ST. LOUIS, Mo. — Precision agriculture has changed the way producers approach seeding rates and nitrogen application in corn. Speakers at InfoAg, the annual precision trade show in St. Louis in late July, updated precision technology providers about managing other corn inputs, as well as soybeans.

 

Managing variable phosphorous (P) applications in corn, for instance, presents various challenges. “The problem is we can’t precisely map P at the resolution we can vary it,” said Josh McGrath, University of Kentuky soil management specialist, during a presentation. Corn’s varying phosphorous need, at different growth stages, is another challenge for splitting applications. “You’ve got to understand what’s happening with that P response early,” said McGrath.

Research in Kentucky last year, which he will repeat this year, indicates variable rate phosphorous applications could be accounting for higher kernel counts. Other variables, like disease pressure, can counteract whatever positive impacts are coming from split phosphorous applications. That is what precision ag researchers and users call “field noise:” disease, moisture, compaction and multiple other variables.

“Use your technology to insert check plots within your (nutrient) prescription and evaluate those yourself,” McGrath said.

That is what Chad Godsey, a farmer and precision ag consultant based in northeastern Colorado, is doing. “

In this day and age, with the technology we have, my goal is to come up with a P recommendation for every one of my clients,” he said. “We want to put that fertilizer, in this case P, closer to the time when the plant actually needs it.” Godsey has found sidedressing phosphorous can positively impact yields on irrigated corn acres in Colorado.

He has documented this by using spatial analysis, provided by XSInc, based in North Carolina, to drill into field data and isolate yield response to phosphorous from other possible contributing factors.

“We always have multiple things going on in a field,” he said. He finds the spatial analytics add a layer of complexity, above what he would normally do in the field, to identify yield impacts from sidedressing P. Managing potassium (K) in corn is a different story. Soil testing and soil test timing are going to have an outsized impact on measuring available potassium.

“Just because K is immobile doesn’t mean it’s static,” said John Breker, soil scientist at Ag Vise Laboratories in North Dakota. Breker, who wrote his master’s degree thesis on potassium, said North Dakota farmers started to see soil potassium levels changing as farms there shifted to a corn-soybean rotation.

The amount of clay in soils impacts potassium availability, which is affected by soil mineralogy, especially in clay. “Clay minerals are kind of like an accordion,” he said. As soil layers open and close, from wetting and drying cycles, potassium levels can change.

The lack of data about soil clays, which would be valuable in figuring precision potassium prescription, means consistent soil test timing is still a key practice for managing potassium.

“Based on our lessons in North Dakota, knowing when you can have the maximum soil test K and minimum soil test K might be the more useful data,” said Breker. “I don’t know how many of these computer models have good clay data or where they’re going to get good clay data.”

Soybeans

Research is showing varying soybean populations within droughty parts of the field can pay off. 

 

“You basically take seeds from the good parts of the field and put them in the bad parts,” said Shawn Conley, University of Wisconsin soybean specialist.

He is involved in a project in the North Central region to collect soybean field data that he said will help generate better seeding rate recommendations.

“We argue that having a database with well-contextualized farmers’ data might be equivalent to running hundreds of field experiments,” he noted.

As precision providers sort through the field noise and mounds of data, they are confident the effort will have an impact on farmer bottom lines. “The ideal rate for everything, not just nitrogen, changes within fields,” said Dan Frieburg, president of Premier Crop Systems in West Des Moines.