Irrigation Scheduling
The goal in irrigation scheduling is to determine the timing of irrigation, the duration of irrigation, and the amounts of water applied based upon crop needs, soil water storage capacity and climatic conditions, all leading to efficient water use. [Courtesy of Agricultural Water Conservation Clearinghouse]
Soil Moisture Sensors
Soil Moisture Sensors are a tool that is useful to directly assess the crop water balance. There are many different types of soil moisture sensors, but most commercial sensors used for agricultural irrigation fall into three categories: total domain reflectometry, capacitance or dielectric sensors, and soil matric potential sensors. TDR sensors typically use producing wires or probes and measure soil moisture by measuring the time difference of a signal passed along the probe, the water content changes the time it takes the wave to travel the probe, this delay is directly proportional to the volumetric soil water content. Capacitance probes sense the water molecules in the soil which have a dielectric property (soil has no dielectric response), and this is related to volumetric soil water content. Soil Matric Potential Sensors (the most common is a WatermarkTM ) measure the matric potential or tension. Tension is a measure of the energy that a plant exerts to extract water from the soil, typically measured in centibars.
Download our fact sheets on using WatermarkTM sensors:
How to Prepare, Test & Install Watermark™ Sensors
How to Use Watermark™ Soil Moisture Sensors for Irrigation
How to Predict the Last Irrigation of the Season Using Watermark™ Soil Moisture Sensors
Atmometers and Evapotranspiration (ET) Gauge
Atmometers are simple to setup and require minimal upkeep. They should be placed adjacent to crop fields, and mounted at least 39 inches high and above the crop canopy, to provide accurate on-site evapotranspiration (ET) information.
At the beginning of the growing season, the atmometer reservoir should be filled with distilled water, and will likely need to be refilled once during the season. The paper wafer, which prevents rainwater from entering the atmometer, should be replaced annually.
Setting the Atmometer
The following sheets have been developed to help Arkansas producers set their atmometers and may not be appropriate for use outside the region. Currently, a chart has not been developed for rice.
Scheduling Irrigation Using an Atmometer with Chris Henry
Arkansas Online Irrigation Scheduler
The decision process of determining when to irrigate crops is referred to as irrigation scheduling. There are several different irrigation scheduling methods available to producers who irrigate. Most of these methods have been evaluated in Research and Extension studies by the University of Arkansas System's Division of Agriculture. The water balance approach to irrigation scheduling has been determined to be the most practical and suitable method for Arkansas producers. This approach is also used by producers in Mississippi, Louisiana, Tennessee and Missouri.
The Arkansas Irrigation Scheduler was developed in the 1980's and we continued to support it until 2020 when the program became too antiquated to support. The scheduler has been discontinued until it can be updated. If the lack of the scheduler causes you hardship or there is not another suitable replacement contact cghenry@uada.edu for assistance with water balance and ET based scheduling.