Water and Radiation Use Efficiency of Winter Sugar Beet Affected by Nitrogen, Irrigation and Growth Duration Management

For investigating the effect of plant growth duration, irrigation and nitrogen mangement on radiation and irrigation water use effeiciency of autumn-sown sugar beet three independent ijeld experiments were conducted during 2003-4 and 2004_5. Loocation of all experiment were Safi-Abad Agric. Res. Center in Kuzestan south-west of Iran. In the first experiment (growth duration), treatments were three planting dates, (Sep. 27, Oct. 14 and Nov. I), two harvesting (dates, 219 and 235 days after emergence (DAB)), and two monogerm varieties (Shirin and Rasol), The experimental design was a split-split plot design replicated four time. In the second experiment (irrigation) water applied (ranged om 25, 50, 75, 100 and 125% of the plant water requirement (PWR)), by drip irrigation system and sugar beet varieties were Shirin and Raso!. The experimental design was split plot with four replication in which water supply was main plot and varieties the subplot. In third experiment (nitrogen) five nitrogen rates (0, 60, 120, 180 and 240 kg.ha01) ,and two monogerm sugar beet varieties (Shirin and Rasol) arranged as factorial in a raridomized block design with four replication. The results of growth duration experiment showed that planting date had significant effect on root and sugar yield, irrigation water use efficiency (IWUE) at I % probability and root potassium and sodium at 5% probability level. The highest root and sugar yield, IWUE for root and sugar obtained by planting at Oct. 14 (83.6, 11.1 t.ha-I , 12.3 and 1.63 kg/m3, respectively). Harvesting after 235 DAB produced higher root and sugar yield (79 and ]].2 Lha-I respectively), whereas harvesting after 219 DAE had higher IWUE for root and sugar (11.2 and 1.5 kglm3 respectively). There were no significant differences between two varieties for all traits. Among different growth duration periods planting at Oct. 14 and harvesting after 235 DAE produced higher root and sugar yield (86.3 and 11.6 t.ha"1 respectively). But planting at Oct. ]4, and harvesting after 2]9 DAE had higher IWUE for root and sugar (13.2 and 1.7 kglm3 respectively). The effect of planting and harvesting date and interaction of them were significant (at I %) for radiation use efficiency (RUE). The highest Rue(1.35 J.tg.r') produced by planting on 27 Sep., and ~arvesting in 215 days after emergence(DAE). Planting in Sep. 27 Or Oct. 14 and harvesting at 235 DAE reduced RUE relative to harvesting at 215 DAE, while this was reverse for planting in Nov. 1. In irrigation experiment, differences among water supply was significant for root yield, a-N, alkali, and lWUE for root and sugar yield. Increasing of water volume taised root yield and alkali and reduced IWUE for sugar and root yi~ld. The 100 and 25% PWR produced the highest (84t/ha) and the lowest (76t1ha) root yield, respectively. The 25% PWR had the highest IWUE for Root and sugar yield which were 18.7 and 2.6 kg/m3, respectively. There were no significant differences between varieties for all yield parameters. There was no significant differences between irrigation treatments for RUE. In the first year of nitrogen experiment, nitrogen had not significant effect on root yield (mean of five rates were 93 t/ha) but changed sugar content significantly. The treatment NO had the highest sugar content (13.7%). In the second year root yield influenced significantly by nitrogen and the treatment ~240 produced the highest root yield (80.9t/ha) whereas sugar content did not change significantly. There were no significant differences between two varieties for all yield parameters in two years. All nitrogen rates had same leaf number and leaf area and canopy closing date during first year. However during second year increasing nitrogen enhanced canopy closing date and raised leaf number and leaf area. Nitrogen use efficiency decreased with increasing of nitrogen in both years. There were no significant differences between nitrogen rates for RUE ..