Deficit Irrigation: How to Strategically Use Less Water

What is Deficit Irrigation?

Deficit Irrigation is the deliberate under-irrigation of a crop to get the most out of every drop of water and maximize profits.

If you farm in California and your water supply comes from pumping groundwater, there is likely not always going to be enough water available for you to apply the ideal amount of water at the ideal time for your crops.

Deficit irrigation is a strategy that intentionally applies less water than the full crop requirement to improve water use efficiency while minimizing yield loss. 

Full Irrigation vs. Regulated Deficit Irrigation

The main difference between Full Irrigation and Regulated Deficit Irrigation is that full Irrigation results in maximum crop yield (or profit) per unit of land. Deficit Irrigation results in maximum yield (or profit) per unit of water applied.

Deficit irrigation can be classified into multiple categories. We focus on two types of Deficit Irrigation: Regulated Deficit Irrigation (or RDI) and Sustained Deficit Irrigation (or SDI).

RDI is a water management strategy that limits irrigation during specific growth stages when crops can tolerate water stress. It deliberately provides crops with less irrigation water than they typically require. RDI is a proven approach that reduces water use while minimizing yield or quality losses. RDI is particularly suited for orchards and vineyards. Numerous studies have demonstrated that RDI can optimize water use efficiency without significantly compromising crop yield.

Since different crops have distinct water-sensitive stages, precise timing is critical to ensure optimal growth and yield. Additionally, while applying water stress can enhance water use efficiency, it must be carefully controlled to avoid irreversible crop damage.

Key steps in Regulated Deficit Irrigation:

Implementing RDI involves several critical steps to ensure its effectiveness and long-term viability.

• Identifying growth stages for deficit irrigation, where crops can tolerate water deficits without significant yield loss. 
• Determining safe deficit levels for each stage, which involves knowing the crop’s drought tolerance during different growth periods. 
• Measuring water deliveries to ensure precise irrigation and ensuring your system has high distribution uniformity, as poor uniformity can lead to ineffective water deliveries across the field.
• Monitoring soil moisture level or plant water status to ensure that water stress remains within acceptable limits, preventing severe stress that could harm the crop. 
• Evaluating water and energy savings and assessing crop yield and quality, allowing for adjustments to optimize both resource use and crop performance.
• Adjusting the timing and levels of deficit irrigation applications in various growth stages as necessary for the following seasons. 

Sustained Deficit Irrigation, or SDI, means giving crops a steady but slightly reduced amount of water throughout the season, typically at a fixed percentage of full crop water requirements. Instead of switching between fully watering and stressing the plants, this method keeps water levels slightly lower in a controlled way to make the most of limited water supplies.
This approach has been explored for various annual crops as a potential way to improve water use efficiency while maintaining acceptable yields. 

SDI is especially valuable when water availability is consistently limited and growers need to stretch supplies across more acres. 

Both types of Deficit Irrigation, Regulated Deficit Irrigation and Sustained Deficit Irrigation, can be strategic ways to maximize the power of every drop of water, saving money and increasing the efficiency of your farming operation.