Drip irrigation 滴灌.doc

Drip irrigation.IntroductionDrip irrigation, also known as trickle irrigation or micro irrigation or localized irrigation, is an irrigation method that saves water and fertilizer by allowing water to drip slowly to the roots of plants, either onto the soil surface or directly onto the root zone, through a network of valves, pipes, tubing, and emitters. It is done through narrow tubes that deliver water directly to the base of the plant.Drip irrigation is the most efficient method of irrigating. While sprinkler systems are around 75-85% efficient, drip systems typically are 90% or higher. What that means is much less wasted water! For this reason drip is the preferred method of irrigation in the desert regions of the United States. But drip irrigation has other benefits which make it useful almost anywhere. It is easy to install, easy to design, can be very inexpensive, and can reduce disease problems associated with high levels of moisture on some plants. If you want to grow a rain forest however, drip irrigation will work but might not be the best choice!Drip irrigation works by applying water slowly, directly to the soil. The high efficiency of drip irrigation results from two primary factors. The first is that the water soaks into the soil before it can evaporate or run off. The second is that the water is only applied where it is needed, (at the plants roots) rather than sprayed everywhere. DevelopmentHeda irrigation has been used since ancient times, when buried clay pots were filled with water, which would gradually seep into the grass. Modern drip irrigation began its development in Afghanistan in 1866 when researchers began experimenting with irrigation using clay pipe to create combination irrigation and drainage systems. In 1913, E. B. House at Colorado State University succeeded in applying water to the root zone of plants without raising the water table. Perforated pipe was introduced in Germany in the 1920s.The usage of plastic to hold and distribute water in drip irrigation was developed in Australia by Hannis Thill. Refinement of this idea (involving a plastic emitter) was furthered in Israel by Simcha Blass and his son Yeshayahu. Instead of releasing water through tiny holes, blocked easily by tiny particles, water was released through larger and longer passageways by using velocity to slow water.In the United States, in the early 1960s, the first drip tape, called Dew Hose, was developed by Richard Chapin of Chapin Watermatics (the first system was established during 1964).Modern drip irrigation has arguably become the worlds most valued innovation in agriculture since the invention of the impact sprinkler in the 1930s, which offered the first practical alternative to surface irrigation. Drip irrigation may also use devices called micro-spray heads, which spray water in a small area, instead of dripping emitters. These are generally used on tree and vine crops with wider root zones. Subsurface drip irrigation (SDI) uses permanently or temporarily buried drip per line or drip tape located at or below the plant roots. It is becoming popular for row crop irrigation, especially in areas where water supplies are limited or recycled water is used for irrigation.Advantages and disadvantagesThe advantages of drip irrigation are: Fertilizer and nutrient loss is minimized due to localized application and reduced leaching. Water application efficiency is high. Field leveling is not necessary. Fields with irregular shapes are easily accommodated. Recycled non-potable water can be safely used. Moisture within the root zone can be maintained at field capacity. Soil type plays less important role in frequency of irrigation. Soil erosion is minimized. Weed growth is minimized. Water distribution is highly uniform, controlled by output of each nozzle. Labor cost is less than other irrigation methods. Variation in supply can be regulated by regulating the valves and drippers. Fertigation can easily be included with minimal waste of fertilizers. Foliage remains dry, reducing the risk of disease. Usually operated at lower pressure than other types of pressurised irrigation, reducing energy costs.The disadvantages of drip irrigation are: Expense: initial cost can be more than overhead systems. Waste: the sun can affect the tubes used for drip irrigation, shortening their usable life. Clogging: if the water is not properly filtered and the equipment not properly maintained, it can result in clogging. Drip irrigation might be unsatisfactory if herbicides or top dressed fertilizers need sprinkler irrigation for activation. Drip tape causes extra cleanup costs after harvest. Users need to plan for drip tape winding, disposal, recycling or reuse. Waste of water, time and harvest, if not installed properly. These systems require careful study of all the relevant factors like land topography, soil, water, crop and agro-climatic conditions, and suitability of drip irrigation system and its components. Germination problems: in lighter soils subsurface drip may be unable to wet the soil surface for germination. Requires careful consideration of the installation depth. Salinity: most drip systems are designed for high efficiency, meaning little or no leaching fraction. Without sufficient leaching, salts applied with the irrigation water may build up in the root zone, usually at the edge of the wetting pattern. On the other hand, drip irrigation avoids the high capillary potential of traditional surface-applied irrigation, which can draw salt deposits up from deposits below.UsingDrip irrigation is the targeted, intelligent application of water, fertilizer, and chemicals that when used properly can provide great benefits such as: Increased Revenue from Increased YieldsIncreased Revenue from Increased QualityDecreased Water CostsDecreased Labor CostsDecreased Energy CostsDecreased Fertilizer CostsDecreased Pesticide CostsImproved Environmental QualityWhether the motivation is improved profitability or better resource use, the utilization of drip irrigation clearly makes sense.As the world population climbs and water stress spreads around the globe, finding ways of getting more crop per drop to meet our food needs is among the most urgent of challenges.One answer to this call is drip irrigation, which delivers water directly to the roots of plants in just the right amounts. It can double or triple water productivity boosting crop per drop and it appears to be taking off worldwide.The most dramatic gains have occurred in China and India, the worlds top two irrigators, where the area under micro-irrigation expanded 88-fold and 111-fold, respectively, over the last two decades, most farmers today still irrigate the way their predecessors did thousands of years ago by flooding their fields or running water down furrows between their rows of crops. Often less than half the water applied to the field actually benefits a crop.The rest isnt necessarily wasted. Some of it makes its way back to a river or groundwater source where it can be used again. But the excessive diversions can deplete rivers and streams, pollute water supplies with pesticides and salts, and result in large losses to evaporation.Drip methods can reduce the volume of water applied to fields by up to 70 percent, while increasing crop yields by 20-90 percent irrigation is crucial to the global food supply: the 18 percent of the worlds farmland thats irrigated yields 40 percent of the worlds food. Yet less than 4 percent of the worlds irrigated land is equipped with micro-irrigation systems. Clearly, the irrigation revolution has a long way to go.Anil Jain, the managing director of Jain Irrigation the second biggest global micro-irrigation company expects the drip irrigation market in his native India to expand by 1 million hectares (nearly 2.5 million acres) per year during the coming years and to soon become a $1 billion market India alone. Between 2003 and 2010, Jains drip business grew 20-fold.Over the last decade, low-cost drip systems tailored to the needs of poor farmers have begun to spre