Using SoyWater to Schedule Irrigation and Monitor Soybean Stages to Guide Decision-Making

By Jim Specht - Emeritus Professor of Agronomy | Haishun Yang - Crop Modeler and Associate Professor of Agronomy and Horticulture


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. SoyWater is available on the Web at hprcc-agron0.unl.edu/soywater/, on 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 five 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.

More than 1,200 people have registered to use SoyWater. 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. For more information on getting started, see this 23-minute video on how to register for and use SoyWater. For a shorter, 3.5-minute video, see this 2016 look at how a Nebraska farmer is using SoyWater.

Getting Started

To become a registered user, access the website at cropwatch.unl.edu/soybeans and create a user account by inputting your email address and a password. Be sure to record your password on paper for easy recall. 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:

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 its own consecutive number to each of your fields.
 
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 menu to select it there.

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 jspecht1@unl.edu if you need more info.

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, but not if you are unsure of the date.
 
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.

Figure 1. A SoyWater crop water use table generated in 2010

SoyWater estimates your crop's depletion of soil water and presents that data in the last column of the SoyWater table (Figure 1). At the top right corner 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. If you would like to see the table results in a chart format (Figure 2), click on the View Chart button. In the chart, click any box to turn on or off any item graphed in the chart.

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 (see 2nd and 3rd columns in the Figure 1 table) 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.

SoyWater – 2017 Update
We are updating SoyWater this year to use the new names that High Plains Regional Climate Center (HPRCC) has assigned to the automated weather stations that it manages in its AWDN network.  Thus, when SoyWater users create new 2017 fields or return to fields they created earlier this year, they will see different station names than they did in the past.  We will also be updating the SoyWater web pages during the summer as part of a project funded by the Nebraska Soybean Board.

SoyWater will work in states other than Nebraska if the automated weather stations in those states are managed by HPRCC.  These states include Colorado, Kansas, Minnesota, Montana, North Dakota, and Wyoming (but not South Dakota). For a list of active stations in Nebraska and those states, see this web page: https://hprcc.unl.edu/awdn.php (bottom of the page).  SoyWater also works with the automated weather stations managed by Michigan State University – see https://enviroweather.msu.edu/homeAlpha.php  If your farm is not located in any of these states (those served by the HPRCC and Michigan), you may still be able to use SoyWater if your farm is located in a state that borders one of the listed states – you will simply have to try SoyWater to see if that is the case.

Keep in mind that SoyWater will reliably track/predict soybean vegetative (V) and reproductive stages in your SoyWater field (see left three columns in Figure 1) and you can click on those stages to see a photo or drawing of the stage. (At the bottom of each photo or drawing is text that tells you how deep the soybean tap root tip is at that stage.) However, this SoyWater V and R stage tracking works ONLY for the indeterminate varieties of the maturity group range of 1 to 4 that are commonly grown in the northern USA; SoyWater does not work for determinate varieties of any maturity group range grown in the southern USA (such as, for example, determinate MG 4 varieties in southern KS). 

Source: unl.edu