摘要:

The Green-Ampt equation developed early in this century is regaining popularity in describing the infiltration of water into the soil as a function of time. The parameters defining the Green-Ampt equation have physical bases, and they can be determined from the physical properties of the soil. However, small variations in the Green-Ampt parameters may result in large deviations in the predicted values of the cumulative infiltration. In this report, I present a nonlinear least-squares scheme for estimation of the hydraulic conductivity,K, the product of available porosity,n, and the capillary pressure head, &phis;t, which appear in the Green-Ampt equation. The method developed requires only infiltrometer data on cumulative infiltration measured at specified times. Four case studies investigated show that, in general, the method calculates the hydraulic conductivity lower and the capillary pressure head higher than do methods reported in literature.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

In this report, we compare three methods (second- and third-order Taylor polynomials and cubic spline) for determining the apparent soil thermal diffusivity as a function of depth through the analysis of time-depth observations of soil temperature. Three methods are tested by using both field data measured in the upper 0.10 m of soil in a corn field and hypothetical data generated by numerical approximation of the partial differential heat transfer equation. The field and generated data are fitted with Fourier series for estimating the temperature parameters (amplitude and phase angle of the temperature wave) and the heat flux phase. The second- and third-order Taylor polynomials and cubic splines are used to estimate the change of temperature parameters with depth. Theories describing heat transfer in uniform and non-uniform soil both use the temperature parameters to calculate soil thermal diffusivity. In general, the cubic spline approach provides reliable values of the apparent soil thermal diffusivity, whereas the second- and third-order Taylor polynomials for the case of nonuniform soil heat transfer sometimes provide physically unrealistic negative values. The results also show the failure of the uniform soil heat transfer theory (amplitude and phase equation) for estimating the thermal diffusivity in non-uniform soil.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Investigations were conducted to provide basic data on the status and distribution of tree oxides in soils overlying limestone in Nigeria. Soils from 13 profiles collected at Ashaka, Sokoto, Gboko, Nkalagwu, Calabar, Ewekoro, and Shagamu were used for this study. The acid-ammonium oxalate and dithionite-citrate-bicarbonate methods were used to extract the free iron from the samples. Iron oxide values obtained with these two extractants were compared. The Fedvalues are higher than the FeOvalues in some of the soils, indicating that a considerable fraction is present in crystalline form. There is co-migration of clay with iron oxide in some of the soils, and this is also evident in the profile distribution of the clay/Fedratio in such soils.The Feo/Fedratio (diagnostic index) values obtained could not be used to separate poorly drained soils from well-drained soils, but their active ratio values estimate the degree of soil development.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

A total of 27 different peat types from Sweden were characterized. Botanical composition, particle-size distribution, elementary constituents, degree of decomposition, calorific value, and concentrations of monosaccharide, amino sugar, amino acid constituents, and bitumen were determined. Altogether 62 variables were recorded. The results were examined using principal component analysis (PCA) to probe any relationship between different peat properties and to group similar peat samples. The 41 samples separated into eight different groups.The main distinction between these peat samples could be explained by differences in the relative amounts ofCarexandSphagnumremains.Carexplants generally seem to be more chemically transformed through microbial decomposition than theSphagnumfragments, which, in combination with differences in the original chemical compositions, causes chemical dissimilarities between the peat samples. Differences in the degradation pattern forSphagnumandCarexpeats were found when two separate PCAs on parts of the sample set were made.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We conducted an investigation to study the relationship of soil fabric and particle-size distribution in a Davidson soil. Samples were taken from genetic horizons of five pedons of a Davidson soil located at different locations in the Southern Piedmont of Georgia. Thin sections were prepared, and analyses were performed to determine particle-size distribution and bulk density. The Normal Related Distribution Pattern (NRDP) of the soil fabric was determined by superimposing the particle-size distribution data on a NRDP triangle. Three types of NRDPs were detected, and we present a proposal to classify them (in the order of increased plasma content) as (1) phyrograni-, (2) granophyri-, and (3) plasmi-porphyric. There was a tendency for the Ap horizons to be characterized by a phyrograni-porphyric; the Bt1 and Bt2 horizons by a granophyri-; the Bt3, Bt4, and Bt6 horizons by a plasmi-; and the BC and C horizons by a granophyri-porphyric fabric. The occurrence of a particular NRDP in each soil horizon was confirmed by statistical analysis. There was a close relationship between clay contents and types of NRDP. More research is necessary for a definite conclusion on this matter. Once the correlation between particle-size distribution and NRDP is firmly established, types of soil fabrics can be determined simply by determining particle-size distribution and projecting the data in a NRDP triangle.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

An analytical solution of the soil-gas diffusion equation coupled with the convective-dispersive solute transport equation under transient conditions is presented. A first-order transformation scheme, a linear, equilibrium, solute adsorption isotherm, gas transport by diffusion, and equilibrium gas solubility were assumed. The solution was obtained by means of Laplace transforms for zero initial concentrations and semi-infinite conditions for both species. Depth and time distribution profiles for soil gas were computed for the intervals 0 <t<,t1, andt>t1, wheret1= time of solute application. Measured values of N2O produced and transported simultaneously with a pulse of NO3- fertilizer in a 1.0-m long soil column were used to demonstrate the applicability of the solution. By using a fitted soil-gas diffusivity and a denitrification rate constant, reasonable agreement was found between predicted and experimental concentration profiles of N2O, especially for early times.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The use of gypsum or phosphogypsum (PG) as an ameliorant of subsoil acidity has been reported. However, the role of these amendments in aluminum (Al) speciation and solubility is not clearly understood. We studied the root growth of soybean [Glycine max(L.) Merr.] cv. Lee in dilute nutrient solution containing 2.0 g L−1PG without the addition of Al or in solutions containing 40 μM Al without any amendments or with the addition of PG, CaSO4. 2H2O, or CaSO4. 2H2O plus varying concentrations of P and F. The prediction of Al speciation by using the GEOCHEM computer program revealed that in solutions containing F∼, either added as NaF or as impurities in the PG, Al was entirely complexed with F∼. The addition of CaSO4. 2H2O (2.07 g L−1) to a solution containing 40 μMAl decreased the predicted activity of Al3+from 36 to 11% and increased that of AlSO4+from 33 to 80%, while the total root length of soybean increased by about fourfold. Addition of PG (2 g L−1) to a solution containing no Al decreased the total root length by 14%. Root growth was very similar in PG-amended solutions with or without the addition of 40 μMAl. The addition of 400 μMF∼ as NaF to Al solutions amended with CaSO4. 2H2O seemed to decrease root growth as compared to that in solutions amended with CaSO4. 2H2O without the addition of F∼. Root growth was very poorly related to the sum of predicted activities of Al monomers. Aluminum measured by the modified aluminon technique (without preacidification and preheating of the solution; 30-min reaction time) failed to exclude Al complexed with SO42-and F∼, which are less phyto-toxic. Therefore, this measure of Al showed a poor relationship with root growth response. On the contrary, Al measured by the modified 8-hydroxyquinoline technique (15 s reaction) excluded about 92% of Al complexed with F∼, although it failed to exclude Al complexed with SO42-. Thus, both of the Al assay techniques used in the present study are poor indicators of Al toxicity when the SO42-ligand plays a major role in the alleviation of Al toxicity. However, Al measured by the modified 8-hydroxyquinoline technique was a better indicator than that measured by the modified aluminon technique when the F∼ligand was responsible for the alleviation of Al phytotoxicity.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Multidimensional spatial processes are often encountered when soil variables such as temperature and water and salt content are observed as a function of space and time. Time- or spatial-domain methods based on state-space models are useful for describing the movement of these series through space and time. The detection of important periodicities can be accomplished using frequency-domain generalizations of regression and analysis of variance. These periodicities and the movement of these series through space or time reflect the nature of the soil-forming processes, agricultural practices (such as cultivation, irrigation, and fertilization) and the interdependency of these variables. Two experiments were conducted in the San Joaquin Valley of California to observe changes in soil properties over space as a result of different quality and quantity of irrigation water and to observe the cyclic behavior of soil properties as affected by quality of irrigation water and other agricultural practices. A number of spatial techniques were used to illustrate these changes.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Several methods for determining the hydraulic conductivity-volumetric water content relationship have been developed. We evaluated on a sand dune soil three different methods for determining hydraulic conductivity values. The first method is known as the internal drainage-instantaneous profile method and was carried out on the field. The second method was analogous to the first but was carried out in the laboratory. The results obtained by these two experimental techniques were then used as a reference for comparing with the hydraulic conductivity functions predicted by the third method, mathematical models. For this numerical approach, the Jackson and the Mualem formulation was selected. For the coarse-textured soil used in this investigation, all three methods resulted in hydraulic conductivity functions that were in fairly good agreement. Moreover, the differences between the laboratory experiment and the field experiment were greater than the deviations of the mathematical models, although subtle differences were found. It seemed that Mualem's model for calculating the hydraulic conductivity function, combined with the van Genuchten equation for the soil water retention equation, is the easiest to use and leads to the most accurate results for this particular soil.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Model simulations of the effects of increases in atmospheric carbon dioxide on air temperature, precipitation, and soil moisture suggest that the resultant “greenhouse effect” will be bad for agriculture. Experimental evidence, however, indicates otherwise, demonstrating that plants can more than compensate for the predicted adverse climatic changes. Indeed, recent evidence from around the globe suggests that a carbon-dioxide-induced stimulation of the biosphere is already in progress.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID