Dry soil can affect soil-test results, and farmers should keep this in mind when testing soil for fertilizer needs.
Despite this season’s drought conditions in many areas of the country, farmers shouldn’t stop analyzing soil samples to determine lime and fertilizer needs, experts say.
“Accurate analysis of representative soil samples to determine lime and fertilizer needs is fundamental to crop production,” says Jim Camberato, an agronomist at Purdue University. “Unfortunately, persistent, dry weather resulting in prolonged periods of low soil moisture can affect potassium and pH, resulting in somewhat misleading results.”
Soil tests can be useful in dry weather if farmers understand the way low moisture can affect potassium and pH test results.
In a dry fall, soil test potassium levels often are lower than expected because most of the potassium the crop had taken up during the growing season remains in the crop residue. If there’s not enough rainfall, it doesn’t return to the soil.
Low rainfall totals during the growing season also can result in lower soil pH measurements because a high level of fertilizer salts remain in the soil at the end of the growing season. Those salts affect the electrodes used to measure pH and can result in an inaccurate, lower pH measurement.
While the end of the season was dry in Indiana, early-season rainfall was enough to ensure normal crop uptake of fertilizer. That means in most cases there was little fertilizer salt left in the soil to affect pH measurements, Camberato says.
“Bottom line, farmers should take advantage of the early harvest and dry soil conditions and continue soil sampling and fertilizing and liming where needed,” he advises. “Most of the potassium taken up by the crop remains in the residues, so farmers need not be alarmed if soil test potassium levels are lower than expected.”