Geologic Soil Parent Material Influence on Forest Surface Soil Chemical Characteristics in the Inland Northwest, USA

Successful fertilization treatments targeted to improve stand productivity while reducing operational complexities and cost depend on a clear understanding of soil nutrient availability under varying environmental conditions. Soil nutrient data collected from 154 forest sites throughout the Inland Northwest, USA were analyzed to examine soil nutrient characteristics on different geologic soil parent materials and to rank soil fertility. Results show that soil parent material explains significant differences in soil nutrient availability. Soils developed from volcanic rocks have the highest cation exchange capacity (CEC) and are relatively high in phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), boron (B), and copper (Cu), but generally poor in mineralizable nitrogen (MinN). Forest soils developed from plutonic rocks exhibit the lowest CEC and are low in MinN, K, Ca, Mg, S, and Cu, but higher in P. Some soils located on mixed glacially derived soils are low only in K, Ca, Mg, and Cu, but many mixed glacial soils are relatively rich in other nutrients, albeit the second lowest CEC. Soils developed from metasedimentary and sedimentary rocks are among those with lowest soil nutrient availability for P and B. Sulfur was found to have the highest concentrations in metasedimentary influenced soils and the least in sedimentary derived soils. Our results should be useful in designing site-specific fertilizer and nutrient management prescriptions for forest stands growing on soils developed from these major geologies within the Inland Northwest region of the United States.