The drought plaguing much of the United States impacts nutrient management decisions in a variety of ways. Purdue University agronomists say dry soils have resulted in a high incidence of potassium deficiency symptoms in both corn and soybeans in Indiana. Dry soil reduces potassium uptake by slowing the movement of potassium from the soil solution to the plant root. Thus, according to Purdue agronomists Jim Camberato and Brad Joern, potassium deficiency will occur in a dry year at higher soil test levels than will occur in a wet year.
If dry soil conditions continue, soil samples taken this fall may provide misleading results for both potassium levels and pH, presenting an added challenge for producers. Potassium levels in soil tests have been shown to vary substantially under dry conditions. Soil pH measurements can be impacted because a dry season and poor plant growth mean much of the fertilizer added this spring and last fall remains in the 8-in. sampling zone in some fields. Higher-than-normal salt (fertilizer) levels affect the way the pH electrode functions and will produce a pH reading about 0.5 to 1.0 pH units lower than the actual pH. In addition, soil moisture has been insufficient for normal amounts of limestone reaction in soils limed this spring or last fall in Indiana, for example. Therefore, soil pH measured this fall will be lower than expected. The lime remains in the soil, however, and when moisture returns it will increase soil pH as expected. Purdue agronomists say re-testing this fall and adding more lime based on a low soil pH measurement may result in excessively high pH in future years.
Learn more about nutrient management considerations during the drought in the Purdue University Department of Agronomy Update online at http://www.agry.purdue.edu/ext/soilfertility/droughtnutrients.pdf.