摘要:

The theory of water flow in swelling clays may be developed in a space coordinate system at rest, assuming that the flux of clay particles can be defined by the space gradients of potential responsible for the movement of clay particles, which is related to the gradients of water potential. Within this framework, the hydraulic conductivity of saturated and unsaturated swelling clays is defined and measured from the water and clay content profiles obtained from infiltration experiments into unsaturated bentonite. As a result, the hydraulic conductivity is found to increase from 10−7to 10−2cm/d when the volumetric water content increases from 0.05 to 0.95 cm3/cm3. These results agreed well with those analyzed by the existing theory, which was developed in the material coordinate system.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

In this paper we identify an error in the literature pertaining to the interpretation of nonintegral slopes in Schubert plots for metal-humate and metal-fulvate systems, and we derive equations that correctly describe the behavior of these systems.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We present an experimental method that nondestructively, relatively quickly, and reproducibly develops data necessary for finite-difference calculations of liquid-vapor diffusivities for water contents between approximately 1% and any intermediate value of interest. Diffusivity functions for five different soils, ranging in texture from fine sands to a clay loam, were determined. Vapor adsorption and transport mechanisms are discussed in the context of the liquid-vapor diffusivity function, using experimentally measured vapor adsorption isotherms. Conductivities calculated from results of experiments conducted using thermocouple psychrometers to nondestructively measure suction heads in a clay loam during the flow process are also presented.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We conducted greenhouse experiments to study the effect of humic acid on corn seedlings grown in sand, receiving 0 to 50 mg kg−1Al and 0 to 350 mg kg−1humic acid (HA). Fertilization was supplied in the form of a Hoagland-Arnon solution adjusted to pH 4.8. In the absence of HA, increasing amounts of Al in the growth media sharply decreased dry matter production. Total dry weight was reduced from 6.8 g/four plants at 0 Al to 4.0 g/four plants at 50 mg kg−1Al. Plants treated with 50 units Al developed symptoms of Al toxicity, which appeared as marginal chlorosis and necrosis. The addition of HA to pots containing Al increased dry matter production by 32.5 to 42.5% over those with 0 unit HA, and the plants appeared healthy and green. The beneficial effect of HA was also reflected in the Al and P contents of the corn leaves. Leaf-Al concentrations increased linearly with increased Al treatments at 0 units HA, but decreased from a high of 86.6 μg g−1at 50 units Al and 0 unit HA to 60.5 and 57.4 μg g−1with 100 and 350 units HA, respectively. The increase in leaf-Al content as a result of Al stress coincided with a decrease in leaf tissue P contents. However, addition of HA suppressed the reduction in concentrations of leaf P, which accompanied Al stress. At treatments with 50 units Al, plants receiving HA contained more P than those at 0 unit HA. Indications suggested that high amounts of Al in solution reacted with P to form insoluble Al phosphates. However, the presence of HA may have chelated most of the Al, rendering it inactive for reaction with P.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We measured the adsorption of aniline and four chlorinated analogues using the batch equilibration method to evaluate the direct and indirect determinations of the adsorbed solute concentration and binary relationships between adsorption constants and selected chemical properties of the adsorbates. Also we assessed the chemical stability of labile organic compounds during the adsorption process, by simultaneously using radioisotopic and liquid chromatographic methods of analysis for14C-aniline and14C-4-chloroaniline. No significant difference in adsorption coefficients and equivalent precision of estimates was found between analysis methods for these two chemicals. Adsorption coefficients derived from direct compound analysis of solution and adsorbed phases were comparable to those derived from solution phase analyses alone. These studies, in which the adsorbed phase was first desorbed and then analyzed, provided assurance that conventional batch equilibration studies, in which the quantity of the adsorbed chemical was derived by difference, were accurately assessing the degree for adsorption of aniline and chloroanilines. The adsorption of aniline and chlorinated analogues was predictable from chromatographic capacity factors and estimates of their octanol-water partition coefficients.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We collected soil samples from four different agricultural projects. Potassium orthophosphate was added to the samples at rates of 0, 25, 100, 200, 400, 800, and 1600 ppm P. The samples were incubated for 0.5, 24, 168, 1000, and 3000 h at constant temperature and moisture. Ec, pH, and concentrations of water-soluble orthophosphate, calcium, and magnesium were determined in the soil water extracts after the incubation.The results showed that a sharp decrease occurred in the concentration of water-soluble P, within 0.5 h after P addition. Using calcium phosphate equilibria phases indicated that β-tricalcium phosphate was the dominant form after 3000 h of addition. Precipitated forms were dicalcium phosphate dihydrate, octacalcium phosphate and β-tricalcium phosphate. Using Mg-phosphate equilibria phases revealed that bobiernite was the dominant form after a short time and a high level of P addition. Calcium phosphate controlled the solubility of phosphate more than Mg-phosphate.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

The downward movement of phosphorus is significant for irrigated coarse-textured soils that are low in organic matter content. We conducted a laboratory study with columns of Valentine loamy sand (Typic Ustipsamment) to determine the effects of ionic strength and monovalent cation source of a leaching solution on P distribution in a soil with depth. Solutions of the chlorides of Na, Li, and K at concentrations of 1.0, 10−2, 10−4, and 10−6mol L−1were added to the columns after an application of 0.3 g diammonium phosphate on the surface of each column. Approximately two pore volumes, 500 ml of solution, were added to the columns, which measured 50 by 4.5 cm (cross-sectional area = 15.9 cm2), after which the columns were sectioned, and the amount of Bray-extractable P in each section was measured. Increasing ionic strength of the leaching solution resulted in an increase in the total amount of extractable P per column. Extractable P in the columns increased with depth as the ionic strength of the leaching solution decreased. Salt source of the leaching solution did not influence either the total amount of Bray-extractable P per column or the distribution of extractable P within the column. Dissolved organic carbon (DOC) in the leachate was found to increase with decreasing ionic strength. Changes in the distribution of extractable P with depth were attributed to increased competition for P adsorption sites by various organic molecules that were released into bulk solution when the organic matter coatings underwent a transition from the spherocolloid to the linear flexible molecule configuration. These transitions are believed to be caused by changes in the ionic strength of the leaching solution.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We studied the effects of climate and land-use history on seasonal variations in available soil nutrients at six northern California annual range sites. Available soil N, S, P, Ca, Mg, and K were measured monthly for 2 yr. Seasonal fluctuations in inorganic N were similar for both years over all sites; levels and variations in N were highest during winter and early spring and lowest during summer. Relative levels of available S, P, and Ca were also higher early in the year and declined later in the growing season, although the patterns were much less pronounced. Exchangeable Mg and K fluctuations were generally inconsistent and relatively smaller. Sheep grazing on unimproved pasture significantly (P < 0.05) increased average levels of available soil N, S, Ca, and Mg and decreased P availability. Seeding subclover (Trifolium subterraneum) and fertilizing with P and S increased available N and S levels. Converting chaparral brush to grassland decreased the availability of Mg and K.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Soil development over volcanic Krakatau “tuff” averaged over 10 cm in depth during the 93 years since deposition of the anomalous ash horizon. The A11 and/or A12 horizons overlying the anomalous tuff (C horizon) varied in thickness according to position in the terrain, but were frequently absent due to erosion and slope influences. Subsurface horizons underlying the tuff resembled the A11 and/or A12 with respect to morphological, chemical, and mineralogical properties to a greater extent than the relatively unaltered tuff horizon. Differences in soil genesis between the precisely dated Krakatau tuff and subsequent in situ horizon development set the stage for further investigations related to soil genesis theory.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We measured labile P in a group of non-calcareous agricultural soils by isotopic exchange at four different levels of carrier P and by an anion resin extraction. The soils were from the Ultisol, Alfisol, and Mollisol orders and had been evaluated as low, medium, and high in available P on the basis of soil test calibration studies. Differences among the labile P values determined at the four carrier levels were found in soils low in P, but not in soils having medium and high P contents. Greatest differences were found on the low-P Ultisols and were attributed to32P fixation.The resin P and labile P measurements were comparable on the medium- and high-P Alfisols and Mollisols, indicating that, when difficulties are not encountered with the isotopic technique, the isotopic and resin extraction procedures will measure the same or nearly the same phosphate pool. On the low-P Alfisols and Mollisols, labile P measurements made at the low (4 x 10−6MP) and medium (2 x 10−5MP) carrier P levels most closely approximated the resin P results. A carrier P level within this range is recommended for use on low-to medium-P-fixing soils to minimize problems with the isotopic exchange procedure.On the high-P-fixing Ultisols comparison of isotopically exchangeable labile P with the resin P values showed that the similarity of the results depended on the amorphous Fe and P content of the soils. The results demonstrate that on soils with a high P-fixation capacity, the isotopic exchange technique should not be used to measure labile P, but that labile P can be measured by an anion resin extraction on these, as well as on low-P-fixing soils.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID