Maybe you pull your own soil samples, or maybe you work with a soils consultant. Perhaps he pulls samples and tests them for you for a set fee per acre. Two things matter no matter who does it: the time of year you sample and how often you sample.
Betsy Bower, with Ceres Solutions, based in Terre Haute, and an Indiana Certified Crop Adviser, believes in sampling at the same time every year. Otherwise your results, especially for potassium and also for phosphorus, may not be consistent. It's difficult to compare back to the last sampling time in a field if the samples are pulled at different times of the year, she notes.
The reason is partly because it takes time for nutrients left behind in stover and stalks to be assimilated into the soil. Spring is likely a better time to sample, but then you fight getting samples pulled on dry ground. The advantage for a purely agronomics testing point of view is that you're more likely to get more consistent results every time you sample a field if you're doing it in the spring after things have settled back down after harvest from the year before.
What you can't do is compare results from samples pulled in the fall with results from samples pulled in the spring and expect them to be consistent, Bower says.
The other dilemma is how often you sample. Some people have their fields on a four-year sampling rotation. While some agronomists would prefer a three-year rotation, you can make sampling once every four years work if you account for crop removal of nutrients since the last sampling time.
Bower notes that removal swings widely with the type of year. Few nutrients were removed by a poor 2013 corn crop, while high-yielding con in 2013 and likely again this year in many areas will remove more nutrients.
Learn more about these topics in articles in the upcoming October issue of Indiana Prairie Farmer.