Supplemental irrigation (SI) , also referred to as Deficit Irrigation, is the application of water below full crop-water requirements, generally in drylands to assist crop growth in areas that experience low rainfall (300-500 mm/year). Supplemental irrigation involves adding limited amounts of water to rainfed crops to improve and stabilise yields when rainfall is insufficient for plant growth. Supplemental irrigation is a valuable and sustainable production strategy in dry regions or when experiencing irregular climatic conditions. This practice requires understanding of the yield response to water and the economic impact of loss in harvest. The aim of this technique is to ensure that the minimum amount of water is available during critical stages of crop growth.
To effectively undertake deficit irrigation:
- Step 1: Determine critical growth cycle of desired crops.
- Step 2: Experiment with SI strategies to determine critical watering times prior to upscaling.
- Step 3: Strict management is required to determine the level of transpiration deficiency allowable without significant reduction in crop yields.
- Step 4: Farmers capable of implementing deficit irrigation must have access to the minimum required water to implement deficit irrigation.
- Step 5: Farmers must have access to a reliable water source, irrigation systems, including water distribution system, sprinklers and/or drip irrigation system.
- The Food and Agriculture Organisation, 2000. Deficit Irrigation Practices. Water Reports.
- The Food and Agriculture Organisation, 2018. Supplemental Irrigation: A Promising Climate-Smart Practice for Dryland Agriculture. Practice Brief Climate-smart agriculture.
- CGIAR, Research Program on Dryland Systems, 2016. Effect of deficit irrigation on growth and yield of garlic, Technical Report of Experimental Activities. North-Western Ethopia.
Benefits
- Increase crop production in dry areas or those experiencing drought.
- Assist farmers manage crops at optimal times (low rainfall).
Drawbacks
- Farmers must have access to enough water to meet minimum water requirements.
- Require water distribution system that is functional.
- Close management of crops to ensure that SI is implemented at critical crop production moments.
