Introduction
It’s easy to move about our communities, oblivious to the fundamental contribution that those giant farm sprinklers provide for our civilization. Indeed, dense population centers like cities would be impossible to maintain without irrigated agriculture. Irrigation is a critical aspect of mankind’s ability to feed the world. It allows farmers to optimize the amount of water provided to crops, creating higher yields. Irrigation also helps to maintain landscapes and protect soil in dry areas and during periods of less than average rainfall. Irrigation also protects crops by shielding them from frost, suppressing weed growth, and preventing soil consolidation.
Ancient Challenges
Irrigation has been an important part of settled agriculture for thousands of years, particularly in regions where precipitation is scarce, seasonal, or unpredictable. The earliest type of artificial irrigation probably was carried out by manually carrying buckets or jars of water, to planted fields, from wells or nearby surface waters. Over time, some farming communities developed systems of ditches and canals to direct water to their fields from nearby surface waters or from large basins dug out to collect and store seasonal rainfall or floodwaters. When it was time to irrigate a field, farmers would open a sluice gate and allow stored water to flow into the field. Once the field was adequately saturated, the gate would be closed, keeping any remaining water safe for the next use.
This ancient form of ditch or row irrigation is still in use in many places across the world. In other places, the same concept is still in use, albeit with some modern improvements. The use of pumps, whether powered by muscle or by machine, has introduced a lot of flexibility to flood and channel irrigation, which no longer depends solely on gravity. The construction of canals and pipes has allowed farmers to irrigate farms at increasing distances from accessible water sources. As technology has advanced, water delivered under high pressure has supported the development of large and increasingly sophisticated sprinkler systems. In other cases, farmers have worked to develop methods of drip irrigation, where water could be slowly delivered at soil level through a perforated pipe. This method uses less water and also protects certain crops who are sensitive to wet leaves.
Of course, no system invented to improve on nature is ever perfect. Even in relatively primitive and low volume irrigated agriculture setups, there were physical and social issues that repeated themselves across place and time:
- Source waters usually carry silt and suspended solids, which settle out as the water slows down in storage basins and canals. Over time, the silt builds up and can block the channels
- Over time, low levels of salt carried in with irrigation water and deposited on the fields will build up; excessive salinity has been demonstrated as early as 2000 BC. If enough salt builds up, the land may become barren, unable to support life.
- Tension over access and rights to use water have been documented as far back as ancient Sumeria, when Mesopotamian city-states clashed over issues like water diversion and irrigation systems ~4500 years ago.
- Over-exploitation of resources is a common theme in the history of human cultures, and agricultural use of land and water is no exception.
- Institutional failure stemming from weakened governments led to deferred maintenance, inability to recover from natural disasters, and collapse of entire agricultural systems. Mesopotamia was once home to one of the most plentiful agricultural systems in the ancient world but after a series of regime changes, and natural disasters, the agricultural infrastructure (particularly irrigation) collapsed and is now largely desert.
Modern Challenges
As they say, “history repeats itself” and the development and use of irrigation in modern times faces remarkably similar challenges to those that plagued ancient farmers.
- Farmers must find ways to manage salinity buildup when considering locations for irrigated crops. However, practices intended to increase efficiency in water usage can make salinity problems more acute.
- Water drawn from ever-depleting sources includes increased loads of silt and mud, which eventually fill in reservoirs and canals, and may cause damage to pumps, or other machinery intended to move water around.
- The battle over access to fresh water, especially in the arid western parts of the US has reached critical levels as the Columbia River reaches historic lows. Dozens of large cities and agricultural regions through several states face devastating water shortages, and conflicts over access to the shrinking supply cross both state and national borders.
Worldwide, only 20% of agricultural land is irrigated, but that land produces 40% of the global harvest. This is good news, especially in developing countries where irrigation can potentially quadruple crop production. Still, irrigation is a two-edged sword and efforts to maximize productivity can have negative consequences on the environment. Today, about ⅓ of the world’s irrigated land have reduced productivity resulting from irrigation practices that have led to excessive salinity and waterlogged soil.
In the US, irrigation has had a profound effect on society by increasing land value, increasing the amount of arable land, boosting food production, and expanding attention to environmental concerns.
