摘要:

An analytical solution is presented for one-dimensional solute transport in soil during ponded infiltration. The pore-water velocityv= q/&thetas; in the convection-dispersion transport equation was obtained by assuming that the water flux densityqin the soil can be calculated with the Green-Ampt infiltration model,q = a + b/I, in whichaandbare constrants andIis the cumulative infiltration rate evaluated using Philip's two-term infiltration equation. The water content &thetas; was approximated by the saturated water content, &thetas;s. Through an appropriate transformation, the solute transport equation for transient unsaturated flow conditions was linearized and solved analytically for a general initial concentration profile given by an arbitrary number of straight line segments. The solution compared well with more complete numerical solutions of the transport problem, as well as with several experimental data sets.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

We investigated the validity of a two-flow domain approach for describing physical nonequilibrium behavior of tritium transport in soils. Tritium breakthrough curves (BTCs) were generated from soil columns using miscible displacement methods. Three soils were used: Mahan, Cecil, and Dothan. The predictive capability of the two-flow domain approach in describing two types of tritium BTCs, one with a pulse duration of only few minutes (about 0.03 pore volumes) and the other with a large pulse of approximately one pore volume, was investigated. Large tritium pulse BTCs were used to calibrate the two-flow domain models. Small tritium pulse BTCs were used for model validation where all model parameters wereindependentlyobtained. The use of the two-flow domain model improved descriptions of all BTCs over the one-domain model. Moreover, observed double or bimodal peaks associated with small pulse BTCs were well described using the two-flow domain model. Model sensitivity analyses provided theoretical bases for interpretation of tritium bimodal results and differences of BTCs from large and small input pulses. Distinct double peaks were apparent when a small input pulse (impulse) was applied. In addition, high water flux and small mass transfer coefficient between the two flow domains enhanced the development of double BTC peaks.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Wick samplers have the potential to improve solute sampling in the vadose zone, but more information is needed about the effect of soil-wick sampling interface disturbances on measured fluxes and solute concentrations. The objective of this paper is to examine how the wick sampler alters the matric potential, streamlines, and solute concentrations in the native soil. Both theoretical analysis and experimental studies were performed. An equation for travel time was developed that included the effect of changes in moisture content in the soil when a wick sampler is installed. Experimental measurements of pressure head near the soil-wick interface were taken, and a travel time moment analysis of narrow solute pulses was conducted for several steady flow experiments. Model and theory agreed well and showed that even when the capillary length α−1is similar in the soil and wick, dissimilarity of the hydraulic conductivity and cross-section flow area may significantly affect soil moisture content above the soilwick interface and on the solute pulse travel time. It was also found that in many cases solute pulse travel time was affected more by the pressure head changes that occurred at the soil-wick interface than by the flow through the wick.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Increasing production of beef, poultry, and swine from confined feeding operations in the Southern Plains necessitates that larger amounts of manure be applied to limited areas of agricultural land. If long-term manure applications of nitrogen (N) and phosphorus (P) in manure exceed crop removal, the accumulation of soil N and P can result in levels that pose a problem of concern to both surface and groundwater resources. We investigated the effect of beef feedlot manure, poultry litter, and swine slurry applications (100–1000 kgN and 37–270 kgP ha−1yr−1) for up to 35 years on the forms of N and P in 20 soils from the Southern Plains. Manure applications increased amounts of organic soil N but had little influence on the distribution or availability of N forms measured. In contrast with N, manure increased available inorganic P (IP) fractions 15 to 187 mg kg−1(bicarbonate extractable). Although manure also increased labile bicarbonate extractable organic P (OP) on average 162%, there was a general shift from OP dominace in untreated soils (64%) to IP in treated soils (60%). The major portion of this IP increase was Ca-bound (HCl extractable). The large amounts of Ca added in manure (2–60 g Ca kg−1) tended to dominate inorganic P availability reactions in manure-treated soils relative to untreated soils, even with soils of pH 6.0. Thus, current soil P tests, particularly acid-based extractants (Bray 1 and Mehlich 3), may overestimate soil P levels available for plant uptake or transport in runoff.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

High resolution diffuse reflectance spectra (3113 spectral points) in the near infrared region (NIR) were recorded for 91 soil samples from Israel. Ten soil constituents (total iron [Fe2O3], aluminum [Al2O2], potassium [K2O], and phosphorous [P2O2], loss on ignition residual [LOI], free iron oxides [Fed], aggregate size (1.5–2mm) fraction [F1], average aggregate size (mm) [AVGR], and sodium adsorption percentages [CNaP]) were measured by routine methods employed in soil laboratories. An empirical model to predict each property from its reflectance spectrum in the near infrared spectral region was developed by adapting the near infrared analysis (NIRA) technique. Several data manipulations were used in order to obtain optimum performance. The optimum performance of several soil constituents was found to be at 3113 spectral points (Al2O3, Fed, and K2O) and 310 spectral points (Fe2O3), whereas for others (SiO2, AVGR, and F1) even 25 spectral points provided sufficient performance. Strong support for the capability of NIRA was obtained by a careful examination of the possible correlation between spectrally active soil properties (clay content [CLAY], specific surface area [SSA], hygroscopic moisture [HIGF] and calcite [CaCO3]), which were studied elsewhere, and the featureless constituents studied here. A slight bias was found for the prediction of Al2O3and Fed, and a greater bias was found for K2O, suggesting that further study regarding the prediction of these constituents is needed. It was concluded that NIRA is a very promising vehicle for rapid and nonrestrictive analysis of soil materials.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

The effects of montmorillonite (Osage, Wyoming) with different interlayers on the adsorption, activities, and kinetic properties of acid phosphatase were examined. Hydroxy polymers of aluminum or chromium (200 cmol kg−1clay) were intercalated in montmorillonite in the absence or presence of citric acid (citrate/Al or Cr = 0.1 and 0.5). The activities of acid phosphatase in the presence of different amounts of clay at three pH values (5.0, 5.5, and 6.0) were determined, and the Michaelis-Menten kinetic parameters were calculated. The amount of enzyme adsorbed by interlayered montmorillonite was considerably lower than that by pure montmorillonite and increased as the citrate/Al or Cr ratio increased. The type of interlayer (Al or Cr) influenced the ease with which enzymes could be removed by washing. Complete adsorption of the enzyme led to the formation of clay-enzyme complexes, which had lower activities than the free enzyme. The order of activity of enzymes following adsorption was Cr-montmorillonite > Al-montmorillonite > montmorillonite. The effect of citrate on enzyme activity in the clay-enzyme complexes was significant only at the higher ratio. Factors that caused a reduction in enzyme activity were adsorption by clay, amount of clay, and increase in pH. These effects were modified by the type of interlayers (Al or Cr), the citrate/Al or Cr molar ratio, and the strength of adsorption. In the presence of clay, the Michaelis-Menten affinity constant (Km), increased, whereas the maximum enzyme reaction velocity (Vmax), decreased compared with the free enzyme. The change of the enzyme kinetics by Al- and Cr-interlayered montmorillonite can be described as partial noncompetitive inhibition.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID