Irrigated farmers or landowners in the Crop Tech Café area should take a look at a new tool developed by UNL to estimate the potential pumping reductions from utilizing variable rate irrigation (VRI). With the rapid development of VRI technology there has been an increasing interest in utilizing VRI to improve irrigation efficiency, increase yields, and reduce pumping costs. The tool, available at http://heeren.unl.edu/map, estimates water savings from VRI that are possible when you reduce irrigation to heavier soil textures while maintaining higher application rates to coarser soils, such as the sand veins that are present in mainly bottom fields along the Platte and Elkhorn rivers.
On the main page you will see a Google map of Nebraska, with counties outlined in black as seen below.
Statewide map of counties
Entering your address and then clicking on your county will bring up a map with most existing center pivots in that county outlined in blue. While over 49,000 center pivots were analyzed statewide for the map, not every center pivot is included.
Center pivots evaluated for potential VRI savings in Colfax County
When you click on a given center pivot field, several pieces of information will pop up. First you will see the acres irrigated by the center pivot. Second you will see a potential pumpage reduction in inches per acre per year as well as total acre feet per year reduction. Last you will see percentages for R. R in this case stands for the amount of available water holding capacity in inches for a 4 foot root zone.
For example a field with “9” R: 100%”, such as the one pictured below, is a very uniform field where all of the soil textures found in that field have a water holding capacity of 9” for a 4 foot root zone. Highly uniform fields such as this are expected to have a very low potential for water savings from VRI when you look at just managing based on soil water holding capacity.
Center pivot irrigated field with very uniform soil water holding capacity
On the other hand, a field such as the one pictured below has much more variability in soil texture, so the tool rates the field as having a much greater potential savings from VRI for soil water holding capacity differences. If your field has an expected water savings from VRI, you can further use the web tool to calculate the potential savings from VRI and to calculate how much you could afford to spend on VRI. Additional instructions on performing these calculations are available on the webpage.
Center pivot irrigated field with variability in soil water holding capacity
Keep in mind that the tool does not account for all of the potential advantages of VRI. One such advantage is avoiding the application of nitrogen or fungicides during chemigation, or manure when pumping from lagoons, to sensitive areas such as streams. Evaluating these other potential advantages is key when looking at VRI so be sure to visit with industry personnel or university specialists about your specific situation.
Take a moment to play with this tool and evaluate your fields this winter. While additional expenses on irrigation improvements may not be in the cards this year given current crop prices, it is great having the knowledge of which fields could have the best potential returns from VRI improvements to guide your future planning.
