Irrigation Scheduling

By Sara Ingell, AAg, Irrigation Agrologist, Crops and Irrigation, Outlook

July 2024

Irrigation scheduling is the process of determining the frequency and quantity of water required for a growing crop. The main goal for irrigation scheduling is to limit crop water stress by using water at the right time, right place and right amount. On farm benefits of effective irrigation scheduling can optimize crop yield, quality, and uniformity and improve farm profitability and efficiency. An environmental benefit of properly managing water is the decrease of the amount of nutrients and water lost through leaching. There are many factors that go into determining when and how much water to apply throughout the growing season and different methods are used to assess these needs.

There are four important pieces of information that are required for irrigation scheduling: soil characteristics, crop and growth stage, climate and characteristics of the irrigation system.

• Soil texture will impact the water holding capacity of soil. For example, a clay loam soil has 2.2 inches (55.88 mm) per foot of available moisture compared to a sandy loam soil that has 1.7 inches (43.18 mm) per foot of available moisture.
• The stage of your crop will influence how much water your crop will need. A canola crop at a seedling stage uses about 0.05 inch (1.5 mm) of water per day compared to the reproductive stage where it will use about 5 mm of water per day.
• Climate plays a big role on water use; a canola crop at the reproductive stage during a rainy and overcast period might only use 0.1 to 0.15 inch (3 to 4 mm) a day compared to a hot, dry and windy period where it might use 0.27 to 0.31 inch (7 to 8 mm) a day. Lastly, understanding your irrigation system is important for your application rate.
• Most quarter section systems are designed to put down 0.27 to 0.31 inch (7 to 8 mm) a day, which keeps up with peak water use for most crops. When practicing irrigation scheduling, it is important to remember that about 70 per cent of water the crop draws comes from the top 50 per cent of the active root zone.

There are three different methods of irrigation scheduling: soil-based, weather-based and plant-based. Soil-based methods are a common practice among irrigators to measure the soil moisture content. Weather data such as temperature, humidity and wind are used to estimate crop water-use when using weather-based methods. The last method uses data from plant responses and weather models to estimate crop water-use when using plant-based methods. Irrigators can adopt irrigation scheduling on their operations with a soil probe and the soil moisture charts from the Irrigation Scheduling Manual for Saskatchewan to measure the moisture content in their soil.

Weekly crop water-use updates are posted throughout the growing season on X (formerly Twitter) through @IrrigateSask. For more information on irrigation scheduling and to speak with an Irrigation Agrologist, call 306-867-5500.