What basic information is needed to formulate the irrigation system for dry crops?

Overview of agricultural utilization of water resources 1. 1 The arid and semi-arid areas in the world cover more than 50 countries and regions, with a total area of about 1/3 of the land area. Of the 65,438.04 million hectares of cultivated land, 80% are drylands whose agricultural production mainly depends on natural precipitation. The global agricultural irrigation area has increased from 5× 107 hectares in the early 20th century to 2.5× 108 hectares at present. It is predicted that by 20 10, the global irrigation area will increase by 19% on the existing basis, that is, the irrigated area of cultivated land accounts for 2 1.2% of the total cultivated land area, and the corresponding irrigation water consumption will increase by 1.2%. From 1950 to 1985, the global irrigated area grew at an average annual rate of more than 5%, accounting for 17.8% of the irrigated area of cultivated land and producing13 of the world's total grain. However, due to global warming and the increasingly serious drought, water resources are increasingly tense, and the cost of developing new irrigation systems is rising, with an average cost of more than 4,500 US dollars per hectare, even as high as 10500 US dollars. The decline in the benefit of irrigated agriculture has restricted the development of irrigated agriculture. Since 1980, the growth rate of irrigated area in the world has obviously decreased, and the annual growth rate is less than 1%. According to the report of the International Food Policy Research Institute, since the late 1970s, the development of new water resources in the world has been slow, the cost of developing new water resources has become more and more expensive, and the investment in irrigation projects has been decreasing, especially in Asia. Due to the single application of technology and the low effective utilization rate of water resources, the land area lost by waterlogging and salinization in the world is 3 million ~10.5 million hectares every year. Due to the differences in physical geography, climate and economic development level, the situation of agricultural water use in different countries and regions is also different. Table 3- 1 shows the water consumption and water consumption structure of 16 1 countries in the world. It is not difficult to see that the global water resources are not only unevenly distributed, but also have different utilization structures. The proportion of agricultural water use in Asia and Africa, two water-deficient and densely populated areas, is as high as 85%, indicating that the water resources situation of food security in these two areas is still grim. Judging from the degree of development and utilization of water resources, Africa is lower than Europe and the United States not only because of the limitation of economic conditions, but also because the total amount of water resources is insufficient and the development is difficult. The degree of water resources development and utilization in Asia is the highest in five continents, reaching 10.7%, but still lower than that in China (23%). The development and utilization of water resources in developed countries and water-rich areas are lower than the world average, and the proportion of agricultural water consumption is less than 50%. Table 3-2 shows the agricultural irrigation situation in 88 member countries of ICID. The total population of 88 member countries accounts for about 80% of the global population, with 86.3% of cultivated land, 99% of irrigated land and an average irrigation rate of 20.5%. The data in Table 3- 1 and Table 3-2 show that the main source of agricultural water is still natural precipitation, especially in areas rich in water resources. Irrigated agriculture is affected by the shortage of resources, rising costs, declining agricultural benefits and other factors, and its growth rate is obviously reduced. Due to the dense population, the degree of water resources development, farmland irrigation rate and agricultural water consumption in Asia are much higher than those in other regions, which shows that irrigated agriculture in Asia is developing rapidly. However, the decline of irrigation investment and the deterioration of ecological environment in Asia in recent years also show that the agricultural development model based on water resources development in Asia has caused excessive consumption of water resources, which will increase the pressure of water resources for further agricultural development. Water saving and high efficiency is the basic direction of agricultural development in Asia. Table 3- 1 Water consumption and water consumption structure in different parts of the world; Total water consumption of millions of people in different countries; Km3/ year per capita water consumption; M3/ Yr water resources development and utilization ratio% water use structure (%) agricultural industry and life in Africa +0.96 1 0.02.885.45.88.7 America+05.88.8888538+065472.3838+00.786.47.76.0 Europe.40886.88888888885 The United States has formulated standards or planning guidelines for rainwater harvesting systems and optimized the design of the systems. Its rainwater collection facilities mainly include steel containers, fiber folding containers coated with rubber or wrapped with plastic, glass fiber tanks, polyethylene containers, mahogany containers and other types. The rainwater collection surface is treated with flexible membrane, asphalt or other impermeable materials. 2) Inter-basin water transfer Inter-basin water transfer is an effective way to solve the uneven distribution of water resources in time and space. The former Soviet Union, the United States, India, Canada, Mexico, Pakistan and other countries have carried out large-scale water transfer, and Iraq, Libya, Turkey and other countries are also actively implementing their own water transfer plans. However, the water diversion project will also have some serious negative effects, such as a series of social and economic problems and environmental problems caused by over-investment, resettlement of immigrants and inundation of cultivated land. 3) Utilization technology of underground reservoir The global underground fresh water accounts for 30. 1% of the global total fresh water reserves, so all countries in the world attach great importance to the development and utilization of groundwater for irrigation. Many irrigation districts in California have established groundwater recharge systems. By regulating the water storage capacity of underground reservoirs, the shortage can be made up and the effective utilization rate of water resources can be improved. 4) inferior water utilization technology inferior water includes industrial and domestic sewage and salt water. In the case of increasing shortage of fresh water resources, many countries regard inferior water irrigation as an important way to make up for the shortage of fresh water resources. Sewage irrigation is regarded as a powerful measure to eliminate pollution, solve the shortage of agricultural fresh water resources and promote agricultural production, which further promotes the development of sewage irrigation. The utilization rate of treated sewage in Israel reaches 70%, ranking first in the world, of which 1/3 is used for irrigation, accounting for about 1/5 of the total irrigation water. At present, more than 3,400 sewage reuse projects have been built in the United States, and 45 of the 50 states in China have adopted sewage irrigation. In the early 1980s, 50% of the sewage in the former Soviet Union, including all industrial wastewater, was used for farmland irrigation. Since 1980s, the sewage used for farmland irrigation in India accounts for more than 50% of the total urban sewage. A large amount of irrigation water in Saudi Arabia, especially for non-food crops, is treated wastewater. The irrigated area of desalinated salt water in Israel reaches 45,000 hectares, while that in Spain and Italy is 29,000 hectares and15,000 hectares respectively. 1.2.2 Water-saving technology for water conveyance 1) Canal anti-seepage technology Channel lining is the main measure to reduce water conveyance loss and improve the utilization rate of irrigation water. The materials used for lining in various countries include rigid materials, soil materials and membrane materials. At present, rigid materials (especially concrete lining) are the main materials. With the development of chemical industry and the progress of mechanized construction technology, the proportion of film lining mainly made of polyethylene and PVC is increasing day by day. Membrane lining has the advantages of good anti-seepage effect, strong durability, low cost and convenient construction. In the United States, there are more and more kinds of polymers used as hydraulic building materials, and their application scope is gradually expanding. In the United States, the excavation of canal bed, the laying of plastic film, the filling of soil or the pouring of concrete protective layer are all done by machinery. Central Asia and Ukraine of the former Soviet Union have also adopted the method of pouring concrete as a whole and laying 0.2 mm thick impervious membrane under the lining of concrete precast slabs in small and medium-sized channels. In Punjab, India, cheap polyethylene film is laid under prefabricated silicon bricks. The channel 15 years has been running well and the engineering benefit is remarkable. 2) Low-pressure pipeline irrigation technology Low-pressure pipeline irrigation technology can not only reduce the loss of water transmission and distribution, but also has the advantages of saving land, strong terrain adaptability, frost heaving prevention and so on, which is beneficial to management. It has become the main direction of field irrigation technology in the world. 1984, the irrigation area of low-pressure pipeline in the United States accounted for 46.9% of the total irrigation area, and all the branch canals below the San Joaquin Valley irrigation area in California were piped, and the water utilization coefficient of the canal system reached 0.97. Japan, Israel, the former Soviet Union, Eastern European countries, Canada, Australia and other countries have also developed rapidly. Foreign low-pressure pipeline irrigation technology has matured, including surface and underground types. Ground pipelines mainly include flexible polyethylene hoses, thin-walled galvanized pipes, aluminum alloy pipes and nylon rubber composite pipes, and underground pipelines include low-pressure concrete earth pipes, plastic-coated thin-walled steel pipes and light semi-rigid plastic pipes. The main research direction in the future is to develop new pipes with better performance and lower price, all kinds of advanced water measuring and drainage equipment, and system types suitable for multi-objective utilization or automatic management. 1.2.3 field irrigation water-saving technology 1) spray micro-irrigation technology is an important way to improve the utilization rate of agricultural water, and spray micro-irrigation technology is the mainstream of irrigation water-saving technology development in the world. 82% of the irrigation area in European countries adopts advanced irrigation technology, and only 14% of the irrigation area adopts ground gravity irrigation. Spray micro-irrigation technology has developed rapidly in Israel, the United States, the former Soviet Union and some European countries. The area of spray micro-irrigation in Israel, Germany and Austria accounts for 100% of the irrigation area in their respective countries. Israel is extremely poor in water resources and attaches great importance to choosing the most water-saving irrigation technology. The proportion of drip irrigation in spray micro-irrigation has reached 70% (Table 3-3). Table 3-3 Total irrigation area with advanced irrigation technology in each country (million hectares) Irrigation area with advanced irrigation technology (hectares) Sprinkler irrigation and drip irrigation area (%) The total area of sprinkler irrigation, drip irrigation and drip irrigation in the United States is 265,438+0.4003,380,006,5438+0.050,004,430. 0002 1.0 France1.610-140,0001.450,00090.0 India 57.0658,500260,0096538+. 000 100.0 Egypt 3.300450.000 1 04.000554.00017.0 Germany 0.532530,0002,000532,000100.0 00080 000425 000 16.0 Slovakia 0.3103/kloc-0 0002 650312 65099.0 Iran 8.050 199 07553 765438. 000 16 1, 00023 1, 000 100.0 Syria1.28093,000155,0001. 00099.0 Czech 0.153151.01.224152,23599.5 Australia 2.000— 100. 00063.0 Hungary 0. 13082 0004 20089 20068.6 Portugal 0.63040 00025 00065 00 10.0 Malawi 0.05543 1935 45048 6448. 60062.0 Cyprus 0.0552, 00025, 00027, 00049.0 Mexico 6.200— 105, 000600, 000 10.0 sprinkler irrigation forms include central supporting shaft sprinkler irrigation, rolling sprinkler irrigation, translation sprinkler irrigation, coiled sprinkler irrigation and artificial seasonal fixed sprinkler irrigation. Compared with sprinkler irrigation, micro-irrigation is more water-saving and energy-saving, and the effect of increasing production is more obvious, so its development momentum is also very strong. The area of micro-irrigation in the world increased from 437,000 hectares in 198 1 year to 3.767 million hectares in 2000. The United States and Israel are developing underground drip irrigation technology, which has achieved better results than surface drip irrigation and is beneficial to the utilization of sewage irrigation. Small micro-irrigation system represented by gravity (low head) drip irrigation is especially suitable for popularization in developing countries. Many developing countries have also taken the road of moderate development according to their national conditions, which has made spray micro-irrigation develop to a certain extent. The development trend of spray micro-irrigation technology is: a. low pressure energy saving; B, spray micro-irrigation is combined with each other; C. actively carry out multi-objective utilization; D. improving equipment and performance; E. products are becoming more and more standardized, serialized and universal; Automation of operation management. 2) Improving surface irrigation technology While developing micro-irrigation technology, countries attach great importance to the improvement and development of conventional irrigation methods, and have successively developed rope-controlled irrigation (the United States), slope irrigation pipe irrigation (the Soviet Union), surge irrigation (the United States), surface infiltration irrigation (Japan), negative pressure differential irrigation, soil net irrigation, small dryer or mist collector water-collecting irrigation (South America) and dish irrigation (India and Brazil). 1.2.4 Agronomic water-saving measures mainly include cultivating drought-tolerant crops and water-saving varieties, improving farming methods and cultivation techniques, and popularizing ground mulching technology. These measures are applicable to both irrigated and arid agricultural areas. 1) Drought-tolerant crops and water-saving varieties can generally avoid the dry season in the key growth period, or have strong stress resistance, or can overlap with the local rainy season, grow rapidly in the rainy season, and make full use of limited precipitation. India and the United States attach great importance to the breeding of sorghum varieties. At present, there are 45 excellent sorghum hybrid varieties popularized and applied in India, with a coverage rate of 38%. These varieties not only have high yield, but also have good quality. The taste of some sorghum can be comparable to that of japonica rice in China. Sorghum is widely used in silage, hay mowing and stubble grazing in arid areas of the United States, which is the key link of stubble mulching and conservation tillage. Sorghum has high water use efficiency and stable production performance, which has become the basis of dryland sorghum/beef cattle farming and animal husbandry system. The United States attaches importance to strengthening the drought tolerance of sorghum. In recent years, Dezhou Agricultural Experimental Station has transformed tall, late-maturing and temperate tropical sorghum germplasm into dwarf, early-maturing, cultivated and temperate types by means of introgressive hybridization, which has expanded the scope of planting and utilization. After years of efforts, researchers in the Plant Molecular Laboratory of Texas Tech University have made a breakthrough in molecular breeding. Tucson experimental station in Arizona is vigorously screening salt-tolerant and water-saving plants to enrich the crop population cultivated today. 2) Improved farming methods and reasonable soil farming have the functions of regulating soil physical properties, storing water and preserving moisture, and increasing available nutrients. Therefore, all countries attach great importance to the improvement and development of farming methods when exploring ways to develop water-saving agriculture. In developed countries, due to the destruction of soil structure by mechanized operation and chemical fertilizer application, soil water loss, water erosion and wind erosion have been caused, so various protective farming methods have been implemented. The basic trend is from more tillage to less tillage and no tillage, from shallow tillage to deep tillage, from ploughing to subsoiling, from single crop continuous cropping to grain and grass rotation or moderate leisure. Pay attention to soil and water conservation, absorb rain and store water, and transfer water with fertilizer. In the United States, with the emergence of efficient herbicides and no-tillage seeders, modern no-tillage technology has been widely used in wheat, barley, cotton, tobacco, sorghum, soybean, sugar beet and feed crops. At present, 70% of the cultivated land in the United States has been ploughed, and the no-tillage sowing area has accounted for 20% of the national grain crop area. According to this prediction, by 20 10, 95% farmers in the United States will replace traditional farming methods with less no-tillage methods. 3) Popularize ground cover technology. Ground cover includes organic matter cover and plastic film cover. It has the functions of inhibiting soil evaporation, storing precipitation, keeping soil moisture and raising ground temperature, and can save irrigation and increase yield. It is a very effective measure to resist drought and increase production, with simple technology and low cost. Crop straw mulching is widely used in the plains of the United States, and the soil water storage capacity covered by wheat straw, sorghum and ginning chips has increased obviously. Japan, the first country to use plastic films, adopted many different kinds of plastic films according to different crops and cultivation methods, including transparent, black, silver-black, aluminized and other colors and materials, as well as plastic films with holes and strips. In order to solve the pollution problem, a variety of degradable plastic films have been developed in recent years. With the emergence of photodegradable plastic film mulching materials, multifunctional plastic films and thin high-strength plastic films, plastic film mulching technology has been widely used in field vegetables, cotton, corn and other crops in western Europe. 1.2.5 chemical water-saving technology 1) chemical mulching chemical mulching is to use a polymer film to prevent the emission of soil moisture, and the water will gather and condense under the film, increasing the water content of topsoil. The former Soviet Union, the United States, Japan, France, India, Romania, Belgium and more than a dozen other countries have used chemical plastic film in farmland abroad, and the yield increase effect has reached 10 ~ 30%. Chemical mulch materials for farmland include paraffin, asphalt emulsion, resin, rubber, plastic, etc. The use method is film forming, foaming and powder covering. 2) Water-retaining agent Water-retaining agent is a kind of soil improvement system, which can be roughly divided into three categories: inorganic, organic and polymer synthetic substances. The water-retaining agent absorbs water quickly (the water absorption capacity can reach 50 ~ 500 times), and it can slowly seep out the water contained in it through diffusion in dry environment, and can absorb water and seep water repeatedly. Usually used for seed coating, seedling root coating and seed granulation. In 1970s, the Northern Research Center of the United States Department of Agriculture synthesized a new type of super absorbent and water-retaining agent, including starch system, cellulose system and synthetic polymer system. Good results have been achieved in seed afforestation, seed coating and seedling transplanting. Japan, Britain, France and the former Soviet Union all developed and used their own water-retaining agents. The polymer composed of vinyl alcohol/acrylate and cross-linked polyacrylate has been studied a lot. The main research direction in the future is to prolong its service life, so as to improve utilization efficiency and ensure economy. Whether the water-retaining agent and its decomposition components have adverse effects on soil and crops needs further study. 3) Anti-transpiration agent According to the researchers' determination, only 65,438+0% of the water absorbed by crop roots becomes the component of crop cells, and the remaining 99% enters the atmosphere through crop transpiration. Part of this water is necessary for crops to maintain their lives, while the other part is ineffective and lost. According to American research data, the use of anti-transpiration agent can reduce soil water loss by about 40%. The main types of anti-Iranian drugs include metabolic type, thin film type and reflex type. 1.2.6 management of water-saving measures 1) the formulation of water-saving irrigation system is not only related to the output of unit water consumption of crops, but also can control the maximum possible water consumption of crops, which is an important content of water-saving agriculture. Since 1970s, many countries have done a lot of research in this field. The experimental results in Israel show that the best irrigation treatment is to obtain the yield close to the highest yield with the least water, which is equivalent to 85% ~ 95% of the highest yield. 2) Paying attention to field water management and farmers' participation in field water management are important components of irrigation water management. In order to improve and strengthen field water management, countries are constantly improving field channels and facilities, adopting advanced irrigation technology, actively exploring ways to reduce water evaporation and leakage, increasing the utilization of soil water and improving the utilization efficiency of precipitation and irrigation water. At the same time, they also attach importance to mobilizing farmers to participate in water management and strengthening the construction of water distribution facilities. Developed countries such as Canada, the United States and Japan began to attach importance to replacing supply management with demand management and implement dynamic management of irrigation water. 3) Strengthening the information management of water use in irrigation areas With the increasingly prominent contradiction between supply and demand of fresh water resources, in recent years, many countries have attached importance to the study of economic water use and modernization of water management in irrigated agriculture. The essence of irrigation water management is irrigation water information management, and reasonable irrigation and its corresponding measures depend on reliable water information. The water information management in developed countries such as the United States and Japan is relatively advanced, such as the CIMIS irrigation management information system in California, which includes the network of more than 70 meteorological stations located in key agricultural areas. Every night, the observation data of each station are automatically transmitted to the calculation center of the Water Conservancy Bureau. The meteorological data collected by the center, including rainfall, soil, temperature, wind direction, wind speed and relative humidity, are stored in CIMIS database after analysis and calibration, and provided to the website, and then provided to farmers by the website for accurate determination. 4) Implement planned water use, and rationally allocate water in irrigation areas with more water and less water. The contradiction between supply and demand between water supply and crop field water demand is prominent. The implementation of planned water use, optimized water diversion technology with limited water supply for main crops, optimized combination of rotary irrigation bucket and agricultural canal, and unified dispatching of multiple water sources in irrigation area can effectively allocate limited water resources and maximize benefits. 5) Promoting the development of irrigation management to automation With the rapid development of science and technology, developed countries generally adopt new technologies such as computer, electricity measurement and remote sensing to manage water use. In the United States, large irrigation areas are equipped with dispatching centers to implement automatic management. Most of the newly built or rebuilt irrigation areas in Japan in the early 1980s are equipped with telemetry and remote control devices from the head of the canal to each water point. Most irrigation districts in Romania realized automatic or semi-automatic management in the early 1980s. All irrigation areas in Israel, regardless of size, adopt automatic control. 6) Regulating water use through water price From a global perspective, the water price of irrigation water is much lower than that of domestic, urban and industrial water. Even in developed countries such as France, Germany and Israel, where irrigation systems can achieve self-sustaining development, the price of irrigation water is still only about110 of other water prices (Table 3-4). Australia, Cyprus, the United States, Egypt, South Africa, India, Pakistan, France and Britain have all formulated corresponding water price policies. 7) Operation and maintenance of water resources management institutions Most countries have institutions for determining different types of water demand and distributing water. Irrigation systems in Australia, Egypt, Pakistan, India and Malaysia are managed by government agencies. However, in Austria, Britain, Mongolia and the United States, the operation of irrigation systems is mainly completed by water users' associations. Other countries, such as Italy, Israel, South Africa and Turkey, are jointly completed by government agencies and water users' associations. The operation and maintenance of irrigation systems vary from country to country, and the proportion of operation and maintenance costs invested by the government and water users is also very different. Cyprus, Pakistan, India, South Africa and Thailand all bear the required expenses by the government, Austria, France, Germany and the United States all bear the required expenses by the water users, and other countries are shared by both. ,,,,,,, References:

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