Effect of Interactions of Planting Date, Amounts of Nitrogen and Plant Density on Some Steckling Characteristics and Sugar Beet (Beta vulgaris) Monogerm Seed Quantitative and Qualitative Traits

Abstract
To study some steckling characteristics and quantitative and qualitative traits of sugar beet monogerm (Cv. Pars) seed under the influence of planting date, nitrogen amounts and density an experiment was conducted as split factorial based on RCBD with four replications at sugar beet elite seed research station of Firouzkooh during two years (2012-2013). Planting date at levels of 1 and 21 July and 10 August were assigned to main plots and density at levels of 10, 20, 30 and 40 plants per square meter and nitrogen levels including 25% less than optimum, optimum and 25% higher than optimum in a factorial arrangement were assigned to sub-plots. Increasing the density at different planting dates decreased steckling weight and increasing nitrogen consumption at different planting dates increased the average weight of stecklings. In the second year of trial stored and vernalized stecklings were evaluated for the traits of the quantitative and qualitative traits of seed in RCBD with four replications To achieve the greatest steckling yield (12.24 tons per hectare), planting 40 plants per square meter on july 1^st and nitrogen consumption at 25% higher than optimum also to reach the highest crude seed yield (122.31 grams per plant) and marketable seed yield (43.74 grams per plant), seed bearing plants obtained from stecklings of planting date of 1 July × plant density of 10 plants per square meter × optimum nitrogen consumption and planting date of 1 July × plant density of 40 plants per square meter× nitrogen consumption at 25% less than optimum respectively are recommended for semi-arid and cold regions such as Firouzkooh and similar regions in terms of climate.
Introduction
The development of mechanization and cultivation of monogerm seeds in the beet growing areas in Iran has increased the importance of producing high quality seeds. The production of sugar beet seeds in Firouzkooh region is done in an indirect way, that is, the transfer of stecklings is done in two years. Nitrogen is necessary to arouse growth in the early stages of growing (steckling production) and increases seed yield also increases seed germination percentage. Generally, increasing the weight of stecklings and reducing density, accelerates ripening, makes the seeds larger and increases the seed viability. Reducing plant density causes an increase in plant biomass, rather than increasing the seed yield, and accordingly, to improve economic benefit from environmental factors, dense planting of small stecklings is better than thin planting of their large types. Also, early planting increases leaf area index and consequently increases dry weight and root yield. Therefore, the purpose of this research was to determine the most suitable seed planting date, plant density and management of nitrogen consumption, to produce the most stecklings with appropriate weight also to determine how the steckling size and agronomic management of steckling production affect the quantity and quality of the seed was produced.
Materials and methods
In this research, the effect of planting date, nitrogen amounts and plant density on some characteristics of stecklings and quantitative and qualitative traits of sugar beet monogerm seed of Pars cultivar at sugar beet elite seed research station of Firouzkooh for two years (2012 and 2013) was investigated. This research was conducted in two separate experiments in two consecutive years. The first experiment was conducted as a split factorial based on RCBD with four replications. Planting date at levels of 1 and 21 July and 10 August were assigned to main plots and density at levels of 10, 20, 30 and 40 (plants.m^-2) and nitrogen levels including 25% less than optimum, optimum and 25% higher than optimum in a factorial arrangement were assigned to sub-plots. In the second experiment (in 2013), a part of the stored and vernalized stecklings that were the result of different combinations of different levels of the factors of the first experiment were investigated in the form of 36 treatments based on RCBD with four replications. The quantitative traits of steckling in the first experiment and quantitative and qualitative traits of seed in the second experiment were evaluated. The obtained data were analyzed using statistical software of SAS (V. 9.1.3) based on the statistical criteria of the design and Duncan’s multiple range test was performed at the 5% level of probability.
Results and discussion
The results showed that planting date of 1 July, plant density of 40 (plant.m^-2) and nitrogen consumption at 25% higher than optimum had the greatest steckling yield with 12.24 (t.ha^-1). With earlier planting, increasing density and increasing nitrogen consumption, steckling dry weight and total dry weight with 324.44 and 576.05 (gr.m^-2), respectively had the highest values. It seems that earlier planting has created suitable conditions for the growth of aerial and underground organs in the plant.  Mean comparisons showed that the treatment combination of planting date of 1 July, plant density of 10 (plant.m^-2) and nitrogen consumption at optimum level in steckling production, had the greatest crude seed yield with 122.3 (gr.plant^-1) in the second year. The highest marketable seed yield (43.74 gr.plant^-1) obtained from the stecklings of planting date of 1 July × plant density of 40 (plant.m^-2) × nitrogen consumption at 25% less than optimum. The higher percentage of seed emptiness in most treatments of density and nitrogen consumption occurred in the later planting date. In general, the treatment combinations related to the first planting date were in a better condition in terms of the percentage of seed viability. It seems that from the earlier planting date, larger roots were obtained and this increased the growth rate of the stecklings, the quantitative and qualitative yield in the second year. Other researchers also stated that in general, increase in steckling weight (caused by early planting) and decreasing density has caused the seed to grow larger and increasing the seed viability.
Conclusions
According to the results of this research to achieve the greatest steckling yield (12.24 t.ha^-1), planting 40 (plant.m^-2) on July 1^st and nitrogen consumption at 25% higher than optimum also to reach the highest crude seed yield (122.31 gr.plant^-1) and marketable seed yield (43.74 gr.plant^-1), seed bearing plants obtained from stecklings of planting date of 1 July × plant density of 10 (plant.m^-2) × optimum nitrogen consumption and planting date of 1 July × plant density of 40 (plant.m^-2)× nitrogen consumption at 25% less than optimum respectively are recommended for semi-arid and cold regions such as Firouzkooh and similar regions in terms of climate.