The Impact of Nitrification on Soil Acidification and Cation Leaching in a Red Alder Ecosystem1
- H. Van Miegroet and
- D. W. Cole2
The objectives of this study were to investigate the impacts of internal nitrification on soil and soil solution acidity and on the rate of nutrient export through NO3− mediated leaching. This was achieved by comparing soil chemical properties and soil solution composition within a naturally N-rich red alder (Alnus rubra Bong.) ecosystem to those of an adjacent Douglas-fir [Pseudotsuga menziesil (Mirbel) Franco] forest where soil N levels were significantly lower and no measurable HNO3 production could be observed. In the red alder system, where > 100 kg ha−1 yr−1 of N were added through symbiotic N2 fixation, the net annual NO3− leaching past the 40-cm soil depth amounted to 3460 mol charges ha−1, and NO3− concentrations in the solutions collected below 40 cm periodically exceeded drinking water standards of 10 mg L−1. The H+ and NO3− release was most pronounced in the forest floor and top 10 cm of the soil under alder occupancy and caused significant acidification of percolating solutions. Less than 1% of the total H+ input from internal (nitrification) and external (atmospheric) sources leached below the 40-cm depth, which was indicative for the strong buffering capacity of this particular soil. The cation displacement reactions involved in this pH buffering caused a 15% decline in base saturation and a significant acidification of the upper part of the soil profile. The presence of large amounts of mobile NO3− in solution triggered accelerated cation leaching, causing a selective redistribution of primarily exchangeable Ca2+ from the A to the B horizon. These field studies lead us to conclude that the rate and the selectivity of NO3− mediated leaching in a red alder system could significantly lower the exchangeable cation pool in the rooting zone or cause nutrient imbalance, if a site is managed for repeated rotations of red alder.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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