Irrigation Systems

Irrigation systems are methods used to supply the water required by plants.

Due to the continuously growing global population, demand for agricultural production—and consequently for water—is increasing steadily. Developing countries use 70–80% of their freshwater resources for agriculture. Therefore, freshwater resources are most extensively utilized in the agricultural sector both globally and in Türkiye. Uninformed irrigation practices by producers lead to the depletion of groundwater sources. Water conservation in agricultural irrigation is achievable by minimizing losses during water delivery from the source to the plant and by ensuring minimal loss during water storage in the root zone.

Agricultural Irrigation

Agricultural irrigation is the process of applying water directly to the root zone when rainfall is insufficient to meet the plant’s water needs. The primary objective in field irrigation is to distribute the applied water uniformly across the entire field with minimal loss. This distribution requires specific methods and equipment. The selection of a method depends on the field’s topographic uniformity, the crop being grown, soil structure, water quantity and quality, and the farmer’s practices. These methods include surface irrigation and pressurized irrigation systems.

Surface Irrigation Method

Surface irrigation relies on the movement of water across the land surface under the influence of gravity, allowing it to infiltrate the soil. These methods typically offer advantages such as low initial investment costs and lower energy requirements compared to pressurized systems. However, significant water losses due to deep percolation and surface runoff, along with dependence on land leveling, are major limiting factors. In Türkiye, surface irrigation methods are still used in the majority of irrigated areas (67%).

Flood Irrigation

This involves delivering water to the edge of the field and allowing it to spread randomly across the surface.

Basin Irrigation

In basin irrigation, the field is divided into rectangular or square plots (basins) surrounded by bunds. Water is released from a source into these basins, where it spreads over the entire surface and infiltrates the soil. This method is subdivided into several sub-methods depending on the slope conditions and intended purpose.

Long Basin Method: A system similar to basin irrigation but using longer and narrower basins. This method is particularly suitable for frequently planted crops such as forage and cereal plants. It can be applied efficiently on soils with high water retention capacity, good drainage, and no impermeable layer. It yields optimal results on fields with a slope of up to 3% in the direction of irrigation and on level ground perpendicular to the slope. On uneven terrain, it can be implemented using sloped basins. The fundamental principle is to arrange the field into long, narrow strips separated by parallel bunds. In design, the length and width of the strips are determined based on factors such as soil infiltration rate and field slope. During operation, water is introduced at the upstream end of each strip to ensure complete coverage.

Conventional Basin (Flood) Irrigation Method: A traditional method commonly used in rice cultivation. The field is continuously flooded to create the necessary conditions for plant growth. It is suitable for cereals, forage crops, forage grasses, and fruit trees that are not sensitive to root suffocation. It is ideal for soils with high water retention capacity and no impermeable layer. However, due to the continuous flooding, this method consumes large volumes of water and creates anaerobic conditions that lead to methane gas emissions. Because of this environmental impact, traditional basin irrigation must be abandoned in favor of sustainable rice cultivation. Key components include channels that deliver water to the basins and bunds that separate them. In design, the size and shape of the basins are determined based on field slope and soil structure. Operation involves maintaining the field flooded for a specific duration.

Contour Furrow Irrigation Method

This is the most suitable surface irrigation method for row-planted crops, vineyards, and fruit trees. Water is channeled through small ditches (furrows) dug between plant rows, allowing it to infiltrate the soil. It can be applied to most soil types except those with very light texture. It enables efficient use of low-flow water sources. However, inadequate furrow planning on sloped land may lead to erosion risks and uneven water distribution. The primary component of the system is the furrows. In design, furrow length, slope, and soil infiltration rate are considered. During irrigation, water is carefully applied to the furrows to ensure adequate wetting of the plant root zone.

Pressurized Irrigation Methods

Pressurized irrigation relies on delivering water to the plant root zone through pipes under pressure generated by pumps or natural elevation differences. These systems offer high water use efficiency, minimize water losses, and allow for the application of fertilizers through the irrigation water. In Türkiye, pressurized irrigation systems are used in 33% of irrigated areas.

Sprinkler Irrigation System

One of the most common pressurized irrigation methods, covering 19% of irrigated land. Water is sprayed under pressure through sprinkler heads in the form of droplets onto the plant or soil surface. It protects the soil surface, prevents erosion, and does not disrupt soil structure. Additionally, land leveling is not required. However, wind can negatively affect water distribution. High pressure and energy demands increase operational costs, and initial installation costs are higher than those of surface irrigation methods. Key components include the main pipeline conveying water from the source to the system, distribution pipes (lateral lines), and sprinkler heads. In design, the spacing of sprinkler heads is determined based on soil infiltration rate, wind speed, and wind direction to ensure uniform water distribution. During operation, irrigation duration, application rate, and frequency are adjusted according to the plant’s water requirements.

Mini-Spring Method

A pressurized irrigation method preferred in orchards where drip irrigation fails to achieve adequate wetting coverage. Micro-sprinkler heads, typically placed beneath each tree, slowly distribute water over the tree’s canopy area. It ensures high efficiency in water and fertilizer use. Since only the root zone is irrigated, water loss is minimal. It can wet a broader area than drip irrigation. Its main limitations are susceptibility to wind and high initial investment costs. Key components include micro-sprinkler heads and lateral pipes supporting them. In design, the flow rate, pressure, and wetting radius of the heads are determined based on the tree’s size and root system. During operation, irrigation duration and frequency are adjusted according to the plant’s water needs.

Drip Irrigation Method

One of the most water-efficient pressurized irrigation methods, used in 14% of irrigated areas in Türkiye. Water is applied slowly and continuously directly to the plant root zone through emitters at low pressure and flow rate. It increases crop yield and product quality while conserving water, fertilizer, and energy. Since areas outside the root zone remain dry, weed growth is suppressed. One of the most important limiting factors is the requirement for clean water; otherwise, emitters may clog. Initial investment costs can be high, and application over large agricultural areas may be costly. Key components include the main pipeline conveying water from the source, distribution pipes, lateral lines, and emitters. In design, emitter flow rate, spacing, and water pressure are determined based on soil structure and the plant’s root system. During operation, the irrigation schedule is precisely adjusted according to the plant’s growth stage and evapotranspiration rate.

Subsurface Irrigation Method

This method is a subcategory of drip irrigation in which emitters are placed below the soil surface to deliver water directly to the plant root zone. It provides more controlled and efficient irrigation than surface methods. Its components are similar to those of surface drip systems, but because the emitters are buried, the depth and spacing of the pipes must be carefully planned according to soil structure and the plant’s root system.