The challenge of management zones and precision nitrogen

There’s nothing easy about farming, and there’s nothing easy about precision ag either.

At the heart of the challenge of precision ag is how to capture reliable data and how to plan management zones for variable rate application.

That challenge was the focus for Raj Khosla of Colorado State, who addressed an audience of precision agriculture professionals at the Info Ag conference in St. Louis this summer. He spoke on the topic of Management Zones & Precision Nitrogen Management.

“If I were to look back at the past 25 years, what is the crux of precision agriculture? We have been trying to quantify variability in space and time, because Mother Nature is highly variable,” he said. “Whether we use soil sampling, imaging or sensing, how do we quantify this variability that’s out there and then convert this data to meaningful information so farmers can know how to apply, where to apply?”

Over decades, spatial variability has been documented in hundreds of papers worldwide, Khosla said.

Different techniques for documenting that variability result in different prescription maps, as seen in the image above.

That image shows the different results from three intervals of sampling: a base level, a 4x more dense level, and a 15x denser level.

“We know for sure that as you increase sample sizes, you’re spending more time getting samples. It’s more labor intensive and spending much higher dollar,” Khosla said, acknowledging the reality that more is not better if it is impossible.

Then, he turned to the next logical question: Are there better ways of measuring spatial variability?

Khosla said his team examined 36 factors for correlation to yield and soil electrical conductivity came out on top.

It still doesn’t explain the whole equation, in space or time, he said, but it’s the best individual answer to the challenge.

The image above shows conductivity’s relationship to yield.“Not every field looks this good,” Khosla said. “Some of the fields have little to no association.”

Still, electrical conductivity is a valuable tool, he said, and still more are on the way.

One promising area Khosla sees offering help to growers in the future is the soil microbiome.

There’s still a long way to go on that front, he said. But the promise is there.

“Who said agriculture is easy?” Khosla said.