A five-step process can help you improve crop management practices on your farm. John McGuire, chief innovative officer for Brookside Labs and the Amplify network of crop consultants, says it’s called adaptive management. Simply put, start with sound basic agronomy, collect high-quality data, learn from quality data aggregated together, test the change you’re considering on your farm, and finally, implement management changes.

“It all hinges on collecting the right information so you have quality data,” McGuire says. “If you don’t have quality data, the whole process falls apart quickly.”

A key piece of information for making crop decisions is soil test results. Since this is a critical piece in decision-making, it’s important to make sure soil test results are based on accurate information, he emphasizes. Here is a closer look.

Soil test information

The main driver for accurate soil test information is grouping soils with similar cation exchange capacity together when laying out sampling zones, McGuire says. “If you combine soils with widely different CEC values into the same sample, then the results aren’t going to be meaningful.

“Your first job, if you’re sampling soils, is to create the sampling zones correctly. You must get the right soil into the right bag. Otherwise, you can’t trust the results when they come back from the soils lab.”

Soils with different CEC values can vary by 50 to 60 bushels per acre in yield potential for corn, McGuire says. Variable-rate seeding prescriptions also won’t match up with the field correctly if they’re based on CEC information that isn’t accurate.

With accurate soil test data that you trust, you can compare changes in nutrient values over time. Soil testing isn’t an exact science, but it’s the trend that matters, McGuire says.

“Take potassium, for example,” he says. “If you’re looking at values for the same zones in the same field over time, you want them to go in the right direction. Your goal should be managing that trend over time, and make sure the trend goes the way you want it to go. That starts with making sure soil types aren’t mixed within each zone.”

An example

Two soil types often associated with each other in eastern Indiana are Blount and Pewamo soils. In central and north-central Indiana, think of Brookston and Crosby soils. They often adjoin each other, but the CEC values are likely different.

“You want to test those separately in separate samples to have quality data and accurate results,” McGuire explains. “If you combine them together, the results won’t represent any one real place in the field. Decisions you make based on the results won’t be correct for that location either.”

So, what if you’re dividing the field into soil testing zones and run across a small area of soil that isn’t like either of the two main soils in the field? If it’s just a small spot, less than an acre, it is what soil scientists call an inclusion.

“Don’t put it in either sample,” McGuire says. “It’s not representative, and it will throw off your results.”