| Abstract|| |
Nutrient elements play an essential role in biological and physiological functions of plants. Nitrogen is the most important factor and is required more than other nutrients. However, little is known about sesame responses to nitrogen. In this case, an experiment was laid out in split plots based on randomized complete block design with three replications at the Lavark Research Farm, Isfahan University of Technology, during May to October 2006 . Three nitrogen rates (50 , 100 and 150 Kg N ha -1 ) and seven sesame genotypes including Nonbranching Naz and Branching Naz ( early-maturing) ; Yekta and Oltan ( moderate-maturing) and Local Ardestan, Darab 14 and Varamin 2822 ( late-maturing) were used in main and sub plots, respectively. Six important phenological phases of sesame including emergence, seedling, early flowering, early seed filling, full flowering and early physiological maturity were studied. Except for the emergence phase, increasing nitrogen rate significantly delayed all phenological phases of sesame and increased the growth period of the plant. However, early-maturing genotypes proved early and late-maturing genotypes proved late. It seems that a delay in the leaf senescence and also the enhancement in chlorophyll content, photosynthetic enzyme content and dry matter production resulted in delayed phenological phases and increased growth period.
Keywords: Sesame, Phenology, Nitrogen
|How to cite this article:|
Sayyad-Amin P. The study of sesame phenology and growth period under different nitrogen rates. Scho Res J 2011;1:1-5
′Originally Published in 2010 in electronic version, through Open Journal Systems and this is republication of the same′
| Introduction|| |
The importance of sesame
Sesame (Sesamum indicum L.) is probably the oldest oilseed crop, which was cultivated by man for oil production  . It possesses the highest oil quality and quantity ( nearly 50 % of seed weight) among all oilseeds. It is grown in tropical and subtropical regions and cultivated as the main crop or aftercrop in many parts of the world especially Asia and Africa , . However, most of the biological and physiological aspects of this plant are still unknown.
The importance of nitrogen
Nutrient elements play an essential role in biological and physiological processes of plants such as their phenology and growth period. Among all nutrients, in agricultural and natural environment, nitrogen is the most important factor and is required for plants more than others  . It is a vital component of chlorophyll, enzymes, plant growth substances etc.  . Because most of the plant compounds contain nitrogen, it extremely affects the plant physiological functions.
This element is widely used as either organic ( manure) or chemical ( fertilizer) forms. Understanding the effects of such an important nutrient will assist the farmers to manage the fields better as the crop takes the required nutrients and completes its growth period timely.
Considering nitrogen's role in plants, it seems increasing the nitrogen level prolongs phenological phases and the growth period of sesame. But, there is little information about different responses of sesame genotypes to nitrogen. Consequently, this study was planned to investigate the phenology and growth period of sesame under different nitrogen rates.
| Methods|| |
The study was conducted at the Lavark Research Farm, Isfahan University of Technology, Isfahan, Iran ( lat. 32: 32 ' N, long. 51: 23 ' E and 1630 m) as irrigated farming during May to October in 2006 . The soil was fine-loamy, mixed, thermic Typic Haplargids with pH: 7 .6 , EC: 0 .07 S m- 1 , OM: 0 .23 %, OC: 0 .13 % and 0 .15 : 7 .2 : 150 mg Kg 1 available N: P: K.
Experimental design and treatments
The experiment was laid out in split plots based on randomized complete block design with three replications. Three nitrogen rates including 50 , 100 and 150 Kg N ha 1 in the form of urea with 46 % nitrogen and seven sesame genotypes including Nonbranching Naz and Branching Naz ( early-maturing) ; Yekta and Oltan ( mid-maturing) and Local Ardestan, Darab 14 and Varamin 2822 ( late-maturing) ( Seed and Plant Improvement Institute, Karaj, Iran) were used in main and sub plots, respectively.
The plants were seeded on May 17 , 2006 and harvested at full physiological maturity for each genotype. The plant density was 35 plants m -2 . One third of each nitrogen rate was applied as the starter before sowing, while the second and third parts were dressed at seedling and early flowering phases, sequentially.
The occurrence of six phenological phases ( emergence, seedling, early flowering, early seed filling, full flowering and early physiological maturity) was recorded from the sowing date ( the date of first irrigation) accordingly.
These phases were determined following these indices:
- Emergence phase: appearance and extension of the cotyledon leaves in 50 % of the plot.
- Seedling phase: appearance of 4 to 6 identifiable regular leaves on the main stem in 50 % of the plot.
- Early flowering phase: appearance of the first flower on the main stem in 50 % of the plot.
- Early seed filling phase: appearance of the first two-centimeter capsule with recognizable seed rows and empty green seeds in 50 % of the plot.
- Full flowering phase: appearance of the first five-millimeter capsule on the forth-identifiable node from the main stem apex in 50 % of the plot.
- Early physiological maturity phase: appearance of the first brown capsule on the main stem in 50 % of the plot.
The identifiable regular leaf was considered as which is fully unfolded or with at least a five-millimeter internode below. The identifiable node is one with an identifiable regular leaf.
The statistical analysis was performed using the GLM procedure in SAS 9 .1 package ( SAS Institute Inc., Cary, NC) . Treatment and their interaction means were separated by LSD test at the P=0 .05 level.
| Results and Discussion|| |
Except for the emergence phase, nitrogen rate affects significantly the occurrence of all phenological phases. As nitrogen rate increased, the occurrence of all phenological phases was delayed [Table 1] .
|Table 1: Nitrogen rate (Kg N ha-1) effect on occurrence of six phenological phases (day). *|
Click here to view
Although an insignificant difference in emergence phase, raising nitrogen rate delayed the occurrence of this phenological phase. Probably, it is related to the lack of efficient root system before emergence that causes the applied nitrogen to be absorbed well by the germinating embryos. So that they germinated and emerged only through their seed store  . Hence, in this phase, any significant difference was not observed among the nitrogen rates.
Following seed emergence and the appearance of cotyledon leaves, which occurs together with chlorophyll formation in plant organs and the beginning of gas exchanges, a significant difference was observed among nitrogen rates. This meant that the efficient root system had risen, which could absorb the minerals from soil by plant transpiration for supplying the required substances for photosynthesis and plant growth. It seems more nitrogen rate led to more chlorophyll and enzyme content like rubisco and thus more photosynthesis. On the other side, the more nitrogen supply, the later senescence  . Therefore, the occurrence of phenological phases was delayed and the period of each phase was prolonged. This situation resulted in significant differences among the phenological phases due to the difference in the nitrogen rates [T able 1] . According to a trial conducted by Subedi et al.  on spring wheat, nitrogen treatment had a significant effect only on the time to reach physiological maturity as zero-nitrogen treatment helped mature significantly earlier than the other nitrogen treatments (60 and 100 Kg N ha -1 ) . There were no differences in the duration of grain filling due to nitrogen application. They hypothesized that the application of nitrogen at a higher rate or split application of nitrogen at boot phase of wheat might extend the grain filling period. Marchetti et al.  found significant increase in the number of days to reach harvesting time in tobacco for increased nitrogen rates. Also, Hawks et al.  and Elliot  had observed this effect on tobacco. However, Andrea et al.  reported that reduced nitrogen availability resulted in an increase in the thermal time requirements up to anthesis and silking phases of maize inbreds, but this trend was significant only for the time till silking phase of one experimental inbred.
In all phenological phases except for the emergence phase, there were significant differences among the genotypes. In this case, the phenological phases occurred earlier in Nonbranching Naz and Branching Naz ( early-maturing genotypes) and later in Local Ardestan, Darab 14 and Varamin 2822 ( late-maturing genotypes) . Yekta and Oltan ( moderate-maturing) were between these two groups [Table 2] . These consequences are probably related to their genetic characteristics.
|Table 2: Genotype effect on occurrence of six phenological phases (day). *|
Click here to view
As mentioned before, the lack of efficient root system might be the cause of insignificant differences among the genotypes. It seems the seed store of the genotypes is similar, so that they emerged almost at the same time. After the emergence phase and rising of an efficient root system, probably due to the gene expression, the occurrence of following phenological phases showed a significant difference among the genotypes as each genotype proved its genetics.
Andrea et al.  concluded that maize inbreds differed significantly in thermal time requirements up to anthesis and silking phases.
Nitrogen and genotype interaction:
Except for the emergence and early seed filling phase, in all phenological phases, the interaction between nitrogen and genotype was significant. In this case, phenological phases occurred earlier in Nonbranching Naz and Branching Naz ( early-maturing genotypes) with 50 Kg N ha -1 and later in Local Ardestan, Darab 14 and Varamin 2822 ( late-maturing genotypes) with 150 Kg N ha -1 [Figure 1] . It appears that, whatever be the increase in nitrogen rate and however late the genotype matures, the occurrence of phenological phases gets delayed and the crop growth also gets prolonged.
|Figure 1: The Occurrence of six phenological phases (day) of sesame is influenced by interactions between|
nitrogen and genotype. Columns with different letters are significantly different at P ≤ 0.05.
Click here to view
Although there was no experiment evaluating the nitrogen rate and genotype interaction, Subedi et al.  did not observe any interaction between nitrogen rates and the planting date of wheat.
| Conclusion|| |
As a result, increasing nitrogen rate delays phenological phases of sesame and extends sesame growth period. Regardless of nitrogen rate, all the genotypes proved their genetics in terms of phenology and growth period.
| Acknowledgement|| |
The author would like to appreciate Seed and Plant Improvement Institute of Iran for providing the seeds.
| References|| |
|1.||Addiscott TM. Nitrate, Agriculture and the Environment. Wallingford: CABI Publishing; 2005 . |
|2.||Andrea KED, Otegui ME, Cirilo AG, Eyherabide G. Genotypic Variability in Morphological and Physiological Traits among Maize Inbred Lines-Nitrogen Responses. Crop Sci. 2006 ;46 :1266 -1276 . |
|3.||Baskin CC ,Baskin JM. Seeds. San Diego: Academic Press; 1998 . |
|4.||Elliot JM. Production Factors Affecting Chemical Properties of the Flue-Cured Leaf. Tob Int. 1975 ; 177 :22 -32 . |
|5.||Frith GJT, Dalling M. The Role of Peptide Hydrolases in Leaf Senescence. In: Thimann KV, ed. Senescence in Plants. Boca Raton: CRC Press; 1980 :117 -130 . |
|6.||Hawks SN, Collins WK, Kittrell BU. Effects of Transplanting Date, Nitrogen Rate and Rate of Harvest on Extending the Harvest of flue-cured tobacco. Tob Sci. 1976 ; 20 :51 -54 . |
|7.||Hwang, LS. Sesame Oil. In: Shahidi F, ed. Bailey's Industrial Oil and Fat Products, Vol. 2 , 6 th . Hoboken: John Wiley & Sons Inc; 2005 :537 -576 . |
|8.||Marchetti R, Castelli F, Contillo R. Nitrogen Requirements for Flue-Cured Tobacco. Agron J. 2006 ; 98 :666 -674 . |
|9.||Subedi KD, Ma BL, Xue AG. Planting Date and Nitrogen Effects on Grain Yield and Protein Content of Spring Wheat. Crop Sci; 2007 :47 :36 -44 . |
|10.||Weiss EA. Oilseed Crops. Bodmin: Blackwell Science Ltd; 2000 . |
|11.||Wink M, Waterman PG. Chemotaxonomy in Relation to Molecular Phylogeny of Plants. In: Wink M, ed. Biochemistry of Plant Secondary Metabolism. Sheffield: Academic Press; 1999 :300 -336 . |
[Table 1], [Table 2]