Effect of N-fixing Bacteria on Nitrogen Fertilizer Requirements for some Sugar Beet Varieties

Two field trials were carried out at Tamiya Agricultural Research Station, (latitude of 29.58°N and longitude of 30.96°E), Fayoum Governorate,Egypt, during 2018/2019 and 2019/2020 seasons to study the relative importance of nitrogen-fixing bacteria i.e. Bacillus polymyxa (BC)and Azospirillum brasilense(AZS) as a soil drench under mineral nitrogen fertilizer levels and their effects on some sugar beet varieties. A split-plot design was used. Four treatments of nitrogen fertilization (80 kg N/fed ”control”, 60 kg N/fed + soil drench with BC, 60 kg N/fed + soil drench with AZS and 60 kg N/fed + soil drench with a mixture of BC and AZS) were occupied the main plots, whereas, six varieties (Beta303, Sirona, Panther,Des9003, Athospoly and Maximus) were distributed randomly in the sub-plots. Adding 60 kg N/fed + soil drench with a mixture of AZS and BC was adequate to produce the economical values of extractable sugar%, root and sugar yields/fed. Varieties Sirona and Maximus had the highest values of root and sugar yields/fed. Significant interactions effects among nitrogen treatments and varieties on the studied traits were discussed. Root and sugar yields/fed were significantly and positively correlated with leaf area index and crop growth rate, root diameter and its fresh weight/plant, in both seasons. Under the environmental conditions of this study, it was found that sowing Sirona and/or Maximus varieties under fertilization of 60 kg N/fed in combination with a mixture of BC and AZS at 5L/fed twice as a soil drench could be recommended to achieve the economical root and sugar yields/fed.