The technology exists on many farms to significantly adjust your planting rate on the go. It’s an idea that makes perfect sense, and many growers are experimenting with it. Exciting new tools that crunch the numbers on yield potential, environment and seed populations are emerging in the marketplace, including Monsanto’s FieldScripts and a new prescription tool from South Dakota State University.

But right now, it’s hard to pin profits to the practice.

“Predicting where and by how much you should vary seeding rates is challenging and may not be repeatable from one year to the next,” notes Pat Reeg, technology manager for the Iowa Soybean Association On-Farm Network. He points out that 146 fixed-rate corn population trials conducted between 2009 and 2011 showed low correlation between optimum population and the variables that are typically assessed in variable rate seeding programs, like yield history, corn suitability ratings, soil conductivity or bare soil reflectance. That makes it difficult to accurately set optimum seeding rates.

On the other hand, agronomists like Norman Mieth of Central Valley Ag Cooperative’s Advanced Cropping Systems swear by the results of variable rate seeding. Mieth says reducing seeding rates from a typical 34,000 ppa to 24,000 on sandy pockets around Wayne, Neb., cut seed costs by $30/a and increased yields by 70 bu./a because plants weren’t fighting for water in droughty soils.

Stay tuned – and expect further fine tuning.