Optical sensors may also help growers deal with extreme weather patterns. Doug Weist, who farms in north-central Montana near Choteau, uses his CropSpec sensor system to better match N applications to soil types, but also to available moisture on his wheat, barley, dry pea and canola fields. In coming years, he plans to add corn and expects sensors to help make that crop more economically viable.

A dryland farmer in an arid region, Weist has transitioned from a grain/fallow rotation to a 4:1 or greater crop/fallow mix. More efficient use of N through in-crop, multiple VRT applications have helped make the transition pay.

“We can control everything but the weather,” says Weist. “Traditionally, wheat and barley growers put on all their fertilizer in January and February and hope for rain. We try for a base rate and then apply in-crop with the sensors, depending on soil moisture and likelihood of rain. If warranted, we’ll make three to four variable-rate applications over the season.”

CropSpec allows Weist to use dynamic calibration to adjust rates on a relative basis across the field; no N-rich strip needed. He varies application amounts from 5 to 15 gal./acre based on an average reading for the first quarter mile. His truck-mounted SprayFlex spray system lets him react quickly to rain forecasts.

“If there is an 80% chance of rain, I can cover the whole farm (up to 2,500 crop acres) in two days,” says Weist.