Ethanol Production Potential of Sweet Sorghum in North and Central Ukraine
Authors: Rakhmetova Svitlana O. , Vergun Olena M. , Blume Rostislav Y. , Bondarchuk Oleksandr P. , Shymanska Oksana V. , Tsygankov Sergii P. , Yemets Alla I. , Blume Yaroslav B. , Rakhmetov Dzhamal B. 
Published: December 2020

Background:
Sweet sorghum (Sorghum saccharatum (L.) Moench) is a unique crop with great potential to serve both the food and energy industries. It is due to the possibility of (bio)ethanol production both from the juice and biomass of this crop. The sorghum stems juice contains sugar in the levels similar to that of sugarcane. Besides, low cultivation requirements for the sweet sorghum make this crop even more attractive for sugar and ethanol production. In terms of technology, sweet sorghum is seen as a transitional feedstock for the first to the second generation bioethanol production. However, effective technological development of the plant cultivation and processing in the Northern and Central Ukraine is restrained by the lack of a collection of sweet sorghum genotypes and adapted varieties for its large-scale cultivation. Additionally, no evaluations of potential (bio)ethanol productivity have been performed for this region, which is important for efficient implementation of novel biofuel-producing technologies and for successful development of a green economy.

Objective:
This research was aimed to create a pool of sweet sorghum genotypes with the involvement of worldwide germplasm, analyze their morphology and breed high-yielding plant lines for the efficient production of liquid biofuels for second-generation bioenergy. Based on that, we also aimed to explore the prospects regarding the efficiency of sweet sorghum cultivation for (bio)ethanol production in the Northern and Central Ukraine.

Methods and Materials:
A valuable gene pool of S. saccharatum (L.) Moench (41 samples) was created; in particular, high-performance genotypes were created for cultivation under the soil-climatic conditions of Ukraine. The bio-morphological features and the yield potential of the plants were determined and the biochemical composition of the phyto-raw materials was determined in different periods of vegetation, in particular, during the technical ripeness of the above-ground mass of plants. The more productive forms and varieties of sugar sorghum in terms of yield, dry matter content, sugar, and energy value of biomass during flowering and waxy ripeness are highlighted. The technological properties of plant biomass for the production of alternative liquid fuels (in particular, bioethanol) have been analyzed. Importantly, optimal cultivation conditions have been elaborated for the newly created sweet sorghum genotypes, and their productivity has also been evaluated. Moreover, for the first time, a detailed study on potential ethanol yield has been conducted.

Results:
Sweet sorghum has considerable potential in Ukraine as a new sugar-producing energy crop. The germplasm collection of this crop has been created (41 accessions), including introduced and acclimated genotypes and newly bred lines and varieties. The biological performance of sorghum in Ukraine and plant morphology have been analyzed. The most promising genotypes were used for breeding of new high-productive sweet sorghum varieties. The potential (bio)ethanol yield for different sugar feedstocks (juice, grain bagasse) can reach up to 11423 L/ha in total from juice, grain and bagasse.

Conclusion:
The estimated values of ethanol productivity are comparable to the results of other similar investigations. In conclusion, a high performance of sweet sorghum in Ukraine can be suggested.