Irrigation is the artificial application of water to land, developed to supplement rainfall and assist in growing agricultural crops. Civilizations have relied on this technology for millennia to manage water resources, particularly in arid regions. Modern agriculture has refined this ancient practice into sophisticated systems. These methods are generally categorized into three main types, defined by how the water is delivered to the field.
Surface Irrigation Systems
Surface irrigation is the oldest and simplest method, relying entirely on gravity to move and distribute water across the land. Water is released directly onto the soil surface from a source, such as an open ditch, and flows downward across the field. This passive delivery system requires the land to have a relatively flat slope to ensure the water spreads evenly and infiltrates the soil.
Several sub-methods exist within this category, including flood, furrow, and basin irrigation. Flood irrigation involves covering the entire field with a sheet of water. Furrow irrigation channels water down small, parallel ditches between crop rows, allowing the water to seep laterally. Basin irrigation divides the field into level plots surrounded by small earth banks, which are then flooded with a controlled amount of water.
The appeal of surface systems is their low initial cost and minimal energy requirements, as they do not typically need pumps or pressurization. However, this method suffers from significant water losses due to runoff and deep percolation below the root zone. Achieving high uniformity in water distribution is challenging, since the section closest to the water source receives water for a longer period than the distant end.
Overhead Sprinkler Systems
Overhead sprinkler systems deliver water by spraying it into the air above the crop canopy, mimicking rainfall. This method requires a network of pipes, a pump, and a power source to pressurize the water before it exits through nozzles. Sprinklers are advantageous because they can be used on uneven terrain and various soil types where surface methods would fail to distribute water evenly.
Common types of sprinkler systems include Center Pivot, Lateral Move, and Fixed Set configurations. Center pivot systems utilize a long lateral pipe mounted on wheeled towers that rotates around a central water supply point to irrigate a large circular area. Fixed set systems use stationary sprinkler heads placed on risers, often used in smaller fields or orchards.
While these systems offer flexibility in application rates and are well-suited for operations like seed germination, they have drawbacks. Pressurizing the water requires considerable energy, leading to higher operational costs. Spraying water through the air also exposes it to wind drift and high evaporation rates, which reduces the amount of water that reaches the plant roots.
Localized Drip Applications
Localized drip applications, also known as micro-irrigation, are the most water-efficient method, applying water directly to the plant root zone. This system uses a network of narrow-diameter tubes, often laid on or below the soil surface, with specialized emitters positioned near individual plants. The water is released as drops or a slow, continuous trickle.
This precise method minimizes water waste by avoiding wetting the entire soil surface or the plant foliage. Delivering water only where the plant needs it reduces losses from both evaporation and runoff. The high water use efficiency, often exceeding 90%, drives its increasing adoption in water-scarce regions.
The localized application of water also helps control weed growth, as the areas between the rows remain dry and inhospitable to unwanted vegetation. A limitation of drip systems is the high initial cost for the extensive network of tubing, emitters, and filtration equipment. Emitters are prone to clogging from mineral deposits or biological growth, demanding a rigorous maintenance schedule and reliable water filtration.