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Although soil surveys of Washington and Benton counties, Arkansas, show large areas of soils with severe limitations for septic tank filter fields, houses with septic tank systems are rapidly being built on these soils. The soil survey criteria for soil evaluation differ from those of the state regulatory agency. Also, mapping unit inclusions of other soils can account for different evaluations. The objectives of this study were to evaluate three mapping units (i) for suitability for septic tank filter fields according to the differing criteria used by the Soil Conservation Service (SCS), the Arkansas Department of Health (ADH), and the U.S. Public Health Service (USPHS); and (ii) for their taxonomic composition. The mapping units were Peridge silt loam, 1 to 3% slopes (fine‐silty, mixed, mesic Typic Paleudalfs); Nixa cherty silt loam, 3 to 8% slopes (loamy‐skeletal, siliceous, mesic Glossic Fragiudults); and Clarksville cherty silt loam, 12 to 50% slopes (loamy‐skeletal, siliceous, mesic Typic Paleudults). Approximately 14 sites in each mapping unit were selected at random for evaluation. The small number of sample sites caused a wide confidence interval about the results. Sampling of the Clarksville mapping unit was biased due to equipment limitations. The Peridge unit contained a 50:50 distribution of similar and dissimilar kinds of soils. Of the Peridge unit pedons, 50% were rated moderate and 50% severe by SCS criteria, 79% passed ADH criteria, and 86% passed USPHS criteria. All Nixa unit pedons were Nixa and similar kinds of soils, all were rated severe by SCS criteria, and all failed ADH and USPHS criteria. The Clarksville unit contained 85% Clarksville and similar kinds of soil. All pedons in the unit were rated severe by SCS criteria, and 62% failed ADH and USPHS criteria. We suggest that mapping units be evaluated by their range in soil properties and by their suitability for use and management in two independent steps.

The clay mineralogy of two Aqualfs occurring on the Illinoian till plain of southwestern Ohio was investigated in order to (i) determine the clay mineral distribution with depth, (ii) examine the clay mineral weathering sequence, and (iii) identify the 2:1 mineral species in which hydroxy interlayers had formed. Despite the presence of multiple parent materials, no obvious discontinuities in clay mineralogy were observed. A weathering sequence involving the transformation of clay mica to vermiculite to low charge vermiculite/high charge smectite occurred. Alkylammonium ion exchange data indicated that weathering created a heterogeneous charge distribution in the 1.4‐nm (expandable) mineral phase resulting in mixed low‐and high‐charge interlayers. The low‐charge interlayers readily formed bilayer complexes with ethylene glycol (1.7 nm), and also accommodated double layers of glycerol (1.8 nm) when the mean layer charge was <0.65. Reductions in layer charge were correlated with the oxidation of octahedral Fe(II) and the expulsion of K and Mg from the mineral structure. The expansion of 2:1 layer silicates in horizons near the soil surface was restricted as a result of Alhydroxy interlayering. After interlayer materials were removed with boiling 0.33 MNa citrate, the previously interlayered minerals exhibited x‐ray diffraction effects following Mg saturation and ethylene glycol and glycerol solvation that were indicative of vermiculite.

The seasonally high water table in Clermont (Typic Glossaqualfs) and Avonburg (Aeric Fragiaqualfs) soils of southwestern Ohio was investigated by monitoring variations in water table depth and in water chemistry of the vadose and upper saturated zones. Piezometers were installed for two pedons at three depths ranging from 70 to 180 cm, and soil‐water samples were collected using 0.1‐MPa porous ceramic cups installed in triplicate at four depths ranging from 32 to 170 cm. During the period of this study (April 1982–June 1983), the water table occurred within 30 cm of the surface during winter and early spring, fell rapidly to a depth of about 150 to 180 cm during late summer and early fall, and then returned to within 30 cm of the soil surface during late fall and early winter. Soil‐water exhibited ranges in pH (5.2–8.6), Eh (153–543 mV), electrical conductivity (7.0–91.5 mS m−1), dissolved O2(0.6–6.1 mg L−1), Ca (2.5–64.1 mg L−1), Fe(II) (0–3.87 mg L−1), and Fe(III) (0–11.48 mg L−1). Soil‐water chemistry was a function of season and depth below the soil surface. While the dissolved O2content decreased with depth, Eh and pH increased. Alternating periods of reduction and oxidation were suggested by significant seasonal variation in the variables monitored. Reducing conditions were indicated by the presence of Fe(II) in solution and an Eh of <400 mV, both of which occurred in the Clermont soil at the uppermost sampling depth during the April through June period. This period was characterized by saturated conditions and a soil temperature higher than 8°C. The highly variable Fe(II) and Fe(III) contents indicated that oxidation‐reduction reactions occurred primarily in microenvironments. The soil‐water system was not at internal equilibrium as evidenced by (i) the simultaneous occurrence of dissolved O2with reduced C (organic matter) and Fe (II), and (ii) a mixed potential for Eh that did not correlate with dissolved O2content.

Soil acidification can result from the application of high rates of ammonia‐based fertilizers, but little information is available concerning the effects of long‐term, annual applications at moderate rates. In this study, plots that were mapped as Smolan silt loam (fine, montmorillonitic, mesic Pachic Argiustolls), 1 to 4% slopes, containing an established stand of smooth bromegrass (Bromus inermisLeyss.) were fertilized continuously with rates of 0, 22, 67, 112, 157, and 224 kg N/ha for 40 yr, or for 20 yr followed by 20 yr without N fertilizer. The objective of this research was to determine the effects of such long‐term applications of NH4NO3on exchange properties. In the continuously fertilized plots, pH and exchangeable Ca2+, Mg2+, and K+decreased in the upper 20 cm of the soil, and neutral‐salt cation exchange capacity decreased in the upper 10 cm, whereas exchangeable Al (1 MKCl) and BaCl2‐triethanolamine (BaCl2‐TEA) extractable acidity increased. In all cases, significant changes were observed only when N application exceeded plant demand. Discontinuation of fertilization for 20 yr resulted in a significant, but incomplete, trend of the exchange properties toward values of the unfertilized soils. Thus, the acidification resulting from NH4application, which occurred at even low application rates, was reversed somewhat after fertilization ceased.

Computer pattern recognition techniques were used to discriminate soil information from the Landsat Thematic Mapper (TM) and the French Systeme Probatoire d'Observation de le Terre (SPOT) satellite data on a native prairie near Manhattan, KS. Digital Elevation Model (DEM) data were merged to Landsat TM and SPOT data to delineate soil mapping units within the study area. Soil mapping units from a conventional soil survey were compared with a classified soil spectral map obtained from Landsat TM or SPOT, and DEM derived elevation, slope, and aspect data, using an overall accuracy assessment. The overall accuracy of soil spectral classes from TM and SPOT data was improved after DEM data were merged. A higher average accuracy for soil mapping units was obtained with a low frequency filtering transformation of the data. For Landsat TM data, Band 5 (middle infrared, 1.55–1.75 µm) was most useful for soil information extraction, and a higher overall accuracy was obtained in the dormant season compared with the accuracy in the growing season. The overall accuracy (about 57%) from SPOT data was slightly higher than the accuracy (about 53%) from Landsat TM at a similar wavelength range. Our results indicate that high resolution Landsat TM and SPOT satellite data can be used to aid second‐order soil surveys in areas where the dominant land use is rangeland.

Three pedons each of Clermont (Typic Glossaqualfs) and Avonburg (Aeric Fragiaqualfs) soils were investigated on the Illinoian till plain of southwestern Ohio in order to evaluate parent material stratigraphy and to determine if paleosols were substantially altered following burial by a thin mantle of loess. The relationship between fragipan development and paleosol properties was also examined. The soils were found to have formed in 57 to 69 cm of Late Wisconsinan (Peoria) loess overlying a composite Early Wisconsinan and Sangamon paleosol. The Sangamon paleosol, which was most strongly developed at approximately 150 to 200 cm, was formed in Illinoian till. The material from about 70 to 140 cm consisted of a mixture of Early Wisconsinan loess and Illinoian till with till characteristics dominating. Evidence for a mixed zone in the upper paleosol included (i) a higher silt content than the lower paleosol, (ii) a maximum in elemental Ca in the total silt fraction, and (iii) an abundance of pedotubules in up to 50% of some horizons suggesting that mixing was caused by bioturbation. Modification of the paleosols has occurred as evidenced by recharge with secondary carbonates and bases leached from the overlying loess. A fragipan was identified in only one Avonburg pedon that had a clay content of 27% in the upper part of the paleosol as compared to 31 to 38% for the other pedons. Fragipans appear to have formed in these soils only if the clay content of the upper part of the paleosol is currently less than about 30%.