Weekly Irrigation Newsletter: Using Soil Water Tension Sensors to Schedule Irrigation in Nebraska

Published: July 26, 2024 | Updated: August 26, 2025

Weekly Irrigation Newsletter: Using Soil Water Tension Sensors to Schedule Irrigation in Nebraska

By Bruno Lena - Extension Educator, Steve Melvin - Extension Educator Irrigated Cropping Systems

Close-up of a center pivot irrigation system spraying water over a cornfield, with water droplets captured mid-air and corn tassels visible in the foreground.

With plentiful rainfall already recorded across much of the region, many fields are close to meeting late-season needs — review this week’s charts to see if your crop is ready to finish without additional irrigation.

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.

Weather and soil monitoring station in a cornfield with a rain gauge, data logger, and soil moisture sensors used for irrigation management.
Figure 1. A Watermark sensor collects real-time data on rainfall, temperature and soil moisture in an east-central Nebraska field. 

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. 

Watermark sensor chart for loamy fine sand showing soil water availability and management zones by centibar reading, with color-coded zones for high drainage, field capacity, desired water range, and low water stress.
Figure 2a. Relationship between watermark readings, plant available water, and soil available water above and below field capacity for loamy fine sand soil.
Watermark sensor chart for silty clay loam showing soil water levels by centibar reading, with color-coded zones for high drainage, field capacity, rain storage, desired water range, and low water stress.
Figure 2b. Relationship between watermark readings, plant available water, and soil available water above and below field capacity for silt clay loam.

Early-Season Crop Evapotranspiration and Irrigation

Three-panel chart showing crop evapotranspiration (ETc) and rainfall from May through September. Top panel: accumulated ETc steadily increases to 14 inches. Middle panel: daily ETc peaks near 0.25 inch in mid-June to July and declines in late August; past 7 days total 0.82 inch. Bottom panel: rainfall is variable with several peaks over 2 inches in June and August, totaling 23 inches for the season.
Figure 3. Daily and accumulated crop evapotranspiration (ETc) alongside in-season rainfall totals.
  • In the past seven days, accumulated crop evapotranspiration (crop water use) decreased from last week to 0.82-inch.
  • This was expected since the crops are past halfway milk line and approaching maturity.

Grower’s Irrigation Decision (Aug. 19-26)

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
Chart showing soil moisture sensor readings for Grower 1 on silt clay loam soil from late May to September 2025. Lines represent sensors at 1, 2, and 3 feet depths, generally staying within the rain storage zone (RSZ) and desired water zone (DWZ). Blue arrows indicate rainfall or irrigation events, with amounts labeled from 0.1 to 4.4 inches. Soil moisture remained mostly stable in the desired range, with brief dips and recoveries after rain or irrigation.
Figure 4. Grower 1 data on soil moisture trends in silt clay loam, with rainfall events and sensor readings at 1, 2, and 3 feet.
  • No rainfall occurred and soil moisture entered the rain storage zone.
  • It is very likely that irrigation will not be required until maturity at this site.
Chart showing soil moisture sensor readings for Grower 2 on loamy fine sand soil from late May to early September 2025. Lines represent sensors at 1, 2, and 3 feet depths, mostly staying in the desired water zone (DWZ). Blue arrows indicate irrigation or rainfall events ranging from 0.1 to 6.6 inches. A fertigation event is noted in early August. Soil moisture remained generally stable with quick responses to irrigation, typical of sandy soils.
Figure 5. Grower 2 data on soil moisture data for loamy fine sand, showing response to rainfall at three soil depths.
  • The grower irrigated 0.75-inch on Aug. 25.
  • Depending on the weather, rainfall patterns and growth stage, irrigation may not be required until maturity at this site.
Chart showing soil moisture sensor readings for Grower 3 on loamy fine sand soil from mid-June to mid-September 2025. Sensors at 1, 2, and 3 feet depths stayed mostly within the desired water zone (DWZ). Blue arrows mark irrigation or rainfall events ranging from 0.1 to 3.9 inches. Soil moisture remained relatively steady, with deeper sensors showing less fluctuation than the shallow sensor.
Figure 6. Grower 3 data on watermark sensor readings in loamy fine sand, highlighting moisture patterns across the root zone.
  • Although this field did not receive any water in the past week, soil moisture sensor remained unchanged.
  • This has been the pattern for this site, which may support the hypothesis that the crop is tapping water from the high-water table.

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. 

Nebraska Extension Educator Steve Melvin demonstrates how to apply the irrigation scheduling method outlined in "Irrigation Scheduling Strategies When Using Soil Water Data" (Nebraska Extension NebGuide EC3036). (Video No. 6 of series)

August Irrigation Scheduling Should Focus on Using Remaining Stored Soil Water

The last few irrigations of the season require some of the most important water management decisions of the year.

Calculating the amount of water needed from rain and irrigation for the crop to reach maturity becomes important starting in August. For more information, check out “August Irrigation Scheduling Should Focus on Using Remaining Stored Soil Water.”

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