November 30, 2020

Does the Drought Change Plans for Fall Soil Sampling?

MaxYield and SciMax Solutions(R) partner with Dr. Rick Vanden Heuvel for our exclusive nitrogen management process. Here is his response when asked about soil sampling this fall:

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 K.

Past seasonal dry periods have taught us that K soil test levels can be run lower than normal since K is retained in crop residues.  Rain will leach K out of plant materials and affect the soil test.   A late season dry spell can reduce this source of K 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 K 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 K 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!

Anhydrous Ammonia

On another note, concerns also arise with anhydrous ammonia applications in dry soil.  This topic has been raised many times in the past.  The key to good ammonia applications is a good seal behind the knife, and not dry soil being unable to hold onto the ammonia.  Even in very dry soil, enough moisture is there to hold onto normal N rates at normal application depths of 6-8″ in medium and fine textured soils.   But if the slit behind the knife is not sealing well, for any reason, an application will have to wait.  If possible, placing ammonia a bit deeper than normal, decreases concerns about ammonia losses from the soil surface.

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