Onions can be irrigated using sprinkler systems (commonly used after sowing to prevent crust formation), drip irrigation systems, or furrow irrigation.
Proper water dosing is very important in irrigation practice. There are two key elements in water dosing: the irrigation dose and the timing of irrigation.
Irrigation Dose: This is the amount of water applied in one irrigation (measured in m³/ha or mm). The irrigation dose should saturate the soil up to the field capacity, meaning the dose depends on the soil type. To determine the irrigation dose, it is necessary to know the soil moisture before irrigation and the soil’s water-holding capacity. The difference between the field capacity and the current water content in the soil represents the irrigation dose.
Timing of Irrigation: This refers to the specific moment when the irrigation dose should be applied, which is crucial for successful and efficient irrigation. If irrigation timing is determined by guesswork, it can be inefficient or even harmful.
For onion cultivation, it is necessary to maintain soil moisture at 70 – 80% of the field capacity to a depth of 20 cm, which is the root depth.
Onions have the greatest water and nutrient needs during the intensive leaf growth phase and the bulb formation phase. Irrigation should be stopped three weeks before the planned harvest to prevent the outer dry leaves from splitting due to subsequent bulb growth.
To achieve the optimal timing for irrigation and determine the irrigation dose, and thus ensure efficient and rational water use, soil moisture meters should be used.
Sprinkler Irrigation
This method distributes water over the soil surface in the form of natural rainfall.
Advantages of Sprinkler Irrigation:
- Can be used in various topographical conditions
- Requires minimal or no land preparation
- Does not occupy arable land
- Does not hinder the use of machinery
- Allows economical use of available water through precise dosing
- Less likely to degrade the soil’s physical properties
- Can irrigate newly sown fields and young plants
- Allows for fertigation (applying liquid fertilizers with irrigation)
In sprinkler irrigation, the system takes water from a source, pressurizes it through pipes, and distributes it over the irrigated area through sprinklers in the form of natural rainfall.
The irrigation system can be portable, semi-stationary, or stationary.
- Portable System: All parts are portable, with pipes connected by quick-connect fittings.
- Semi-Stationary System: Has a fixed water intake and main pipeline, while the sprinklers and rain wings are portable. The main pipeline is usually buried, with only hydrants on the surface for connecting the rain wings.
- Stationary System: All parts are fixed. Sprinklers are connected to a pipe network, usually buried in the ground.
Each sprinkler irrigation system consists of a water intake, pipe network, sprinklers, and fittings. The water intake can be gravitational or use a pump unit. In the case of a pump unit, water is drawn from the source and pressurized through the pipe network to the sprinklers. The pump unit consists of a drive motor and a pump, usually centrifugal. It is essential to match the power of the drive motor to the pump’s requirements.
The pipe network carries water from the source to the sprinklers. It consists of suction pipes, main pipelines, and rain wings. The rain wings have branches at regular intervals for connecting sprinklers.
Sprinklers: They have a crucial role in the sprinkler system, distributing water over the soil surface in the form of droplets. Sprinklers vary based on water pressure, water throw range, water output, coverage area, spraying intensity, type and number of nozzles, operation method, and spraying method.
Choosing the right sprinkler is crucial for sprinkler irrigation. For vegetable crops, light sprinkling is preferable, so low-intensity and short-range sprinklers are best.
Drip Irrigation (Localized Irrigation)
Drip irrigation allows for watering onions at any time of day without causing shock from applying cold water to hot plant parts.
Avoiding wetting the leaves also prevents creating favorable conditions for fungal diseases.
The system operates at low pressure, minimizing disturbance to the soil’s crumbly structure, which is beneficial for growth. The lower operating pressure (0.3 – 1.5 bar) also reduces energy consumption.
Localized water delivery reduces the irrigated area, thus minimizing water losses through evaporation or leaching (water conservation).
An advantage of drip irrigation is the possibility of fertigation, or applying liquid fertilizers along with irrigation.
A significant issue with drip irrigation is the clogging of drippers, whether mechanical or chemical. Clogging is directly related to the quality of the water used for irrigating onions and its physical, chemical, and microbiological factors. Filters can prevent mechanical clogging of drippers. Chemical clogging occurs due to the formation of insoluble salts at the dripper opening or within the dripper.
The drip system consists of a pumping unit with the system’s head, filter unit, main pipeline, laterals or distribution pipes, and drippers. The dripper is the component where the working pressure is reduced from the pipes, releasing water onto or into the soil in the form of droplets.
This irrigation method has two systems: surface and subsurface irrigation. In surface irrigation, the pipes and drippers are placed above or on the soil surface, while in subsurface irrigation, they are buried in the soil.
Furrow Irrigation
Furrow irrigation is one of the older methods used in vegetable cultivation.
The furrow irrigation system consists of an inlet canal, distribution channels, distribution furrows, furrows, and portable gates. Distribution furrows can be replaced with plastic, rubber, or metal pipes that transfer water from the distribution channel to the furrows.
The system can be upgraded with portable piping. This allows the inlet and distribution channels, as well as the distribution furrows, to be replaced with pipes. The pipes are made of lightweight materials for easy transport. The diameter is usually 15 cm. Pipes that replace distribution channels or furrows have openings at adjustable intervals for directing water into the furrows.
For vegetable cultivation, the furrow spacing is 50 – 100 cm.
For this method, the terrain should be relatively flat with a uniform slope, ideally between 2% and 4%.
Furrow depth ranges from 15 – 25 cm. The irrigation dose depends on soil characteristics, the crop being grown, and current soil moisture levels. This method does not disturb the soil structure and reduces the risk of crust formation while using less water, which is why this ancient method remains in use today.
