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A Useful Tool for Irrigators

Friday, December 1, 2017
filed under: Irrigation/Water Use

Jonathan Aguilar, KSU Extension Ag Engineer
       USDA-Webster’s dictionary Sunflower producers who grow the crop under irrigation are among those in the High Plains who can benefit from a water management program developed by Kansas State University irrigation specialists.  The “Crop Water Allocator” (CWA) planning tool helps producers determine the optimum combination of crop mix and irrigation amount for a specific field, calculating net return per acre for each increment of water volume applied.
       Jonathan Aguilar, extension agricultural engineer with Kansas State University’s Southwest Research-Extension Center at Garden City, says the CWA framework is based upon crop yield curves developed by now-retired KSU-Garden City irrigation engineer Norman Klocke and others several years ago.  Rob Aiken, crops research scientist with the KSU Northwest Research-Extension Center at Colby, collaborated in the compilation of the sunflower yield curve data.
       “The beauty of this Crop Water Allocator is that it doesn’t just look at your production, but also at the economics,” Aguilar says.  The program projects net income levels based on crop inputs and water allocation, allowing the producer to look at a suite of different crops and see the projected net returns.  While that’s always important, it’s especially so in the present farming environment, given current crop price levels, increased restrictions on water allocations in many districts, and declining water yields from numerous wells. 
       There’s substantial flexibility in the KSU Crop Water Allocator.  For example, if a producer believes that the default input costs it provides for a given crop are too high or too low for his own operation, he can revise them accordingly.  Also, he can modify the incremental calculations of water use to suit his situation.  The CWA looks at it in 10% increments, Aguilar notes.  So if a producer has 10-inch water allocation on a split-pivot field containing sunflower and another crop, for example, and puts two of those inches on sunflower and eight inches on the other crop, the CWA goes through all the calculations to come up with a per-acre net return, based on that ratio of water application.  The CWA can go so far as to split a field into four crops, Aguilar adds, and factor in all the possibilities.  Along with 50:50 and 25:25:25:25, other field-split acreage options are 75:25, 50:25:25 and 33:33:33.  It also, of course, calculates on a single-crop basis.
       The range of applied irrigation built into the CWA goes from zero up to 28 inches.  Having zero irrigation means this could be used in dryland conditions; and it considers fallow as an option.  It also factors in soil type, irrigation costs and pumping capacity, and irrigation efficiency percentage.  Everything can be tailored to each producer’s operation.  “He (the grower) has all of the control” when using the program, Aguilar emphasizes. 
       The Crop Water Allocator should — and does — take into account natural precipitation.  “We are able to verify our numbers based on [annual rainfall] ranging from 11 inches up to 24 inches,” Aguilar notes.  That range pretty much encompasses any part of the High Plains, making the KSU tool useful for irrigators in nearby states as well.
       While the CWA was originally developed for pre-season planning, “we also could use it for drought mitigation planning, because you can change the rainfall,” Aguilar says.  “For example, if you are in an 18-inches-of-rainfall location but you know a drought has been forecast, you could plug in ‘10 inches’ and then run your scenarios based on that lower level of expected rainfall.”
       The Crop Water Allocator additionally can be used for multi-year calculations, which is becoming increasingly important for those producers operating within a Locally Enhanced Management Area (LEMA) district. As an example, if a producer has a total five-year allocation of 55 inches, the CWA can run any combination of scenarios to come up with projected net returns, either by individual year or averaged across that five-year period. (This multi-year capability is still in beta version and is available upon request.)
       The Kansas State University Crop Water Allocator is available in two versions:  a compiled one that can be downloaded to a computer and an online version that can be operated on mobile devices. To visit the CWA site, click here.
— Don Lilleboe   
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