Now's the Time to Install ET and Soil Moisture Sensors - UNL CropWatch, May 26, 2011

Now's the Time to Install ET and Soil Moisture Sensors - UNL CropWatch, May 26, 2011

May 26, 2011

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Even though many parts of the state have received adequate or in many cases, excessive precipitation, now is the time to begin planning for the upcoming irrigation season.

Photo - water sensor

Figure 1.  An ETgage installed in York County.

Producers in the Nebraska Ag Water Management Net (NAWMN) have been using ETgages and soil water sensors to aid their irrigation planning and management. If you’re interest in implementing these tools in your irrigation management program, you’ll want to install them in your fields now.

ETgages

ETgages should be placed in open areas such as grass, fencelines, alfalfa, small grains or soybean fields at least one foot above the canopy. These gages take into account the area humidity, temperatures, solar radiation, and air movement to provide an accurate estimate of potential crop evapotranspiration or ET.

Think of the ETgage (Figure 1) as being the opposite of a rain gauge. Instead of catching rain, it measures how much the water level has dropped. This occurs as the water evaporates from a ceramic plate covered with green canvas to simulate a crop leaf. The ETgage is read at least once a week. If you know that amount and the crop stage of growth, you can estimate crop ET.

For information about using ETgages go to UNL's water.unl.edu website and click on the NAWMN link. At this site, you can view information from producers as well as the crop coefficients for various crop growth stages.

Also see the ETgage information on this site. Last year we added several automatic weather stations, which show up as blue balloons on the map. These provide daily reference ETs as well as readings for the past week. If the ETgage readings are not updated, you’ll have current weather station data.

If you have an ETgage, we hope you’ll consider posting your information to the website so that other producers can access the info.

Watermark Sensors

ETgages do a great job of estimating crop water use, but it’s important to also monitor soil water status. The NAWMN has been using Watermark sensors that are installed at 1-, 2-, 3-, and even 4-foot depths in representative areas of the fields. The sensors are usually placed in the row between plants. If your corn or soybeans have emerged, this would be a great time to install them. The sensors are glued onto PVC pipe so they can be installed, used, removed at the end of the season, and reused next year.

Before heading to the field to install Watermark sensors, you’ll need to do a little preparation. The sensors need to be soaked in water and then allowed to dry out, preferably a couple of times prior to installing them in the field. When installing sensors, be sure they are wet. Also, be sure to check and make sure that no extra water has soaked up into the PVC tube by tipping the sensor and making sure no water sloshes around.

More Information

Our goal is to get the sensors installed when conditions permit before the crop gets too large. For more information on these sensors as well as installation tips, visit http://water.unl.edu/cropswater/nawmdn. This site also includes videos and publications on water management.

Also see this table of irrigation triggers by soil type.

Gary Zoubek
Extension Educator in York County

Aaron Nygren
Extension Educator in Colfax County