With fertilizer and other Iowa State University Extension soil fertility specialist, says “drier production areas, such as the Great Plains,” can benefit from deeper soil tests to measure residual nitrate than more humid areas such as the eastern Corn Belt where rainfall amounts don't lead to accumulation of nitrate in the profile. The exception would be dry seasons and when corn will follow corn, he says.

“Where profile nitrate sampling is practiced, soil samples can be 3-5 ft. deep depending on the recommended depth for different areas,” he says. “Since there isn't excess precipitation to leach nitrate out of the soil, the profile samples collected in the fall or spring will reflect N that remains in the rooting profile and available for the next crop.”

Brent Bean, Texas A&M University Extension agronomist for High Plains growers in the northern Panhandle, says deep samples should pay. “Historically we have taken soil tests from 0-6 in. or 0-8 in.,” he says. “But roots pull N from 4 ft. deep and there can be a lot of variability in N availability. There may be 60 lbs. of N in deeper soil samples.”

KNOWING HOW MUCH of that N is available is essential, says Brad Farr, a Crop Production Services, Inc. crop consultant who works with Houghtelling. The operation features a one-pass strip-tiller, which runs in front of the planter.

“We run a deep chisel and plant strip-till in the chisel mark,” says Farr. “We till 8 in. to 1 ft. deep. We're going to the second foot with soil tests because it's important to get the benefits out of the deep root zone.”

Nitrogen and P fertilizers are applied about 8 in. deep at planting via chiseling. Starter fertilizer is also applied about 2 in. beside the seed.

Basic soil tests cost about $29 each, no matter what depth, says Farr. They are taken randomly across a field.

“We may be able to back up some on fertilizer applications,” says Farr. “And we've been able to identify the need for more N in the tighter soil as well as the bottomland more sandy soil.”

A savings of $20-30/acre on N or P costs improves the bottom line, says Houghtelling, as well as the higher yields from having more N where it's needed.

Sawyer says that due to rainfall greater than evapotranspiration seen in Iowa and across much of the Midwest, profile sampling for N isn't generally recommended. It can be an accepted practice with some soils in the upper Midwest where soils freeze and stay frozen all winter, he says. In Iowa, when sampling for soil nitrate, those samples are collected in late spring to a 1-ft. depth, usually around June 1.

“For P, K and pH, a 0-6-in. sample depth is recommended because that's the depth where our soil tests are calibrated,” Sawyer says.

Gary Hergert,

Crop advisers can provide the most accurate recommendations if you provide cropping history and intended crops for the upcoming seasons, realistic yields, fertilization practices, past (especially recent) lime applications and history of manure applications.