7.3.2 Irrigation Systems

Various irrigation methods, such as surface, subsurface, sprinkler, and drip irrigation, are available to irrigate upland crops. The selection of an irrigation method generally depends on the environmental, economic, and social setting. The contextual background of a region, in turn, determines the efficiency of resources used, economic viability, and sustainability of upland farming systems.

Photo by Steve Harvey on Unsplash

In the past, surface irrigation such as basins, borders, and furrows have been widely used to irrigate upland crops in many world regions due to its simplicity and low costs. To this day, surface irrigation remains the major irrigation for upland crops worldwide. During surface irrigation, water is applied over the entire field, or if furrows are used, the water is applied to the top of a furrow so that water can flow down the field based on gravity. While the water flows across the field, it infiltrates into the soil and provides water to the root zone of the crops. However, water distribution uniformity and application efficiency depend on the degree of land leveling. As a result, land leveling and preparation cause high labor costs. However, due to increasing energy and labor costs, surface irrigation has been replaced by new irrigation methods such as subsurface, sprinkler, or drip irrigation.

Untitled Global distribution of irrigation systems at country level, based on AQUASTAT statistics. Cells that include irrigated areas are hatched, based on Siebert et al. (2015).

Based on AQUASTAT statistics, the map above shows the global distribution of irrigation systems at the country level. Surface irrigation is the dominant irrigation method, followed by sprinklers dominating the Northern hemisphere.

Irrigation Efficiency by Technology

The efficiency of irrigation systems is a crucial aspect when looking at water availability in regions. The table above shows the water application efficiencies of different irrigation systems. One can see that surface systems consume higher water quantities for irrigation when compared to the other methods. This is because surface systems cover the entire crop field with water, resulting in excessive water not reaching the root zone. Water might be lost through deep percolation, surface runoff, or evaporation. An alternative to open surface irrigation is pressurized irrigation systems. Pumping systems powered by diesel or other energy sources transport water from its source to a pipe system on the field.

Implementation of Irrigation Techniques

  1. A successful implementation of irrigation techniques requires a thorough characterization of and knowledge about the social and agro-ecological context (Holzapfel & Mariño)
  2. A lack of knowledge and limited experience result in inefficiencies, waste of resources and/or failure of the provided irrigation equipment (FAO. 2014)

General Considerations

The implementation of irrigation systems is not simply a matter of technological implementation. Knowledge of how to use, monitor, and maintain a system is also essential.
 

  1. Natural conditions:
    • Water Supply: Where does the water come from? Is it surface water or groundwater? How is the water quality? How much rainfall do I have? Will it be supplemental or full irrigation?
    • Water quality and salinity: High salt contents in the water supply lead to additional water requirements. The extra water must be applied to the field to leach salt below the root zone. Additionally, salinity and sediments can adversely affect the irrigation system by plugging or abrading nozzles or orifices in sprinkler and drip/microsystems.
    • Climate: Precipitation patterns determine how much irrigation is required: The main types are supplementary and full irrigation. In this context, the feasibility and adaptability of the selected irrigation method to the local climatic pattern are essential considerations. Critical factors for consideration include temperature, frost conditions, humidity, and wind. i.e., since strong wind can disturb the spraying stream from sprinklers.
    • Soils: Soil texture determines the storage capacity and infiltration rate, affecting the frequency of required irrigation. All three irrigation methods can be used in fields with low infiltration rates like loam or clay soils. However, Surface irrigation is more commonly found.
    • Slope: Land leveling affects the hydraulics of piping systems and water distribution to the crops. Therefore, sprinkler or drip irrigation should be favored over surface irrigation on steeper or uneven lands.
    • Water Table: The water table has to be known for any irrigation design. Furthermore, the potential impacts of the irrigation system on the water table have to be assessed.
    • Energy: If an energy source is unavailable or unreliable, irrigation methods such as sprinkler or drip irrigation should not be considered. (However, there might be an opportunity to integrate solar panels into the irrigation systems if technical and financial factors allow for it).

  2. Crop Types: One has to consider Crop characteristics, vulnerability to pests, diseases, and weeds. For instance, sprinklers can carry pathogens that spread across the field via water drops.

  3. Previous Experience with irrigation: Introducing irrigation methods which have been previously unknown to a farmer may lead to unexpected complications.  

  4. Technology types: Selected technology types should aim for efficient operation and water distribution to the crops, with no erosion and minimized losses due to percolation or runoff.

  5. Socioeconomic Aspects: In case an irrigation technique is introduced into a small-scale farming context, it is necessary to consider:
    • the farmer’s age
    • occupation
    • off-farm employment status
    • access and availability of irrigation equipment
    • awareness
    • assistance

Solar Powered Irrigation Systems

Untitled

SPIS Toolbox Handbook –GFA Consultants (2019)

Solar-powered irrigation systems (SPIS) combine water pumps, solar generators, irrigation systems and agricultural production (Poompavai & Kowslaya, 2019, energypedia). The solar generator provides electricity to the water pump when solar energy is available, and water is pumped to the water reservoir. A valve controls the irrigation of the crops. The water reservoir acts as indirect energy storage, balancing out the solar generator’s fluctuating energy production and, thus, taps WEF synergies. The annual water outtake should not exceed the yearly groundwater renewal to avoid a phreatic decline and ensure an ecosystem-friendly operation.

On energypedia.info, a user-friendly toolbox on SPIS can be downloaded. The aim is “to enable advisors, service providers and practitioners in the field of solar irrigation” and “ provide broad hands-on guidance to end-users, policy-makers and financiers.” The toolbox features calculations sheets, checklists, and guidelines to accompany all system implementation steps from first information to the maintenance of an installed system.



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References
Bjorneberg D.L , IRRIGATION | Methods, Reference Module in Earth Systems and Environmental Sciences, Elsevier, 2013. 11-Sep-13 doi: 10.1016/B978-0-12-409548-9.05195-2. https://eprints.nwisrl.ars.usda.gov/id/eprint/1568/1/1524.pdf

Energypedia. Toolbox on Solar-powered Irrigation Systems. Available online: https://energypedia.info/wiki/Toolbox_on_SPIS

FAO, Irrigation Water Management: Irrigation Methods. Chapter 1. The Practice of Irrigation https://www.fao.org/3/t0231e/t0231e03.htm#1.2%20irrigation%20methods%20and%20their%20selection>

FAO Irrigation Water Management: Irrigation Methods Chapter 7. Choosing an Irrigation Method https://www.fao.org/3/S8684E/s8684e08.html

FAO, 2014 Irrigation Techniques for Small-Scale Farmers https://www.fao.org/3/i3765e/i3765e.pdf

Holzapfel et al., 1985 Procedure to Select an Optimum Irrigation Method, https://www.researchgate.net/publication/245287767_Procedure_to_Select_an_Optimum_Irrigation_Method

Holzapfel, E. A., & Mariño, M. A. (2008). Irrigation in Agriculture. Encyclopedia of Ecology, 2033–2039. doi:10.1016/b978-008045405-4.00628-5

Gunarathna et al., 2017. Optimized Subsurface Irrigation Systems (OPSIS): Beyond Traditional Subsurface Irrigation, https://www.mdpi.com/2073-4441/9/8/599/htm

Jägermeyr et al., 2015, Water savings potentials of irrigation systems: Global simulation of processes and linkages, https://www.researchgate.net/publication/280014032_Water_savings_potentials_of_irrigation_systems_Global_simulation_of_processes_and_linkages/figures

Poompavai, T., Kowsalya, M., 2019. Control and energy management strategies applied for solar photovoltaic and wind energy fed water pumping system: A review. Renewable and Sustainable Energy Reviews 107, 108–122. https://doi.org/10.1016/j.rser.2019.02.023.

Siebert et al. 2015

USDA, Irrigation Technologies Comparisons https://www.ars.usda.gov/ARSUserFiles/21563/Irrigation%20Technologies%20Comparisons.pdf

Figure by SPIS Toolbox Handbook-GFA Consultants (2019). Available online: https://energypedia.info/wiki/File:SPIS_components.PNG