Knowledge Title: Irrigation

Other Title: irrigation

Knowledge Content:

    According to the requirements of crop water demand, artificially to the farmland to replenish water and other measures of farmland. Irrigation can meet the demand for water for crops in time, improve soil water, fertilizer, gas, heat and salt, improve the microclimate of farmland, and achieve the goal of increasing agricultural production.

    China is one of the earliest countries in the world to develop farmland irrigation. Qin and Han before the irrigation of farmland is called “immersion”, to the Han Dynasty has the name of “over- " or “irrigation”, the West Han time “irrigation” and “irrigation”, “irrigation” and use. After Tang used to use the word “irrigation”, and continue to use it to this day.

    Irrigation PrincipleS Crops require a lot of moisture from seed germination to plant maturation. Crop water demand includes both physiological water and ecological water demand. Crop physiological water demand refers to the water required for various physiological activities (such as steaming, photosynthesis, etc.) in the course of crop life, and the water needed for the development and development of crops in the process of fertility. The former is represented by leaf steaming, which accounts for about 60 to 80% of the amount of water needed for crops, while the latter is represented by evaporation between plants, which represents about 20 to 40% of the amount of water needed for crops. If the amount of water absorbed by the plant is less than the amount of water consumed, i.e. when the water balance in the plant is out of balance, light causes temporary wilting and heavy dry death. Atmospheric drought or soil drought will cause the crop stems and leaves to suffer in varying degrees of wilting, resulting in the weakening of photosynthesis, affecting the production and accumulation of organic matter, while the root system water absorption function is weak, the body organic nutrient transport is destroyed. Water scarcity is more harmful to young crops and organs.

    Irrigation can replenish soil moisture and regulate the moisture status of farmland. The need for irrigation of farmland and the amount of water needed for crop irrigation depend on factors such as hydrology, meteorology, soil conditions and agricultural technology level, and precipitation and regional dryness are the decisive factors. Year-round water supply irrigation is required in arid areas, seasonal irrigation in semi-arid areas is required in rain-affected areas, supplementary irrigation is required during rainy seasons in semi-humid areas (recurrent irrigation is required in rice areas), drought-resistant irrigation at critical times is required in wet areas when rainfall is unstable, and marshes can be properly irrigated on the basis of need after drainage improvement. In short, due to the uneven distribution of precipitation and precipitation in time and space, in order to obtain stable agricultural production and high yield, different regions need to have some irrigation to supplement the demand for water for crops. Especially in the interior of northwest China, there is no agriculture without irrigation.

    The development of modern science and technology and the mutual penetration between disciplines have promoted the modernization of irrigation and the development of farmland irrigation theory. Based on the disciplines of plant physiology, agrohydrology, agrometeorology, soil science, hydrogeology, agronomy, agricultural engineering, etc., people are studying the function of water in the farmland-plant-atmosphere system, exploring the changes of farmland water, fertilizer, gas, heat and salt, and further mastering the laws of crop water demand and the principle of irrigation of farmland. In order to make more rational use of agricultural water resources, improve soil, increase crop yields.

    Irrigation types according to different irrigation technology can be divided into: ground irrigation, irrigation, drip irrigation, underground irrigation and so on. According to water source conditions and water diversion methods can be divided into water storage irrigation (see water storage irrigation project), water irrigation, water diversion irrigation (see water diversion irrigation project), well irrigation, sewage irrigation, etc. According to hydrometeorological conditions and the purpose of farming needs can be divided into: (1) supplementary irrigation. That is, according to the law of crop water demand, water is introduced into farmland in a timely and appropriate manner, so that water storage is stored in the soil layer available for crop use (dry fields), or the formation of water layer (rice paddies) on the field surface, to meet the physiological and ecological water demand requirements of crops and water. (2) Fertilization (drug) irrigation. Dissolved fertilizer (pesticides) in water and then poured into the field by irrigation, drip irrigation, or other irrigation methods. (3) Temperature irrigation. Irrigation is used to regulate the microclimate in the field. Such as winter irrigation to benefit wheat safe winter, with spray irrigation frost, spray irrigation against drought wind damage or high temperature. (4) Salt washing irrigation. That is, in the cultivated land of saline soil, water pressure salt is poured to change the distribution of salt in the soil profile and flush the salt, in order to improve the saline soil. (5) Desilting irrigation. That is, the use of water and sand resources, silting fertilizer fields, in order to improve the soil. (6) Water storage irrigation. That is, when farmland needs less water and the water source is relatively abundant, a large amount of irrigation water is stored in the soil for later use. (7) Weed irrigation. That is, the use of rice paddies deep water flooding to eliminate weeds. In addition, there are irrigation sparing lying to improve soil farming or prevent wind erosion.

    Irrigation technology and standards All kinds of irrigation technologies should aim at timely and appropriate and uniform irrigation without destroying soil structure. Irrigation standards, also known as drought-resistant standards, refer to the degree of guarantee of irrigation water use by irrigation facilities. It is an important indicator of water supply capacity of irrigation projects, generally expressed in the number of days that can be guaranteed to use water for crops during persistent drought. Irrigation standards are determined according to factors such as soil and water resources, crop types and water demand, the basis of the original water conservancy facilities, agricultural development requirements and the level of local production development. The standard seisted in the typical year of designing irrigation works is often called the irrigation design standard.

    The drought and flood standard of precipitation can be selected by hydrological analysis to test the laws of historical drought and flood, and the representative year is selected by the typical year or frequency method. Frequency method generally guarantees the rate of 50%, 75%, 90% of the three indicators, respectively, representing the perennial, moderate to dry years, dry years of drought, according to the drought design, to the dry year as a school. According to the planting area of various crops and the irrigation system of each crop to determine the irrigation system of irrigation areas, the effective precipitation during the growth period of the crop is deducted to obtain irrigation water demand and water use process. The water quantity and water diversion process that need to be referenced from the water source are then determined according to the planned irrigation area and the effective utilization rate of water in the irrigation system, which provides the basis for the design and planned water management of the irrigation system. According to the ability of water source to supply agricultural water under comprehensive utilization conditions, the development scale and irrigation standard of farmland irrigation are determined, so that there is a better and more stable water balance between irrigation water demand, effective precipitation and water supply. Because the size of river runoff is determined by the amount of water coming upstream of irrigation area, its drought and flood frequency are not consistent with the precipitation frequency in irrigation area, in the absence of water storage, we must reasonably adjust the planting structure, crop layout, soil and water resources utilization, planning economic indicators and so on to achieve water balance. Water storage irrigation should be developed when natural runoff is insufficient.

    Irrigation system The water transmission system consisting of various channels and supporting water conservancy project buildings in the irrigation area. Generally comprises 3 parts: (1) water engineering systems, i.e. buildings that draw water from rivers, reservoirs, etc.; (2) water transmission and distribution systems, which are to transport water from the head of the canal and assigntoe to fixed channels at all levels throughout the irrigation area; and (3) field irrigation networks, i.e. field pipes or temporary channels below the last fixed channels. Farmland irrigation system is usually matched with the farmland drainage system to form the irrigation and drainage system of irrigation area. In the irrigation season, the water demand for irrigation of farmland varies with the size of the rain, and the overwater of the irrigation system changes within a certain range, which causes the water level of the channel to rise and fall. This requires the irrigation system to adjust so that it can reach self-flowing watering at low water levels. In the shortage of water, it is also necessary to adjust the layout of irrigation crops, adjust irrigation area, irrigation quota to reduce the amount of irrigation water, and organize reasonable round irrigation in irrigation areas, so that the water volume to achieve balance to meet the needs of agricultural production, received good economic benefits.

    The combination of large, medium and small reservoirs and ponds created in China, combining water storage, water diversion and water lifting, is a successful experience. This irrigation system can combine the use of reservoirs, ponds and other water sources to fill the gap, improving the ability of water sources such as reservoirs and ponds to store and use water resources effectively.

    Problems and trends With the rapid increase of the world's population and the development of industrial and agricultural production, the world generally feel that water resources are insufficient, irrigation water is tight, and water pollution is becoming more and more serious. Energy constraints and rising energy prices have also contributed to the shortage of irrigation energy and the rising cost of irrigation. Under the condition of large-scale water diversion irrigation, the water table rises in some areas, which produces secondary salinization of soil, and the water table drops in some areas due to over-extraction of groundwater, which causes social hazards such as subsidence of the ground.

    Therefore, farmland irrigation technology will develop in the direction of comprehensive utilization of water resources such as power generation, irrigation and flood control, water conservation and energy conservation new technologies will be further developed, and ground irrigation technology and water resources management will be further valued. In the case of ever-expanding irrigation area, systematic analysis methods are adopted to adjust the relationship between supply and demand, the optimal scheme of water supply and irrigation should be selected to meet the water demand of irrigation, and a good ecological balance should be established, and the operation of irrigation systems should be controlled by electronic computer technology gradually, and under the premise of appropriate restrictions on groundwater over-extraction. It is of great significance to study in depth the artificial irrigation technology to control the subsidence of the ground.

    Bibliography  K.K. Framji, L.J. and Drainage in The World, International Commision on The Drainage, New Delhi, 1969.