Understanding soil nutrients and characteristics in the Pacific Northwest through parent material origin and soil nutrient regimes

A convenient method is necessary for assessing the availability of soil nitrogen in plantation Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands in the Pacific Northwest. The objective of this research was to use soil parent materials (SPMs) and soil nutrient regimes (SNRs) to determine the most efficient method to characterize soil nitrogen availability in Douglas-fir stands. It was hypothesized that SPMs and SNRs would effectively separate stands with distinctive climate, site, and soil characteristics and forest floor and soil carbon and nitrogen reserves. At 60 Douglas-fir stands, SPMs and SNRs were determined, and soil particle percentages, soil depth, and forest floor and soil nitrogen and carbon contents were measured to a depth of 1 m. Soils of sedimentary origin and very rich and rich SNRs contained greater nitrogen and carbon contents than those from glacial and igneous origins and medium SNRs. Sedimentary SPMs and very rich SNRs were developed from older parent materials and had significantly greater soil depths and finer textures than those from glacial SPMs and medium SNRs. SNRs and SPMs are recommended as good estimators of soil nutrient pools and soil characteristics in Douglas-fir plantation forests of the Pacific Northwest.