DRIP IRRIGATION UNDER DIFFERENT CLIMATIC CONDITIONS ON SUGARCANE IN CHINA S GUANGXI PROVINCE Guo Pan, Li Jianxin 1, Liang Meiying, Tang Jianjun 2 ABSTRACT Based on an analysis of the precipitation over the sugarcane-growing areas in the Guangxi Zhuang Autonomous regions under different climatic conditions from 1955 to 2014, the lower limit of soil moisture when irrigation is needed has been set. The paper suggests developing a set of high-efficient and water saving irrigation technologies for sugarcane, which cover the segments from headwaters to farmland. Compared with the traditional irrigation methods, modern technologies for drip irrigation have increased sugarcane yield by 35122kg/hm2 and decreased irrigation water by 1125m3/hm2; project investment has accordingly reduced by 17%. Keywords: Different climates; sugarcane; sustainable development. 1. INTRODUCTION Guangxi is the most important base of sugarcane in China. The sugarcane fields here comprise 70% of China s total area. The total output of cane sugar accounts for more than 60% of the sugar production in China. The sugarcane industry s turnover has exceeded one hundred billion Yuan in Guangxi Province. The planting area of sugarcane in Guangxi is about 1.07million hectares. In recent years, Guangxi has been promoting the construction of sugarcane bases with high yield and high glucose. The government plans to build up a highly efficient and water-saving irrigation base for sugarcane that covers an area of 330,000 hectares. Now the part completed totals an area of 67,000 hectares, which accounts for only 6.25% of the construction project. There is great potential for developing irrigation technologies for the high yield and high glucose of sugarcane. A research on modern irrigation technologies for sugarcane under different climatic conditions is of practical significance to the construction of sugarcane bases with high yield and high glucose. Sugarcane in Guangxi Province is mainly planted on hill slope and are grown mostly without irrigation facilities. The average annual rainfall in Guangxi ranges from 1300mm to 1500mm. The water requirements of sugarcane range from 750mm to 1125mm. However, since the distribution of precipitation is erratic, the water scarcity is particularly prominent. On the basis of the sixty years rainfall data, the authors have summarized modern irrigation technologies and irrigation systems under different climatic condition in sugarcane areas in Guangxi Province, with a view to providing technical support for the sustainable development of sugarcane. 1 Guangxi Agricultural Irrigation and Drainage Engineering Technology Research Center, Guilin, Guangxi Province, China, 541105; 2 Irrigation Experiment Station in the Guangxi Zhuang Autonomous Region, Guiline, Guangxi Province, China 541105. 1
2. ANNUAL PRECIPITATION AND WATER REQUIREMENTS FOR SUGARCANE IN GUANGXI PROVINCE 2.1 The Annual Precipitation from 1955 to 2014 Located in the subtropical zone with a monsoon climate, Guangxi ranks above many other provinces of China as one with heavy annual precipitation. Yet the distribution of inter-annual and seasonal precipitation is uneven; wet years and dry years appear with different frequency; in addition, under the influence of the El Nino phenomenon, precipitation in Guangxi Province is rather unsteady, and the sustainable production of sugarcane cannot be guaranteed. Precipitation (mm) 2000 1600 1200 Annual rainfall Average annual rainfall 800 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Figure 1. Precipitation during 1955-2014 in Nanning in Guangxi Table 1. The Rainfall Distribution of Nanning with Different Probabilities Level years Design rainfall frequency Typical year Rainfall(mm) Wet years 25% 1978 1445.2 Normal years 50% 1993 1250.2 Dry years 85% 1958 1063.8 2.2 The Monthly Precipitation in Wet, Dry and Normal Years The physiology of sugarcane is greatly influenced by climatic factors. Differences in water requirements arise in years with different amounts of rainfall. The correlation between monthly precipitation and monthly water requirements of sugarcane in major sugarcane fields of Guangxi Province in years with different amounts of rainfall shall be seen in Figure 2. As seen from the above picture, from April to September, the rainfall accounts for 80% of the total rainfall of the year. The other six months has comparatively less rainfall. As in Guangxi Province, rain and high temperature appear at the same period, the use efficiency of natural precipitation is greatly reduced. The rainfall is overly concentrated, which fail to correspond to the crucial period when the water demand of sugarcane is most urgent. Especially throughout the period from June to December, a phase that determines the yield and quality of sugarcane, natural precipitation cannot meet the water requirements of sugarcane, and supplementary irrigation is a must. 2
Water Demand and Rainfall(mm) 480 320 160 0 Rainfall in wet years Rainfall in normal years Rainfall in dry years 1 2 3 4 5 6 7 8 9 10 11 12 Months Figure 2. Monthly rainfall distribution in wet, normal and dry years 2.3 Water Requirements of Sugarcane in Wet, Dry and Normal Years The cycle of sugarcane s water demand begins in March and ends in December. At the early and late growth stages, the water demand is low, while at the middle stage of growth, the water demand is comparatively higher. Figure 3 shows the water requirements of sugarcane in Nanning in years with different amounts of rainfall. Water Demand and Rainfall(mm) 300 200 100 0 Water demand in wet years Water demand in normals years Water demand in dry years 1 2 3 4 5 6 7 8 9 10 11 12 Months Figure 3. Water demand of sugarcane under varying rainfall in Nanning 2.4 Correlation between Precipitation and the Water Requirements of Sugarcane Based on an analysis of the distribution of monthly rainfall, the correlation between the natural precipitation in years with different amounts of rainfall and the water requirements of sugarcane in major sugarcane fields in Guangxi Province is shown in Figure 4. 3
Monthly Rainfall Residual value of water (mm) 2 nd World Irrigation Forum 300 210 Wet years Normal years Dry years 120 30-60 3 4 5 6 7 8 9 10 11 12-150 Months Figure 4. Monthly Average Rainfall in wet, normal and dry years. As shown in Figure 4, in years with different amounts of rainfall, Guangxi sugarcane is short of water in varying degrees. In wet years, the water scarcity issue arises in July and November. In normal years, the water scarcity issue arises in March, July, September, October, November and December. In dry years, the water scarcity issue is prominent in the entire growth season. Specifically, in wet years, the annual water shortage calculated is190.9mm; in normal years, the annual water shortage calculated is 393.7mm; in dry years, the annual water shortage calculated is 525.0mm. For the purpose of further exploring the correlation between precipitation and the water requirements of sugarcane in Guangxi Province, the authors have analyzed the rainfall distribution on a fixed interval of five days in the representative area, as shown in Figure 5. After water balance analysis of Guangxi sugarcane, it is seen that the rainfall during the ten month (March to December) differs radically in time. The duration of water shortage is long and it is large in quantity. Except for July, when precipitation characteristics of South Guangxi can fully satisfy the water requirements of sugarcane and no supplementary irrigation is needed twenty days before harvest, the other eight months need supplementary irrigation. In Central Guangxi and North Guangxi, except that no supplementary irrigation is needed twenty days before harvest, it is a must in other months. The main reason is that the intra-annual distribution of precipitation in Guangxi Province is uneven. About 75% of the annual rainfall concentrates in the flood season (from April to September), while the rainfall during the flood season concentrates in May, June and July, which sometimes concentrates in a shorter time span. Especially in flood years, the rainfall is more concentrated. The rainfall during the six-month nonflood period accounts for only about 25% of the annual rainfall. Although the water demand during the entire growth season of sugarcane ranges from 724 to 939mm, the annual precipitation is 1153.1~1798.2mm. Therefore, according to the precipitation characteristics of Guangxi and the water demand of sugarcane at different stages of its growth, except for twenty days before harvest when irrigation is not needed, supplementary irrigation is a must, the volume of which amounts to276~ 389mm. 4
Every 5-day Rainfall Residual value of water (mm) 2 nd World Irrigation Forum 160 120 80 In Southern Guangxi Central region of Guangxi In Northern Guangxi 40 0-40 3 4 5 6 7 8 9 10 11 12 Mouth Figure 5. Five-day Rainfall minus Five-day Water Requirements at Guangxi 3. TECHNOLOGIES FOR DRIP IRRIGATION ON SUGARCANE IN GUANGXI PROVINCE 3.1 The Irrigation Quotas for Sugarcane in Guangxi Province Through an experimental study on the utilization of precipitation by sugarcane and its water demand, the authors conclude that the target yield of sugarcane in dry years is 50% higher than that without irrigation. The irrigation quotas of sugarcane based on the premise that it is cultivated in clay and under drip irrigation are as follows: Region I wet years (p=25%) 675m3/hm2, normal years (p=50%) 1005m3/hm2, dry years (p=75%) 1485m3/hm2;Region II wet years (p=25%) 585m3/hm2,normal years (p=50%) 870m3/hm2,dry years (p=75%) 1260m3/hm2; Region III wet years(p=25%) 765m3/hm2, normal years(p=50%) 1140m3/hm2,dry years(p=75%) 1680m3/hm2; Region IV wet years(p=25%) 645m3/hm2, normal years(p=50%)960 m3/hm2, dry years(p=75%)1425m3/hm2. The regional division is shown in Table 2. 3.2 The Irrigation Systems in Sugarcane in Guangxi Province According to the irrigation quotas determined by precipitation and water requirements of sugarcane at different stages of its growth under different climatic conditions, and based on the best time and optimal frequency of irrigation of sugarcane at different growth stages, the planned depth of the moist soil layer as well as proper control of soil moisture content, the optimal irrigation system of sugarcane under drip irrigation and under different climatic conditions in major sugarcane fields of China s Guangxi Province is determined, as shown in Table 2. Specifically, the planned depths of the moist soil layer of sugarcane at its germination stage, seedling stage, tillering stage, elongation stage and ripening stage are respectively 25cm, 25cm, 35cm, 40cm, 30cm; the percentage of wetted soil area is invariably 100%; when the irrigation reaches its upper limit, the soil moisture content is 85%; when the irrigation is at its lower limit, the soil moisture content is 65%. 5
Table 2. The Irrigations Systems of Sugarcane at Different Growth Stages under Drip Irrigation in Years with Different Amounts of Rainfall Type of Years Wet Years (P=25%) Normal Years (P=50%) Dry Years (P=85%) Crop stage Seedling Tillering Elongation Ripening Seedling Tillering Elongation Ripening Germination Germination Germination Seedling Tillering Elongation Ripening Region I Irrig. freq. 1 1 1 2 1 2 1 1 3 2 2 2 2 5 2 Irrig. quota 90 90 120 135 105 90 90 120 135 105 90 90 120 135 105 Region II Irrig. freq. 1 1 1 2 1 2 1 1 3 2 2 2 2 5 2 Irrig. quota 60 75 105 120 90 60 75 75 120 120 60 75 75 120 120 Region III Irrig. Freq. 1 1 1 2 1 2 1 1 3 2 2 1 1 3 2 Irrig. quota 105 105 135 150 120 105 105 135 150 120 105 105 135 150 120 Region IV Irrig. Freq. 1 1 1 2 1 2 1 1 3 2 2 2 2 5 2 Irrig. quota 75 75 120 135 105 75 75 120 135 105 75 75 120 135 105 Note: Region I: Baise City, Hechi City; Region II Nanning City, Guigang City, Laibin City, Chongzuo City; Region III Beihai City, Fangchenggang City, Qinzhou City; Region IV: Liuzhou City, Guilin City Irrigation Cycle: day; Irrigation Frequency: time; Irrigation Quota: m 3 /(hm 2 *time) 6
(WIF2) 4. CONCLUSIONS Through a research on sugarcane planting areas in Guangxi Province under different climatic conditions from 1955 to 2014, as well as an experimental study on the water demand and irrigation of sugarcane, with natural precipitation taken into consideration, and by utilizing the technologies for drip irrigation, the author of this thesis concludes that under different climatic conditions, the yield of Guangxi sugarcane based on modern drip irrigation technologies is 70% higher than that under conventional irrigation and fertilization management; the quantity of water saved is 1125m3/hm2; the brix has increased by 2%; and project investment has been reduced by 17%. Guangxi sugarcane is mainly planted on sloping lands. Therefore, the water conservancy infrastructure is unsatisfying. The natural effective irrigation area accounts for less than 10%. Although Guangxi has abundant rainfall, natural precipitation cannot be fully utilized because of its uneven distribution in space and time. As a district for strategic sugar reserve, the sustainable development of Guangxi sugarcane is still faced with such constraints as poor water conservancy infrastructure and outdated irrigation technologies. In order to ensure the sustainable development of Guangxi sugarcane, the government must increase investment in water conservancy infrastructure, promote advanced irrigation methods, such as drip irrigation, and foster the integration of water and fertilizer. Additionally, mechanized management and cultivation is a supplementary key point. ACKNOWLEDGEMENT This thesis is completed under Professor Li Xinjian s instructions. The content mainly consists of the research findings confirmed in 2012 Guangxi Scientific Project on Water Conservancy Applied Research on High-Efficient and Water-Saving Irrigation Technologies and Water Consumption Quota for Sugarcane in Guangxi Province (project number: 201225,201308-1), 2013-2015 Public Projects of the Ministry of Water Resources Research on the Development Model of High-Efficient and Water- Saving Irrigations on Sugarcane in Guangxi Province (project number: 201301013), 2014-2015 the Agricultural Science Technology Achievements Transformation Fund in Guangxi Autonomous Region Integration and Demonstration of Key Technologies for High-Efficient and Water-Saving Irrigation on Millions Mu of Sugarcane Fields in Guangxi Province (project number: 2014CB25). The programs are funded with a total funding of 3.13 million yuan. 7