Factors affecting methane production in flooded soils
Date
1997
Authors
Andales, Marie Jane Flores
Major Professor
Advisor
Tabatabai, M. A.
Committee Member
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Abstract
Flooded soils are a major source of atmospheric CH₄, which is influential in global climate change. The objectives of this study were to (i) determine the relationship between soil properties and CH₄ production, (ii) to assess the potential of organic acids as C precursors of CH₄ production, and (iii) to investigate the impacts of organic materials and trace elements on CH₄ production in soils. Incubation experiments were conducted by placing 25 g soil (<2 mm mesh), 50 mL deionized water and treatments, if any, in a 200-mL spoutless beaker. The beaker was sealed with a rubber stopper equipped with a Pt electrode, gas outlets and an access for a pH combination electrode. The beaker assembly was incubated under N₂ at 30C̊ for a total of 7 weeks; CH₄ ,pH and Eh7 were measured weekly. In Part I, CH₄ production was studied in 27 Iowa surface soils.
In Part II, results of the effects of 29 organic acids (19 aliphatic and 10 aromatic acids), 16 organic materials (4 each of plant materials, animal manures, sewage sludges and biotechnology by-products) and 10 trace elements on CH₄
production in Harps (pH 7.9) and Nicollet (pH 6.4) soils are reported. The organic acids and trace elements were applied on an equimolar basis (20 and 5 mmol kg-1 soil, respectively); and the organic materials were added on an equal C basis (9 g C kg-1soil). Results showed that the rates of CH₄ production were significantly correlated with organic C, water-soluble fraction of the organic C, reducing sugars, total N and total S. It was significantly, but negatively, correlated with Eh7. The highest rates of CH₄ formation occurred at around pH 6.9-7.3. The clay content, initial pH, SO4-S, and the biologically-reducible Fe and Mn contents of the soils showed no effect on the rates of CH₄ production. Most of the organic acids served as C precursors for CH₄ production in Nicollet and Harps soils.
The potential of organic acids as C precursors of CH₄ depends on the nature of the acid and the properties of the soil. Salicylic acid inhibited CH₄ formation in both soils. All the organic materials enhanced methanogenesis in different magnitudes. Methane formation was completely inhibited by As(V), Ag(I), Cd(II), and Se(IV); it was delayed and repressed by Mn(II), Mo(VI), Ni(II), Pb(II) and Zn(II); CU(II) completely inhibited CH₄ in Nicollet, but not in Harps soil.
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