Introduction

In 2024, Nebraska Extension started a new collaboration with three growers located in east-central Nebraska. We installed a set of three watermark sensors at 1-, 2-, and 3-feet soil depth and the sensors were connected to datalogger (IC-10 model from Irrometer) to record and store hourly data at one-hour intervals. The data can also be accessed remotely for quick irrigation decision.

Prior to the beginning of the irrigation season, two Nebraska Extension educators and three growers met and discussed the plans for irrigation decisions. The goal of the discussion was to show how to use the soil sensor data to make informed irrigation decisions using the Extension Circular EC3036. At the end of the meeting, the growers agreed they would use the soil moisture sensor data to schedule irrigation. They also agreed to share their irrigation decision in this weekly newsletter.

The goals of this collaboration are to increase awareness about the use of soil moisture sensors and perceived benefits in year 1, so they will adopt the technology in year 2 and beyond.

How to Use Soil Tension Data from Watermark Readings

In simple terms, watermark sensors provide a reading of soil tension. The smaller the tension, the more water available in the soil, and the larger the tension, the less water available in the soil.

Below are two charts showing the relationship between watermark reading, plant available water, and soil water storage above and below field capacity (taken from EC3036). The soil types are the same as those found in the growers’ fields where sensors were installed. A grower irrigating in a silt loam soil will have to wait for the watermark to reach the desired water zone, and irrigation should be applied to recharge the soil at the bottom of the rain storage zone (55 cb). If managing irrigation in a loamy fine sand that has low water holding capacity, irrigation should be applied to return the soil to field capacity.

Grower’s Irrigation Decision (Week 1 — July 22-28)

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 past week, sensor located at 1’ and 2’ approaching the desired water zone.
• Grower was concerned with load control and decided to irrigate 0.7 inch on July 26 to stay “ahead of the game”.
• Sensor at 3’ soil depth entered the rain storage zone, showing that the subsoil moisture is near field capacity (plenty of water).

• The past week, sensor located at 1’ and 2’ approaching the desired water zone.
• Grower was concerned with load control and decided to irrigate 0.7 inch on July 26 to stay “ahead of the game”.
• Sensor at 3’ soil depth entered the rain storage zone, showing that the subsoil moisture is near field capacity (plenty of water).

• After a back-to-back irrigation of 0.35 and 0.41 inch on July 22 and July 23, sensors located at 1-foot soil depth moved quickly from the water zone to the low water zone.
• The grower irrigated 0.85 inch on July 28 to prevent water stress.
• Deep soil layers (2 and 3 feet) are still showing saturation conditions because of the high water table. This field is located two miles south of the Platte River. As more growers start to irrigate, the water table may drop and sensor at 2 and 3 feet may enter the desired water zone.