Document Type

Article

Journal/Book Title/Conference

Soil Science Society of America Journal

Volume

49

Issue

5

Publisher

American Society of Agronomy

Publication Date

1985

First Page

1274

Last Page

1279

Abstract

Precipitation, throughfall, forest floor, and soil leachate samples were monitored continuously in 1981 and 1982 in a N-poor Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] forest and a red alder (Alnus rubra Bong.) forest growing adjacently on a glacial soil in western Washington. The purpose of the study was to quantify the relative importance of atmospheric vs. natural sources of H+ input to forest soil acidification, and to determine the role of N transformation processes in the overall H+ balance of soils with different N status. Rainwater samples had an avg pH of 4.7 and annual H+ deposition via precipitation averaged 320 mol H+ ha–1 yr–1. This was modest compared to internal H+ production associated with HCO-3 and NO-3 formation. In the soil under alder cover, which was naturally enriched in N through symbiotic N2-fixation, nitrification released up to 4500 mol H+ ha–1 annually to the solution percolating through the upper part of the soil profile. In the N-poor soil no nitrification could be observed and N transformation processes had a minor influence on the soil H+ balance. The main internal acidification source in this case was H2CO3 dissociation releasing 420 mol H+ ha–1 yr–1. In both instances, soil solutions appeared well buffered against these external and internal acidification sources, and few H+ leached below the 40-cm soil depth.

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