摘要:

Theoretical evaluations reported in the literature disagree with respect to which is the valid exchange expression for determining ideal solid solution behavior and for calculating adsorbed-ion activity coefficients. One group of scientists argues that the Argersinger approach, which uses the Vanselow exchange equation and employs the mole fraction, is the correct approach. Another group argues that the Gaines and Thomas approach, which employs charge fractions, is equally valid and whichever of the two is used in soils is a matter of preference. Because the two approaches lead to different numerical answers, a need exists for an algebraic evaluation of the interrelationships between the two equations (Vanselow versus Gaines and Thomas). Additionally, a need exists to establish differences between the two approaches for estimating and evaluating thermodynamic parameters statistically, employing experimental data. In this study, algebraic analysis of the interrelationship between the Vanselow (Kv) and Gaines and Thomas (Kc) exchange selectivity coefficients for monovalent-bivalent exchange (Na+– M2+;M= Ca2+or Mg2+) showed thatKc= 0.5K→vwhenENa→ 0 and whenENa→ 1,Kc= 0.71Kv(ENa= charge fraction of Na+on the exchanger). The overall relationship betweenKvandKc,Kc= (Kv)[1 +ENa]1/2, is slightly curvilinear. Furthermore, it is shown that the correspondingKvandKcadsorbed-ion activity coefficients γiandfi, respectively, are interrelated byfNa/γNa= 2/(1 +ENa) andfM/γM= 1/(1 +ENa). We tested the above relationships by employing previously reported experimental data for Na-Ca and Na-Mg exchange of clay minerals and soil, carried out in perchlorate background media. The results of the experimental data confirm that these interrelationships are met.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Isothermal capillary rise was allowed from a fixed water table in soil columns of different soils of Haryana, India, to continue til the maximum height of capillary rise was reached. Maximal capillary rise fluxqmwas monitored along the advancing wetting front at various heights in the soil columns. Theqmdata fit satisfactorily the analytical solution of a flow equation with hydraulic conductivityK(h)being related exponentially with suctionhasK(h)=ae−b(h-h→), wherehais the air entry suction head. The saturated hydraulic conductivityK, and wilting point &thetas;wpwere related empirically to the soil constantsAandb. The empirical relationships established were ln (A/a) = 5.636 + 1.326 x 10−6K→– 0.31 &thetas;wp; andb= 0.1068 + 6.547 x 10−8K→– 4.563 x 10−3&thetas;wp, whereA=aebh→. This may be used for determining more simply and quickly the maximal capillary rise fluxqmas a function of height from water tablez, and the hydraulic conductivityKas a function of suctionhfrom the readily determinableK→and &thetas;wp. Air entry valueh→is also shown to be estimated fromK→and &thetas;wp.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We conducted an experiment in 27 large columns to determine the impact of soil type (sandy loam, silt loam and clay), salinity of irrigation water (1.5, 3.0, and 6.0 dS m−1), and leaching fraction (drainage/irrigation, 0.09, 0.18, and 0.27) on oxygen diffusion rate measurements (ODR) taken with platinum electrodes. Electrodes were left in place (15, 30, and 60 cm deep), and ODR was measured over a 6-mo period. At the end of 6 mo, electrodes were removed and observed under a low-magnification microscope for the presence or absence of precipitate. Selected electrodes were then photographed under a scanning electron microscope, analyzed using x-ray diffraction techniques, and analyzed for percentage of atom composition using x-ray photoelectron spectroscopy. Results indicated that soil type, salinity, and leaching fraction all influenced ODR measurements. The formation of precipitate on the platinum electrodes was observed equally in all three soils, but to a greater extent under high salinity and low leaching fraction conditions at the greater depths. Precipitate composition was similar to soil composition in both the silt loam and clay soils, but poor agreement was observed in the sandy loam soil, as indicated by Si/Al and C/O ratios. Results would suggest that aluminosilicates were either incorporated into calcium carbonate as it precipitated out of solution onto the platinum or platinum oxides in the presence of high salinity and calcium were bridged to aluminosilicates through a charged exchange reaction.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

This work provides data on the interaction of fulvic acids extracted from a Spodosol soil, dissolved in water, with other aqueous solutions of various pesticides (amitrole, chlordimeform, diquat, and paraquat) in diverse concentrations. A strong interaction was observed, precipitates appearing that were more abundant with greater concentrations of the pesticide used. Both the weights of the precipitates obtained and the coloring of the equilibrium solutions indicate that some FA persist in solution in spite of an excess of pesticide. The quantity of precipitate followed the order: diquat > paraquat > chlordimeform >> amitrole. The interaction mechanisms between the FA and the pesticides were determined by infrared spectroscopy. The adsorption of these pesticides by FA is a cation-exchange process to which are added H-bonding and charge-transfer mechanisms.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Polymers have been demonstrated to improve soil physical properties under some conditions. This study was conducted to determine the effects of polyanions on a soil that was treated to severely disrupt the aggregates. Three negatively charged polymers, two polyacrylamides and a polysaccharide guar, were tested as soil conditioners. Arlington loamy soil was structurally disrupted under different conditions. The buildup of new aggregates and their stability after treatment were determined by dry- and wet-sieving, respectively. Treatment with polymers affected soil aggregation positively, negatively, or neutrally as compared with no polymer treatment, depending on specific experimental variables. Despite complex interaction between various treatment variables, the resultant comparative effects of various treatments were qualitatively the same for both aggregate stability under wet-sieving and the weight of <53-μm aggregates under dry-sieving.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We performed two greenhouse trials to determine the effects of 0, 0.2, 2.0, 20.0, and 200.0 kg ha−1of polyacrylamide (PAM), a soil conditioner, on seedling emergence of sideoats grama (Bouteloua curtipendula[Michx.] Torr.), alkali sacaton (Sporobolous airoides[Torr.] Torr.), and Boer lovegrass (Erogrostis chloromelasSteud.). The pots of the first experiment were irrigated every 5 d, and pots in the second experiment were irrigated every 8 d. A soil with unfavorable physical conditions and with a history of crusting was used as a support medium. Shear strength and water infiltration were also evaluated.Emergence of 100% within 22 d of planting for sideoats grama was obtained in experiment 1 with 200 kg ha−1PAM application. As expected, the real effect of PAM was more noticeable in the second experiment, where emergence of 100% was noted for both 20− and 200-kg-ha−1PAM applications, though only 50% emergence occurred in control pots. No significant differences in seedling emergence were found for alkali sacaton in experiment 1. In experiment 2, however, significantly more seedlings were obtained in PAM treatments than in the control pots. Plants of alkali sacaton became desiccated 1 month after emergence. Boer lovegrass emergence was not improved with PAM applications in experiment 1, but in experiment 2, more seedlings were obtained with PAM applications. Like plants of alkali sacaton, Boer lovegrass began desiccating 1 mo after emergence.Values of shear strength showed that PAM worked well as an anticrustant amendment. In general, as PAM rates increased, shear strength values decreased. Infiltration rates did not show a clear trend; infiltration was improved in experiment 1, but no effect was noted for experiment 2. It seems reasonable to conclude that application of PAM may be a viable method of assuring good stand development of seeded grasses on crusting range soils.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We studied the spatial auto- and covariation in the growth of 264 trees and their root zone soil sodicity in a fine loamy natric Haplustalf sampled from four depths at 30-cm increments by the regionalized variable theory. Stochastic heterogeneity was modeled after the deterministic trend was removed nonparametrically. Variability in the soil pH, sodium adsorption ratio (SAR), and DTPA-extractable Na and in tree height measured 1, 2, and 3 yr after planting was anisotropically spatially structured. Interdependence between soil sodicity and tree growth was also anisotropically spatially distributed. Autovariability, and especially cross-variability, was relatively higher in the northwest to southeast direction than in the northeast to southwest direction. Cauchy-Schwarz's condition of inequality of cross-variogram functions was always satisfied. Predictability of variation of the two intrinsic random fields was validated by computing various statistics of the values kriged by jackknifing and actually measured observations. Possibilities of improving the precision of evaluating afforestation techniques through spatially sensitive statistical procedures for realizing better management of sodic soils are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We studied the retention of 15 elements by 11 soils from 10 soil orders to determine the effects of element and soil properties on the magnitude of the Freundlich parametersKdandn. The magnitude ofKdandnwas related to both soil and element properties. Strongly retained elements, such as Cu, Hg, Pb, V, and P had the highestKdvalues. The transition metal cations Co and Ni had similarKdandnvalues, as did the group IIB elements Zn and Cd. Oxyanion species tended to have lowernvalues than did cation species. Soil pH and CEC were significantly correlated with logKdvalues for cation species. High pH and high CEC soils retained greater quantities of the cation species than did low pH and low CEC soils. A significant negative correlation between soil pH and the Freundlich parameternwas observed for cation species, whereas a significant positive correlation between soil pH andnfor Cr(VI) was found. Greater quantities of anion species were retained by soils with high amounts of amorphous iron oxides, aluminum oxides, and amorphous material than were retained by soils with low amounts of these minerals. Several anion species were not retained by high pH soils. Despite the facts that element retention by soils is the result of many interacting processes and that many factors influence retention, significant relationships among retention parameters and soil and element properties exist even among soils with greatly different characteristics.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Forest soil on a 23-ha watershed in New Hampshire was sampled quantitatively by excavating 60 0.5-m2pits by horizon in the forest floor and depth strata in the mineral soil. Carbon (C), organic matter (OM), and bulk density (BD) were measured to determine relationships among these properties by soil depth. Because BD and soil depth are frequently used to estimate soil C reserves, we wished to compare actual measured values with values predicted by regression analyses. Bulk density was calculated based on measured soil mass and soil volume exclusive of the > 2-mm coarse fragments. Standard methods were used to determine soil carbon and organic matter. Carbon concentration decreased more rapidly with depth than OM concentration, resulting in a decrease in C/OM ratio from 0.56 in the Oi + Oe of the forest floor to 0.44 in the Bs2 horizon. The accuracy of estimates of soil C reserves can be improved by employing C by OM regressions developed by horizon or depth strata. The relationship between bulk density and organic matter in the mineral soil is described by a regression equation similar to equations developed in other New England forest soils. The similarity between OM and BD regressions observed in this study and those reported for other New England forest soils using other methods supports the use of OM measurements to obtain estimates of bulk density for use in the calculation of soil C pools.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID