Managing variable nitrogen, irrigation

Down in the Weeds: The interaction of water and nitrogen in crop growth brings many variables into play, and managing VRI in tandem with variable-rate nitrogen is no small task.

Editor’s note: Listen to my conversation with Nebraska Extension nutrient management specialist Tim Shaver by clicking on the audio link above.

For the last six years, Tim Shaver, Nebraska Extension nutrient management specialist, has been researching variable-rate irrigation systems at the Water Resources Field Laboratory near Brule in western Nebraska. Why is a nutrient management specialist interested in VRI? Shaver is taking a different approach to VRI research; he's researching VRI used in conjunction with variable-rate nitrogen.

"In the last few years, VRI is something that's become available to farmers," Shaver says. "This made us think, if we're going to vary the amount of water we're putting down, we probably should be varying the amount of nitrogen we put down with it, because those two things are so linked together — nitrogen being so water soluble, wherever the water goes nitrogen goes with it."

"It sounds like a simple concept, but it's actually very complicated, because the interaction of water and nitrogen in crop growth really brings a lot of variables into play," Shaver says.

So, to determine how much water and nitrogen to apply and when, Shaver is using several different kinds of soil moisture sensors, as well as crop canopy sensors like reflectance sensors to respond to what the plant's needs are.

Using the reflectance sensors, Shaver notes the idea is to bring the corn back up to a reference standard. "So we take a measurement in a part of the field where the corn is really green, really sufficient in nitrogen and compare the two, and essentially we're trying to bring it back up to that level," he says.

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