Evaluation of sweet sorghum and sudangrass varieties by the viewpoint of bioethanol production

On the score of the results of the year 2009 it can be set that sudangrasses have a lower theorical ethanol capacity than sweet sorghums have. In the case of sweet sorghums 1860.29–2615.47 l ha ethanol yields had been calculated, while the sudangrasses had only 622.96– 801.03 l ha. After that throughout three years (2011–2013) the sweet sorghum hybrids have been evaluated in order to determine the fluctuations of the ethanol production capacity caused by the impact of the years. As a result 2425.44–4043.6 l ha theorical ethanol capacities have been


NTRODUCTION
Plant biomass known as a promising energy resource which can be the base of biofuel production and has a lower emission of greenhouse gases (Berndes et al., 2003;Antonopoulou et al., 2008).Furthermore, bioenergy can stabilize the farmers' incomes, and can maintain and improve the ecological and social sustainability (Parikka, 2004;Xiong et al., 2008).
Bioethanol and other biofuels, approached by the viewpoint of environmental protection, are more environmental friendly than fossil fuel technologies, because these kinds of fuels are relatively carbon neutral (Tillman et al., 2006), during the production process hazardous compounds do not appear and the transport of fuels can be reduced (Drapcho et al., 2008).Moreover the emission of toxic exhaust and greenhouse gases can be decreased (Nguyen and Li, 1991;Zhang et al., 2003).
Another important consideration is the fact that before 2004 the European Union had less than 1% of the world's oil resources, while 20% of these oil resources were used in the EU countries (Vajda, 2004), therefore besides the environmental protection the economics and the energy-policy are very important in this field as well.The European Union had enacted a program to promote the consumption of biofuels by setting minimum targets in fuel substitution for the member countries of the EU.According to the 2009/28/EC Directive the European Union would like to increase the use of bioenergy and biofuels, therefore 20% of the energy consumption and 10% of the fuel consumption should come from renewable resources in Hungary.
Ethanol is mostly produced from sugar and starch.Lignocellulose as feedstock for ethanol production will be used in the very near future (Hamelink et al., 2005), as the processing technology turns economical.Sweet sorghum has therefore been considered as a potentially important feedstock for bioethanol production (Lynd et al., 1991;Mamma et al., 1995;Buxton et al., 1999;Liu et al., 2008).
Nowadays bioethanol production is based on mostly maize and sugarcane (Berg, 2004;RFA, 2010), but due to the agrononomic flexibility and productivity, sweet sorghum can be a viable option in some regions of the world (Blaskó et al., 2008;Daliva-gomez et al., 2011).The juice extracted from the sweet sorghum's stem contains approximately 16-18% different kinds of sugar mostly sucrose, glucose and fructose (goshadrou et al., 2011).According to Kovács et al. (2011) the sweet sorghum's ethanol production capacity is between 1000 l ha -1 and 5000 l ha -1 while according to Mojovic et al. (2009) this value is 1365 l ha -1 .
In this study sweet sorghum varieties have been evaluated to determine the differences among the varieties in the bioethanol production capacity caused by the genetic variability.During the research four vegetation periods were studied in order to appoint the influential impacts of the climatic conditions.

MATERIAL AND METHODS
The researches of the energetic use of sorghum in the Research Institute of Karcag started more than thirty years ago (Kapocsi et al., 1983).The goal of these researches is to determine the potential role of these plants in the biomass energy.In this survey six sweet sorghum hybrids, two sudangrass hybrids and a sudangrass variety have been studied.The experiment was made with nine varieties and they were sown on meadow soil at Karcag in 2009.Later the experiment was continued with six hybrids for three years in the period of 2011-2013.
The climatic conditions in the evaluated years were quite variable.The average precipitation in 2011 and 2012 was 385.7 and 344.5 mm, which differs from the fifty years' average value of precipitation (503.3 mm).The annual average temperatures also differ from the fifty years' average value of annual temperature (10.0 °C) (Table 1).

RESULTS
By right of the data measured in 2009 the theorical bioethanol production has been calculated for each variety (Table 2-3).The results denoted that sudangrasses have lower pontetial in bioethanol production.Sudangrasses reached only 622.96-801.03l -1 average ethanol capacity with a low standard deviation (p=0.05), and relatively small range 181.95-779.95l ha -1 .In the case of sweet sorghums the situation was different.These plants have provided 1860.29-2615.74l ha -1 average ethanol potential, with a bit higher standard deviation and range.After 2009 the research was confined to sweet sorghum.In the years of 2011-2013 the weight of stems of 1 m 2 , the water content of the stems and the refractometric dry matter content were measured.on the score of three years data the influential impacts of the years' climatic conditions can be eliminated, which was the base of the statistical analysis.
In the period of August-November the average refractometric dry matter content was the highest generally in october (Figure 2).In some sampling dates the standard deviations are very high which is caused by the climatic differences of the years.In the case of some hybrids like Berény the changes of the refractometric dry matter content is a bell-shaped curve, while in other hybrids like Sucrosorgo these data show a growing graph, which is coherent with the length of the hybrid's vegetation period.
The maximum of the refractometric dry matter content was in october in every case, thus the data of yield, water content and refractometric dry matter content measured in october of every year, were analyzed in ANoVA to determine the less significant difference of the hybrids by the investigated aspects.
According to the results there are significant differences of the hybrids by the viewpoints above (Table 4).Hybrids with the same letters are in the same group by the evaluated aspect.The average bioethanol potential of the hybrids' was between 2425.44-4043.60l ha -1 which absolutely expresses the differences.The average Rdm content was the highest in Berény, but the Sucrosorgo had a higher average yield, thus the ethanol potential is higher in this case (Table 5).
In the sweet sorghum based bioethanol production the sugar content and the yield of stem are very important, because these parameters are decisive in the bioethanol production.The differences of these parameters caused by genetic variability can determine the capability of a variety for biofuel production.

CONCLUSIONS
Biofuels can be a very important part of the European Union's transportation.Therefore a program had been made up to increase the part of the renewable resources of the energy consumption.By the 2009/28/EC directive more emphasis will be put on the bioethanol production.This goal needs stocks that makes the principle of this survey.In this study sweet sorghum and sudangrass varieties had been evaluated to determine their suitability for bioethanol production.By the results it can be laid down that sudan grass may has a greater potential in other fields of bioenery (eg.: biogas), while sweet sorghum can be an adequate stock to produce bioethanol.on the score of three years observation 2425.44-4043.6l ha -1 theorical ethanol yield was calculated of the sorghum hybrids which make this plant a promising feedstock in the biofuel production.The different hybrids have different ethanol production capacity due to the genetic variability.The different sorghum genotypes adapt to the weather and other conditions (eg.agrotechnical factors) differently, but generally sweet sorghum hybrids are a competitive solution to produce the green fuel.
In Hungary mostly sweet sorghum hybrids with a medium-long vegetation period are grown, but in some cases the production of hybrids with longer vegetation period can be efficient.A sweet sorghum based bioethanol plant requires large sweet sorghum production sites.By using hybrids with different vegetation periods, the harvest season can be elongated which can effect advantages in the sugar yield.

Figure 2 :
Figure 2: The average refractometric dry matter contents (Brix°) and their standard deviations in the case of the investigated hybrids (2011-2013)

Table 1 . Temperature and precipitation data in Karcag Source
: Research Institute of Karcag Average temperature (°C)