The Weekly Irrigation Newsletter 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 Monday.
Summary
The 2024 growing season was much cooler and wetter when compared to the past two years. During the peak of water demand (July and August), the average daily corn crop ET in 2024 was 0.18-inch per day, much lower than the 0.25- to 0.30-inch per day observed in 2023 and 2024 during the same time of the year. The crops still need 1-2 inches to mature, meaning that the total crop water use will be around 19-20 inches in 2024, about 2-3 inches lower than the previous years.
Rainfall data collected from a weather station five miles northeast Columbus, Nebraska registered abundant rainfall during spring until early July. All that rainfall might have influenced the root system to grow shallower than the previous years. This was observed during the growing season at the three locations we installed soil moisture sensors, in which the bottom sensor (3 feet soil depth), maintained at higher soil moisture during the entire growing season because the root system did not reach that layer.
At this point in the season, most growers are quitting irrigation. Therefore, this is going to be the last weekly newsletter published in 2024.
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 (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 7 — Aug. 26-Sept. 2)
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
- This grower applied a total of 2.95 inch in 2024.
- The 3-inch soil depth sensor was kept fairly wet during the grower season, and most changes happened in the top 2 feet soil layer.
- This grower decided to apply another two irrigation events for a total of 5.1 inches during the growing season.
- This field received the least rainfall amount during the growing season, making the sensor located at the 3 feet soil depth the driest among all fields. Yet, that soil layer was kept within the rain storage zone and never entered the desired water zone.
- The same sensors were installed in the same field in 2023, and the bottom sensor ended at 170 cb reading, which is something desirable to allow room for off-season rainfall and less changes of nitrogen leaching.
- The total irrigation amount was 3.91 inches in 2024.
- Even though this field has a light-textured soil, which theoretically would require more frequent irrigations, the high-water table combined with abundant rainfall resulted in lesser irrigations than in previous years.
