The Weekly Irrigation Newsletter on CropWatch features results from a collaborative Nebraska Extension research study involving three Nebraska growers, who are utilizing soil moisture sensors to schedule irrigation throughout the growing season. Results are updated every Tuesday.
Introduction
In 2024, Nebraska Extension launched the Weekly Irrigation Newsletter to share timely insights on irrigation decisions, featuring three growers located in Nebraska. Due to the positive feedback, we are continuing the program in 2025. In each of their corn fields, we installed a set of three Watermark (Irrometer) sensors at 1-, 2-, and 3-foot soil depths to track soil moisture throughout the growing season. A rain gauge was also installed to monitor both rainfall and irrigation events. These instruments are connected to an IC-10 datalogger (Irrometer), which records data at one-hour intervals. With a telemetry system in place, the data is transmitted remotely, allowing for timely irrigation decisions.
We will also share weekly data in video format of a field with Watermark sensors at the South Central Agricultural Lab near Clay Center, Nebraska.
How to Use Soil Tension Data from Watermark Readings
In order to get familiar with the data presented in this weekly irrigation newsletter, we highly recommend reading “Irrigation Scheduling Strategies When Using Soil Water Data” (Nebraska Extension NebGuide EC3036). If you would rather take a look at videos on the topic, watch "How to Schedule Irrigations with Soil Water Data" — a great five-part video series on the CropWatch YouTube channel. The method is simple, yet accurate and can be used in the field or at the office to make precise decisions in just a few minutes.
In simple terms, Watermark sensors measure soil water tension, or how tightly water is held in the soil. Lower tension values mean water is more readily available to plants, while higher tension values indicate less available water. Below are two charts (adapted from EC3036) showing the relationship between Watermark sensor readings.
Early-Season Crop Evapotranspiration and Irrigation
- In the past seven days, accumulated crop evapotranspiration (crop water use) was 1 inch.
- Seasonal accumulated is a little over 10.6 inches.
- The consistent low weekly crop evapotranspiration combined with sufficient rainfall is resulting in favorable soil water levels at all locations where the sensors were installed in the east-central part of Nebraska.
Grower’s Irrigation Decision (July 29 – Aug. 5)
Understanding the chart:
- solid line — sensor at 1 foot soil depth
- dashed line — sensor at 2 feet soil depth
- dotted line — sensor at 3 feet soil depth
- blue arrows — rainfall in inches
- green arrows — irrigation in inches
- The rainfall of 0.5-inch that occurred on July 29 increased moisture content again near field capacity.
- Irrigation is still not needed at this field.
- This field has experienced another big rainfall event on July 29 (1.7 inches).
- Total rainfall in this field since sensor installation was about 20 inches, which is double the amount of water needed by the crop (about 10 inches since emergence).
- The sensor at 3 feet is saturated due to a high water table. This field is about a mile north of the Platte River.
- There is a possibility that the crops are taping water from the 3-foot depth, which explains why the sensors located at 1- and 2-foot depths are still showing wet conditions.
SCAL Irrigation Scheduling Video Update
Check this week's update from a set of soil moisture sensors installed at South Central Agricultural Lab in this video.
