Use UNL's SoyWater to Schedule Irrigation, Guide Decision-Making

Use UNL's SoyWater to Schedule Irrigation, Guide Decision-Making

Get the most from your irrigations with SoyWater, an easy to use, irrigation management tool. It provides timely crop water use information specific to your field and this year's growing conditions. It is available on the Web at, the UNL CropWatch Soybean page, or simply Google the words "UNL SoyWater."

This decision support tool was developed by the University of Nebraska-Lincoln with support from soybean checkoff funds provided by the Nebraska Soybean Board. Unlike many other management tools, SoyWater doesn't require you to install anything on your home computer or spend time learning a new software program. It guides you through four simple steps to input information so you can get field-specific irrigation recommendations.

SoyWater can help you determine how much water your field needs and when it needs it, eliminating unnecessary irrigation events. An acre-inch of water applied is equivalent to 27,154 gallons of water. Thus, saving one unnecessary one-inch irrigation event could save you 5,424,800 gallons of water on a 200-acre pivot. Moreover, you would also save pumping energy cost and time. Such savings would allow you to optimize your input use efficiency (bushels per acre per inch of water applied or energy used).

Even if you don't irrigate, SoyWater can help you fine-tune your management. Both rainfed and irrigated producers can use it to track and predict the dates when a field will reach a specific soybean stage. Pest control and disease management are much more effective if the pesticide or fungicide is applied precisely at the soybean stage that researchers recommend.

About 920 people  have registered to use SoyWater since its official launch on May 1, 2010. We invite you to join this group and learn how to more effectively schedule soybean irrigation events to apply just the right amount at just the right time. sample page


Figure 1. A SoyWater crop water use table generated in 2010.  (Links to larger view.)

Chart of SoyWater data

Figure 2. Chart of data developed using SoyWater. Note that these figures show the user irrigating on precisely the dates recommended by SoyWater, applying just the right amount of water at just the right time.

Getting Started

To become a registered user, access the website at and create a user account by inputting your email address and a password. You will receive a four-digit activation code by email. Use that code to get 24/7 access to SoyWater this year and in future years.

To get started, you'll need to provide some basic information about your field. (Note: Your information is strictly confidential — no one else has access to your field information.)

The first step is to identify the field location. An easy-to-use Google map tool is provided so you can locate your field based on an aerial view. SoyWater will then identify the field's GPS coordinates and use them to identify the nearest automated weather station. Data reported to this weather station will be used to estimate your crop's daily evapotranspiration (crop water use).

SoyWater then needs only five more items from you:

  1. A field name. Choose something easy to recall (e.g., Smith Pivot 5, CP#8, etc.) if you have many fields to enter. Otherwise SoyWater just assigns a number to each one.
  2. The predominant soil texture in the field. SoyWater provides a menu of choices, but if you're unsure about which one to use, page down to the Google soil texture map tool for help in identifying a soil texture for your field.  Zoom in on the map until your field occupies the entire view frame to best estimate the acres of each soil type. Choose the predominant one for your field, then page back up to the original soil texture. 
  3. Initial soil water Field Capacity (FC) Percentage. The default is 100%. Most soils will be at field capacity soil moisture content by planting or shortly after emergence each year so choose 100%. If the top six inches is dry, don't plant — wait for a rain. Contact if you need more info.
  4. The date of planting. This is the default. You enter the planting date here. If you know the date of emergence check that circle and enter that date. 
  5. The two-digit maturity group (MG) number (for example, 3.1) of the variety you planted in the field. The MG number is typically embedded in the brand's variety number. (For example P93M11 is MG 3.1, A3005 is MG 3.0, etc.)  Contact your seed dealer for details if you do not recognize the two-digit decimal MG number in the branded variety number that you planted.

A Season-long Decision Aid

Once your account is established, you can log into it any time to view the updated information as the crop season progresses. As irrigation or rain events occur, you will need to input the date and amount of water applied or rain measured at the site. Do not sum up your rainfall over a week and plug in the summed values. SoyWater needs the daily values.

SoyWater estimates your crop's depletion of soil water and presents that data in the last column of the SoyWater table.  At the top of your SoyWater table, you choose the percentage of soil water depletion by the crop that you want to use as an "irrigation trigger."  On the calendar dates when soil water depletion reaches or exceeds your chosen depletion number, the cells in the last column of the SoyWater Table are highlighted in yellow. This recommendation is based on the soil water depletion percentage value. The default is 35%, and for new users is the best choice, but that percentage can be toggled between 20% and 60% to have fewer or more days between
"irrigation events" — but be careful with the latter choice.

Using SoyWater for More than Irrigation Management: Estimating Growth Stages

SoyWater uses a crop model (SoySim) to create a table showing the calendar date for each soybean vegetative and reproductive stage from emergence to maturity with corresponding and daily and cumulative soybean crop water use values specific to your field. This will help you assess when you can expect certain critical stages such as R3, which is the best stage for a canopy fungicide treatment to be effective, if you plan to apply fungicide to the canopy.

James Specht, Professor
Jessica Torrion, Former Research Associate (now at Montana State University)
Department of Agronomy and Horticulture



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