The clay mineralogy of Coastal Plain soils with sandy epipedons was studied with respect to taxonomic class, horizon, and the presence or absence of sand grain coatings. Relative estimates of claysized minerals were based on x‐ray diffraction peak height ratios after calibration with standards and normalization. Clay mineralogy of sandy horizons was related to whether the clay occurred as grain coatings or as loosely adhering floccules. Clays from coated (⩾5% silt + clay) and slightly coated (<5% silt + clay) sands were consistently high in hydroxy‐interlayered minerals (HIM), and usually contained gibbsite. Clays from floccules in the matrix of stripped (coating‐free) sands contained large amounts of quartz, variable smectite, little or no HIM, and no gibbsite. Mineralogical differences between clays associated with stripped sands vs. coated/slightly coated sands were highly significant statistically. Clay mineralogy of coated/slightly coated sandy horizons was similar regardless of taxonomic class or horizon depth. The A and E (stripped) horizons of Haplaquods were similar to stripped Quartzipsamment horizons in being depleted in HIM relative to other phyllosilicates. Haplaquod Bh and E′ horizons (coated to some degree) were relatively high in HIM and therefore were mineralogically similar to coated/ slightly coated Quartzipsamment horizons and to Arenic and Grossarenic Paleudult epipedons. Clay fractions from chemically reduced loamy horizons of Paleudults and Haplaquods were depleted in HIM relative to overlying coated sandy horizons. Results suggest that pedogenic processes that promote the destabilization of grain coatings (i.e., podzolization, chemical reduction) also promote the loss or redistribution of HIM associated with these coatings.

Tillage pan characteristics in Lakeland, Norfolk, Red Bay and Orangeburg soil series were studied at 20 paired locations of cultivated and virgin areas. Pits for sampling were dug following periods of heavy rainfall. Tillage pans were identified by pocket penetrometer readings of the compaction. Sampling depths from adjacent virgin sites corresponded to those in the cultivated sites. These pans showed consistently higher compaction, bulk density, and less pore space than the soil above or below the pan or the corresponding adjacent virgin soils. Sand, silt, and clay contents were not significantly different between virgin and cultivated samples.Sequential extraction with hydrogen peroxide, dithionite‐citrate, and 0.5N NaOH was made of the cultivated and virgin soils for depths above, in, and below the pan. Dithionite‐citrate extraction for free Fe removed less Al and Si than the subsequent extraction with 0.5N NaOH. Accumulations of Fe, Al, and Si were significantly greater in the pan but these were not consistent for each soil series. Organic matter probably helped to filter and encourage accumulations of some compounds in the pan which might be important in cementation properties. Roots either failed to penetrate these tillage pans or were constricted to much poorer lateral growth compared to roots above or below the pan.

Possible differences in soil characteristics between ortstein and nonortstein Spodosols were studied. Organic C, fine particles (silt plus clay), and extractable Al by dithionite‐citrate, pyrophosphate, acid NH4 oxalate, and NaOH were all higher in Bh than other horizons, except silt plus clay contents in Btg horizons of the St. Lucie County soils. While dithionite‐citrate‐extractable Si was higher at the surface, larger amounts of Fe seemed to occur in lower horizons. Both contents were much lower than extractable Al with the exception of Si in the A and E horizons. Quartz, gibbsite, kaolinite, and hydroxy‐Al interlayered vermiculite were dominant clay‐size minerals. In general, no consistent differences were found in soil properties between the paired ortstein and nonortstein Spodosols except that the ortstein horizons contained more clay and more extractable Al. The cementing materials were shown to dissolve in reagents commonly used for Al and Fe extractions. The dithionite‐citrate reagent was the most effective extractant. The amounts of extractable Al and Fe by dithionite‐citrate, acidic oxalate, and NaOH were small after the ortstein samples were treated with pyrophosphate. These findings suggested that Al in the cementing materials was likely in organic complex form. Ratios of pyrophosphate‐extractable Al to oxalate‐extractable Al and the percentage of maximum Al‐organic complexes supported this assumption. Higher fulvic‐C contents and higher fulvic‐C to humic‐C ratios in ortstein than in nonortstein spodic horizons indicated the complex probably was an Al‐fulvate form.

Mineral distributions in three Florida Paleudults were investigated with respect to particle size, horizon, depth, and location within the soil matrix. Mineralogy of sand, silt, and clay was determined using optical microscopy, x‐ray diffraction, and thermal analysis. Also, mineralogy of sand‐grain coatings was compared with intergrain matrix material. Elemental‐oxide composition of siltsized phyllosilicate grains was determined by electron microprobe analysis. Sand fractions consisted mainly of quartz, with lesser amounts of feldspar and mica, which were more prevalent in lower horizons. Coarse‐ and medium‐silt fractions were also dominated by quartz, but contained appreciable feldspar and mica in B horizons. Kaolinite and hydroxy‐interlayered vermiculite (HIV) were most prevalent in fine‐silt and clay fractions. Abrupt changes in silt and clay mineralogy across the E‐ and B‐horizon boundary (E‐B) included a decrease in quartz and HIV and an increase in kaolinite. Relative amounts of HIV did not markedly change with depth in arenic epipedons, but decreased steadily below the E‐B boundary for all pedons. Sand‐grain coatings from Bt horizons contained more mica than did the intergrain matrix, whereas coatings in A and E horizons contained appreciably more HIV. Distribution of phyllosilicates in these pedons could be explained by a hypothetical sequence of processes which includes (i) illuviation of kaolinite formed from weathering or dispersed from clay lenses in the sediments, (ii) comminution of sand‐ and silt‐sized mica, (iii) incorporation of finegrained mica in sand‐grain coatings, and (iv) transformation of finegrained mica to HIV in highly permeable eluvial horizons.

Four soils with sandy/loamy boundaries occurring at various depths were studied with respect to distribution of clay‐sized minerals within the soil matrix. Mineralogy of coarse and fine clay was determined by horizon using x‐ray diffraction. Also, mineralogy of clay from ped interiors vs. exteriors (coatings) was determined for the Bt horizon of one soil. Mineralogical differences in coarse‐clay distribution were observed with respect to location above or below the sandy/loamy boundary. Clay above the boundary was consistently high in hydroxy‐interlayered vermiculite (HIV) and quartz, regardless of depth to the boundary. One exception was the A horizon of a Spodosol, which consisted essentially of quartz; however, the Bh horizon of this soil (above the boundary) did contain appreciable HIV. Below the boundary, the upper Bt horizon exhibited an increase in kaolinite and a sharp decrease in quartz relative to overlying E or Bh horizons. A marked decrease in HIV below the upper Bt horizon was also evident. Fine clay contained more kaolinite and less HIV and quartz than did coarse clay, and exhibited less intra‐pedon variation. Possibly HIV comprises a greater proportion of the clay residue in eluvial horizons because of the greater size of its precursor, which could be mica, and subsequent resistance to translocation. The greater abundance of HIV in ped coatings relative to ped interiors suggests that some contemporary translocation of coarser clay from HIV‐dominated eluvial horizons has occurred along major voids between peds. The d001 peak shift with heat treatment for HIV was similar for all samples, suggesting that depth and landscape position have had little influence on degree of interlayer polymerization in these soils.