Flooded soil

Redox conditions in soils vary widely over short distances because O2 must diffuse through pores of various sizes and water-filled pores. In aerobic soils the interior of soil aggregates may be partially anaerobic. The change from oxygen sufficiency to deficiency can occur within a few millimeters. In wet soils, only the largest pores are open to gas diffusion from the atmosphere. 

Ponnamperuma (1972) reviewed the chemistry of flooded soils. This research has understandably concentrated on the soil conditions of paddy rice agriculture. Only some generalizations are mentioned here. The behavior of C, N, S, Fe, and Mn generally follows that shown in Table 4.3. When rice paddies are drained before harvest, redox potentials rise, Fe2 1 and Mn2+ concentrations decrease, and C, N, and S oxidize. When the soils are flooded again, the reactions reverse. 

Phosphate apparently precipitates as Fe(III) and A1 phosphates during the dry part of the rice culture cycle. Under subsequent reducing conditions, the Fe(III) phosphate is reduced to more soluble Fe(II) phosphate. This reduction can account for the rather high availability of phosphate for centuries in paddy soils. The Fe(III) phosphate may be slightly more stable than AI phosphate so the Al phosphate that precipitates initially slowly transforms to Fe(UI) phosphate. Similar aerobic soils often supply inadequate phosphate to plants because Fe(III) phosphate remains insoluble. 

A second noteworthy flooded soil is acid sulfate soil. Sediments along tropical and subtropical coastlines and river deltas may contain significant quantities of Fe(II) sulfides. When dr ained, these sulfides oxidize to H2SO4 and the acidic Fe3+ ion. The soil acidity can increase to pH 2. Such conditions are highly phytotoxic and can be remedied under aerobic conditions only by extensive leaching and lime applications. If resubmerged, acid sulfate soils revert rapidly to near neutrality as the Fe(III) and sulfate are reduced back to Fe(II) sulfides. 

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Studies have found that methyl parathion degrades more rapidly in anaerobic soil than in aerobic soils (Adhya et al. 1981, 1987 Brahmaprakash et al. 1987). An average half-life of 64 days was determined for nonflooded (aerobic) soils compared to an average half-life of 7 days in flooded (anaerobic) soils (Adhya et al. 1987). In experiments with " C-labeled methyl parathion, 35% of the labeled compound was recovered from nonflooded soil after 28 days, compared with 9% recovered from flooded soil (Brahmaprakash et al. 1987). 

Results from other studies support the rapid degradation of methyl parathion in soils with a high water (i.e., low oxygen) content (Adhya et al. 1981, 1987 Brahmaprakash et al. 1987). Experiments in flooded and nonflooded soils showed that the redox potential affected both the rate of degradation and the transformation products of methyl parathion (Adhya et al. 1981, 1987). Transformation to volatile products was suggested by Brahmaprakash et al. (1987) as the reason that significant amounts of " C from labeled methyl parathion could not be accounted for, especially in flooded soils. 

Adhya TK, Wahid PA, Sethunathan N. 1987. Persistence and biodegradation of selected organophosphorus insecticides in flooded versus non-flooded soils. Biol Fertil Soils 4 36-40. 

Sharmila M, Ramanand K, Sethunanthan N. 1981. Hydrolysis of methyl parathion in a flooded soil. 

Lueders T, B Pommerenke, MW Friedrich (2004) Stable-isotope probing of microorganisms thriving at thermodynamic limits syntrophic propionate oxidation in flooded soil. Appl Environ Microbiol 70 5778-5786. 

Rood BE, Gottgens JF, DeUrno JJ, Earle CD, CrismanTL. 1995. Mercury accumulation trends in Florida Everglades and savannas marsh flooded soils. Water Air Soil Pollut 80 981-990. 

The principal degradation products of bifenox are the free acid, 5-(2,4-dichlorophenoxy)-2-nitrobenzoic acid, and the amino derivatives, methyl 5-(2,4-dichlorophenoxy)anthranilate and its free acid, in flooded soil. A free acid is observed in nonflooded soil. When [ " C]chlomethoxfen was used to treat rice field soil, chlomethoxfen was extensively transformed into unextractable products with organic solvents however, the amine, the A-demethylated compound and the formyl-amino and acetylamino compounds were isolated and identified as the metabolites of chlomethoxfen. ... 

Under flooded soil conditions, the diphenyl ether herbicides are substantially transformed into the amino derivatives, which are incorporated tightly into the soil particles. An analytical method for these amino derivatives in soil has been developed. 

Guimaraes, J.R.D., Meili, M., Hylander, L.D., Castro e Silva, E., Roulet, M., Mauro, J.B.N., and Lemos, R.M.A., Mercury net methylation in five tropical flood plain regions of Brazil High in the root zone of floating macrophyte mats but low in surface sediments and flooded soils, Science of the Total Environment, 261 (1-3), 99-107, 2000. 

The saturated soils that occur during wetland, or lowland, rice cultivation give rise to a set of physical, chemical, and biological properties that are quite different from upland soils. Rice is the only major row crop produced under flooded-soil conditions and the absence of air-filled pores along with reduced soil-atmosphere interactions result in an almost entirely different set of processes than those occurring in upland cropping systems. 

Patrick WH, Jugsujinda A. Sequential reduction and oxidation of inorganic nitrogen, manganese, and iron in flooded soil. Soil Sci. Soc. Am. J. 1992 56 1071-1073. 

The partial pressure of C02 in the soil air controls the concentration of both dissolved C02 and undissociated carbonic acid. At 0.003 atm of C02 (g) as a reference level for soils, [H2C03°] is about 1.04 x 10 4 M (Lindsay, 1979). At a normal atmospheric level of 0.0003 atm C02 (g), [H2C03°] is approximately 1.04 x 10 5 M. In most soils, C02 (g) is higher than in the atmosphere. C02 is released from soil and plant root respiration. In flooded soils, C02 (g) partial pressure increases to 0.01-0.3 atm, about 1000-fold higher than normal upland soils due to strong microbiological activity (Lindsay, 1979). 

Flooding increased Fe, Mn and Cu concentrations in rice grown on arid soils in Australia with a soil of pH 7.3-7.5 compared to upland conditions, but decreased Cu uptake from flooded soils (Beckwith et al., 1975). Plant uptake of Co was also increased by waterlogging soils since Co was released from the dissolution of Mn oxides. However, the wetting incubation of 24 arid soils from Colorado farms with a wide range in texture... 

Jugsujinda A., Patrick W.H.Jr. Growth and nutrient uptake by rice in a flooded soil under controlled aerobic-anaerobic and pH conditions. Agron J 1977 69 705-710. 

Martin M, Violante A, Barberis E (2007a) Fate of arsenite and arsenate in flooded and not flooded soils of South West Bangladesh irrigated with arsenic contaminated water. J Environ Sci Health, Part A 42 1775-1783 Martin M, Violante A, Barberis E (2007b) Comparing surface interaction of arsenite and arsenate on soil colloids I Adsorption. Soil Sci Soc Am J (submitted)... 

Porvari, P. and M. Verta. 1995. Methylmercury production in flooded soils a laboratory study. Water Air Soil Pollut. 80 765-773. 

Siddaramappa, R., A.C. Tirol, J.N. Seiber, E.A. Heinrichs, and I. Watanabe. 1978. The degradation of carbofuran in paddy water and flooded soil of untreated and retreated rice fields. Jour. Environ. Sci. Health B 13 369-380. 

In laboratory tests, several fungi and cultures of actinomycetes isolated from garden soil readily degraded disulfoton (Bhaskaran et al. 1973). In flooded soil under anaerobic conditions, the reduction of disulfoton sulfoxide to disulfoton was due to biological conversion (Tomizawa 1975). 

Table II. Redox potentials (expressed in millivolts) at two depths in a flooded soil. 

Table III. Degradation of [14C]trifluralin in a flooded soil (expressed as percent of extracted radioactivity). ...

Figure 2.1 Changes in water potential with depth in a puddled flooded soil...

Effects of Flooding and Redox Conditions onfs. I know of no published data on this. Bnt it is likely that the natnre of particle surfaces in intermittently flooded soils wonld restrict snrface mobility. For ions to diffuse freely on the surface there must be a continuous pathway of water molecules over the surface and uniform cation adsorption sites. But in intermittently flooded soils the surface typically contains discontinuous coatings of amorphous iron oxides on other clay minerals, and on flooding reduced iron is to a large extent re-precipitated as amorphons hydroxides and carbonates as discussed above, resulting in much microheterogeneity with adsorption sites with disparate cation affinities. 

In flooded soil or sediment, bubbles form through heterogeneous nucleation at the surface of sohd particles, rather than by homogeneous nucleation in free solution. Because of this, bubbles form easily and the sum of the partial pressures of volatile solutes tends to be maintained at or near the hydrostatic pressure. Therefore, for a methanogenic sediment. 

These equations can be solved simultaneously with Equations (4.33)-(4.35) to obtain values of pe, pH, [O2] and [Fe +] over the course of reduction. Eigure 4.7 shows results for realistic flooded soil conditions, expressed in terms of the amounts of CH2O oxidized in the different reactions. Eigure 4.7(a) gives results in the absence of pH and cation buffering by the soil Eigure 4.7(b)-(d) gives results for different values of hs. CEC and [X Jl. 

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