Effect of sowing date, planting density and cultivar on solar radiation interception indices in sugar beet. II. Radation use efficiency

In order to evaluate the effect of sugar beet sowing date, planting density and cultivar on solar radiation interception, a study was conducted in Kamal-Abad Agricultural Research Station of Sugar Beet Seed Institute (SBSI) in 2005 and 2006. The experimental design was split-split plots based on Randomized Complete Block Design (RCBD) with three replications with two sowing dates as the main plot (the earliest possible date including 04-April and 22-April in 2005 and 2006 and 40 days later including 23-May and 31-May in 2005 and 2006, respectively), four plant densities as the sub-plot (6.0, 7.5, 9.0 and 10.5 plants.m-2) and three sugar beet monogerm cultivars as the sub-sub-plot (Jolgah, Hybrid 428 and DS 4027). In terms of the effect of sowing date, it was shown that sugar beet sowing in Karadj at the earlist possible date (Mid-March) compared to the sowing date delayed for 40 days only led to an increase in intercepted radiation by 425 MJ.m-2; while radiation use efficiency (RUE) for producing dry matter which was in the range of 1.43-1.48 g.m-2 MJ-1 did not differ between the two sowing dates. The increase in plant density from 6.0 to 10.5 plants.m-2 led to a non-significant increase in intercepted radiation. RUE did not show a linear response to plant density, too; while the increase in plant density led to a decrease in radiation extinction coefficient and improvement of radiation distribution in canopy. The cultivar DS 4027 had better RUE than the cultivars Jolgah and Hybrid 428 (1.85 and 1.43 g.m-2.MJ-1, respectively). The main reason for this difference was the higher RUE of DS 4027 (1.54 g.m-2.MJ-1) in producing root system than the other two cultivars (1.10 g.m-2.MJ-1). In terms of RUE in producing shoot system, there was no significant difference between Jolgah and Hybrid 428 (0.34 g.m-2.MJ-1) and DS 4027 (0.32 g.m-2.MJ-1). According to the results, it can be conclude that improving the main drawback of domestic cultivars i.e. low R/S ratio should be given priority.