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Similar to effect of submergence in soils and its management
effect of submergence in soils and its management
- 1. EFFECT OF SUBMERGENCEIN SOILS AND ITS MANAGEMENT Presented by Preethi.K.D 2014602009 TNAU, Coimbatore
- 2. Submerged soils • Soilmass is drowned in water • Soils are saturated with water for a long time in a year • Result in the formation of gley horizons due to oxidation – reduction processes.
- 3. • The oxygenmovement through the flooding water is usually much slower than the rate at which oxygen can be reduced in the soil. • This situation may result in the formation of two distinctly different layers being formed in a waterlogged soil. • On the top is an oxidized or aerobic surface layer where oxygen is present, with a reduced or anaerobic layer underneath in which no free oxygen is present.
- 4. Oxidized and reducedsoil layer
- 5. Changes • Physical changes •Biological changes • Chemical changes
- 7. Depletion of oxygen •Under submerged condition the water replaces the air in the pore spaces. • As a result oxygen diffusion in the water layer above the soil is very slow. • Oxygen trapped in blocked pore spaces is rapidly utilized by facultative anaerobic organisms
- 8. • The rapiddeclines of O2 from the soil are accompanied by an increase of other gases produced through the microbial respiration. • The major gases that accumulate in the flooded soils are carbon dioxide (CO2), methane (CH4), nitrogen (N2), and hydrogen (H2).
- 9. Soil compaction • Compactionis the increase in soil density caused by dynamic loading. • As moisture increases the cohesion among the soil particles decreases, this leads to compaction
- 10. Bulk density • Incompacted soil the voids are filled with water i.e., no air voids are present and no soil water is expelled from the voids, the soil is saturated and its bulk density is maximum. • PB = Ppγw / 1+ (Pp w /100). Where, PB Bulk density Pp Particle density w Water content γw Unit weight of water
- 11. Puddling • Puddling isvery common in Asian rice-producing countries. • Puddling, intensive wetland cultivation, breaks the natural aggregates to finer fractions. • Puddling as mixing soil with water to render it impervious.
- 13. • In submergedsoils, aerobic microorganisms become quiescent or die, and facultative and obligate anaerobic bacteria proliferate. • In the absence of oxygen, many facultative and obligate anaerobic bacteria oxidize organic compounds with the release of energy in a process called “anaerobic fermentation” • In the submerged soils, organic-matter decomposition is retarded because of lower carbon assimilation rates of anaerobic bacteria.
- 14. • In asubmerged soil, the facultative and obligate anaerobic organisms utilize nitrate (NO3−), manganese (Mn4+), iron (Fe3+), sulfate (SO4 2−), dissimilation products of organic matter, CO2, and H+ ions as electron acceptors in their respiration, reducing NO3− to dinitrogen (N2), Mn4+ to Mn2+, Fe3+ to Fe2+, SO4 2− to sulfide (S2−), CO2 to CH4, and H+ to H2 gas
- 16. pH • Soil pHis an important chemical property because of its influence on soil microorganisms and availability of nutrients to plants. • Soil pH indicates acidity, alkalinity, or neutrality of a soil.
- 17. Under submerged condition •The pH of acidic soils increases and alkaline soils decreases • Overall, pH of most soils tends to change toward neutral after flooding • A majority of oxidation–reduction reactions in flooded soils involve either consumption or production of H+ /OH− ions
- 18. In acidic soils •The increase in pH of acidic soils is mainly determined by reduction of Fe and Mn oxides, which consume H+ ions. These reduction processes are shown in the following equations: • Fe2O3 + 6H+ + 2e− ↔ 2Fe2+ + 3H2O • MnO2 + 4H+ + 2e− ↔ Mn2+ + 2H2O
- 19. In alkaline soils •The decrease in the pH of alkaline soils is associated with the microbial decomposition of organic matter, which produces CO2, and the produced CO2 reacts with H2O to form carbonic acid, which dissociates into H+ and bicarbonate (HCO3−) ions.
- 20. Oxidation – reductionpotential • Oxidation–reduction or redox potential has significant influence on chemistry of iron and other nutrients in the submerged soils • Oxidation–reduction potential is measured in millivolts, and symbol used for this chemical change in flooded soil is Eh. • Oxidized soils have redox potentials in the range of +400 to +700 millivolts, whereas waterlogged soils’ redox potential is generally in the range of -250 to -300 millivolts
- 21. • As theO2 depletes from the waterlogged soils, reduction processes occur in sequence. • Nitrate and manganese compounds are reduced first, then ferric compounds are reduced to the ferrous form, and at last sulfate is reduced to sulfide. • Redox potential decreased with flooding of rice soils
- 22. Nutrient availability • Availabilityof essential macro- and micronutrients is significantly influenced in the submerged soils
- 23. Nitrogen • Nitrogen isa key nutrient in improving growth and yield of crop plants in all agroecosystems. • Its main role is in increasing the photosynthesis process in the plants, which is associated with improving grain yield. • A major part of N in the flooded soils is lost through leaching and denitrification
- 24. • Nitrate producedin the surface oxidized layer of a waterlogged soil can easily move downward by diffusion and percolate into the underlying reduced layer, where it is rapidly denitrified • Accumulation of NH4+ in the waterlogged soils would mean that the N is not lost from the soil–plant system,
- 25. Phosphorus • Phosphorus (P)plays an important role in the growth and development of crop plants. • Phosphorus availability is increased in the flooded soils because of the reduction of ferric phosphate to the more soluble ferrous form • P uptake in flooded alkaline soils also improves because of the liberation of P from Ca and calcium carbonate resulting from the decrease in pH.
- 26. Potassium • The reducingconditions caused by flooding result in a larger fraction of the K ions being displaced from the exchange complex into the soil solution. • This may leads to greater availability of K
- 27. Sulphur • In floodedsoils, SO4 2− ion is reduced to hydrogen sulfide (H2S) by anaerobic microbial activities. Furthermore, in flooded soils, Fe3+ reduction to Fe2+ precedes SO4 2− reduction. • Fe2+ will always be present in the soil solution by the time H2S is produced, so that H2S will be converted to insoluble iron sulfide (FeS). This reaction protects microorganisms and higher plants from the toxic effects of H2S • Overall, availability of S is reduced in flooded soils due to formation of insoluble FeS.
- 28. Zinc and Copper •Zinc and copper (Cu) concentrations generally decreased after flooding soils. • The decrease in concentration with the flooding may be associated with increase in soil pH after flooding.
- 29. Conclusion • The mostsignificant chemical changes are increase in the pH of acidic soils and decrease in the pH of alkaline soils, reduction in the redox potential • Availability of P, K, Si, Fe, Mn, and Mo increased in flooded soils, and availability of S, Zn, and Cu decreased. Availability of N depends on its proper management.