Updated: Sep 8, 2020
Agricultural irrigation techniques are methods of supplying water to crops and are classified as surface irrigation, sprinkler irrigation and micro irrigation. Deciding whether to select an irrigation technique or to switch to a more efficient technique is complicated. From a water conservation point of view, the choice is simple, water savings increase when moving from surface irrigation to sprinkling and from sprinkling to micro-irrigation.
However, the success of an irrigation technique will depend very much on the area, shifting situational factors and the standard of management used. The existing irrigation technique must be evaluated very precisely before switching to another technique.
Surface Irrigation Methods
Surface irrigation methods are ranked in order of increasing efficiency by:
Surface Irrigation (also known as flood irrigation)
Surface Irrigation (also known as flood irrigation)
Irrigation water is brought in by runoff from the field ditches without limiting the movement of water. This is often compared to a wild flood.
Although these methods are interesting for their low initial cost and for the work required, they are actually inefficient and have a low degree of uniformity. This method is generally used on hilly terrain when it is not possible to install planks, basins or rays and where the water to be supplied is sufficient.
Border irrigation is the supply of water through long, sloping, rectangular plots. The planks are generally laid out in the direction of the greatest slope, 30 to 65 feet wide, 300 to 1300 feet long with earthen berms between the strips to channel the water during irrigation.
The ground between the boards must be leveled perpendicular to the direction of the water. Board irrigation is very suitable for most types of crops and soils, but is favored by soils with a slow infiltration rate and crops that tolerate prolonged puddling.
While with other surface irrigation techniques water covers the entire plot, furrow irrigation covers only a fifth or half of the surface. Rays whose size varies, can be placed in the direction of the slope or according to the contour lines. Small, shallow furrows, called corrugations, are typically used for dense crops such as low grain and alfalfa. The wider and deeper lines are suitable for row crops like corn.
Compared to other surface irrigation techniques, furrow irrigation allows on-farm management of water with more flexibility. The unit flow is considerably reduced and this technique can be practiced with slopes of up to 12% if the lines are placed according to the contour lines with a flow dimensioned to be non-erosive. If the lines are not arranged according to the contour lines, the maximum recommended slope is 3% or less. With this irrigation technique, the smaller wetted area reduces evaporation losses. Rays offer more possibilities for the irrigator to manage irrigations more efficiently when conditions on the plot vary during the season. However, furrow irrigation is not always efficient and higher runoff flows may occur if a constant inlet flow is maintained during watering. Different methods, such as dual flow watering or wave irrigation can be used to reduce runoff.
The basins are generally rectangular in shape, leveled and surrounded by a dike to avoid runoff. Basins impoundment is generally neither directed nor controlled and can be efficient if a large flow is available to quickly cover the plot.
Some crops and soil types are unsuitable for basin irrigation and are best suited for poorly filtering soils and dense, deep-rooted crops. Leveling the ground is very important to achieve high uniformity and efficiency for all surface irrigation techniques.
Sprinkler irrigation is a versatile way to water any type of crop, soil and topography. It can be efficient in soil conditions or topographies for which surface irrigation methods are not suitable. In general, systems are defined according to the type of movement of the booms on which different types of sprinklers are fixed.
The ramps are fixed or mobile. In the latter case they are moved manually or mechanically. Sprinkler irrigation is highly efficient but poses problems due to labor requirements and investment costs.
Manually moved ramps require the lowest investment but very high labor requirements. This system can only be used on crops with low development.
Micro-irrigation is an irrigation technique that brings water to the soil slowly, with high frequency, operating pressure, low and controlled flow rates. Properly designed, a micro-irrigation installation can increase yields and reduce the need for water, fertilizers and labor. Micro-irrigation includes: micro-sprinklers, drip and buried drip irrigation.
Micro-sprinklers correspond to small distributors placed on small extension tubes above the surface of the ground. The water projected into the air travels a short distance before reaching the ground. With this technique, the small area wetted by the distributor is easily controlled with accuracy and can have different shapes corresponding to the types of watering chosen. Irrigation systems by micro-sprinklers help fighting frost and have greater flexibility during watering and a lower sensitivity to clogging.
Drip systems bring water directly onto or into the soil and only wet part of the soil. They provide benefits because the water is brought directly or just next to the root zone of the plants thus minimizing losses by percolation.
Surface Irrigation or Sprinkler Irrigation: Which one to choose?
One of the most common water saving solutions is the switch from surface irrigation to sprinkler irrigation. The reasons for this conversion lie in the fact that surface irrigation techniques are inherently less efficient and require more labor than sprinkler irrigation. However before making this conversion, various factors must be taken into account: the effects on yields, water, energy and labor savings, the economic aspect, climatic conditions and characteristics of the field.
To choose an irrigation method, the farmer must know the advantages and disadvantages of the different methods. Unfortunately in many cases, there is not a single good solution because all methods have their advantages and disadvantages. It also has the advantages and disadvantages of one irrigation technique over another. If an irrigation system is not particularly well suited to a given situation, it may not be more efficient or save more water than the initial irrigation method.