Changes in soil chemistry following a watershed-scale application of wollastonite (CaSiO3) at Hubbard Brook, New Hampshire, USA.

Decades of acidic deposition in the northeastern United States is believed to have caused the loss of substantial amounts of calcium from forest soils. This process of ‘calcium depletion’ affected the chemistry of drainage waters in the region and may have impacted forest health. To study this phenomenon, we applied 45 Mg of wollastonite (1316 kg Ca ha -1 ) to watershed 1 (W1) at the Hubbard Brook Experimental Forest, in New Hampshire, USA in October, 1999. Exchangeable Ca (1 M NH 4Cl) and soil pH increased significantly in the Oie and Oa horizons, and in the top 10 cm of the mineral soil, in samples collected 1, 3, and 7 years after treatment. Exchangeable acidity (1 M KCl) decreased significantly in the Oie and Oa horizons after treatment, but the effect in the upper mineral soil was not clear. Base saturation and effective cation exchange capacity (CEC e) increased significantly after wollastonite application in all layers studied, primarily on the strength of the increased exchangeable Ca. We did not observe compensatory decreases in exchangeable Al, or other exchangeable cations, as initially hypothesized. Therefore, while wollastonite addition has improved the base status of W1 soils, it has not resulted in decreases in exchangeable Al.