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Natraqualfs were studied on poorly drained, silty, fluvial terraces in the humid Coastal Plain region of Mississippi. They are underlain by contrasting geologic formations of different ages. The soils have fine‐loamy and fine‐silty textural families. Soil reaction of pedons ranges from extremely acid to strongly alkaline. Acid Natraqualfs are dominant on older geomorphic surfaces, and they are deeper to natric horizons than alkaline pedons. Argillic subhorizons have a SAR > 13 and an exchangeable sodium percentage (ESP) > 15 to qualify as natric horizons. Exchangeable Ca + H is greater than Mg + Na in the acid Natraqualfs. Soil extracts have relatively low electrical conductivities and electrolyte concentrations. Sulphate and chloride are the dominant water‐soluble anions. Barite is a common mineral constituent of the natric horizons.

We examined two Ultisols formed from glauconitic sediments of Eocene age for chemical, physical, and mineralogical characteristics. The parent glauconitic sediments have been subjected to intense weathering that has resulted in the release of large quantities of iron and the alteration of glauconite sequentially to vermiculite → smectite → hydroxy-interlayered vermiculite. These soils exhibited high capacities to adsorb K and P. Most of the naturally occurring K was adsorbed on high-energy-specific adsorption sites. Fertilizer K would be expected to be strongly retained by the clay minerals in these soils. Phosphorus adsorption was proportional to the clay and iron oxide content, exchangeable Al3, and surface area. Adsorbed P was not easily removed by extraction with dilute CaCl2, indicating that it was not readily utilized by plants.

Selected horizons from 45 Mississippi soils have been examined for noncrystalline clay content as determined by 0.5MNaOH and 0.2Mammonium oxalate (pH 3). The soils represent the major soil resource areas of the state. Parent material varied in age from Cretaceous to Holocene. Only small amounts of amorphous clay were extracted from the weakly developed Inceptisols and Entisols, from calcareous soils of the Blacklands and from the alkaline Natraqualfs of the Coastal Plains. Under these nonacid conditions crystalline clay minerals are the more stable phase. The strongly developed Ultisols released large amounts of noncrystalline material with a low silica/alumina molar ratio. The low molar ratio is indicative of gibbsite; however, the large quantity of silica extracted suggests that silica may be adsorbed on the crystalline minerals. When only soils high in smectite are considered, the following trends in noncrystalline clay formation were observed. The silica/alumina ratio increases with smectite content. The quantity of noncrystalline clay increases with increased soil acidity. The poorly drained soils contain less amorphous clay indicating that smectite is the more stable mineral in this environment. Extraction of the clays with acid ammonium oxalate resulted in an average increase in cation exchange capacity of 14 cmol (½ Ca2+) kg−1due to the removal of surface coatings blocking exchange sites.

The clay minerology of four soil pedons formed on Pliocene‐Pleistocene terraces was investigated. These pedons are in the Typic Hapludult, Typic Fragiudult, Aquic Fragiudult, Typic Ochraqualf subgroups and vary, respectively, in drainage from well drained to poorly drained. Smectite was the major mineral in all of the clay fractions with the maximum quantity usually coinciding with the zone of maximum clay accumulation. Hydroxy Al‐interlayered 2:1 clay was generally confined to the upper horizons of these soils. In the deeper horizons, particularly for the poorly drained Aquic Fragiudult and Typic Ochraqualf, the polymeric Al interlayers were replaced by Al(H2O)63+. These soils are all very acid and in the deeper horizons, which are continuously wet, Al‐polymers do not form. In cases where hydroxy Al‐interlayered minerals were deposited by sedimentation the Al‐polymers have been removed. Evidence is presented for a low charge smectite (montmorillonite) and a high charge smectite (beidellite) in these soils. In the surface horizons beidellite is the dominant species with Al‐interlayers, however in the deeper zones both types of smectite are found.

Potentiometric cation activities, electrophoretic mobilities and specific conductance at variable frequencies were determined on suspensions of five reference clay minerals and five soil clays. The objectives of this work are: (i) to determine the relationship between clay mineralogy and specific conductance with a variable frequency power source, (ii) to determine the interrelationship among the various electrochemical measurements, and (iii) to study the effect of different exchangeable cations on the electrochemical properties. Montmorillonitic minerals with a charge deficiency in the octahedral layer showed the greatest change in specific conductance with increasing frequency. Vermiculite, on the other hand, showed less evidence of a change in conductance with frequency; illite showed no change. This was taken to indicate that a greater proportion of the exchangeable cations on montmorillonite was in the Stern layer whereas the cations on the higher surface charge density clays were distributed between the Gouy and the chemisorbed layer. A Stern layer on the montmorillonite minerals developed to a greater extent for monovalent cations than divalent. The divalent cations were apparently located between the unit layers of the mineral and did not conduct electric current even at high frequencies.

The Orangeburg soil used in this study was formed from unconsolidated sand of the Kosciusko formation. Weathering of this profile has been intense due to the porous nature of the sand and warm, humid climatic conditions. Methods used in this study consisted of X‐ray diffraction, DTA, an alkali differential dissolution technique for amorphous constituents, heavy mineral analysis of sand, total elemental analysis of the clay fractions, and surface area measurements. Minerals present in clay fractions are kaolinite, amorphous material, mica, a 14Å. montmorillonite‐vermiculite‐chlorite intergrade and quartz, in approximate order of abundance. Kaolinite and amorphous material increases whereas quartz decreases with profile depth in the coarse clay fraction. According to Jackson's weathering sequence this would place the lower horizons in a higher weathering stage than the surface horizon. The evidence gained in this study suggests that coarse quartz particles are being broken down to smaller particles resulting in this apparently anomalous sequence. The 14Å. intergrade mineral is more prevalent and stable in the surface horizons and apparently forms from montmorillonite.

The reactivity of finely divided feldspar particles in the presence of neutral salt and acidic solutions was studied. In the case of albite, evidence on surface stability in presence of dilute salts near neutrality is given. Microcline, albite, oligoclase, andesine, labradorite, by‐townite and anorthite were converted to surface homionic systems in two ways and the bonding energies of the cations were determined. Large variations with lattice composition were found. Experiments on the entry and release of cations (Na, K, Ca, NH4, Mg, and Sr) showed the apparent exchange capacity of the surface layer was a sensitive function of the ions concerned. At least two types of cationic bonding were indicated. The ammonium ion was found to be an extremely effective displacer, and after entry a large proportion of it was found to be fixed with a high bonding energy. It is concluded that under the conditions of these experiments, any poorly organized surface layer must be thin, that is not more than a very few unit cells in depth.