Questions have been asked if soil sampling plans for the upcoming fall should change because of the drought we have experienced in 2012.
The quick and short of it is it should not alter your schedule to resample. Different forces could be at work to increase or decrease soil test levels, particularly potassium.
Past seasonal dry periods have taught us that potassium soil test levels can be run lower than normal since potassium is retained in crop residues. Rain will leach potassium out of plant materials and affect the soil test.
A late season dry spell can reduce this source of potassium being returned to the soil, lowering soil test levels. But recommendations from universities and laboratories in the past have not gone as far as to drop soil testing from the fall to-do list. Their suggestion was to stay on the normal cycle, normally sampling every 4 years.
This year is no exception. In fact, this year’s drought was particularly strong, came early and remains today in wide areas. In this case, plant growth can be so dramatically reduced that total potassium uptake would be unusually low, reducing removal rates, and residual fertilizer materials remaining in the soil.
For some of these fields, or parts of fields, this year’s drought could have the opposite impact on soil test potassium levels by increasing them. Predicting whether soil test levels are going to be lower or greater than normal gets pretty difficult.
If more residual fertilizer were present in the field, and if it were enough to impact soil test levels, you would want to be aware of that. It could reduce fertilizer rates for the coming year.
You need to be aware of what is happening. Stay on your sampling schedule!