From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Fall 2005, No. 5


Seasonal variation in soil test results is real…and has been recognized by soil scientists for more than four decades. Sizeable fluctuations in soil test levels can occur seasonally (monthly) and are associated with changes in soil temperature and moisture, soil microbial activity, crop residue decomposition, clay mineralogy, and nutrient cycling. Shallow soil samples (0 to 2, or 0 to 4 in.) may be more susceptible to seasonal fluctuations in test results than samples collected from deeper depths.

How much variation can be expected across seasons, within a year?

There is no practical or reliable way to adjust results or recommendations based on the environmental conditions. The adage is “sampler beware.” What should farmers and crop advisers do to obtain consistent and accurate soil test results and recommendations? Determine a representative sampling time and be consistent from year to year, but be ready to adjust your sampling schedule to avoid aberrations from the “normal” environmental conditions. If you have not used this strategy in the past, start this year. Improve nutrient management decisions and nutrient use efficiency in your fields by starting with a quality soil sampling program…based on knowledge of seasonal variation.


For more information, contact Dr. Cliff S. Snyder, Midsouth Director, PPI, P.O. Drawer 2440, Conway, AR 72033-2440. Phone: (501) 336-8110. E-mail:

Fall 2005 Agri-Briefs#5.pdf
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