Interactive Effects of Gibberellic Acid and Nitrogen Fertilization on the Growth, Yield, and Quality of Sugar Beet

Two field trials were conducted during the 2014/2015 and 2015/2016 seasons at Aweesh Al-Hagar Village, center of Mansoura, Dakahlia Governorate, Egypt. A split-split-plot design with four replicates was used. The main plots were assigned three nitrogen fertilizer levels, i.e., 165, 220, and 275 kg/ha. The sub-plots were restricted to four gibberellic acid (GA3) concentrations, i.e., 0, 80, 160, and 240 mg/L, and the sub-sub plots received GA3 application twice, i.e., 60 and 120 days after planting (DAP). The results showed that both root length and diameter, root and foliage fresh weights/plant, and root and foliage yields/ha increased with the incremental level of nitrogen and/or GA3 concentration. Foliar application of GA3 and N-fertilizers also significantly decreased quality parameters including sucrose and total soluble solid (TSS) percentages. Early application of GA3 (60 DAP) had an active role on sugar beet growth, yield, and quality compared with spraying at 120 DAP. Generally, fertilizing sugar beet with 275 kg N/ha or spraying GA3 with a concentration of 160 mg/L at 60 DAP is the recommended treatment for raising sugar yield under the ecological circumstances of this research.