Response of Sugar Beet Yield to Deficit Irrigation under Drip Irrigation System

Abstract

A field experiment of drip-irrigated sugar beet (Beta vulgaris, L.)was conducted at the research field of the Nubaria Agricultural Research Station, Egypt at 30° 54' 21'' N, 29° 52' 15'' E and 11.0 m altitude above mean sea level during 2011/2012 growing season.The aim of the present study was to evaluate the impact of deficit irrigation on sugar beet productivity, and quantitative and qualitative characteristics of sugar beet root yield under drip irrigation. The sugar beet (Beta vulgaris, L) variety Gloria (polygerm) was planted on 13 October 2011. Sugar beet plants were thinned to one plant at distance of about 0.3 m on the rows at the 4th week after planting. After emergence, the plots were irrigated by the drip irrigation method.The present study consisted of 5 treatments. The irrigation treatments were based on replenishment of soil water depletion according to reference evapotranspiration (ET0). The irrigation treatments were: Irrigation at 40, 60, 80, 100 and 120% of ET0. Sugar beet vegetative growth, sugar beet yield and yield components, and juice quality and impurities content were determined. The results clearly indicated a significant effect of different irrigation regimes on all sugar beet growth characters except leaf area per plant and foliage water content as compared with control (100% of ET0). The results alsoclearly indicated a significant effect of irrigation regimes on sugar beet yield and yield components. Irrigation at 40% of ET0 gave a highest value of root length (32.7cm) and root diameter (13.0 cm), but 60 % of ET0 gave the highest values of average root fresh weight (1500 g/plant) and root gross yield (100.0 ton/ha). The highest value of root/top ratio (1.31) was attained at irrigation with 120% of ET0. The percent increase of root gross yield of sugar beet at 60% of ET0 was account as 49.99%, for gross sugar yield was 45.66% and for white sugar yield was 44.16% over the common treatment (100% of ET0). The different irrigation regimes significantly affected the juice quality and impurities contents of sugar beet. Irrigation at 40 and 60% of ET0 gave the highest value of TSS (total soluble solids), 23.0%, white sugar yield (13.71 ton/ha), gross sugar yield (16.97 ton/ha) and loss sugar yield (3.26 ton/ha) were attained at 60% of ET0. The highest values of polarity or sucrose content (17.76 %), effective polarimetric assay of sugar (15.46%),thick purity juice, TPJ (90.66%), white sugar content (14.94%) and juice purity (84.13%) were attained at 60% of ET0. The increase in sugar yield was due to both increase in sugar content and root yield in which sugar yield was adversely affected by water deficit. Increasing the impurities in the root of stressed plants decreased extraction of white sugar. So, deficit irrigation improved sugar beet quality by reducing these impurities. The findings in this study strongly recommend that up to 60% deficit irrigation of sugar beet would be advantage if the farmers target is to maximize root and white sugar yield. But if the target is to put more area into production under limited water supply, irrigation at 40% of reference evapotranspiration in sugar beet may be feasible.