Soil redox

Kongchum M. Effect of plant residue and water management practices on soil redox chemistry, methane emission, and rice productivity. PhD Diss. Louisiana State Univ., Baton Rouge 2005. 

Hou AX, Chen GX, Wang ZP, Van Cleemput O, Patrick Jr WH. Methane and nitrous oxide emissions from a rice field in relation to soil redox and microbiological processes. Soil Sci. Soc. Am. J. 2000 64 2180-2186. 

Soil redox also strongly affects solubility of the compounds of other trace elements in arid soils. Amrhein et al. (1993) found that Fe, Mn, Ni and V in an evaporation pond soil were more soluble under reducing conditions. Han and Banin (2000) reported that after one year of saturated incubation, the solubility of Fe, Mn, Co, V, Ni, Cu and Zn in two Israeli arid soils with 0.5-23% CaC03 increased, while the solubility of Cd decreased with time. During saturated incubation, soil pH in highly calcareous arid soil containing high content of carbonates decreased. In a loessial soil from Israel, Han and Banin (1996) reported that soil pH decreased from 8.0 to 7.0-7.4 over saturated incubation. With the decrease in Eh over incubation, the parameter pe+pH also decreased from initial values of 12-13.6 to 4 after initial 7-9 days of saturation incubation. 

Bartlett R.J. Soil redox behavior In Soil Physical Chemistry, Sparks D.L., ed, Boca Raton, FL CRC Press, Inc., 1986. 

In the following sections the biogeochemistries of important trace metals and metalloids in submerged soils are discussed. They are important either because of their redox chemistries or because they are particularly affected by soil redox... 

Marin AR, Masscheleyn PH, Patrick WH, Jr. 1993. Soil redox-pH stability of arsenic species and its influence on arsenic uptake by rice. Plant and Soil 152 245-253. 

Soil Boesten et al. (1992) investigated the transformation of [ C]l,2-dichloropropane under laboratory conditions of three subsoils collected from the Netherlands (Wassenaar low-humic sand, Kibbelveen peat, Noord-Sleen humic sand podsoil). The groundwater saturated soils were incubated in the dark at 9.5-10.5 °C. In the Wassenaar soil, no transformation of 1,2-dichloropropane was observed after 156 d of incubation. After 608 and 712 d, however, >90% degraded to nonhalogenated volatile compounds, which were detected in the headspace above the soil. These investigators postulated that these compounds can be propylene and propane in a ratio of 8 1. Degradation of 1,2-dichloropropane in the Kibbelveen peat and Noord-Sleen humic sand podsoil was not observed, possibly because the soil redox potentials in both soils (50-180 and 650-670 mV, respectively) were higher than the redox potential in the Wassenaar soil (10-20 mV). 

Uchida, S Sato,T. Okuwaki, A. (1993) Synthesis of monodispersed micaceous iron oxide by the oxidation of iron with oxygen under hydrothermal conditions. J. Chem. Techn. Biotechn. 57 221-227 Ugwuegbu, B.J. Prasher, S.O. Ahmad, D. Dutilleul, P. (2001) Bioremediation of residual fertilizer nitrate II. Soil redox potential and soluble iron as indicators of soil health during treatment. J. Environ. Qual. 30 Ills... 

Mitsunobu, S., Harada, T. and Takahashi, Y. (2006) Comparison of antimony behavior with that of arsenic under various soil redox conditions. Environmental Science and Technology, 40(23), 7270-76, and supplements. 

In soil solutions the most important chemical elements that undergo redox reactions are C, N, O, S, Mn, and Fe. For contaminated soils the elements As, Se, Cr, Hg, and Pb could be added. Table 2.4 lists reduction half-reactions (most of which are heterogeneous) and their equilibrium constants at 298.15 K under 1 atm pressure for the six principal elements involved in soil redox phenomena. Although the reactions listed in the table are not full redox reactions, their equilibrium constants have thermodynamic significance and may he calculated with the help of Standard-State chemical potentials in the manner... 

Bartlett, J.B. and James, R.J., 1995. System for categorising soil redox status by chemical field testing. Geoderma, 68 211-218. 

Soil redox potential is also critical in controlling elemental mobility. Some elements are much more soluble and mobile in one oxidation state than another (examples include Cr, Mn, Se, and others). The elements classified as chalcophiles (e.g., Hg, Cu, Pb, Cd, Zn, As, Se) form insoluble sulfide minerals in reducing environments where sulfide (S ) is generated from sulfate reduction (see Chapters 4 and 7). Mobility for chalcophiles is then extremely low unless oxidizing conditions are restored in the soil. Those elements that, in the sulfide form, have the very lowest solubility products (notably mercury, copper, lead, and cadmium) are the most Ukely to become highly immobile and unavailable in reduced soils. ... 

Mn, despite being the most weakly complexing transition metal, bonds with oiganic matter, oxides, and silicates and its solubility decreases. Small changes in the soil redox potential or pH can shift the Mn —Mn oxide reaction. Low pH or low Eft (see Chapter 7) favors the reduction of insoluble Mn oxides and an increased sol-uDility of Mn. As a result, Mn solubility within any particular soil can fluctuate tremendously over time, sometimes ranging from deficient to toxic levels. 

Selenium, a chalcophile, tends to be associated with sulfide minerals in rocks. Weathering processes in the soil oxidize these very insoluble reduced forms, including elemental Se (Se ), the selenides (Se ), and selenium sulfides, to the more soluble sel-enites (SeO ) and selenates (SeC ). With numerous oxidation states possible for Se in soils, redox potential is a critical factor in Se behavior. 

Farrell, R.E., Swerhone, G.D.W. van Kessel, C. (1991) Construction and evaluation of a reference electrode assembly for use in monitoring in situ soil redox potentials. Commun. In Soil Sci. Plant Anal., 22, 1059-1068. 

Nitrogen reactions are generally highly irreversible, and enzymatic catalysis is necessaiy for nitrogen conversions in soils. Redox irreversibility is unfortunate from the standpoint of studying redox reactions, but is absolutely necessaiy for life. Reversibility would bring with it equilibrium, and all organisms would be transformed into CO2, N2, NOJ, and H2O. 

Under aerobic conditions the redox potential deviates widely from the potentials of soil redox couples. In anaerobic soils, redox potentials may be more quantitatively related to ion activities. The Fe24" and perhaps Mn2+ concentrations are high and tend to dominate the redox potential. The range of redox potentials that have been measured in soils is shown in Fig. 4.7. The envelope around those data was considered by the investigators to be the extreme limits of likely redox potentials and pH values in soils and natural waters. Redox potentials can closely approach the H+-H2 potential, because it is nearly reversible at the platinum electrode. 

Bartlett RJ (1999) Characterizing soil redox behavior. In Sparks DL, ed. Soil Physical Chemistry, pp. 371-391, CRC Press, Boca Raton, EL. 

Arsenic uptake from soil (i.e., arsenic bioavailability) depends on soluble arsenic species present in soil, on soil properties (i.e., the type and amount of the sorbent components of the soil), redox (Ej,) and pH conditions and microbiological activity (see Section 6.4.2.1). Uptake into plants further depends on phosphate (often originating from fertilizers) and vanadate levels, as the behavior of arsenate is similar to that of phosphates and vanadates (see also Section 6.6.1). 

FIGURE 4.10 Influence of electron donor (soil organic matter) on soil redox potential. 

The quantitative capability of the Nernst equation to predict the activity of chemical species is valid only under equilibrium conditions. Most of the redox couples are not in equilibrium, except in highly reduced soils steady-state condition may result in pseudoequilibrium conditions. In soils, redox equilibrium is probably never reached because of the continuous addition of electron donors and acceptors. Biological systems add and remove electrons continuously. Thus, redox potential measurements cannot be used to accurately predict the activity of specific reductant and oxidant of the system. 

P-Glucosidase activity is influenced by soil redox conditions, with higher values under aerobic conditions than nnder anaerobic conditions (Figure 5.19). p-Glucosidase activity is influenced by... 

Note Soil redox conditions were maintained by addition of nonlimiting supply of electron acceptors. DQC = dihydroindole quinone carboxylate ND = not detected SIR = substrate-induced respiration (McLatchey and Reddy, 1998). 

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