UNL CropWatch Summer 2010: Weekly Insights into Data Analysis and Irrigation Scheduling

UNL CropWatch Summer 2010: Weekly Insights into Data Analysis and Irrigation Scheduling

Summer 2010

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  • Week of September 22 — This week we will review the growing season and how it affected irrigation scheduling at the two fields we've been following near Curtis. Aspects of this year include a wet spring that delayed planting, two extended dry periods, and several big rains. This will be the last update for the year.
  • Week of September 15 — This week we are looking at late-season crop water use and the depth from which water is being drawn. We'll also be talking about how much off-season precipitation will be needed to refill the soil profile.
  • Week of September 8 — We experienced the Achilles heel of soil water monitoring systems this past week. Take a look to see what happened and how we are finishing up the irrigation season.
  • Week of September 1 — We have made it to September. Because we want to use any rain that may still come and as much soil water as we can without lowering yield, we are delaying our last irrigation and still calculating the amount of water me may need to apply.
  • Week of August 25 — The end of the irrigation season is in sight and we are making some of the most important decisions of the year.  Since we have almost enough water in the soil, the question is whether we put on more water or wait a little longer to see if we get rain.
  • Week of August 18 — This week we start making some of the most important irrigation decisions of the year by calculating the water needed from rain and irrigation to mature the crop. The objective is to use as much of the soil water as possible without lowering the yield. Most years, in most of Nebraska, the offseason precipitation is adequate to refill the soil water profile on irrigated fields. Also see the Aug. 13 CropWatch article, Predicting End of Season Irrigation Needs, by the same author. 
  • Week of August 11 — The rapid drop in daily crop water use this time of year combined with a nice rain on our fairly wet fields are reflected in this week's charts. The long-term daily crop water use chart shows that the water use rate has dropped from 2.1 inches per week at silking to 1.68 inches per week at milk and will drop to only 1.26 inches per week by the full dent stage.
  • Week of August 6 — Four small rains (0.09, 0.05, 0.51, and 0.12 inches) plus 1.5 inches of irrigation this past week resulted in excellent soil water level. Small rains (less than 0.25 inches) do not add much to the soil water, but can result in lower ETs the following day and four in one week can add up.
  • Week of July 29 —  Starting this week I have switched the Water Miser strategy to the Deficit Irrigation strategy because the Water Miser and the Fully Watered strategies are the same after tassel stage. Most years in southwest Nebraska, irrigation is required before tassel with the Fully Watered option, but not with the Water Miser option. With the good rains we've had this year, the two management strategies would indicate the same irrigation amounts all summer. Thus,  to show examples of two different strategies, I decided to make the switch to the Deficit Irrigation Strategy.
  • Week of July 22 — This week we have a major change in the water miser strategy as the corn moves from the vegetative to the reproductive stage. See how this change affects the scheduling procedure and learn how much irrigation water was saved this year by using the water miser strategy.
  • Week of July 15 — This week I discuss how the 3.24 inches of rain we received last week affected the soil water reading and the need for irrigation in both the fully watered and water miser strategies. In addition we will talk about how irrigation scheduling changes as the corn changes from the vegetative stage to the reproductive stage.
  • Week of July 5 — Introduction to the webinar series following irrigation scheduling for two fields near Curtis; includes how soil moisture data can be used for irrigation scheduling.

The decision of when and how much irrigation water to apply is as old as irrigation itself. Soil water monitoring equipment can help by generating a lot of data, but by itself, the data isn’t very useful. To make good irrigation scheduling decisions, the data needs to be carefully analyzed.

Sometimes growers have shared that while they installed soil water monitoring equipment, they still didn’t feel comfortable using the data to make irrigation scheduling decisions.

To develop a better understanding of how to use this data, I’m offering a weekly on-line video series where I’ll discuss irrigation scheduling based on that week’s soil moisture readings for two corn fields in southwest Nebraska. Think of it as a weekly visit with a neighbor who’s been using a new technology you’d like to use, then grab a cup of coffee and catch the show.

Field Specifications. The first plot will be watered according to the traditional Full Watered Strategy, and the second one will be scheduled using the water conserving strategy. The example fields are on the NCTA Learning Farm at Curtis. The irrigation capacity for these fields allows for application of about 2 inches of water per week or about 5.5 gpm/acre. Curtis is in a 20 inches per year rainfall zone.


Links to the webinars will be posted to this page weekly.  Background information to help viewers better understand the updates also is available:

You can also follow the irrigation decision-making process for these two fields weekly on Facebook or Twitter

Steve Melvin
Extension Educator, Frontier County


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