摘要:

Besides the 10 common failings that can confront earth scientists, as recently listed in a book by S. A. Schumm (1991, To interpret the earth: Ten ways to be wrong. Cambridge University Press, Cambridge), submitted manuscripts and published papers frequently have problems with the improper use of regressions or of statistics in general and with what is termed in this note fortuitous results due to compensating errors. These are defined as several minor inaccuracies having opposite signs which cancel each other and produce apparently reasonable results. This occurrence seems common not only in complex analytical procedures but also when gross simplifications of manifold data are employed or unwarranted extrapolations are made. Several examples from the soil science literature are discussed. Reasonable results based on dubious premises should not be propagated. A call is made for a more critical evaluation of data based on a better understanding of soil processes.

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Eleven soil cores (30–40 cm length, primarily O2/A/B, soil type: volcanogenous regosol) were collected near fumaroles in Oniishi, Osorezan, an active volcanic region of Japan. The retrieved cores were cut into ca. 5-cm sections and analyzed for pH, C and N exchangeable (Ex-) cations, and chemical states of S. The soils exhibited extremely low pH {pH(H2O): 2.49–3.93, av. = 3.21; pH(KCl): 2.06–3.42, av. = 2.80)} and were depleted not only in Ex-base cations (base saturation: 0.2–19, av. = 3.8%), but, to a considerable extent, in Ex-Al. The short-term pH-buffering of soil appears to involve Fe-oxide dissolution and subsequent Fe3+-hydrolysis in the soil water and H+-exchange at strong acid sites where soluble and insoluble organic matter and clays are present. About 90% of cation exchange capacity (CEC) resulted from organic matter in the organic (av. C = 19.4%) layers, while more than 80% of CEC was due to clays and Fe-oxides in the mineral (av. C = 4.4%) layers. In spite of the continuous exposure of soil to volcanic H2S up to 2300 μg S/cm2/month, S-species other than organic S and SO42-could not be detected in the soil, except for FeS2, which was present as a minor S-constituent at the surface, suggesting rapid H2S-oxidation. SO42-was retained by poorly crystallized Fe-oxides in the mineral layers not only by adsorption, but also by occlusion, although such SO4-retention was inhibited by organic matter. A dense population ofSasa kurilensissignificantly affected the soil chemistry, probably due to supply of fresh litter and recycling of elements within the plant-rhizosphere ecosystem.

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Changes in the chemistry of a Ferriorthic Podzol soil are studied by comparing a field site covered since 1890 with an exposed site. Analytical chemistry data for composite samples from the A2, A2/B, B, B/C, and C horizons were used. The exposed site has a higher exchangeable acidity in the four upper horizons and a lower base saturation in the A2, A2/B, and B/C horizons. The content of nonextractable metal cations is markedly lower in the exposed site, and the amount of extractable metal cations is larger. This is interpreted as the effect of more intense weathering due mostly to infiltrated acidic precipitation. The results reveal that long-term changes of the soil chemistry, including the estimation of metal fluxes, can be determined by this method.

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

A device to monitor matric potentials in soils was designed and constructed to automatically scan and log eight individual tensiometers, each using their own pressure transducer. Differences in pressure of 26.9 Pa in the range of 0 to –90.22 kPa can be detected. The measuring and logging part is based upon a Basic-programmable single board data logger. Using a set of commands the device can be operated by a computer through an RS232 serial interface, for example to program the scanning interval, to retrieve stored measurements, or to check the status of the device. By using an internal routine that determines a linear calibration line, it is possible to retrieve measurements directly in any unit desired, for example cm water column, kPa, or PSI. The apparatus can also be used as a stand-alone battery-operated device, as a front-end device giving eight voltage signals proportional to the measured pressures, or as an intelligent slave module in a large measuring system. The device is built into a small, waterproof of epoxy box so that it can be installed into the ground. It is also equipped with a valve system that enables flushing of the connected tensiometers so that the device with tensiometers can remain installed for an indefinite period of time.

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Theory describing heat and water transfer in porous media is tested for various experimental conditions: three initial soil water contents (0.08, 0.14, and 0.18 m3/m3) and three mean soil temperatures (10, 27, and 50°C). The experiments are performed in horizontal closed soil columns. The soil columns are unsaturated, and all are nonisothermal with a temperature gradient of 100°C/m. Two approaches are used to estimate water transport coefficients. One approach is empirical, making use of observations of steady-state heat and water distributions, whereas the other approach is to compute coefficients based upon earlier theoretical development. Predicted soil temperature distributions are similar to observations for all columns. Predicted soil water content values compare well with observed values when the initial soil water content is greater than 0.14 m3/m3. For initial soil water content of 0.08 m3/m3, prediction by using theoretical transport coefficients overestimate observed soil water contents at positions close to the hot temperature boundary. Predictions of soil water contents by using empirical transport coefficients are within the observations.Theory using either empirical or theoretical values of transport coefficients predicts soil water distributions well for mean temperatures of less than 27°C. For columns with a mean soil temperature of 50°C, predictions using the theoretical transport coefficients overestimate soil water content at positions close to the cold end.Columns of initial soil water content of 0.14 had the largest net water transfer from the hot half to the cold half. Columns of initial soil water content of 0.08 m3/m3had the lowest net water transfer. Increasing column mean soil temperature caused the net water transfer to increase.

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

This paper presents an approximate analytical solution for a nonlinear irreversible reaction involving the movement of solute when two substrates are involved. The presence of the second substrate determines when the reaction will proceed. The implicit solution obtained enables the continuum of irreversible reactions to be explored through the Michaelis-Menten form. The effect of the second substrate being present or not at the start of the reaction is investigated. Validation of the approximate analytical solution is achieved by systematic comparison with a numerical solution. The effect of boundary conditions on the solution for a finite column is examined. With a change from aerobic to anaerobic conditions initially, the effect on the breakthrough curves and concentration profiles of having a flux-concentration inlet boundary condition with a zero-flux outlet condition for a finite column is compared with a fixed-concentration inlet condition for a semi-infinite column. The approximate solution is also applied to an experimental breakthrough curve to estimate nonlinear denitrification parameters.

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Development of expert systems and appropriate integrative models for management of crop production and water quality in irrigated agriculture has been limited because of extensive data collection requirements in the field. Remote, automated sensing of atmospheric conditions of the soil-plant-atmosphere continuum has been demonstrated; however, similar such systems for plant and soil parameters of importance have yet to be developed. This paper proposes a conceptual model for an integrated soil-plant-atmosphere sensor network as well as an automated, microprocessor-controlled circuit capable of monitoring remote soil sensors.

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Many soil nitrogen studies have included estimations of nitrification or denitrification rates in soil column systems based on simple mass balance considerations. This approach does not take into account the effect of the solute dispersion. The present study presents a simple, inverse finite difference model (IFDM) for estimating temporal and spatial variations in nitrification or denitrification rates from measured nitrogen concentration profiles at steady water flow. The model takes into account both convective and dispersive transport of nitrogen by using a Crank-Nicolson finite-difference discretization of a paraphrased convection-dispersion equation for solute transport including a reaction term. A test procedure is suggested and used to find criteria for avoiding numerical errors in the calculations. Significant numerical errors are inherent in the IFDM but can be avoided if the depth increment and the ratio of time increment to depth increment are chosen carefully. The possible applications of the simple IFDM are illustrated by using the model on soil column data for rapid, continuous leaching of nitrate through water-saturated porous media at steady water flow. The IFDM-based analysis showed a large influence of soil composition and temperature on the temporal and spatial variations in nitrate removal rates. The IFDM assumes constant pore water velocity and solute dispersion coefficient. In order to use the IFDM not only for qualitative but also for quantitative predictions, these two parameters need to be carefully measured.

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

Mineral stability in soils can be affected by seasonal changes in parameters such as solution composition and temperature. This study investigated the effects of seasonal changes in soil temperature and soil solution composition of a subalpine Spodosol on the stability of the soil clay minerals. Soil solutions were collected monthly using two methods—centrifugation and lysimetry; these two methods were utilized to determine if collection method would affect detection of seasonal differences. Stability diagrams were developed for E, Bs, and C soil horizons. As temperature effects on mineral equilibrium constants were found to be substantial in this high-elevation system, the average seasonal temperature of each horizon was used to determine mineral equilibrium lines. Stability diagrams show differences in mineral stability among horizons and between solution types. Lysimeter solutions do not show seasonal differences in mineral stability; however, the centrifuge solutions do indicate differences in mineral stability with season. An overall pattern of mineral dissolution in spring and stability in summer was found for clay minerals using the centrifuge solutions; stability during fall and winter is mineral-dependent. Changes in solution H4SiO4were the most important factor in mineral stability of the E horizon. The seasonal path of the centrifuge solutions relative to mineral equilibrium lines varies among horizons. This seasonal cycle of mineral stability was evident in a temperate subalpine soil where environmental changes between seasons are substantial, but such cycles of mineral stability could also occur with other climatic regions.

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1992

数据来源: OVID