GPS-based variable-rate fertilizer application has become more mainstream in the past decade, thanks to research, technology, retailers’ promotion of the practice and growers’ success with it.

But according to site-specific leader Jess Lowenberg-DeBoer, the economic return has been modest at best due to added labor, test and equipment costs. Higher energy and fertilizer prices make variable rate more attractive, says the Purdue ag economist, but he’s unsure whether it will dramatically change the profit picture.

His best advice:

  • Variable-rate lime applications are good value.
  • If you have fields with geo-referenced data points of yield along with soil sample data points by management zone (random samples by soil type, not grid), then you’re better able to gain value from variable-rate N, P and K.
  • Realize that cost savings and yield increases won’t always accompany site-specific fertilizer management.
  • On fields you own or fields where you have longer-term lease agreements, build geo-referenced maps of yield, fertility and in-season attributes (drainage problems, weeds, insects, hybrids/varieties, etc.) and learn how to use history to make smart management decisions.
  • Experiment with aerial crop sensing (see OptiGro story below) and other in-season research projects that could boost your bottom line.

Most experts agree that the next wave of on-the-go sensor technology — which will detect various nutrient levels, organic matter, soil texture and more — will truly help improve the value of variable-rate farming, especially when combined with RTK auto-guidance. Stay tuned.