## 1 Introduction  
Cassava (_Manihot esculenta_ Crantz) is a species of tropical plant found in Asia, Africa, and South America [1]. It is a multipurpose crop with applications including fodder, biofuels, textiles, paper, adhesives, sweeteners, glues, and plywood [2]. Economic development and the advancement of industrial technology have changed the development of cassava from a food crop to an industrial raw material and energy crop. Additionally, in Africa and South America, more than two-thirds of the total production of cassava is consumed daily [3]. [PERSON] [3] also suggests that dried cassava is the cheapest energy source in large areas of the lowland tropics. From feedstock production (source) to fuel combustion, [PERSON] et al. [4] assess the net energy, the external cost of carbon dioxide (CO\({}_{2}\)) emissions, and the cost of using cassava-based ethanol as an alternative automotive fuel based on its holistic lifecycle. Their research shows that the net energy yield of cassava-based ethanol is found to be 0.37 MJ/MJ, i.e., about 49% of that conventional gasoline. They conclude that cassava-based ethanol has great potential in the future. However, its cultivation is increasing worldwide, mainly for human consumption: cassava production increased from 230 million tons in 2010 to 277 million tons in 2013 [5]. It can be seen that the demand of cassava is growing. Today, cassava is one of the most cultivated plants in the world after wheat, rice, and maize [6]. Due to the limited areas of tropical conditions in China (defined as: annual accumulative temperature \(\geq\)10 \({}^{\circ}\)C, frost-free days \(\geq\)280 days, and annual average rainfall \(\geq\)1000 mm), cassava is mainly planted in the provinces of Guangxi, Guangdong, Hainan, Yunnan, Fujian, and the south of Jiangxi Province. The total output of cassava in these six provinces accounts for 97% of the total output in China. Among them, Guangxi Province has the largest acreage, accounting for 60% of the total cassava output in China [7]. In 2011, the total output of tapioca starch reached a record high of 90.05 million tons. Compared with other ethanol-fuel raw materials, [PERSON] and [PERSON] [8] conclude that cassava is the most suitable starch material for ethanol-fuel production in China. In 2012, cassava ethanol-fuel production was 1.6 million tons, which is also the highest level recorded to date. The rapid development of the cassava-processing industry requires an adequate supply of raw materials (cassava raw material refers to cassava root, cassava starch, and cassava slices). However, there have been several changes in output levels. Cassava output has gone from soaring to stagnating. Since 2009, China's cassava output has not exceeded 2% of global output and has had a decreasing trend, with total output hovering around 4.55 million tons (If not specifically mentioned in the paper, all the data are from FAOSTAT) for many years. The total output of cassava was 4.51 million tons in 2009 and 4.59 million tons in 2013. Meanwhile, the total output of cassava was far below that of other Southeast Asian countries. In 2013, cassava output in Thailand was 30.23 million tons, making a 41% increase compared with the output of 21.44 million tons in 2004. Vietnam's cassava output in 2013 was 9.74 million tons, forming a 167% increase compared with the output of 4.59 million tons in 2004. However, statistics showed that, in the same year, China only made a 20% increment to 4.59 million tons compared with the output in 2004, which stood at 3.82 million tons. The increment of Chinese cassava output was much smaller than Thailand and Vietnam. Comparing China's output to Thailand's 25.64 million ton and Vietnam's 5.15 million ton outputs, it can be concluded that China has a long way to go to catch up with these countries in terms of cassava output. The planting area of cassava also suffers from a slow increase. In 2009, the total planting area in China was 270,600 hectares and increased to 290,100 hectares in 2013. The average increase was only 2.2%.