摘要:

An evaluation was made of four models for determining apparent stability constants of Cu(II) complexes with humic acids (HA), using experimental data for both the amounts of Cu(II) bound to the complexes (ISE measurements), and for protons released from reactive sites (base titrations). A continuous distribution model based on the Scatchard plot showed the greatest promise for modeling the binding data. Constants obtained in this way are considered to reflect variations in binding energies without regard to the manner in which Cu(II) is bound. Binding affinity of a soil HA for Cu(II) was affected by pH, ionic strength (I), and, at pH 4, the concentration of HA. Values for log Kintat pH 4, 4.5, and 5 (I of 0.005 M) were 7.62, 7.80, and 8.50, respectively. At pH 4, log Kintdecreased with increasing I, absolute values being 7.62, 7.10, 7.00, and 6.81 at I values of 0.005, 0.025, 0.05, and 0.1, respectively. Results of base titrations showed that, at pH 4, an average of 1.45 protons were released per molecule of Cu(II) bound, indicating the formation of 1:1 and 2:1 complexes (i.e., CuL−and CuL2, where L is the reactive site of the macromolecule). Complexation of Cu(II) by HA can best be explained on the basis of the formation of polynuclear complexes.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The batch equilibrium and a continuous flow (column) procedures were compared to determine if similar pesticide distribution coefficients could be obtained for the two methods. Using a low infiltration rate of 2.7 cm day−1, essentially identical values were obtained by the two methods for the distribution of napropamide and lindane between the sorbed and solution phases in a Pachappa sandy loam. Values for Kocof 421 and 1300 L kg−1were measured for napropamide and lindane, respectively, at 20°C. Distribution coefficients decreased with increasing temperature. In the column experiments, similar values for the distribution coefficients were obtained regardless of whether the amounts of pesticide sorbed were determined by direct extraction of the soil or by the difference between quantities added to the columns and the quantities of solute in the effluent. Both linear and Freundlich isotherm models were used to calculate distribution coefficients. The soil column breakthrough curves were reproducible in duplicate runs for both napropamide and lindane. When distribution coefficients were estimated using a chemical retardation factor from the column experiments, the coefficients were consistently larger than those determined by the batch equilibrium method.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

An investigation of the influence of the aggregate sizes on some elements of an oxisol is presented. Proton Induced X-ray Emission (PIXE) has been used to carry out this analysis. Aggregate sizes from <0.5 mm to 4.7 mm have been used, and results confirm that the presence of Cl and Ca was greater in the small aggregate fractions. The content of K was greater in the large aggregate fractions. Fe, Al, Si, and Ti showed small differences in their concentration as a function of the aggregate sizes.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The adsorption of the herbicide Alachlor on montmorillonite saturated with different cations (Al3+, Cu2+, Ca2+, Mg2+NH4+, Na+, Li+, Rb+, and Cs+) was studied in aqueous suspension. Equilibrium adsorption isotherms at 5° and 22°C fit the Freundlich relationship. A correlation between adsorption and the polarizing power of the exchangeable cation was observed. A decrease in temperature from 22° to 5°C resulted in an increase in adsorption except for Al-, Rb-, and Cs-montmorillonite. The isosteric heats of adsorption were also determined. The interaction of Alachlor with homoionic montmorillonites was also studied by FT-IR spectroscopy in an organic solvent. The results indicated that the molecule is adsorbed on monoionic montmorillonite by a coordination bond, through a water bridge, between C==O groups and the exchangeable cation of the clay. Further, the coordination strength is directly correlated with the polarizing power of the cation. X-ray diffraction analyses showed that the herbicide was able to penetrate the interlayer space of montmorillonite saturated with polyvalent cations. On moderate heating (70°C for 6 h) Alachlor adsorbed on Al-, Cu-, Ca-, Mg-, and NH4-clay is partially decomposed to 2-chloro-2′,6′-diethylacetanilide.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Increased demand for food production, extensive agricultural cultivation, and destructive processes occurring naturally in soil (erosion, weathering) will necessitate use of lower quality soils, thus promoting the use of soil conditioners. In order to draw attention to the unforseen and possibly hazardous effects of soil conditioners along with their positive effects, a laboratory experiment with two anionic polyacrilamide (PAM) polymers was conducted at three application levels and on three soil types. It was found that these PAMs harmed, improved, or barely affected sandy, loamy, and clay soils, respectively. The applied PAMs drastically affected soil physical properties, e.g., aggregates size distribution and water retention, thus affecting plant production above and below the soil surface. Only a semi-systematic response of the nematodes, bacteria, fungi, and actynomicetes population to the above treatments was found.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Paragonite is a dioctahedral mica that contains Na rather than K in the interlayer position, but is otherwise virtually identical to muscovite. Reports on the occurrence of paragonite in soils are rare, and its influences on soil properties and pedogenesis are not well characterized. Paragonite was identified in soils derived from quartzmica schist landslide colluvium at elevations between 670 and 2010 m in the Klamath Mountains of northern California. X-ray diffraction (XRD) peaks from rock samples and sand, silt, and clay fractions of the soils match characteristic d-spacings of 0.962 nm for paragonite and 1.00 nm for muscovite. Paragonite:muscovite XRD peak height ratios indicate that the amount of paragonite relative to muscovite is lowest in the silt and clay fractions of the most weathered soil horizons, perhaps as a result of dilution when inherently larger muscovite particles are comminuted. Energy dispersive spectroscopy revealed the presence of both Na and K in micaceous grains. Paragonite and muscovite apparently are intimately associated, but variations in d-spacings indicate limited substitution of K in paragonite and Na in muscovite. X-ray diffraction, rather than optical microscopy, is required to distinguish between paragonite and muscovite.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Soils were classified in riparian bur oak (Quercus macrocarpa) woodlands in the foothills of the Black Hills, South Dakota. The soils in these gallery forests represented a blending of grassland (Mollisol) soils and forested (Alfisol) soils. Four soillandscape units were identified: (i) relatively young soils on steep slopes (usually Ustochrepts); (ii) soils adjacent to stream channels that were subject to episodic flooding and burial by new layers of alluvium or colluvium (Fluventic Mollisols); (iii) low relief, concave surfaces on stable floodplains away from stream channels (Cumulic Mollisols); (iv) Alfisols and Mollisols with argillic horizons on stable surfaces up off the floodplain. The actual taxonomic classification of similar pedons was often quite different, reflecting changes over time in the overstory and understory. In general, soil types and vegetative communities were poorly correlated. Soil pedons may provide a glimpse of history that helps us to understand past processes in formation, but this knowledge may not be very useful in understanding current plant distribution patterns.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Adequate characterization, mapping, and precise delineations of areas with soil pollution are essential for optimizing decontamination. Heterogeneity in soil sodification and associated growth of Silver oak (Grevillea robusta A. cunv.) trees were studied. Soil samples from 6 × 6-M grid patterns in four layers at a depth increment of 0.3 M were analyzed. Annual tree height observations recorded for 7 years were also statistically analyzed. Average (of four layers) CVs of the 1 N Ammoniumacetate-DTPA-extractable sodium (Na), sodium adsorption ratio (SAR), pH, and phosphorus (P) were 123, 117, 66 and 65%, respectively. CV in tree height was also high and fluctuated around 26% during the last 3 years. Two-way average trend variations were 41, 18, 20, 19, and 24% of variance of pH, SAR, Na, P, and tree height, respectively. About 29,43,55, 23, and 33% of variance of pH, SAR, Na, P, and tree height was locally spatially structured. Cross-variability among soil layers and SAR with tree height was predominantly structured. Mapping with optimal, unbiased, and minimum estimation variance was also validated. Delineation of soil sodicity with regionalized variable theory showed areas requiring different amounts of ameliorants. This technique was useful for optimizing soil reclamation.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID