Journal of Energy Bioscience 2024, Vol.15, No.6, 358-367 http://bioscipublisher.com/index.php/jeb 364 8.2 Cultivation practices and biomass yields The cultivation methods of sorghum may vary in different regions, but everyone's goal is similar, which is to increase biomass yield and enhance the ability to resist environmental pressure. For instance, in Iowa, the United States, high-biomass sorghum can still produce more than 20 tons per hectare of above-ground parts under drought conditions, with most of the roots concentrated in the soil surface layer. In Queensland, Australia, sweet sorghum varieties like SE-81 can produce 46.9 to 82.3 tons of biomass per hectare, and the methane yield can also reach 3 059.18 Nm³ CH4 (Mathias et al., 2023). In the North China Plain of China, the rotation of medium-maturing sweet sorghum (CT2) and winter wheat can produce 24.9 tons of dry matter per hectare in two seasons a year, and the total energy output reaches 394.6 GJ per hectare (Tang et al., 2018b). 8.3 Outcomes: energy production, environmental benefits, and socioeconomic impacts Sorghum is a versatile crop that can be used to produce various bioenergies, such as bioethanol, biogas and biomethane. In Central and Eastern Europe, sorghum varieties like Sorghum 506 have been effectively used to produce lignocellulosic ethanol, and have performed well whether as the main crop or a rotation crop (Batog et al., 2020). In Queensland, Australia, the methane production of some sweet sorghum varieties is very high, showing their great potential in biogas production (Mathias et al., 2023). Sorghum has another important advantage, which is that its root system is very deep. These roots can increase the organic carbon in the soil, improve the soil structure and also reduce nutrient loss. In the research in the United States, it has been proved that sorghum roots can effectively improve soil health (Lamb et al., 2021). Studies have pointed out that growing sorghum in the United States can also achieve net carbon sinks, which is very helpful for addressing climate change (Gautam et al., 2020). In terms of social economy, the utilization of sorghum has also enhanced the efficiency of land use and energy output. In the North China Plain of China, the double-cropping of sweet sorghum and winter wheat not only increases energy output but also makes full use of land resources (Tang et al., 2018b). In Queensland, planting sweet sorghum during the off-season of sugarcane not only generates renewable energy but also boosts the local economy and reduces reliance on fossil fuels (Mathias et al., 2023). 9 Challenges and Limitations 9.1 Technical challenges in conversion processes There are still some technical difficulties in the process of converting sorghum biomass into bioenergy, especially in the pretreatment and fermentation stages. Pretreatment technologies such as saccharification, fermentation, transesterification, hydrothermal liquefaction, pyrolysis and gasification are all rather complex and require continuous optimization to improve efficiency and reduce costs (Stamenković et al., 2020). Because the biomass of sorghum contains a relatively high content of lignocellulose, it is crucial to first break the cell walls through effective pretreatment methods to release fermentable sugars (Appiah-Nkansah et al., 2019). There are also differences in the contents of cellulose, hemicellulose and lignin among different sorghum varieties, which makes the transformation process more complex (Batog et al., 2020). If too much water is used in these conversions, or if a large amount of nitrogen fertilizer (such as ammonia from the energy-intensive Haber-Bosch process) is used, it will increase costs and be detrimental to the environment (Calvino and Messing, 2012). 9.2 Competition with food crops and land use concerns Sorghum, as a bioenergy crop, also faces an important problem, that is, it may compete with food crops for farmland. The arable land resources are limited. If a portion of it is used to grow sorghum, it may affect food production, thereby raising the cost of living and potentially causing food security problems (Calvino and Messing, 2012). However, sorghum has one advantage, that is, it can grow on marginal land. Marginal land is usually not suitable for growing grain, but it can be used to grow sorghum, which can reduce the competition for high-quality cultivated land. However, it should also be noted that the conditions in marginal areas are generally poor, and the yield of sorghum in these areas may not be high, which will affect the final biomass output and economic benefits (Nenciu et al., 2021).
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