Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Chemical and Physical Composition of SoilsGeneral Composition of SoilFractional volumes of solids and pores varies with location and depth.Thus, bulk density (ρB = mS / VT) varies depending on compaction / loosening.Particle density (ρS = mS / VS) varies with relative proportions of different solids.Together, ρB and ρS determine the porosity (VP / VT).VP = VT – VSVS = mS / ρB and mS = ρB VTVP / VT = 1 – ρB / ρS.ρS does not usually vary much among mineral soils since thedensities of common soil minerals does not vary much.However, packing of discrete particles and their organization intolarger secondary bodies (aggregates) greatly affects ρB, porosity and distribution of pore sizes.Pore-size distribution greatly affects fluid (air and water) flow.Consequently, it greatly affects biological and chemical processes.Sand 2.000 – 0.050 mmSilt 0.050 – 0.002 mmClay smallerVery approximately and ignoring the effect of aggregation on pore size,pore-size matches particle size. Sand = big poresClay = tiny poresFurthermore, mineral particle surface area is inversely related to particle size.Example, for cubeV = S3and A = 6S2A / V = 6 / SThis situation is exaggerated for sheet-like clay minerals.V = λS2A = 2S2A / V = 2 / λ where λ << S and S is very smallMany of the most important reactions in soils are surface reactions.So the capacity of sandy soils for these is very limited compared to finer-texturesoils, particularly fine clay soils.Although one may thoroughly characterize a certain volume of a soil and know texture, density, porosity and pore-size distribution, a nearby volume at the same depth may very well be different. A volume of soil above orbelow it will very likely be appreciably different.In part, this is due to overburden compaction. In part, this is due to the pedogenic history of the soil which has led to the development of a sequence of vertically oriented zones in the soil that are biologically, chemically and physically different. This is called a profile.OAEBCMineralogyPrimary or secondaryPrimary less stable than secondaryand the latter predominate in soils that have been subject to weathering.Primary Secondary layer aluminosilicates Al and Fe oxidesMinerals commonly have local irregularities in structure / composition.In many minerals, this is so spatially frequent as to contribute to the average composition, e.g., isomorphic substitution in layer alumniosilicates.Al3+ exists where Si4+ would otherwise be or Mg2+ instead of Al3+.In other cases, the co-precipitation phenomenon manifests asAn inclusion (separate mineral)Surface adsorbed and occluded speciesSolid solutionOnly ~ 2 % of soils are predominantlyorganic. Although the rest are calledmineral, this terminology diminishesthe importance of soil organic matterin affecting biological, chemical andphysical processes. The importance of organic matter is especially big incoarse soils.Soil organic matter is a vague and broadly inclusive term. It includes everything organic in a soil from livingroots, etc., through their identifiable residues, to organic substances foundonly in soils –humic substances.Humic substances are understood to derive from organic residues through partial(maybe substantial) structural degradation and concurrent synthesis of other structures.People say there are three types of humic substances –Fulvic acid C135H182O95N5S2Humic acid C187H186O89N9Swhich are extractable from soils by base andHuminwhich is not extractable.Some speak of fulvic acids and humic acids to be more precise because these are likesnowflakes.Mineral matter and organic matter are the two general types of solids in soils.Air and soil water are the two types of fluids that fill pores.The soil is alive and respiring.Questions:1.Gaseous diffusion in soil is rapid, comparable to diffusion in this room(True / False).2.Therefore, the composition of soil air is much the same as in this room(True / False).3.Furthermore, the extent to which soil pores are saturated with water neitheraffects rate of gaseous diffusion nor the composition of soil air (True / False).Obviously, false to all.Not only is diffusion restricted by limited cross sectional area (pores) andlonger path length (tortuous connectivity through pores), but water also occludes pores.O2 from the above ground atmosphere does dissolve in soil water O2(aq) = KH PO2but diffusion is orders of magnitude slower than in air.As for soil water, the other fluid, it is a solution, like soil air is a solution,and some people call it the soil solution.It is conceivable that the climate will change where the leftmost profile occurs and itwill undergo much more rapid pedogenesis, including mineral weathering, andsomeday resemble the rightmost profile.In passing through the Jackson-Sherman sequence, its constituent mineralswill be altered by general weather reactions—Dissolution, including acidic dissolutionHydrolysis, in which water is a reactant and is cleavedComplexation, in which structural elements are abstracted into solutionOxidation-reduction, which is structurally destabilizing Hydration-dehydrationStructural modifications more extensive that hydration-dehydration but thatleave much of the parent structure intactAssigned Problems (5)K2[Si6Al2]Al4O20(OH)4(s) + 0.8Ca2+(aq) + 1.3Si(OH)40(aq) =1.1Ca0.7[Si6.6Al1.4]Al4O20(OH)4(s) + 2K+(aq) + 0.4OH-(aq) + 1.6H2O(l)This is Eq. 1.5. Coefficients are discussed on pages 20 – 21. Starting with formulae given in Eq. s1.6, decide whether you like thesecoefficients. If you do not like them, say what set of coefficients you dolike.Do problems 6, 8, 9 and 12.Day Sample HPLC Conc Concentrate Density Volume Mass Mass Total Mass Total Mass Total Mass Recoveryg µM g g mL-1mL µmole mg mg mg m-2g m-22194.297.238.63 0.804010.73 0.0776 0.0155 0.1005 68.2 0.0682 0.6824190.767.357.04 0.80008.80 0.0647 0.0129 0.0823 55.9 0.0559 0.5598197.823.709.12 0.806011.32 0.0418 0.0084 0.0551 37.4 0.0374 0.37416187.221.918.29 0.798010.39 0.0199 0.0040 0.0248 16.8 0.0168 0.168Pesticide Dissipation Data Converted to Recovery, (Mass / Area)t>0 / (Mass /