Evapotranspiration: Needs and Water Availability at Holdrege, Nebraska .

The following graphs are generated from data taken from the High Plains Regional Climate Center located in Lincoln .  The HPRCC operates an automated weather station that collects weather data, including precipitation and evapotranspiration information.  This Holdrege site was put into service in 1988. 

The site collects potential ET and, then, the HPRCC uses a formula to compare the growth stage of a plant to the actual ET data.  Using the HPRCC server, we asked it to compute the ET rate for medium season corn for each day for 1993 through 2004.  The following charts show HPRCC data for 12 years.

“ET required” is the amount of water the HPRCC says a medium season corn crop will need in order to meet maximum yield.  The light blue shaded area is the precipitation received during the growing season.  The green shaded area that is visible is the amount of water that must come from irrigation or from the soil profile for the plant in order to make maximum yield.  The line with the diamonds is the average amount of water that is needed according to the Holdrege station.  The line without marks is what Dr. Derrel Martin reports is needed.  The line with the squares shows how much water needs to come from the soil or from irrigation.

Summary

The Holdrege data for the last 12 years shows that there is a need for an average of 10.10 inches of water to come from irrigation or the soil profile during the growing season.  The non-growing season precipitation and the soil type you have will determine how much of that can come from each source. 

Soil Holding Capacity

Soil Type

Inches/foot

Coarse Sands

0.60-0.80

Fine Sands

0.80-1.00

Loamy Sands

1.10-1.20

Sandy Loams

1.25-1.40

Fine Sandy Loam

1.50-2.00

Silt Loams

2.00-2.50

Silty Clay Loams

1.80-2.00

Silty Clay

1.50-1.70

Clay

1.30-1.50

Source: Colorado State University ,  http://www.ext.colostate.edu/pubs/crops/04707.html

The effective root zone for mature corn is 2.5 feet.  To estimate the amount of water available from the soil profile, multiply 2.5 by your soil type. Some reports show corn roots going as deep as 6 feet however over 90% of all water taken from the soil is done within the top 2.5 according to Colorado State University.

If you have a fine sandy loam soil and the soil profile is fully water charged, then there would be between 3.75 and 5.00 inches of soil profile water available to you.  The balance must come from precipitation during the growing season or irrigation.

The difference between the blue and the green areas must come from irrigation or from water stored in the soil.  Refer to the above tables to see what the soil holding capacity is for your soil type.  The yellow line is the amount of water required according to Derrel Martin.  The green area above the yellow line is the amount his average ET number underestimates the need by.

We add this second graph for the Champion area (8 miles west of Imperial) for comparison purposes.

For Holdrege, Nebraska

  Average Median Low High
ET for corn medium growing season 25.79 26.10 20.98 30.66
Growing Season Precipitation 15.69 13.82 7.87 29.48
Total Precipitation 23.14 21.57 12.47 35.92
Irrigation or Soil Profile Water Needed 10.10 12.52 -8.50 22.79
 

For McCook, Nebraska

  Average Median Low High
ET for corn medium growing season 26.90 27.80 20.31 31.40
Growing Season Precipitation 13.56 12.98 5.79 20.36
Total Precipitation 19.29 19.09 12.53 24.23
Irrigation or Soil Profile Water Needed 13.34 14.92 0.83 24.66

 

For Champion, Nebraska

  Average Median Low High
ET for corn medium growing season 29.46 29.64 24.84 32.79
Growing Season Precipitation 11.33 10.52 5.22 20.50
Total Precipitation 16.60 16.77 8.15 23.30
Irrigation or Soil Profile Water Needed 18.13 18.43 4.34 27.58