Water Demand Of Sugarcane And Technologies Of Drip Irrigation On Hill Slopes In Guangxi, China

Guangxi is the major sugarcane producing area in China. In order to promote the development of sugar industry, great efforts are being dedicated to the construction of the modernization of water conservancy in sugarcane areas. As the majority of sugarcane areas in Guangxi are located on hill slopes, it is difficult to apply irrigation through traditional channels. The modernization of water conservancy in these sugarcane areas can be achieved depending on large-scale development of efficient water-saving irrigation. Drip irrigation is a water-saving irrigation technology for locally controlled irrigation, which directly delivers water or a mixture of water and fertilizer to the root zone of crops, evenly and accurately, through emitters. Owing to the distinct advantages of drip irrigation, its combination with wide-narrow row planting of sugarcane and water-fertilizer coupling, among other agronomic technologies, has greatly contributed to the high and stable yield in sugarcane areas and thus become one of the key modes of irrigation technology for the modernization of water conservancy in sugarcane areas on hill slopes in Guangxi.However, the development of drip irrigation in sugarcane areas of Guangxi starts late and there is a lack of relevant research and practical experiences. Additionally, differences exist in the growth characters of sugarcane, meteorological characteristics, soil type, and terrain conditions. Consequently, there remains a lack of research support for the water demand of sugarcane, appropriate irrigation frequency and amount of sugarcane in years with different level of rainfall, key technical parameter selection of drip tape in field, optimal design of field pipeline network on hill slopes, and measures of pressure regulation. Therefore, the sugarcane areas in Guangxi are not acclimatized in the development of drip irrigation, and the benefits acquired by drip irrigation are substantially reduced, affecting the extension of drip irrigation technology.In oder to research these problems, The main job of this study are as follows:(1) Basing on crop water consumption theory and farmland water balance theory, the water demand patterns of sugarcane were estimated using the Penman-Monteith equation and sugarcane crop coefficient. The irrigation frequency and amount in sugarcane areas were analyzed for typical years in different regions of Guangxi using the farmland water balance model. The amount and structure of rainfall also exhibited a clear trend towards extreme torrential rain. Meanwhile, the frequency of different levels of drought showed an increasing trend. In particular, the frequency of moderate and heavy drought with great harm to sugarcane production increased significantly.(2) Basing on soil moisture migration mechanism, soil water movement and distribution patterns were analyzed for the major types of soil in sugarcane areas using laboratory soil-column experiment and HYDRUS-3D modeling. The main factors which showed significant effect on the size, shape, and water distribution of wetted soil volume under drip irrigation were analyzed. The criterion for selecting appropriate parameters of drip tape, the appropriate irrigation time and the appropriate irrigation amount of sugarcane in different growth stages in sugarcane field was obtained.(3) Basing on the perforated pipe hydraulic calculation method, the effects of basic parameters of drip tape on irrigation uniformity and the influences of the inlet pressure of the field pipeline network, the pipeline network layout form, the slopes were determined by constructing a hydraulic analysis model of the field pipeline network for drip irrigation. Furthermore, a branch pipe pressure regulating device was developed, which guarantee the irrigation uniformity of the entire field pipeline network on hill slopes.The main innovations of the study are as follows:(1) This study presented the water demand patterns of sugarcane and irrigation frequency and amount in sugarcane areas for typical years in different regions of Guangxi.(2) This study proposed the criterion for selecting appropriate parameters of drip tape, the appropriate irrigation time and the appropriate irrigation amount in sugarcane field. These were obtained by analyzing soil water movement and distribution patterns in typical types of soil under drip irrigation in sugarcane areas of Guangxi using laboratory soil-column experiment and HYDRUS-3D simulation.(3) This study developed a branch pipe pressure regulating device, which took advantage of changing the local head loss caused by pipeline hydraulic conditions to regulate branch pipe pressure. This device featured a simple structure, low investment, and easy maintenance. It can be directly buried in the ground and is applicable for use in field pipeline network construction in sugarcane areas on hill slopes in Guangxi.