Dr. Kurtis Schroeder, Dr. Jae Ryu
Soil pH has been declining in northern Idaho due mainly to the long-term use of ammonium-based nitrogen fertilizers. The parent soils in many regions of northern Idaho are forest-derived, which means they have a lower buffering capacity, making them more susceptible to changes in pH as well. Acidification of soils in northern Idaho and eastern Washington was well documented during the 1980’s by Dr. Mahler at the University of Idaho.
A recent survey revealed that soils have continued to decline in pH, with the majority of northern Idaho field having a pH of 5.2 or lower (76%) in the upper 6 inches. Furthermore, 34% of fields sampled were below a pH of 5. As a result of this reduction in soil pH, soluble aluminum quantities are increasing in soils and many are at risk of or are experiencing aluminum toxicity.