摘要:

The assumption that particle-size distribution (PSD) in Mil may often be described as approximately lognormal was tested and found to be inadequate for many textures. With texture specified by mass fractions of clay, silt, and sand in a texture triangle, it is shown that the unimodal lognormal distribution can describe PSD, to within chosen degrees of approximation, over only about half of the USDA triangle. “Disallowed” textures are excluded primarily by their width of textural spread, requiring excessive undersize (d< 0.02 μm) or oversize (d > 2 mm) tails in the distribution. They would require alternative distribution functions (e.g., skewed unimodal, bimodal). Equations are given for the two lognormal (size “mean” and “spread”) parameters for eligible textures within the “allowed” triangle area. The theory enables mapping between triangles of different texture systems (e.g., USDA, International) for eligible textures. The rationale of predicting soil properties from two-parameter textural representations is discussed. Two. classes of property are identified, according to their likely optimal regression parameters: (1) properties dominated by the clay or colloidal fraction (mass-fraction parameters, only two of which are independent) and (2) properties dependent on overall particle- or poresize distributions (transformed, size-distribution parameters). The lognormal parameters derived here offer a new basis for regression of class 2 properties for eligible textures.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Three pedons within a 0.5-km2area (near the smelters) in the Copper Basin of Tennessee were located on upland, mid-slope, and toeslope landforms. Two pedons were located in some distant forests in areas unaffected by the smelting operations and accretion of sulfur. Morphological, physical, and chemical analyses were carried out on these soils. Mineralogical analyses were also made of sand, silt, and clay fractions by x-ray diffraction, thermal, petrographic, and chemical techniques. The clay and fine silt fractions contain interstratified mica/hydroxy-inter-layered vermiculite in the upper horizons. Kaolinite and gibbsite dominate subsoil horizons. The C horizon saprolite fine silt and clay fractions have kaolinite, vermiculite, and muscovite along with translocated or neoformed gibbsite. The sand fraction of A, B, and C horizons is composed mainly of quartz, muscovite, and kaolinite pseudomorphs of biotite. Albite and microcline feldspars occur in Cr horizon material and in the less weathered but oxidized underlying metagraywacke and quartz-mica schist.It is theorized that most of the kaolinite originated from feldspars and biotite while muscovite weathers to a muscovite-ver-miculite interstratified phase. Gibbsite, concentrated in the fine clay fraction, is neoformed, although some in the coarse clay and fine silt fractions may have transformed directly from feldspars in upper B horizons or from the increased desilication of kaolinite in the uppermost A and E horizons, a direct result of the acid-sulfate deposition from past open roasting and smelting of copper sulfide ores. Gibbsite in C horizons has been either neoformed or translocated as fine clay-sized particles from A and upper B horizons. No gibbsite was detected in Cr horizons or in the hard but oxidized rock beneath except as translocated coatings on crack and joint faces as opposed to large quantities of gibbsite in the Cr horizon of the pedon not affected by sulfur accretion. A definite relationship exists between landscape position and clay mineralogy. Permeable and freely drained upland and sideslope soils are dominated by gibbsite throughout, whereas lower sideslope and toeslope soils, which are either less permeable, have fluctuating water tables, or receive lateral surface and subsurface flow from higher areas, have less gibbsite, more kaolinite and vermiculite, higher base saturation, and other less weathered primary and secondary silicate minerals. Generally, there are no major soil mineralogical differences between soils affected and those not affected by sulfate, but there are obvious differences in pH and related chemical properties.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Diffusion coefficients of Cl−, NO3−, K+. and Ca2+in variable-charge soils from diffusing sources consisting of mixed salts were determined. The effects of diffusing ion species, soil surface charge, and other ions on diffusion coefficients were similar to those in single-salt systems. However, the diffusion coefficients were larger for anions when soil pH was low and for cations. The difference in diffusion coefficient between anion species was larger and that between cation species was smaller than when a single salt diffused alone. These differences were interpreted in terms of the interactions between ions and soil surface charges and among ions during diffusion.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The concentrations of available phosphorus and H2PO4−activities were determined with depth in a silty clay soil receiving 40 kg P ha−1yr−1(surface broadcast with no incorporation on brome sod) for 20 or 40 yr. The soil was sampled in increments to a depth of 3.0 m. Available P, by the Bray and Kurtz P-1 method, and H2PO4−activities, from total solubilities in 0.01MCaCl2extracts, were determined. Available P was found to be greater in fertilized soils than in the unfertilized control soil to a depth of 45 cm. Similarly, Bray-P concentrations were greater to a depth of 30 cm in soils receiving continuous fertilization than soils in which fertilization was stopped after the first 20 yr. The activity of H2PO4−was strongly dependent on soil depth, P fertilization, and soil pH. Measured H2PO4−activities showed only weak correspondence to solid phase solubilities, but a short equilibration time and a lack of Al3+activity data made the comparison incomplete. Available P and H2PO4−activities were correlated when both were high, but there was no correlation when Bray-P concentrations were less than 13 mg P kg−1. The high activities in the soil extracts indicate that leaching of inorganic P may have a major role in the translocation of P, but the role of highly mobile organic P compounds could not be discerned from the present data.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We investigated in the laboratory the changes in the diethylenetriaminepentaa-cetic acid (DTPA)-extractable Zn and Cu in 26 acidic to near neutral alluvial soils on submergence and observed that there was always a decrease in their contents. The percentage of decrease was significantly correlated with initial pH, organic C, clay, cation exchange capacity (CEC), and initial DTPA-extractable contents. The pH seemed to play the most important role in influencing the magnitude of decrease. Multiple regression equations showed that 40.06 and 39.44% variability in the magnitude of decrease of Zn and Cu, respectively, could be accounted for by some of the initial soil properties.On submergence, there was an increase in pH, CO32-, S2-, and DTPA-extractable Fe and Mn. The percentage of decrease in DTPA-extractable Zn and Cu was positively correlated with the magnitude of increase in pH (not with Cu), CO32-, S2-, and Fe and was negatively correlated with Mn. Of the variability in the percentage of decrease in Zn and Cu, 57.30 and 59.30% could be accounted for by the change in these parameters, thus lending support to the hypothesis that the decrease in availability of Zn and Cu in acidic to near neutral soils on submergence is due to their precipitation as hydroxide, carbonate, sulfide, and iron compounds.The results of path coefficient analysis revealed that increase in pH directly contributed 36.96% of the percentage of decrease in DTPA-extractable Zn in soil on submergence. The total contribution of pH, comprising both direct and indirect effects through CO32-, S2-, and Fe, was 56.40%, suggesting that mechanisms other than those mentioned are operative to cause decrease in Zn availability in soils on submergence. Further research is necessary for their elucidation.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

A prime farmland soil in the Southern Mississippi Valley Alluvium was drastically disturbed to a depth of 3.5 m to simulate surface mining. The soil was replaced in various soil segregation treatments to study the progression of pedogenic events. Particle size distributions were functions of parent materials used to construct the soil segregation treatments. Drastic disturbance created on “open” soil structural matrix with large voids and channels that resulted in fewer gleyed colors than normal in parent materials. Between 424 to 886 d after replacement, subsidence had closed the large voids and channels, resulting in structural annealing of unlike materials. Leaching of soluble salts, cations, and labile clay declined with subsidence and structural annealing. Organic matter increased 327% in one treatment 886 d after replacement, forming an A horizon with granular structure. Drastically disturbed soils in this study exemplified dynamic systems attempting to reach equilibrium with the genetic factors acting upon them.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

A soil column study was conducted to assess the movement of Zn in sewage-sludge-amended soils. Variables investigated were soil properties, irrigation water quality, and soil moisture level. Bulk samples of the surface layer of six soil series were packed into columns, 10.2 cm in diameter and 110 cm in length. An anaer-obically digested municipal sewage sludge was incorporated into the top 20 cm of each column at a rate of 300 mg ha−1. The columns were maintained at moisture levels of saturation and unsaturation and were leached with two waters of different quality. At the termination of leaching, the columns were cut open and the soil was sectioned and analyzed. Zinc movement was evaluated by mass balance accounting and correlation and regression analysis.Zinc movement in the unsaturated columns ranged from 3 to 30 cm, with a mean of 10 cm. The difference in irrigation water quality did not have an effect on Zn movement. Most of the Zn applied to the unsaturated columns remained in the sludge-amended soil layer (96.1 to 99.6%, with a mean of 98.1%). The major portion of Zn leached from the sludge-amended soil layer accumulated in the 0− to 3-cm depth (35.7 to 100%, with a mean of 73.6%). The mean final soil pH values decreased in the order: saturated columns = sludge-amended soil layer > untreated soils > unsaturated columns.Total Zn leached from the sludge-amended soil layer was correlated negatively atP= 0.001 with final pH (r= −0.85). Depth of Zn movement was correlated negatively atP= 0.001 with final pH (r= −0.91). Multiple linear regression analysis showed that the final pH accounted for 72% of the variation in the total amounts of Zn leached from the sludge-amended soil layer of the unsaturated columns and accounted for 82% of the variation in the depth of Zn movement among the unsaturated columns. A significant correlation was not found between Zn and organic carbon in soil solutions, but a negative correlation significant atP= 0.001 was found between pH and Zn (r= −0.61).

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Few studies have examined residual fertilizer N recovery from conservation tillage soil. Tillage and fertilizer placement effects on fertilizer N recovery under sorghum (Sorghum bicolorL. Moench) cropping in 1985 and 1986 were evaluated in a field study on a Weswood soil (Fluventic Ustochrept) near College Station, Texas. Nitrogen-15-depleted NH4NO3(150 kg N ha−1) was surface broadcast or subsurface banded in microplots under notillage or conventional tillage management to measure accumulation of fertilizer N in sorghum and recovery from soil. Fertilizer N accumulation by sorghum, residual fertilizer N recovery, and total (soil plus plant) fertilizer N recovered for each year varied with placement treatment. More fertilizer N was accumulated by sorghum in banded treatments, resulting in less fertilizer N recovered in the soil. Higher total fertilizer N recovery in 1985 reflected greater fertilizer accumulation by sorghum than in 1986. More total Kjeldahl N was present in no-tillage soil but was apparently not available to the sorghum, as indicated by higher fertilizer N accumulation in no-tillage treatments both years. However, tillage did not influence fertilizer N recovered from the soil. Most fertilizer N recovered from soil in banded treatments was from the location of original band placement, with some minor lateral movement. Comparison of soil excavation sampling and probe sampling indicated equal ability in detection of treatment differences. However, the excavation method was the most effective for quantifying fertilizer N recovery.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The feasibility of using expanding polyurethane foam as an alternative to sand or water in estimating bulk density by the excavation method was tested. The procedure for using foam was similar to other excavation techniques except that the hole was filled with foam and the resulting hardened case was immersed in water to estimate the volume of the hole. Bulk density estimates for three different soils were determined by the more traditional sand cone and core methods and were compared to estimates derived by the use of the polyurethane foam. No significant differences were found among the three methods for three soils tested. Advantages of using the foam technique are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The publications on soils by W. Cobbett (1830), J. Morton (1838), and C. S. Sprengel (1837) can be included among those considered as precursors, or forerunners, of pedology as an independent science. Considering M. V. Lomonosov and A. von Humboldt, whose work (although significant) was only marginal to soil science, as its founders seems inappropriate.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID