Stricter soil sampling needed to satisfy U.S. regulations

Farmers and consultants have no choice but to get serious with their soil sampling programs when university soil test recommendations turn into government regulations.

That is what has transpired in Iowa, prompting Frank Moore to invest nearly $50,000 in a new AutoProbe this winter.

Moore farms a couple of thousand acres in northern Iowa and runs a private agricultural consulting business, which does contract consulting for state natural resources departments in Iowa and southern Minnesota.

The focus of his AutoProbe efforts will be assessing the effectiveness of manure management plans in areas with intensive livestock operations.

“DNR (Department of Natural Resources) has started paying closer attention to fields where manure is applied here in Iowa,” said Moore.

The change has fostered a greater need for high efficiency mechanized soil sampling, he added.

“The regulations are 10 years old and really do need to be updated, but both sides are afraid to re-open the books,” he said.

“Farmers are afraid a review will result in tighter controls. Environmental groups are afraid a review will result in relaxed controls.”

Moore said the standoff was broken to some extent when Iowa environmentalists sued the U.S. Environmental Protection Agency for not enforcing its own federal Clean Water Act, thus forcing it to crack the whip on the state natural resources department. The state government had no choice but to crack the whip on farmers and their manure management practices.

Farmers applying manure are now required to better document what’s in their soil, particularly phosphorus and potassium.

Moore said it’s not possible to complete the Iowa Phosphorous Index document without valid soil tests. Six inches is considered to be deep enough because all yield responses to soil testing are based on a six inch sample analyzed by Iowa State University.

The university also says a farmer must have 15 to 20 cores for each single sample. As well, one sample cannot represent more than 10 acres.

Moore said few people comply with those criteria. Some people pull only eight to 10 cores per sample, while others pull as few as three cores per sample.

“You need 25 to 35 cores per sample to be statistically significant for phosphorus … So clearly, a lot of samples do not meet the criteria,” he said.

“That’s where this AutoProbe machine enters the picture. Our AutoProbe pulls 20 to 40 cores per sample. And instead of having one sample represent 10 acres, one sample from the AutoProbe represents 2.5 acres. So it exceeds the requirement by far.”

Another problem inherent in conventional soil sampling methodology is the tendency to gather samples from the central area rather than spread them out, whether the operator is pulling cores on a grid system or a topographical zone system.

AutoProbe makes a straight line across a zone or grid square, pulling a new core every 17 feet, regardless of artificial boundary lines.

As a result, cores are never clustered in a bunch.

Cores for a single sample that are taken in close proximity don’t give a true picture of soil conditions at other spots in that zone or grid square. Taken to the extreme, Moore said he can detect soil changes down to the 10 sq. foot level, if that’s what his client wants.

Moore will charge $10 to $15 per acre this year, depending on the depth of detail that the farmer requires. Everything is automatically GPS geo-referenced and layered over existing maps, so there is no charge for that service. Basic lab costs are also included.

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