogen fertilization level from 30 up to 90 kg N/fed increased root length, root and top fresh weight/plant. However, the differences between both (60 and 90 kg N/fed) were significant in their effect on these traits compared with 30 kg N/fed. Root and top dry matter/plant were increased as nitrogen rate increased from 30 to 60 up to 90 kg N/fed.
2. Increasing nitrogen fertilization rate from 30 to 90 kg N/fed statistically increased root yield ton/fed. Application of 60 kg N/fed was enough to produce the favorite yield and additional increment in root yield amounted to 44.1 %, 42.18 % and 42.94 % over than gained by applying 30 kg N/fed treatment in the first, second seasons and their combined analysis, respectively.
3. The results appeared that top yield gradually increased with increasing dose of nitrogen up to 90 kg N/fed, in the two seasons and their combined analysis.
4. Increasing nitrogen fertilizer from 30 to 60 and 90 kg N/fed raised the values of sugar yield by 65.52 % and 70.09 % in the first season, 59.93 %; by 71.30 % in the second season and by 62.41 % and 96.64 % in the combined over the both seasons.
5. Nitrogen fertilization rate of 90 kg N/fed surpassed both other rates (30 and 60 kg N\fed) in sucrose and purity percentages, while the highest value of total soluble solids percentage was recorded with application of 30 kg N/fed, in the two seasons and their combined analysis.
6. Nitrogen content in root was significantly increased as the applied dose of nitrogen fertilizer increased in both seasons and their combined. Potassium and sodium contents in root were insignificantly affected between 30 and 60 kg N/fed in the combined. Based on these results, it could be recommended by nitrogen application to decrease the impurities (potassium and sodium) consequently increased sugar extraction.
7. Application of 90 kg N/fed attained a significant increase in the values of nitrogen content in the top. However, application of 30 kg N/fed was enough to produce the highest contents of potassium and sodium in top of sugar beet in both seasons and their combined analysis.
8. Nitrogen uptake in root significantly with increasing nitrogen fertilizer rate. However, potassium and sodium uptakes in root insignificantly responded to the applied rates between 60 and 90 kg N/fed, in the two seasons and their combined analysis.
9. Increasing nitrogen application tended to increase the values of nitrogen, potassium and sodium uptakes in top of sugar beet plants in the two seasons and their combined analysis.
10. The studied characters were insignificantly affected by the interaction between mineral nitrogen fertilizer rate and season, except nitrogen uptake in root was significant.
4. Effect of bio-nitrogen fertilizer source:
1. The combined analysis of the two seasons showed that inoculation of sugar beet seed with Azospirillum brasilense gave the highest root fresh weight/plant, root dry matter and top dry matter and surpassed that inoculated with Bacillus polymyxa and check treatment.
2. The highest value of root dry matter significantly increased by inoculation of sugar beet seed with Azospirillum brasilense, while the lowest ones were recorded by the un-inoculated, in both seasons and their combined analysis.
3. Inoculation of seed with Azospirillum brasilense increased root yield by 7.73%, 7.52% and 7.65%, corresponding 11.14%, 6.15% and 8.67% when inoculation with Bacillus polymyxa higher than that produced without inoculation in the first, second seasons and their combined, respectively.
4. Inoculation of seed with Azospirillum brasilense gave the greater top yield/fed than that produced without inoculation and Bacillus polymyxa by 1.45 and 0.48 ton/fed in the combined, respectively. Sugar yield as a result to inoculation by Azospirillum brasilense reached 16.71%, 13.92% and 15.31%, corresponding to 18.51%, 10.38% and 14.54% when inoculation of seeds with Bacillus polymyxa higher than that control treatment, in the first and second seasons and their combined analysis, respectively.
5. In the first, second seasons and their combined, respectively, inoculation of seed with Azospirillum brasilense significantly raised the values of sucrose percentage over that of control (without bio-fertilizer) amounted by 9.19%, 7.48% and 8.31%, while, inoculation with the same inoculation significantly raised the values of purity percentage over that of control amounted by 15.67%, 6.38% and 3.83%.
6. Sucrose and purity percentages reach the level of significance between inoculation of seed with Azospirillum brasilense and/or Bacillus polymyxa compared with control treatment in both seasons and their combined analysis.
7. The highest value of nitrogen content and the lowest values of potassium and sodium in roots were recorded by inoculation of seed with Azospirillum brasilense, while, the highest values of potassium and sodium in roots were recorded without bio-fertilization, in the two seasons and their combined analysis.
8. The lowest value of potassium in top was recorded by inoculation of seed with Azospirillum brasilense, while the lowest value of sodium in top was recorded by inoculation of seed with Bacillus polymyxa in both seasons and their combined analysis.
9. Nitrogen uptake in root was significantly increased by inoculation of seed with Azospirillum brasilense followed by Bacillus polymyxa. Sodium uptake in root recorded the lowest value by inoculation seed with Azospirillum brasilense in both seasons and their combined analysis.
10. Nitrogen, potassium and sodium uptakes in top among the studied bio-fertilizer were significant compared without inoculation, in the two seasons and their combined, except the second season for potassium uptake in top.
11. The studied characters were insignificantly affected by the interaction between bio-nitrogen fertilizer source and season, except root length, root fresh weight; as well as total soluble solids and purity percentages.
5. Interaction effects:
5. a. Effect of interaction between sowing date and mineral nitrogen fertilizer rate:
1. In both seasons and their combined, the highest values of root diameter were recorded with 90 kg N/fed with 15th September sowing date. The difference combination between 60 or 90 kg N/fed and 15th September sowing date was significantly responded on root length compared with the interaction between 30 kg N/fed with the same sowing date, in both seasons and their combined analysis.
2. The difference values of top yield between sowing date 15th September or 15th October were significantly whether the sugar beet plants fertilized by 60 or 90 kg N/fed compared with the delaying date as the same rates of fertilization, in the two seasons and their combined analysis.
3. Increasing the applied nitrogen fertilizer up to 90 kg N/fed caused a relative increase in sucrose in the two seasons and their combined. However, the difference between the nitrogen rate (60 kg N/fed) and the sowing date on (15th September or 15th October) was significantly in their influence on sucrose compared with the sowing date on 15th November as the same rate of fertilization, in both seasons and their combined analysis.
4. Results showed that even under the same nitrogen rate, delaying sowing date from 15th September to 15th October and 15th November increased the values of nitrogen percentage in root.
5. The results obtained cleared that sodium percentage of top significantly affected by the different combination between nitrogen rate and sowing date in the two seasons and their combined analysis.
6. The highest values of nitrogen uptake in roots were recorded with sowing sugar beet on 15th October with 90 kg N/fed in the two seasons and their combined analysis.
7. The middle nitrogen rate (60 kg N/fed) attained the highest values of sodium uptake in top of sugar beet plants sown on 15th September in the second season and the combined analysis.
8. With the exception of nitrogen percentage and nitrogen uptake in roots, the other traits showed insignificant differences due to the effect of interaction between sowing dates, mineral nitrogen fertilizer rates and seasons.
5. b. Effect of interaction between sowing date and bio-nitrogen fertilizer source:
1. Root length was significantly increased by the effect of interaction between sowing date of 15th September and inoculation of seed with bio-fertilizers compared without inoculation.
2. Inoculation of sugar beet seed with bio-fertilizers appeared a distinct effect on root and sugar yields in both early sowing dates (15th September and 15th October) compared by control treatment in both seasons and their combined analysis.
3. The highest values of purity percentage were recorded with sown sugar beet on 15th September and/or 15th October compared by sown on 15th November under inoculation of seed with bio-fertilizers in the two seasons and their combined analysis.
4. The lowest values of sodium percentage in roots were recorded with inoculation of seed with Bacillus polymyxa under the first sowing date i.e. 15th September; this observation was true in the two seasons and their interaction.
5. The effect of interaction between sowing date, bio-nitrogen fertilizer source and season was insignificant on root length, root and sugar yields as well as purity and sodium percentages.
5. c. Effect of interaction between mineral nitrogen fertilizer rate and bio-nitrogen fertilizer source:
1. The highest root diameter and top yield were recorded with the combination between 90 kg N/fed with inoculation of sugar beet seeds with Azospirillum brasilense, but it was not enough to reach the level of significance between 60 and 90 kg N/fed. in both seasons and their combined analysis.
2. The highest values of sucrose percentage was found with the combination between 90 kg N/fed with inoculation of seeds with Azospirillum brasilense, in both seasons and their combined analysis.
3. Using nitrogen fertilizer and/or nitrogen fixation bacterial sources attained a significant increase in the percent of nitrogen in sugar beet top.
4. Using rates up to 90 kg N/fed with inoculation of sugar beet seeds with Bacillus polymyxa were still suitable to attain a distinct increment in the values of purity percentage in the second season and the combined analysis.
5. With the exception of nitrogen percentage in top, the other traits showed insignificant differences due to the effect of interaction between mineral nitrogen fertilizer rates, bio-nitrogen fertilizer sources and seasons.
5. d. Effect of interaction among sowing date, mineral nitrogen fertilizer rate and bio-nitrogen fertilizer source:
1. The highest value of sucrose percentage recorded by the early sowing date (15th September) with 90 kg N/fed under inoculation of seeds treatment with Bacillus polymyxa as a fixation to nitrogen element, in both seasons and their combined analysis.
2. The lowest value of nitrogen percentage was recorded under sown on 15th October with 30 kg N/fed with out bio-fertilizer treatments, in the two seasons and their combined analysis.
3. The highest values of nitrogen uptake in top were recorded when the plant had fertilized with 90 kg N/fed and Azospirillum brasilense inoculation sugar beet seeds under sowing date on 15th September, in the first season and the combined analysis.
4. The effect of interaction between sowing dates, mineral nitrogen fertilizer rates, bio-nitrogen fertilizer sources and seasons was insignificant on sucrose percentage, nitrogen percentage in root and nitrogen uptake in top.
6. Correlation study:
Results cleared that root yield/fed, top yield/fed, root fresh weight/plant, top fresh weight/plant, sucrose percentage and purity percentage recorded a positive correlation with sugar yield.
Conclusion
According to the presented resulted from this investigation, it can be concluded that sowing dates on 15th September and/or 15th October with applying 60 or 90 kg N/fed and inoculated sugar beet seed with bio-nitrogen fertilizer sources (Azospirillum brasilense and/or Bacillus polymyxa) could be recommended for maximizing sugar beet productivity.
Inoculation of seed sugar beet with Bacillus polymyxa and applied 90 kg N/fed in the first sowing date (15th September) gave the highest values of sucrose percentage. On the other hand the highest sucrose percentage was obtained by sowing date of sugar beet on 15th October with applied 90 kg N/fed and mixed bio-fertilizer Azospirillum brasilense. The above mentioned results could be responded under Kafr El-Sheikh Governorate.