Adjusting fertility programs for lower than expected yields
If you use soil test results to track trends on your farm, which is a good practice to monitor fertility programs, you may note some soil test results this fall that do not follow trend. Dry soils can affect soil chemistry, soil structure, short-term nutrient cycling and ultimately soil test results. Wait until more normal soil moisture conditions before taking a soil sample. Make sure the soil probe can get into the ground to your standard soil sampling depth of 6-8 inches. Factors which may be affected by dry soil are:
pH- Water pH maybe 0.1-0.3 units more acidic but differences in buffer pH used to calculate lime recommendations are not large or consistent so lime recommendations will not be different under dry conditions.
P&K- Soil K levels are influenced by dry soil. Soils with low K may show an increase in soil test K while soils with high K may show a decrease in soil test K. Soil P test results probably will be affected little by dry soil conditions.
Phosphorus, Potassium and pH Management Issues Following Drought-damaged Crops. Mallarino, A. and Sawyer, J. http://www.extension.iastate.edu/CropNews/2012/0823mallarinosawyer.htm [verified 13 September 2012.]
Cover Crops Following the Summer 2012 Drought. Kladivko, E. https://ag.purdue.edu/agry/extension/Documents/CoverCropsFollowingDrought.pdf [verified 13 September 2012]
The presidedress soil nitrate test for improving N management in corn. Sylvie M. Brouder and D.B. Mengel https://www.agry.purdue.edu/ext/pubs/AY-314-W.pdf [verified 13 September 2012]
Nutrient Management Related to Dry Soil Conditions and Poor Crop Yields. Jim Camberato and Brad Joern. http://www.agry.purdue.edu/ext/soilfertility/droughtnutrients.pdf%20 [verified 17 September 2012]