## 1 Introduction
Compared to the rest of the world, China ranks ninth in terms of planting area size with 290,100 hectares, while Nigeria is at the top with 3,850,000 hectares. These data show that the planting area not only has a slow increase, but is also considerably lower than countries that are highly developed in cassava production. The yield of cassava is steadily diminishing. Due to technological advances, the yield witnessed a quick increase from 15.27 tons per hectare in 2002 to 16.27 tons per hectare in 2011, which marked the peak yield. The yield of cassava in China ranks sixth in the world, behind India, Indonesia, Thailand, Vietnam, and Ghana. The average yield of cassava in the world is 16.80 tons per hectare. Although the output per hectare in China is greater than the global-average level, it still has a gap to close when compared with the main cassava producing countries. From a price point of view, the price of cassava raw material keeps rising due to increased demand. Theoretically, the joint interaction between China-produced and Association of South East Asian Nations (ASEAN)-produced cassava raw material should stabilize the price. In fact, ASEAN-produced cassava raw material accounts for nearly 80% market share in China. Therefore, farmers lost their pricing power in China [9]. There are several causes for cassava price changes. Firstly, the price of cassava raw material rises year by year because of the demand of downstream cassava-processing manufacturers. According to our investigation, due to the insufficient supply of cassava, some tapioca manufacturers are even processing cassava for less than four months per year. In Guangxi Province, the price of cassava root rose from 320 Yuan/ton in 2005 to 590 Yuan/ton in 2014 (one yuan was worth 0.16 US dollars in 2014). Simultaneously, the booming demand for cassava, especially in the domestic tapioca and alcohol industry, also pushes the price up. Secondly, the price of cassava is deeply influenced by output. After 2012, the general output and price showed the same downward momentum. In contrast, strong demand arises from the birth of several domestic ethanol producers, thus causing the price to rise. Thirdly, cassava price is also influenced by imported cassava raw material. The imported cassava keeps the price relatively stable in China. The establishment of the China-Asian Free Trade Zone (CAFTA) after 2010, which promotes trading cooperation between China and Southeast Asian countries, has also especially affected the price. Table 1 is the cassava supply and demand balance in China. As one of the big cassava producers, China's cassava cultivation-process management is extensive but there is a gap between output per unit area and other advanced countries. At the same time, due to the rapid growth in demand for domestic cassava, the development of cassava planting lags behind in China. The imports of cassava in China have been increasing year by year, with an increasing dependence on foreign countries [11]. No significant increase has been found in planting area, yield, or production output from 2009 to 2014 in China. But, as one of the most important industrial raw materials, downstream-processing-industry demand has increased. Table 1 shows that China-produced cassava of 1,860,000 tons only meets 17% raw-material demand and 83% of the cassava required must be imported from Thailand, Vietnam, and other ASEAN countries. The importing of cassava starch with high quality and low price, on the one hand, inhibits the price of domestic tapioca starch and, on the other hand, suppresses the motivation of farmers. The contradiction between the shortage of the supply of cassava raw materials and the increasing demand for cassava raw materials in the downstream-processing industry has become the bottleneck of the development of the cassava industry in China. It can be seen from this analysis that China's cassava industry has entered a state of stagnation.