Irrigation Management Update/Podcast for Eastern Nebraska

Irrigation Management Update/Podcast for Eastern Nebraska

Water sensor in soybean


Gary Zoubek checks a water sensor in soybeans.  While the top foot may have lost some soil moisture in the last week, water at the two and three foot levels were at full capacity.

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Corn height July 4, 2011

From waist high to head high in a week

A warm week can make a big difference in plant growth. Gary Zoubek stands in a field of corn that's head high July 4. Compare that to the same field (below) on June 28. (Photos courtesy of Gary Zoubek.)

Corn height June 28, 2011

July 6, 2011

This is the fifth in a series of weekly podcasts by Exension Educator Gary Zoubek on the use of ETgages and water sensors to improve irrigation management.

With the hotter temperatures this past week, ETgages in the Mead and York areas showed an increase in potential crop water use.  For the week

  • ETgages dropped an average of 1.6 inches,
  • temperatures ranged from from 79° F to nearly 100° F,
  • humidities ranged from 52% to 84% and averaged more than 71%, and
  • soil water in the top foot decreased, but was at field capacity at the second and third foot depths. 

This week I want to share our ETgage readings, estimated crop evapotranspiration or ET, and the soil water status of some corn and soybean fields in eastern Nebraska. The Watermark Sensors, ETgages, and rain gauges are located in the York area and near UNL's Agricultural Research and Development Center near Mead.

As I mentioned in earlier podcasts, an ETgage is a tool that takes into account the humidity, solar radiation, air temperature, and air movement to estimate potential crop evapotranspiration, also known as ET. For more information on how to use ETgages, please listen to previous podcasts in this series or see ETgage information at past week the ETgages at the ARDC and York dropped an average of 1.60 inches, an increase over last week's 1 inch drop.

To estimate the actual crop water use, multiply the crop coefficients for your current growth stage by the ETgage drop. As the crop gets larger, the crop coefficients also get larger. Crop coefficients for the state's major crops are available in the Weather section of CropWatch or on the Nebraska Ag Water Management Network section of the Water webpage.

The early planted fields that I'm monitoring are in the V12-V13 stage with the later planted fields in the V9-V10 stage. The crop coefficient for the V12 stage of corn is 0.88 compared to a coefficient of 0.69 for V10 corn. To estimate crop water use we multiply the crop coefficient by the drop shown by the ETgage. We would multiply the drop in the ETgage of 1.60 inches by the crop coefficient of 0.88 for a total crop use of 1.41 inches for the week or an average of 0.20 inch per day.

1.60 x .88 = 1.41 crop water use for the week for V12 corn

To calculate the crop water use for corn in the V10 stage, multiply the 1.60 inch drop in the ETgage by the crop coefficient of 0.69. This gives you a crop water use of 1.1 inches or 0.16 inch a day.

1.60 x .69 = 1.10 crop water use for the week for V10 corn

The field near Mead received 0.75 inch of rain this past week. In the York area we received 0.3 inch. A check of the Watermark soil water sensors indicates that soil water in the top foot of the profile has decreased; however, soil water at the second and third foot sensors are reading at field capacity or above.

In the York area with Hastings Silt Loam soils the sensors in the top foot are reading 50, so that's a depletion of about 0.32 inch of soil water. However, we still have 0.78 inch available soil moisture in the top foot plus 2.2 total inches in the second and third foot depths.

It's important to know your soil type when using Watermark Sensors. A list of irrigation trigger levels for various Nebraska soils is available at For the Hastings Silt Loam soils we want a trigger more like 90, which is a depletion of about 35% of the soil water for that zone.

At the ARDC, the soil sensors in the top foot are reading 25, but since it's a fine sandy loam soil, that's a depletion of about 0.40 inch of soil water. That means 0.30 inch is available in the top foot plus 1.80 inches in the 2nd and 3rd foot depths. The irrigation trigger level for this soil type would be 45.

Our goal in managing our irrigation is to leave some room for what we may receive from Mother Nature. If we don't receive rainfall this week, I'm sure we'll be irrigating the fields by the end of the week or the start of next week, especially the one near Mead that's on a fine sandy loam soil.

For more information about these and other irrigation management tools, see CropWatchNebraska Ag Water Management Network, or email me at I'm sure we are going to see a big change in the crop again this week and it won't be long until the earliest corn will be tasseling!

Catch up with Previous Podcasts

This is the fourth in a series of irrigation management podcasts for eastern Nebraska from Gary Zoubek.  Also see:

Gary Zoubek
Extension Educator, York County



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A field of corn.