INTRODUCTION
Agriculture is the backbone of the Ethiopian
economy. This particular sector determines the growth of all other sectors and
consequently the whole national economy. It constitutes over 50% of the gross
domestic product (GDP), accounts for over 85% of the labour force and earns
over 90% of the foreign exchange. On average, crop production makes up 60% of
the sector’s outputs, whereas livestock accounts for 27% and other areas
contribute 13% of the total agricultural value added. The sector is dominated
by small-scale farmers who practice rain-fed mixed farming by employing traditional
technology, adopting a low-input and low-output production system. The land
tilled by the Ethiopian small-scale farmer accounts for 95% of the total area
under agricultural use, and these farmers are responsible for more than 90% of
the total agricultural output (Diriba Welteji 2018).
The primary source of energy in Ethiopia is biomass, which
accounts for 91% of energy consumed, Petroleum supplies about 7% of total
primary energy and electricity accounts for only 2% of total energy use.
Biomass consumption accounts for over 98% of total supply in the residential
sector. The World Development Indicators and many other studies show that the
national energy balance is dominated by a heavy reliance on firewood, crop
residues, and dung. Due to the dependence on biomass for cooking, CO2 emissions
in Ethiopia have increased from 5.1 million tons in 2005 to 6.5 million tons in
2010. On a per capita basis, this amounts to 0.06 tons of CO2 in 2005, 0.075
tons in 2010, and 0.19 tons in 2014. (Md Alam Hossain Mondal et al. 2018).
Bioethanol is one such dominant global renewable transport biofuel
which can readily substitute fossil fuels. Conventionally, bioethanol has been
produced from sucrose and starch rich feedstocks (edible agricultural crops and
products) known as 1st generation bioethanol; however this substrate conflicts
with food and feed production. As an alternative
to 1st generation bioethanol, currently there is much focus on advancing a
cellulosic bioethanol concept that utilizes lignocellulosic residues from
agricultural crops and residues such as bagasse, straw, stover, stems, leaves
and deoiled seed residues (Almodares, A. and Hadi, M.R. 2009).
Bio-ethanol is one of the most
common biofuels that can help to reduce environmental contamination associated
with the use of fossil fuel. In general, bioethanol from agricultural raw
materials has become popular as an alternative energy source to petroleum-based
fuels because it is both renewable and environment friendly (Chalachew and Rebuma,
2018).
Sweet sorghum [Sorghum bicolor (L.) Moench], a C4 Graminaceous crop which has
sugar-rich stalks and which is a water-use efficient crop has a very good
potential as an alternative feed stock for ethanol production. It is the only crop
that provides grain and stem that can be used for sugar, alcohol, syrup, jaggery,
fodder, fuel, bedding, roofing, fencing, paper and chewing (C. V. Ratnavathi
2011).
Sweet sorghum can be used as a feedstock for ethanol production
because, it has higher tolerance to salt and drought comparing to sugarcane and
corn that are currently used for biofuel production. In addition, high
carbohydrates content and high fermentable sugar content in sweet sorghum stalk
makes it to be more suitable for fermentation to ethanol. Therefore, it is suggested
to plant sweet sorghum for biofuel production in hot and dry countries to solve
problems such as increasing the octane of gasoline and to reduce greenhouse
gases and gasoline imports (Almodares, A. and Hadi, M.R. 2009).
The government of
Ethiopia is promoting bioethanol for house hold cooking to save forests and
maintain soil fertility. Sweet sorghum is also being considered as potential
feedstock for bioethanol processing.
Therefore, the objective of this study was to evaluate sweet sorghum genotypes
for agronomic traits, brix value and stalk yield in the Central Rift Valley of
Ethiopia.
MATERIALS
AND METHODS
The
experiment was conducted during the July to October rainy season of 2018 at
Melkassa Agricultural Research Center. The Center is located 17 km southeast of
Adama in the semi-arid region of the Central Rift Valley of Ethiopia at 8o
24’N latitude and 39o 12’E longitude and Its elevation is 1550 meter above sea level
(m.a.s.l.). The site receives 763 mm mean annual rainfall. The area has a mean
maximum and minimum annual temperature of 34°C and 19°C and monthly temperature
of 38.06°C and 21.06°C during main season, respectively. Melkassa soil is classified as Andosols, well-drained sandy
loam, with an average pH of 7-8.2.
The experiment was carried out in Randomized
Complete Block Design consisted of 30 Sweet Sorghum genotypes sown in three
replications. The plot was plowed twice
and disc harrowed using Tractor. Ridges were made at 75 cm between rows and
seeds were drilled and thinned to 15 cm spacing. Plot size was 3.2 meters wide and 5 meters
long. Seed rate was 10 kg/ha and fertilizer was applied at the rate of 100
kg/ha DAP and 50 kg/ha Urea. DAP
fertilizer was applied during planting and UREA was at the four leaf stage and
other agronomic practices were applied for each treatments.
Observations were recorded for Days to flowering, (the
number of days from planting to 50% heading) while Days to maturity was recorded
the number of days from planting to 85% physiological maturity for each
genotype in each plot by checking the maturity of seed from sample plants),
Plant height (measured at physiological
maturity from the soil surface to the top of the head from randomly selected
plants), Brix
value was recoded as refractometer reading at dough stage and grain maturity. The samples were weighed wet, oven-dried, and weighed dry to
determine the water content after correcting for leaf weight.
Juice and sugar yield were calculated in three steps:
CSY = (FSY – DSY) × Brix × 0.75;
JY, 80% extracted = [FSY – (DSY – CSY)] × 0.8;
SY = JY × Brix × 0.75;
Where CSY is conservative sugar yield (Mg ha−1), FSY is
fresh stalk yield (Mg ha−1), DSY is dry stalk yield (Mg ha−1), JY
is juice yield (Mg ha−1), and SY is sugar yield (Mg ha−1). Sugar
concentration of juice is 75% of Brix expressed in g kg−1 sugar juice.
Stalk
yield was recorded as the weight of stalks from the central two rows. Grain yield (measured in gram for each plot of each entry
from central rows and then converted to kilogram per hectare for analysis),
RESULTS AND DISCUSSIONS
Days to
Heading, Maturity and Plant Height
Mean square
of the 8 characters from analysis of variance (ANOVA) at Melkassa is presented
in (Table 1). Analysis of variance showed that
there was highly significance difference (P ≤ 0.01) among the sweet sorghum
genotypes for days to heading, days to maturity and plant height (Table 2). The
mean value for days to heading ranged from 74 to 94 days after sowing (das)
with an average value of 83 days. There were seven genotypes (Ent.#64DTN, E 36-1, IESV 94021 DL, ICSR
93034, IESV 91104 DL, IESV 92028 DL and S 35) headed before
the local check.
Similar
to days to heading, twenty genotypes were early maturing genotypes ranges from 106 to 122 days. The mean number of
days to maturity was 120.(Table 2). There were eight genotypes matured before the
check while genotype MR#22XIS8613/2/3-1-3 was
the late maturing with 133 days. Genotype Ent.#64DTN shown to head and mature early in both characters. In case
of plant height, twelve genotypes were found to be taller than the check. The range
of plant height was 136 to 215 cm with a mean of 170cm. Genotype IESV 91104 DL was taller than other all
genotypes with the height 215cm. In sweet sorghum, tall and thick stems contribute
more towards the millable cane yield and juice yield was reported by Sandeep Singh Tomar et al. (2012).
Brix Value
Brix value
was determined using refractometer at dough and physiological maturity
stages. The Brix value was generally
high during dough stage and a little lower during maturity. Then range of brix value was 13.9-23.1 at the
dough stage and 15.1-23.0 during maturity. If the values on dough are
considered then twelve genotypes have brix values greater than 18% before grain filling while only ten
genotypes scored greater than 18% at maturity stage. The genotype, IESV 92001 DL, was the superior
genotype in brix values before grain filling and ICSB 654 also revealed highest in brix value at
physiological maturity. This shows that as the crop matures the sugar
content in the stalk decreases as the sugar is translocated to the sink. Brix
values as high 23.1% was recorded at the dough stage. The sugar content in the
juice of sweet sorghum varies in different varieties (Almodares et al., 1994a).
The Brix range in different varieties of sweet sorghum is 14.32-22.85% (Table
2) was reported by (Almodares and Sepahi, 1996). High brix is essential for
maximizing the amount of sucrose and ethanol produced per unit area cultivated
was also reported by Sandeep Singh
Tomar et al. (2012). Compared to grain sorghum, sweet sorghums feature
more rapid growth, higher biomass production, wider adaptation, and have
greater potential for ethanol production (Reddy et al., 2007).
Number of
Tiller, Stalk Yield and Grain Yield
The range
of number of tillers was 1.4 to 5.2 with a mean of 3. There were twenty two
genotypes shown large number of tillers than local check. Main stems with less
or no tillers became prone to lodging. Removal of tillers results in decreased
number of stalks per hectare, resulting in the reduction of the economic yield.
Almost all
genotypes of sweet sorghum showed higher stalk yield than local check. The
range of stalk yield was 10 to 27 ton/ha with a mean of 18 ton/ha (table 2). This is approximately 1852 to 5000 liters of bioethanol
per hectare assuming that 54 kg of sweet sorghum results to one liter of
bioethanol. The stalk is a value
addition to the primary product of grain production. However this includes
processing, transportation and overhead cost but one can assume that it can be
an excellent feedstock for a Bioethanol Micro Distiller Enterprise. Farmers in
Ethiopia use the stalk for various purposes but its value has never been
studied. Farmers usually use it as fire wood, livestock feed or temporary
construction of huts.
Grain yield is the important component of plant performance
under a set of growing conditions. Any physiological or agronomic parameter at
a given stage of growth would be of further use only when its effect is
reflected on yield either way. Grain yield is a function of HI and dry matter
production (Ludlow and Muchow, 1990).
There were three genotypes IESV 92008DL, MR # 22XIS8613/2/3-1-3 and IS 2331 were found
significantly superior over local checks with grain yield of 2791 kg/ha, 3416
kg/ha and 2677 kg/ha respectively. The range of grain yield was 1090 to 3416
kg/ha with a mean of 1971 kg/ha.
CONCLUSION
Based
on this study the performance of sweet sorghum genotypes evaluated for their
traits revealed highly significant difference between the genotypes for most
traits and significant difference among genotypes were observed. In current
results twelve
genotypes have brix values greater than 18%
before grain filling while only ten genotypes scored greater than 18% at
maturity. In addition these genotypes IESV 92001 DL, MR # 22XIS8613/2/3-1-3 at dough stage
and ICSB 654, IESV 92207 DL at physiological maturity were superior
genotypes in brix values respectively.
Among
the studied genotypes the highest mean of grain yield/ha obtained from IESV 92008DL, MR#22XIS8613/2/3-1-3 and IS 2331 were the most important genotypes for showing
excellent performance on grain yield per hectare 2791 kg/ha, 3416 kg/ha and
2677 kg/ha respectively than the check variety (2530 kilogram per hectare). Therefore, the availability of high yielding genotypes both
in brix value and grain yield might be promising for the development of tall
and thick stem genotypes for maximum ethanol production that could be exploited
in future sweet sorghum breeding in the central rift valley.
REFERENCES
Chalachew E and Rebuma M.
2018. Productivity of Sweet Sorghum
Genotypes under Contrasting Fertility Management for Food and Ethanol
Production. Journal of Adv Crop Sci Tech 6: 348.
Diriba
Welteji (2018) A critical review of rural development policy of Ethiopia:
access, utilization and coverage. Agriculture & Food Security 7: 55.
C.V. Ratnavathi,
S. Kalyana Chakravarthy,V.V. Komala, U.D. Chavan, J.V. Patil. 2011. Sweet
Sorghum as Feedstock for Biofuel Production: A Review 13:399–407.
Md
Alam Hossain Mondal, Elizabeth Bryan, Claudia Ringler, Dawit Mekonnen, Mark
Rosegrant. 2018. Ethiopian energy status and demand scenarios: Prospects to
improve energy efficiency and mitigate GHG emissions. Energy
149:161-172.
Almodares,
A. and Hadi, M.R. (2009). Production of Bioethanol from Sweet Sorghum: A
Review. African Journal of Agricultural Research, 4, 772-780.
Supriya Mathur, A. V. Umakanth, V. A. Tonapi, Rita
Sharma & Manoj K. Sharma. 2017. Sweet sorghum as biofuel feedstock: recent
advances and available resources. Biotechnology for Biofuels 10:146.
Almodares
A, Sepahi A (1996). Comparison among sweet sorghum cultivars, lines and hybrids
for sugar production. Ann. Plant Physiol. 10: 50-55.
C.
S. Wortmann, A. J. Liska, R. B. Ferguson, D. J. Lyon, R. N. Klein, and I.
Dweikat. Dryland Performance of Sweet Sorghum and Grain Crops for Biofuel in
Nebraska" (2010). Agronomy- Faculty Publications. Paper 387.
