Date of Award
Doctor of Philosophy
M. A. Tabatabai
The effect of pH (4, 6, and 8) on nitrogen mineralization was evaluated in three Iowa surface soils treated with crop residues (corn (Zea mays L.), soybean (Glycine max (L.) Merr.), and sorghum (Sorghum vulgare Pers.), or alfalfa (Medicago sativa L.)) and incubated in leaching columns under aerobic conditions at 30°C for 20 weeks. In general, N mineralization was significantly depressed at soil pH 4, compared with pH 6 or 8. The types of crop residues added influenced the pattern and amount of N mineralization.;A study on the effect of 19 trace elements on the nitrate reductase activity of four Iowa surface soils showed that most trace elements inhibited this enzyme in acid and neutral soils. The trace elements Ag(I), Cd(II), Se(IV), As(V), and W(VI) were the most effective inhibitors, with >75% inhibition. Mn(II) was the least effective inhibitor, with aliphatic acids > mineral acids. The results on the effect of these acids on metal release in soils under these conditions, or by sequential extractions, showed that increasing the acid strength from 1 mM to 10 mM resulted in significantly greater amounts of metal release. The amounts of metals released followed the order: Mn > Fe > Al > Zn, with aliphatic acids > aromatic acids > mineral acids.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Fu, Minhong, "Effect of pH and organic acids on nitrogen transformations and metal dissolution in soils " (1989). Retrospective Theses and Dissertations. 9123.