Environmental Problems, Their Causes, and Sustainability 1

Figure 15-20 Major irrigation systems. Because of high initialcosts, center-pivot irrigation and drip irrigation are not widelyused. This may change because of the development of newlow-cost drip irrigation systems.Gravity flow(efficiency 60% and 80% with surge valves)Water usually comes from anaqueduct system or a nearby river.SolutionsReducing Irrigation Water Waste• Lining canals bring water to irrigation ditches• Leveling fields with lasers• Irrigating at night to reduce evaporation• Using soil and satellite sensors and computersystems to monitor soil moisture and add wateronly when necessary• Polyculture• Organic farming• Growing water-efficient crops using droughtresistantand salt-tolerant crop varieties• Irrigating with treated urban waste water• Importing water-intensive crops and meatFigure 15-21 Solutions: methods for reducing water waste inirrigation. Which two of these solutions do you believe are themost important?Drip irrigation(efficiency 90–95%)Above- or below-ground pipesor tubes deliver water toindividual plant roots.Center pivot(efficiency 80% with low-pressuresprinkler and 90–95% with LEPA sprinkler)Water usually pumped fromunderground and sprayed frommobile boom with sprinklers.emitters in the tubing deliver drops of water at a slowand steady rate close to the plant roots.Another innovation is DRiWATER ® , called “dripirrigation in a box.” It consists of 1-liter (1.1-quart)packages of gel-encased water that is released slowlyinto the soil after being buried near plant roots. Itwastes almost no water and lasts about 3 months.Drip irrigation is very efficient, with 90—95% ofthe water reaching the crops. It is also adaptable becausethe flexible and lightweight plastic tubing can befitted to match the patterns of crops in a field and leftin place or moved around.Bad news. Drip irrigation is used on just over 1% ofthe world’s irrigated crop fields and 4% of those in theUnited States. However, this percentage rises to 90% inCyprus, 66% in Israel, and 13% in California. The mainproblem is that the capital cost of conventional drip irrigationsystems is too high for most poor farmers andfor use on low-value row crops.Also, irrigation water is underpriced because ofgovernment subsidies. Raise water prices enough anddrip irrigation would quickly be used to irrigate mostof the world’s crops. Good news. The capital cost of anew type of drip irrigation system is one-tenth asmuch per hectare as conventional drip systems.Figure 15-21 lists other ways to reduce waterwaste in irrigating crops. Since 1950, water-short Israelhas used many of these techniques to slash irrigation324 CHAPTER 15 Water Resources