Phosphorus and lime response of Sitka spruce, western hemlock seedlings, and romaine lettuce on two coastal Washington soils

Abstract

Greenhouse growth tests using Sitka spruce (Piceasitchensis (Bong.) Carr), western hemlock (Tsugaheterophylla (Raf.) Sarg.), and romaine lettuce (Lactucasativa) and soil analysis were used to evaluate the fertility status of two soils from the coastal region of Washington State. Available N determined by aerobic incubation was low (5–12 ppm). Nitrification in these acid soils (pH = 4.1 and 4.2) was negligible even after 2 months of incubation. Neither the lettuce nor the conifer seedlings responded to N addition in spite of the low available N. Extractable soil P was low and a growth response to added P was observed. Lettuce was not an adequate predictor of conifer growth. In the growth study, the soils were amended with lime and combinations of N, P, S, K, and Mg. Both Sitka spruce and western hemlock grew best in treatments with lime and P added. The lime response was smaller than the P effect. Mycorrhizal development on the spruce and hemlock was quite limited and may have enhanced the phosphorus response.