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University of Nebraska-Lincoln experts have developed a website, called “SoyWater,” that promises to make it easier for soybean growers to schedule irrigation during the growing season.

The SoyWater Internet-based program has been in development for about two years, says James E. Specht, professor of agronomy and horticulture at UNL and one of several collaborators on the project. It was tested by a few soybean growers and UNL Extension experts during the 2009 growing season.

At press time, the website was expected to be fully functional and available in late April. To reach the site, type www.hprcc3.unl.
edu/soywater
into your Internet browser. Contact Specht via e-mail at jspecht1@unl.edu or phone him at 402-472-1536 for more information.

“In the past, it has been difficult to schedule irrigation to any crop because you have had to use a checkbook approach,” says Specht. “This required you each day to update that checkbook by first deducting yesterday’s withdrawal of soil water by the crop — evaporation from the soil surface and transpiration from the leaves, collectively known as ET. Then you had to deposit yesterday’s rainfall and/or irrigation amounts, if any. Doing so allowed you to discover where the crop stood today with respect to the soil water.”

It’s very difficult for producers to obtain daily ET amounts for their specific area every day during the growing season, Specht says.

As more growers have obtained fast Internet connections, it’s become more feasible to develop a website, such as SoyWater, that can gather those daily ET values and then do the checkbook calculations, he says. Using the website, growers or consultants only need to input their planting dates or crop emergence dates for a given field, and thereafter input the rainfall and irrigation amounts when these occur.

“Soybean growers just need to go to the website and see a table for each field that tracks the crop’s withdrawals from the stored soil water in the crop root zone,” Specht says. “Yellow highlighting in the table tells them when the first — or next — irrigation should occur.”

SoyWater goal: easier scheduling

The goal of SoyWater is to make it easier for producers to schedule irrigation in a just-in-time manner, whether the irrigation event is the first or the last of the growing season.

“We think if they use SoyWater for irrigation scheduling, they could potentially save up to an inch of water or more per year,” says Specht. That would be significant because nearly half of the state’s 4.5 million acres of soybeans are irrigated to some extent.

Even soybean growers who don’t irrigate can benefit from SoyWater. “This website, although it is designed more for the producer who irrigates, predicts the date of your soybean growth stages, too,” says Specht. “Producers who rely solely on rainfall to grow soybeans could use it to help determine what stage their soybeans are today or at some point in the future. This would allow them to plan to apply particular sprays that require specific growth-stage timing, such as herbicides or canopy-applied fungicides.”

Jessica A. Torrion and Tri Setiyono, postdoctoral research associates, have spent considerable time developing and refining the SoyWater website to make it as producer-friendly as possible, says Specht.

Other collaborators in this project included Kenneth G. Cassman, Nebraska Center for Energy Sciences Research at UNL; Suat Irmak, UNL Biosystems Engineering; Ken Hubbard, senior scientist at the UNL High Plains Regional Climate Center; and Martha D. Shulski, director of the UNL High Plains Regional Climate Center, who along with HPRCC programmers Bill Sorensen and Jun Li provided the links needed for SoyWater to acquire daily data from the state’s automated weather stations.

Carlton writes from Lincoln.

2 ways to use SoyWater irrigation scheduling program

The University of Nebraska-Lincoln’s newly developed SoyWater Internet-based irrigation scheduling program can be used in two ways, says James E. Specht, UNL agronomy professor and soybean researcher.

The typical irrigation strategy is one of irrigating on a just-in-time basis, whereby you irrigate only when the water is needed by the crop, says Specht.

SoyWater handles this strategy in all soil texture types by tracking the soil water balance in the field. The user simply selects a critical soil water depletion level, such as 35%, which is the amount of soil water the crop is allowed to deplete as a percentage of the total available water in the root zone.

This depletion “trigger” strategy tells SoyWater to notify the producer when the crop’s withdrawal of soil water reaches 35%. Producers can choose their own desired depletion percentage level.

For producers who have heavier soil texture types, such as silty clay loam, and the field has been brought to field capacity by snowmelt or spring rains before planting or emergence, the strategy of deferring all irrigation to the soybean R3-stage, the reproductive developmental stage when pod elongation begins at one of the four uppermost nodes, can be used. This is typically about 60 days after emergence following an early soybean planting (last week of April through first week of May).

Many soybean fields in Nebraska have silty clay loam soils that are brought to field capacity in most years by pre-season rainfall. These soil types have high water-holding capacity, and soybean plants can exploit that stored water for vegetative development even if rainfall is sparse prior to R3, says Specht.

Early irrigation on these particular soils produces excessive canopies (leaf area) that will lead to plant-lodging during the seed-filling period and promote even more water use from the greater leaf area. Specht has conducted many irrigation-timing experiments that have shown soybean irrigation prior to R3 on silty clay loam soils provides little or no yield benefit.

When a soil is at field capacity at planting, about 6 inches of plant-available water is stored in the soil within 3-foot zone rooting depth. UNL soybean researcher Jessica A. Torrion has shown that the soybean taproot tip is already 6 inches long at seedling emergence (stage VE) and thereafter moves downward at a linear rate of 0.8 inch per day.

So 10 days after VE, the taproot is 14 inches deep. Just 20 days after VE, it is 22 inches deep. Soybean taproots can extend well into the 4-foot zone just before R3. Thus, the available water stored in the soil in combination with expected rainfall is generally adequate to attain maximum yield potential without irrigation up to R3.

Soybean vegetative stages and reproductive development are provided in the Crop Water Use table of the SoyWater program. If there is sufficient soil water projected by the program calculations for the date when the producer’s soybean crop will reach the R7-stage (at least one mature brown pod per plant), irrigation can be terminated.

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SOYWATER DEVELOPERS: Jessica A. Torrion and Tri Setiyono, postdoctoral research associates, have developed the UNL’s SoyWater website with user-friendliness as a top priority.

This article published in the May, 2010 edition of NEBRASKA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.