Response of Sugar Beet Yield and Water Use Efficiency to Deficit Irrigation and Weed Competition under Drip Irrigation System

Abstract

Under drip irrigation condition, two field experiments of sugar beet (Beta vulgaris L.) were conducted, in sandy soil, at El-Bostan area, Aly Mubarak Experimental Farm, Southern El-Tahrir Region, El-Buhira Governorate, Egypt, during 2013/14 and 2014/15 winter seasons, to evaluate the impact of water deficit irrigation and its relation with the critical period of weeds infestation on sugar beet yield, quality and water use efficiency. The experimental design was a split-plot design, where three water irrigation regimes treatments, i.e. 60, 80 and 100 % of evapotranspiration (ET0), were allocated in the main plots, and the ten weed removal intervals were allocated in the sub-plots which included five weed free for 3, 6, 9, 12 weeks after planting (WAP) and weed free the whole season, and five weed infestation for 3, 6, 9, 12 (WAP) and weed infestation for the whole season. The main findings indicated that the highest significant reduction on the fresh weights of grassy, broad-leaved and total weeds was obtained by irrigation at 60 % ET0 by14.8, 16.0 and 15.6 %, respectively, in 2013/14 season and 25.0, 13.6 and 17.3 %, respectively, in 2014/15 season, as compared to 100 % ET0, which reflected in increases on root and gross sugar yield per faddan by 58.8 and 60.2 %, respectively, in 2013/14 season and 65.5 and 40.1 %, respectively, in 2014/15 season, as compared to irrigation at 100 % ET0. Furthermore, water use efficiency of irrigation at 60% ET0 gave the highest values of root and sugar yield by 7.2 and 1.2 kg/m3, respectively, in the first season and 7.1 and 1.3 kg/m3, respectively, in second season. The dominant annual weeds were the broadleaf weeds with infestation rates 3.0 kg and 3.5 kg fresh weight /m2 in the first and second seasons, respectively. Whilst, the infestation rate of the grassy weeds was 1.3 kg and 1.4 kg fresh weight/m2 in the both seasons, respectively. In the both seasons, the highest reduction on the fresh weight of the two weeds categories and their total was obtained from all weed free and weed infestation treatments (> 90 %) as compared to weed infestation for the whole season, except with weed free for 3 weeks (< 70%). These results reflected on sugar beet yields (ton/fed). In the first season, the significant increasing on dry weight of tops, roots and the gross sugar yield (ton/fed) was between 118.6, 302.5 and 353.8 %, respectively, in weed free for the whole season to 58.5 % for tops by weed free for 3 weeks, 135.2 % for roots by weed free for 6 weeks and 50.0 % for gross sugar yield by weed infestation for 9 weeks, as compared to weed infestation for the whole season. In second season, the significant increasing on dry weight of the tops, roots and gross sugar yield (ton/fed) was between 98.8, 311.3 and 288.7 %, respectively, in weed free for the whole season to 37.5 % for the tops and 35.0 % for the roots in weed free for 3 weeks and 106.5 % in weed infestation for 6 weeks, as compared to weed infestation for the whole season. While, the rest weed free and weed infestation treatments in the both seasons didn't reach to significant increasing values. For sugar beet quality i.e. TSS, sucrose and purity %, all weed free and weed infestation treatments gave the same values approximately in deferent intervals. Also, different weed removal intervals can raise water efficiency by 240-320 % compared to leave the weeds to compete sugar beet plants for whole season. Concerning the interaction effects, the data indicated that the great reduction on the fresh weight of the two weed categories and their total was obtained from irrigation at 60 % ET0 with weed free for whole season, weed competition for 3 WAP and weed free for 12 WAP, in both seasons. Also, the interactions between both 60 and 80% ET0 irrigation regimes with both weed free for 12 weeks and the whole season gave the highest increasing on the roots and gross sugar yields (ton/fed) in the both seasons. The findings also revealed that the critical period of weed interference between 3 and 12 weeks after planting and the yield losses in this period. Thus, we can conclude that to save water irrigation and maximize root and sugar yields of sugar beet (ton/fed) must be irrigate at 60% ET0 with controlling weeds until 12 week from planting.