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A Trifecta of Water-Planning Tools

20 October 2014

As fall progresses into winter and harvest comes to a close, crop producers might want to consider planning their future crop rotations, crop mixes and irrigation use.

The increasing demand for water in the future gives producers an even greater obligation to efficiently use the resource while optimizing yields.

That obligation is felt by many producers throughout Kansas, according to Danny Rogers, agricultural engineer for K-State Research and Extension. Through being involved in developing Kansas Gov. Sam Brownback’s 50-year water vision this past year, he knows water concerns, albeit different concerns, have risen in all parts of the state.

The largest single water user in the Kansas economy is irrigation, Rogers said, which in western Kansas is primarily provided by the High Plains Aquifer System, or in extreme western Kansas, called the Ogallala Aquifer due to the Ogallala Formation that makes up a majority of the geological High Plains Aquifer mass. Research at Kansas State University found that as much as 69 percent of the Ogallala would be depleted in the next 50 years, as water usage is exceeding the recharge.

In eastern Kansas, Rogers said various sedimentation issues are affecting many of the reservoirs that serve both public water supplies and crop irrigation. Some of those reservoirs are direct diversions from rivers administered by the Division of Water Resources, which means irrigators in eastern Kansas at times face unanticipated water limitations.

“Whether you’re in western Kansas facing declines, therefore limiting the total volume that you can physically apply during the season, or you’re in eastern Kansas where you might have an administrative reduction in your water right allocation by a certain percentage, now is the time to plan how to best optimize the use of that water in the next (crop production) seasons,” he said. “We have the tools that can help you do that.”

For those irrigators who are challenged with water availability in their irrigation programs, free online and downloadable tools are available on K-State Research and Extension’s Mobile Irrigation Lab to help them make the most of their water resources.

Among the variety of resources on the website, three main user-friendly and practical tools are available for crop producers to make water-planning decisions: the Crop Water Allocator, a tool used to plan optimum crop mixes for the next growing season; the Crop Yield Predictor, a tool used to predict yield, based on the amount of water and timing of irrigation within a specific season; and KanSched, an evapotranspiration, or ET-based scheduling tool used within a season to maintain acceptable levels of irrigation in fields.

Crop Water Allocator (CWA)

Rogers said the CWA was primarily designed for western Kansas, as it was m developed using data from K-State agricultural research centers in Colby, Tribune and Garden City.

Using the tool, irrigators can select from major Kansas crops they plan to plant and set their field conditions—volume of water, anticipated precipitation levels, soil type and acreage. All of the inputs are easy to select and change if needed using drop-down boxes on the new Web-based version. The resource is customizable for each producer.

Jonathan Aguilar, K-State Research and Extension water resource engineer, said making the Web-based CWA within the last year has been a positive change for irrigators and made the tool easier to use.

“When we developed the Web-based version, we also considered those people who are using mobile devices,” Aguilar said. “We envision the CWA being used while (producers) are out in the field and are able to share with other farmers what they are planning for the next season. Then maybe they can also get some feedback from the other farmers.”

Both the new Web-based version and downloadable software version are available on the Mobile Irrigation Lab website, and producers can use whichever version they prefer. The two versions work with the same end goal—achieving optimum returns—in mind.

“You can put in the limitations that your field experiences, and then the CWA will look at different combinations of crops for different water levels,” Rogers said. “It is a useful tool to help irrigators establish a crop rotation they might want to consider for the next few years. As we move to more deficit irrigation, crop rotation becomes an important consideration for those producers.”

As an example, Rogers said assume fully irrigated corn in a particular area might on average require 16 inches of irrigation, but a producer only has the ability to apply 10 inches. That producer can choose to grow corn at 10 inches for the entire field, or he or she might want to look at corn on part of the acres with other crops, or even fallow as an option on the other part of the acreage.

The allocator looks at the water availability a producer has in 10 percent increments of the available water. The land allocation can be split into units of land area as small as 25 percent sections of the total cropland base. The producer then selects which crops to be considered and customizes inputs such as yield potential and crop prices for the analysis.

Each crop will be evaluated in the different land segments with each increment of water, and eventually the CWA compiles the best combination of crop and water application depth for the producer to review.

“You can use this whether you’re looking at a single-field application or a whole farm application,” he said. “That would be your long-term strategy if you started a particular rotation. This is a guide to model what combination you might want to consider.”

Inputs in the allocator have default general values, and producers could use these values if they are applicable to their area, Aguilar said. But, producers can customize those, particularly their own yield goals and available irrigation levels, as needed.

Crop water use curves, showing the production increases with increased water use up to the crop’s yield potential, are built into the program, and producers would input what they believed to be their upper limit of productivity.

“Because there are differences in location due to soils and other various aspects, you wouldn’t want to input a 300 bushel an acre corn yield when the best yield you’ve ever had was 180 for fully irrigated corn,” Rogers said. “That would make it an unrealistic projection.”

Aguilar said in the past year, many on the K-State water team have hosted trainings to help producers better understand the CWA, its benefit to producers and how to properly use it. He is optimistic that those who attended the trainings will let others know how to use the tool, because they saw its usefulness firsthand.

In-season water planning tools

While the CWA could help producers with next season’s crop mixes and planning their long-term rotation strategy, another tool called the Crop Yield Predictor is available for in-season decisions.

“Using this tool, if you decided you wanted to plant a particular crop, and you’re projecting you’re going to put on a certain amount of water, you could play with what would be the best strategy of timing that irrigation,” Rogers said.

“It’s a seasonal look at water that has a yield component in it, and it will tell you for this particular crop and this level of water what would be the best strategy.”

The Mobile Irrigation Lab’s baseline irrigation scheduling tool is KanSched, and it’s the tool Rogers said he strongly recommends that every producer, whether they’re deficit irrigating or fully irrigating, use for in-season daily decisions on irrigation.

“I often hear producers say, ‘I’m deficit irrigating. Once I start irrigating, I don’t have any other decisions to make.’ That’s not true,” he said. “It’s hard to remember, since we’ve gone through about four years of drought now, that there are times we have above-normal precipitation in western Kansas, and that there are opportunities to save water.”

October 2014

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