Chandra A. Madramootoo 2015-02-23 23:27:56
It is sometimes remarked that the world is in the midst of several interconnected crises— a food crisis, a water crisis, and an energy crisis. All of these crises are magnified and compounded by the effects of a changing climate and the more frequent occurrences of floods and low rainfall in several parts of the world. World hunger and malnutrition will regrettably increase if we fail to conserve our precious and fragile land and water resources, and better manage the energy inputs to the agricultural system. Agricultural and biological engineers are well positioned to find solutions to these global problems. Sustainable management of natural resources, development of bioenergy systems, and the use of biologically engineered systems to mitigate the impacts of climate change are at the heart of the solutions. The world population is expected to increase to about 9 billion by 2050, and the United Nations FAO projects that world food supplies will have to at least double to meet the increased demand. In some regions, such as Southeast Asia, food supplies may have to increase by as much as 75%. The land base for increasing food production is limited, particularly in the developing world, and further land expansion will lead to deforestation, soil erosion, and loss of soil organic matter. Destruction of savannah lands will also negatively impact biodiversity. There is already concern in North America and Europe that the drainage of sensitive wetlands for agriculture not only alters hydrologic regimes but also destroys waterfowl habitats as well as important vegetative and aquatic species. Many parts of the world, including the U.S., the Middle East and North Africa, and the semiarid tropics of India, China, Africa, and Central America, are already facing severe water scarcity. Crop production in these regions is limited by low and unpredictable rainfall. Crop yields are often too low to provide household food and nutrition security, let alone augment household income through the sale of surplus commodities. Continual depletion of both surface water and groundwater, due to a combination of high consumptive use and low recharge rates, puts both rainfed and irrigated crop production in jeopardy. New water management technologies and more efficient delivery and on-farm water systems will be at the heart of the solutions to global food security. On a global scale, irrigation water use accounts for just over 70% of total freshwater withdrawals. There is also a growing use of groundwater for irrigation in areas where surface water does not exist or is scarce. The countries with the largest areas under groundwater irrigation are India (39 Mha), China (19 Mha), and the U.S. (17 Mha). However, given concerns about the sustainability of large irrigation water withdrawals, in light of competing economic and environmental demands for water, and rainfall variability due to climate change, it is essential that the irrigation sector develop more innovative techniques to conserve water, and use less water to produce more biomass. There are 1500 Mha of cropland globally, of which about 300 Mha are irrigated, with the remainder being rainfed. It is remarkable that these 300 Mha of irrigated land, about 20% of global cropland, produce approximately 40% of the world’s food. The importance of irrigated agriculture for food security is therefore well demonstrated. In order to improve the performance of irrigation systems, the major push is toward improved canal delivery systems, moving from a supply-driven irrigation network to a demand-driven system with gated controls, and also pipeline conveyance systems in some cases. At the field scale, where possible, there are conversions from flood and surface irrigation to drip systems, and low-energy, low-pressure application (LEPA) sprinklers. Another recent innovation is the implementation of precision irrigation, in which water application is matched to soil type, crop type, and crop growth stage. The current evolutionary stage in centerpivot systems is variable-rate irrigation (VRI), in which management zones are defined by several parameters, including soil physical and chemical properties, land elevation, and farming practices. Using solenoid valves and electronic controllers, the application rate can be varied by management zone. The travel time of the pivot can also be regulated to vary the application by management zone. One benefit of VRI is that low elevations in the field are not overirrigated and higher elevations are not underirrigated. Consequently, salinity and waterlogging are better controlled. More uniform crop yields can be achieved, and there is less leaching of agrochemicals to the groundwater. The improved irrigation uniformity made possible with VRI leads to water savings. There is also potential to achieve further savings through the use of soil water sensors to better schedule irrigation applications. The goal is to use soil water and crop canopy sensors to monitor water stress in plants, and then input these data into climate and crop growth models to predict irrigation requirements on a real-time basis. Water savings in the range of 25% to 30% could be achieved through the implementation of the technologies that have been described here, and these technologies already exist. ASABE Fellow Chandra A. Madramootoo, P.Eng., James McGill Professor of Bioresource Engineering and Dean, Faculty of Agricultural and Environmental Sciences, McGill University, Montreal, Canada; email@example.com. Top photo by Jack Dykinga, courtesy of USDA-ARS. Bottom photo by the author.
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