摘要:

Surfactants have potential use with respect to in situ removal of organic contaminants from soil. The efficiency and effectiveness of using surfactants for this purpose may depend on their mobility under unsaturated flow conditions. For this reason, transient horizontal unsaturated column tests were used to study anionic surfactant transport characteristics in a loamy soil. Two commercial anionic surfactants, an alkyl ether sulfate (AES) and a linear alkylbenzene sulfonate (LAS), were tested. For each surfactant, the concentration and moisture content profiles plotted versus the Boltzmann transform (column distance/(test time)0.5) exhibited similarity between experiments having the same boundary conditions but different time durations. Concentration profile similarity is an indication that soil/surfactant interactions were reversible and equilibrium conditions quickly achieved for AES and LAS during testing. Penetration of the AES and LAS concentration fronts were, respectively, one-half and one-fifth the advance of the wetting front, indicating a high degree of sorption. Where present at substantial concentrations, both surfactants reduced soil moisture diffusivity values significantly.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

The influence of the amount and kinds of organic and inorganic amendments on phosphorus (P) sorption characteristics was determined on two soils from Oregon, Jory (Xeric Haplohumult) and Tolo (Typic Vitrandept), and three soils from Rwanda, Mata (Sombrihumult), Kibeho (Paleudult), and Kinigi (Typic Placandept). Steer manure (manure), alfalfa(Medicago sativa),or wheat straw(Triticum estivum)residues were added to Jory soil samples at the rates of 1, 2.5, and 5% (wt/wt). Separate Jory soil samples were amended with CaCO3or CaSO4at 1, 1.5 or 3 times the CaCO3equivalent required to neutralize exchangeable aluminum (Al). Other soils received only the highest amount of each soil amendment. After 28 days of incubation, the soil samples were air-dried and P sorption isotherms, pH, exchangeable Al, and extractable phosphorus were determined. Increasing the rate of manure or alfalfa increased pH, P in equilibrium solution, and extractable P and decreased the exchangeable Al. In turn these amendments decreased values for the affinity constant, adsorption maxima, and P sorbed at 0.2 mg P L-1. Soils amended with CaCO3produced results similar to manure and alfalfa but did not markedly influence the extractable P or the affinity constant. Wheat straw had a variable and negligible effect on P sorption in most of the soils. High rates of CaSO4decreased exchangeable Al, but did not affect the pH, extractable P, the affinity constant, and P sorbed at 0.2 mg P L-1(P0.2). Overall, organic amendments with high P content, such as manure and alfalfa, may substitute for CaCO3as a soil amendment to increase pH and decrease P sorption capacity in soils. The magnitude of the response to amendments varied with the type of soil and amendment. However, all soils responded to the application of high rates of manure, alfalfa, or CaCO3.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Previously, we found that organic amendments decreased P sorption that was related to changes in some soil chemical properties (e.g., pH and exchangeable Al). However, addition of organic residue to soils may also affect P sorption by adding PO4(Pi) or releasing organic P (Po) during mineralization of residues and affect redistribution of P among P pools in soils. The objective of this study was to determine the effects of organic amendments (manure, alfalfa(Medicago sativa)and wheat straw(Triticum estivum)compared with inorganic amendments (CaCO3and CaSO4) on P fractions after 28-day incubations. The five acid soils with high P fixation characteristics used in the study were Jory (clayey, mixed, mesic xeric Haplohumult) and Tolo (medial over loamy, mixed, frigid typic Vitrandept) from Oregon, and Mata (Sombrihumult), Kinigi (Placandept), and Kibeho (Paleudult) from Rwanda. Manure and alfalfa residues increased resin Piand NaHCO3-Pi(biologically available) and NaHCO3-Po(readily mineralizable) and NaOH-Pi(chemisorbed) in all soils. The Tolo soil showed the least increase of chemisorbed Piand the greatest increase of resin and NaHCO3-Pi, which corresponded to previous findings of lower P sorption by Tolo than by the other soils. Wheat straw residues had relatively little effect on P fractions as a consequence of its low total P content. In all soils, both NaOH-Pi(and to lesser extent NaOH-Po) increased with manure or alfalfa amendments. These fractions are sites for P sorption; thus, increases in these fractions provide evidence that P-rich organic amendments can decrease future P sorption in soils by reacting with these sorption sites. Calcium carbonate or CaSO4·2H2O had little or no effect on P distribution, indicating that redistribution of P fraction does not occur with reduction in exchangeable Al and Fe (CaSO4and CaCO3) or change in pH (CaCO3).

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Previous studies have shown that organic amendments decreased P sorption and affected distribution of P fractions in soils. The objective of this study was to determine the effects of different amendments on the chemical speciation of P in soil solution. Soil samples of Jory (Xeric Haplohumult) and Tolo (Typic Vitrandept) were treated with 5% manure or 3 times the CaCO3or CaSO4required to neutralize exchangeable Al and incubated for 28 d. After incubation the samples were air-dried and subsequently brought to field capacity with deionized water or with a P solution of KH2PO4(33 mmol P kg-1soil) and allowed to react (equilibrate) for 12 h. Soil solutions were extracted by centrifugation. Total concentrations of metals, inorganic ligands and DOC were measured in the soil solution. The computer program GEOCHEM was used to calculate the concentrations of the free metals, ligands and their complexes. Adding manure decreased the total soluble Al and Fe in soil solution and increased base cations and SO4. Total P in solution increased in: the samples that received manure or CaCO3in Jory soil; and manure or CaSO4in Tolo soil. Phosphorus was oversaturated with respect to strengite and the percent distribution of phosphate with respect to this solid tended to decrease in the presence of manure. Calculation of the ion activity product (LAP) for variscite showed that P was in equilibrium with an amorphous analog of variscite. Citrate of the organic acids measured (malic, maleic, malonic, citrate, succinic, formic, and acetic) was the only organic acid that had a significant effect on P speciation. Model calculations suggest that citrate forms soluble complexes with Al, Ca, and Fe, preventing precipitation of strengite and solid Ca-PO4.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

In several experiments with soils and mineral phases, extraction of Al (and Fe) by pyrophosphate reagent (0.1MNa4P2O7, pH 9.5 - 10.5) was tested with regard to its use for the characterization of Al in humus complexes. Results showed that, independent of the soil content of organic C, pyrophosphate reagent removed nearly the same amount of Al from illuvial horizons of podzolic soils as did acid NH4-oxalate reagent. In some horizons, pyrophosphate extracted even more Al than the NH4-oxalate and dithionite-citrate bicarbonate reagents. Pyrophosphate-extractable Al (mmol kg-1) also exceeded the content of organic acidity (mmolckg-1). Experiments with amorphous Al(OH)3and gibbsite showed high release of Al from these phases by pyrophosphate because of the high pH of the extractant. Adsorbed organic matter increased the solubility of amorphous Al(OH)3, perhaps by enhanced peptization. Pyrophosphate completely removed synthetic coatings of amorphous Al(OH)3from soil material. These results indicate that pyrophosphate-extractable Al may not be attributable only to Al bound in humus complexes, but also to alkaline dissolution of Al hydroxide phases and peptized Al hydroxide associated with adsorbed organic matter. Thus, pyrophosphate should not be used to estimate Al in humus complexes.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Inorganic reactions supplying soil phosphate (P) to plants depend on the quantity (Q) of available P and on the solution concentration (intensity (I)). A critical factor in the description ofQ/Irelationships of different soils is the time-dependence of the reactions and the lack of standardization of methods of observation. Here we compare two methods for measuringQ/Irelationships. Increasing P amounts were added to soil suspensions, and the sensitivity ofQ/Ito times of equilibration from 0.4 to 10 days was tested using: (i) the added P removed from solution, i.e., the sorbed P (Ps) vs. the P concentration in soil solution (CP); and (ii) the time-dependent amount of isotopically exchangeable P (E) vs. CP. Relationships were determined for both a tropical soil and a temperate soil with low P sorption capacity by adding P to obtainCpup to 10 mgL-1. TheCp,Ps, andEvalues increased with increasing P rates and decreased with equilibration time. Regression constants forPsvs. CPcurves differ by a factor greater than 2 between 0.4 and 10 days of equilibration, whereas regression constants forE vs. CPcurves are only slightly (<10%) affected. This is explained by the fact thatE vs. CPcurves describe the dynamic in the kinetic of gross exchanges between P in solution and both the added P, which was sorbed, and the pre-existing P, onto the soil solid phase, whereas thePsvs. CPcurves only characterize the dynamic in the net exchange of added P after a defined period of equilibration. The use ofPsvs. CPcurves is, therefore, limited to comparisons under identical experimental conditions, invalidating many comparisons between published values, whereasE vs. CPcurves allow equilibration time-independent comparisons. BecauseE vs. CPcurves are not strongly affected by times of equilibration, they better assess Q/I relationships of soil P supply, which is necessary to gain insight into the understanding and description of phosphate supply to plants.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID