Date of Award
Master of Science
Plant, Soil and Environmental Sciences
J. D. Wolt
John Reynolds, John Graveel
Alteration of surface soil chemistry by acid rain may influence establishment of small seeded forage grasses. Orchardgrass (Dactylis glomerata L.) germina-tion was monitored concurrently with application of simulated acid rainfall applied at 0.46 cm per event on Etowah silt loam (Typic Paleudults) and Statler variant sandy loam (Humic Hapludults) surface soils. Ambient rainfall was not excluded from the experiment which received five rainfall events totaling 6.4 cm (avg. pH 4.28) throughout the 29-day duration of the study. The range of simulated rainfall selected (pH 4.3 to 2.5) had been identified as the region of maximum biological response in previous controlled environment studies. Orchardgrass germination was differentially influ-enced by rainfall pH over time after initiation of simulated rainfall treatments. Germination was significantly affected by rainfall pH on six of sixteen counting dates. Increasing rainfall acidity stimulated more rapid onset of germination and resulted in higher total percent germination on both soils throughout the ment. Responses were indicative of an interactive effect of rainfall composition on biological response of seeds and seedlings. Surface soil samples were collected from all test plots to a 1.5 cm depth and soil solutions obtained by vacuum displacement. Soil solutions were analyzed for pH, EC, Ca2+, Mg2+, K+, Na+, Al3+, NH4+, Cl-, NO-3 and SO2-4. 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 Al3+, Na+, and NH4+. Effects of soil series (Etowah vs. Statler) were signi-ficant except for Al3+, Ca2+, and Cl-, but the rainfall pH by soil interaciton was seldom significant with Al3+ and Na+ being exceptions. Calcium activity increased slightly while Al3+ activity increased markedly with decreased rainfall pH, resulting in decreased Ca2+:Al3+ mol ratios with decreasing pH of simulated rainfall. Several subtle changes occurred within the soil solution following additions of acid rain, but no association between orchardgrass germination responses and soil solution changes was apparent.
Haun, Guy Wesley, "Soil solution composition and orchardgrass germination as influenced by simulated acid rain in a field environment. " Master's Thesis, University of Tennessee, 1987.