Even though fertilizer is the single-largest cost in corn production, only a relatively small percentage of U.S. acreage is being soil tested.

That's hard to understand, say soil scientists, because applying fertilizer without a current soil test is like planting a corn hybrid without knowing anything about how it performs.

A survey for 1992-1996 (the latest available) by the Soil and Plant Analysis Council shows that sampled acres did rise in the North Central region (the Dakotas, Nebraska, Kansas, Minnesota, Iowa, Missouri, Wiscon-sin, Illinois, Michigan, Indiana and Ohio) during that period. Still, the total acreage tested remained relatively small.

For example, Illinois had one of the higher percentages of sampling among those states. Yet Ted Peck, a University of Illinois soil scientist, estimates that only 20-30% of Illinois ground gets tested.

“By extrapolating what the soil test labs are reporting about their sampling volume, versus the total acres being farmed, I would estimate that only about one-third of all Midwestern farmland is being sampled today,” says Byron Vaughn of Harris Laboratories, Lincoln, NE. Vaughn is secretary-treasurer of the Soil and Plant Analysis Council, a group of university, USDA and independent soils specialists.

Why the dearth? “Some of the co-ops used to do quite a bit of sampling,” Vaughn replies. “But with all the co-op mergers, plus the small margins in fertilizer sales, most of them have backed off. Ironically, the soil labs have reduced their prices and so the testing analysis itself has gotten cheaper.

“I'm particularly concerned about low pH and lack of liming,” Vaughn says. “Without proper pH, other nutrients aren't optimized.”

John McNeil, an independent crop consultant at Mt. Vernon, IL, points out that although farmers are spending a considerable amount of money on fertilizer, much of it could be misspent on the wrong nutrients or the wrong proportion or amounts of nutrients. “That's a real risk when they don't sample their soils before making the fertilizer decisions,” he says. “For as little as soil sampling costs, it's definitely money well invested.”

Soil testing is the rule in some localities. “I'd estimate that more than half the ground in our area gets sampled,” says Ken Oyen, an independent crop consultant with Advanced Crop Care, Inc., Milledgeville, IL. His firm serves northern Illinois and southern Wisconsin.

Oyen pulls samples for his own farmer-clients and for several fertilizer dealers. This past fall he worked dawn to dusk to finish sampling.

“We sample in 2½-acre grids so that lime and fertilizer can be applied to each grid as needed,” Oyen explains. “I've seen pH levels as low as five in some of the grids we have sampled, and those areas need immediate correction.

“By raising the pH to a proper level across an entire field, we optimize the other nutrients and that, by itself, usually more than offsets the cost of sampling,” Oyen notes. “Testing for P and K is then essentially free.”