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Effects of Simulated Acid Rain on Soil Solution Composition and Orchardgrass Seedling Viability

Department of Plant and Soil Science, P.O. Box 1071, Univ. of Tennessee, Knoxville, TN 37901-1071

* Corresponding author.

ABSTRACT

Acid, low cation exchange capacity (CEC) surface soils in low intensity management forage ecosystems may be sensitive to acid rain. Alteration of surface soil chemical properties by acid rain may influence establishment of small seeded forage grasses. Viability of orchardgrass (Dactylis glomerata L.) seedlings was monitored concurrently with simulated acid rainfall applications (pH 4.3-2.5) on Etowah (Typic Paleudults) and Statler (Humic Hapludults) surface soils sampled from established sod which had been unfertilized in the prior 2 yr. Simulated rainfall of pH 3.1 tended to result in increased seedling viability in comparison to other rainfall pH, but the effect of rainfall pH was significant in only six of 16 counting dates. Maximum seedling numbers and days to maximum were unaffected. Increased rainfall acidity (pH 4.3-3.1) increased total seedling dry weight. Soil solutions from the surface 1.5 cm obtained by vacuum displacement were analyzed for pH, electrical conductivity (EC), and total concentrations of Ca, Mg, K, Na, Al, NH₄, Cl, NO₃, and SO₄. Soil solution pH decreased and EC increased with increasing acidity of simulated rainfall. Generally, increasingly acid rainfall resulted in linear (sometimes quadratic) increases in cation and anion components of soil solution with the exception of Al, Na, and NH₄. The rainfall pH x soil interaction was not significant for any solution component. Calcium ion activity was unaffected, while Al³⁺ activity increased from 5.62 x 10^–8 to 3.16 x 10^–6 with increased rainfall acidity (rainfall pH 4.3-2.5). The Ca/Al activity ratio decreased 64-fold with increasing acidity of simulated rainfall. No association between orchardgrass seedling responses and soil solution composition was apparent.

The research described in this article has been funded in part by the North Carolina Agric. Res. Serv. under a Special Grants Program Agreement with the USDA Cooperative State Res. Serv. Contribution from the Dep. Plant and Soil Science, Univ. of Tennessee. The investigators' opinions do not reflect the opinions of either the Cooperative State Res. Serv. or North Carolina Agric. Res. Serv.

Received for publication August 3, 1987.