All plants need water to grow well. And, water can be a limiting factor in good crop yields on farms. Relying on natural rainfall to come at the right time, in the right place, is an unreliable way to assure we have enough food to feed the world.
Irrigation involves artificially maintaining adequate soil moisture level for proper crop growth. This has been done for centuries, though today’s modern techniques can apply water in very precise amounts. Let’s look at the history of irrigation.
Agricultural societies could irrigate based on the geography of the area and the availability of water. The oldest records of irrigation system are almost as old as the advent of agriculture. The Egyptians and Mesopotamians were the pioneers in irrigating their crops around 6000 BC.
They dug trenches to guide the flooded waters of the Nile in Egypt, and the Euphrates in Mesopotamia for the field crops. With technological advancements, the systems were upgraded to check dams and stone walled canals. The dams helped to hold water longer in the area, and the stone canals reduced the amount of water seeping into the soil.
The Romans further contributed to irrigation system technology. They made hollow cylindrical structures from baked clay to carry their water from rivers to the fields – basically rudimentary pipes. Until this point, all the irrigation systems depended on natural sources of water like rivers or freshwater lakes. Civilizations continued to migrate, and soon a trade of seeds began. This led to agriculture being expanded in areas with no natural source of fresh water.
The Persians developed a “revolution” in agricultural irrigation around 500 BC. They developed an efficient way to use groundwater, located well below the surface. Commonly known as a Persian wheel, it had a horizontal wheel rotated by ox or horses. The horizontal wheel further rotated a vertical wheel with chain of buckets attached to it to bring our ground water.
With the invention of the small-scale turbine engine in the 1940s, irrigation rates were greatly increased. By using these modern pumps, water could be spread further and faster, far from any natural sources.
Irrigation efficiency became a field of study in the late 1970s. Surface irrigation methods and were prone to losses due to evaporation, percolation, and runoff. Irrigation efficiency looks to prevent these losses and provide only the amount of water required by the crops. The solution was to either mimic rainfall for the crops for a uniform distribution, or to provide water to the crops at the root zone for direct absorption. The first idea developed into sprinkler irrigation and the second idea developed into drip irrigation.
In sprinkler irrigation, the irrigation system lets the water flow through a small opening, causing it to build pressure. Water coming out with pressure breaks into smaller droplets and falls uniformly over the crops. This is not unlike your showerhead, or the shower setting on a garden hose.
Drip irrigation circulates water throughout the field in above- or below-ground pipes. The limited openings deliver water directly to the plants.
There are pros and cons to each of these modern irrigation techniques. The efficiency of surface irrigation systems (like canals, tube wells, etc.) is only around 40-75%, based on climatic conditions and soil type. Sprinkler irrigation efficiency ranges from 60-85% and drip irrigation efficiency is 80-95%.
Though the efficiency of drip irrigation is the highest, it is hindered by the high cost of installation and maintenance. The lines are very hard to move around a farm. Sprinkler irrigation can be either fixed or movable and is a relatively low maintenance system.
For these reasons, sprinkler irrigation is common for crops with large acreages. You’ll commonly see wheat, rice, corn, alfalfa, and potato fields with sprinkler systems on them. The overall production cost of these crops is low. Drip irrigation is more popular for high value crops with smaller acreage such as strawberry, avocados, etc.
Newer innovations are making irrigation even more adaptable. Fertigation is a mixture of irrigation and fertilization – where the fertilizer is dissolved in the irrigation water. Wireless and automated technologies have helped in enhancing irrigation efficiency. Sprinklers and drip systems can be operated wirelessly using a PC or a smartphone. For example, if a grower must drip irrigate avocado plants on a day they will be out of town, the smartphone can be used to start and shut off the irrigation!
Water efficiency is also important on farms. Some areas of a farm retain water better than others. Now, the amount of water can be varied within a field based on the water requirement. Some farms have peanuts, sorghum and cotton, all needing to be watered. A moving sprinkler system can be used, running in a pre-defined irrigation field plan. Nozzles are adjusted by a program to vary the amount of water on different crops. This leads to adding adequate amount of moisture to the soil and preventing over watering.
From early days, farmers have innovated ways to grow more food to feed the world. Irrigation started with ancient, hand-dug irrigation ditches, through the advent of using a wheel-bucket-animal system to increase the amount of water available. Engines, computers and continuous feedback loops of data from the farm field to the grower has enabled irrigation to be even more efficient. This efficiency is necessary to preserve water and the environment, while providing nutritious, accessible food for all.
Answered by Sayantan Sarkar, Virginia Polytechnic Institute and State University
About us: This blog is sponsored and written by members of the American Society of Agronomy and Crop Science Society of America. Our members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting our environment. We work at universities, government research facilities, and private businesses across the United States and the world.