摘要:

A nonlinear Extended Kalman Filter approach is used to explicitly account for measurement and model uncertainty in field soil hydraulic conductivity function determination. The standard deviation that such a procedure provides for hydraulic conductivity, as a function of water content, is estimated from water content and matric potential measurements. These measurements were obtained following 43 days of water redistribution in a two-layer soil profile previously ponded with water. Except for a brief initial period during redistribution, water content changes can be described with a single exponential conductivity function. Also, reducing the frequency of measurements by 50|X% and 80|X% would change the mean hydraulic conductivity function less than -|Mp1. standard deviation, i.e., half an order of magnitude. The filtering scheme, which accounts for both model and measurement uncertainty, provides an improved description of in situ hydraulic conductivity functions when compared with previous methods, which fail to supply fiducial limits of uncertainty

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Simulation models of soil drying require relationships between the water content of the soil and the energy status (water activity or potential) of the soil water. A simple, one-parameter model has been found to be adequate for many such simulations. The model has the form:h= exp {−(Mw/RT)exp[(1 −w/w1)ln(−ψo)]} wherehis equilibrium relative humidity or water activity; MwR, and T are molecular mass of water, gas constant, and Kelvin temperature;wis gravimetric water content; and ψois the water potential of oven dry soil. The parameter, w1, is soil dependent, but can be predicted from measurements of clay fraction or air dry water content. Regression fits for the one-parameter model, using data from nine soils with different clay content, were comparable to those obtained with the three-parameter Fink-Jackson model.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The authors present an initial version of a soil classification system based on selected soil properties believed to be useful in describing water and chemical transport through soils. The system is based primarily on surface texture, clay mineralogy, and nature of soil structure. We now have developed this system for the more extensive soil series in South Carolina, and these soils have been grouped into eight different classes. While variability of some soil properties within a given class certainly exists, a class is distinct from each of the other seven classes in water and chemical transport characteristics. A classification system such as this can help to identify those soil properties that most affect transport processes and will help to provide the framework for development of mathematical transport models that incorporate these same soil properties.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Information on the effect of temperature on B adsorption by soils and soil minerals is scant. These data are needed to understand B availability. Boron adsorption on goethite, gibbsite, kaolinite, montmorillonite, calcite, and two arid zone soils was investigated as a function of solution pH (3–12) and reaction temperature (10, 25, and 40|MoC) after 2 h of reaction time. Boron adsorption on all materials increased from pH 3 to 7, exhibited a peak at pH 7.5 to 10, and decreased from pH 10.5 to 12. Temperature dependence measured as the increase of the B adsorption maximum at 10|MoC compared with 40|MoC on reference minerals increased in the order: calcite (3|X%) < goethite (7|X%) < gibbsite (18|X%) < montmorillonite (-20|X%) < kaolinite (26|X%). The kaolinitic soil exhibited greater temperature dependence than the smectitic soil. The B adsorption reaction was exothermic since B adsorption decreased with increasing temperature for all materials, except for montmorillonite at high pH. Highly specific ion adsorption is expected to be exothermic, suggesting an inner-sphere adsorption mechanism for B on all reference minerals except montmorillonite.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Predicting N availability from legumes to a subsequent crop has been problematic. We tested the hypothesis that corn (Zea maysL.) grain yield and whole plant N accumulation could be predicted from N mineralization indexes of soil samples containing representative amounts of incorporated residues from the previous crop. Soil samples were taken from a crop rotation study conducted at four locations in Minnesota, in which corn was grown following eight crop treatments, including fallow, alfalfa (Medicago sativaL.), soybeans [Glycine maxL. (Merr.)], corn, and wheat (Triticum aestivumL.). Corn received from 0 to 224 kg of fertilizer N/ha. Soil was procured from the plow layer during the 2 weeks before planting and to 1.5 m (for inorganic N) within 1 week after planting. Subsamples were subjected to acid permanganate, autoclave, and glucose extractions, inorganic N determination, and aerobic and anaerobic incubations. With stepwise multiple regression, 1 week of aerobic incubation contributed as much as did incubation times up to 12 weeks to models of grain yield and total N uptake at physiological maturity. Results of acid permanganate, autoclave, and glucose extractions, and of anaerobic incubation did not consistently contribute to the models. Over all locations, topsoil inorganic N and 1 week of aerobic incubation explained between 65 and 81|X% of the variability in grain yield and total N accumulation of nonfertilized corn. For fertilized corn, N application rate alone accounted for the majority of variability in grain yield and total N uptake. Two independent crop rotation experiments provided data used to validate the predictive capability of the regression models. Despite promising relationships derived from the initial experiment, results from validation experiments were not reliably predicted by these equations. Although analyses of soil samples containing crop residues for inorganic soil N and a particular N mineralization index may relate well to yield and N uptake by corn in a given year, variability among years may preclude general use of these models for predictive purposes.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

This is a study of a sequence of five soils developed in the Red River valley of Vietnam along a transect extending from the foothills to old terraces. Most of these soils are chemically depleted, having, in particular, a very low CEC. The mineralogical study shows that the

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Modification of subsoil characteristics caused by drainage tile installation was examined on loamy glacial till soils in Nova Scotia and New Brunswick, Canada. The objectives were to evaluate the effects of different drain line installation techniques, trenchless vs. trenching, and system age on subsoil physical characteristics. The area of disturbance caused by trenching (both machine and hand dug) tends to be uniformly 30–40 cm wide in the subsoil portion of the profile, whereas a zone of disturbance 7–17 cm wide was created by the trenchless plow. Although both methods result in bulk density of the disturbed subsoil being significantly lower than the undisturbed subsoil, disturbance caused by trenching exhibited lower bulk density than that of the trenchless plow. Percent reduction in bulk density did not significantly change over time periods of up to 30–40 years. Increase in macroporosity of disturbed subsoils correlates significantly with reduction in bulk density. With increase in macropores, saturated hydraulic conductivity of the disturbed subsoil was significantly higher than found originally, except in newly drained (1 and 2 years) fine-loamy till soils. Saturated hydraulic conductivity of disturbed subsoils resulting from trenching was significantly higher than that of the trenchless plow. Although not always statistically significant, organic carbon content of the disturbed subsoil was considerably higher than that of the undisturbed. The difference in organic carbon between the disturbed and the undisturbed subsoils decreased with increasing time. A significant correlation was found between the loga rithm of the rate of organic carbon decomposition and average age of installation (r2= 0.9). This indicates that the shallow rooted crops being grown (corn and forages) did not, or could not, possibly because of low pH values, take advantage of the modified subsoil conditions created since little organic matter from decaying roots was added to the disturbed soil mass. As a result of subsoil modifications, surface soil moisture content immediately above the drain line was lower than the adjacent surface soil.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Thousands of hectares of wildlands are burned annually in the western United States. The composition and mineralogy of wood-ash produced by severe burning, and the changes in pH of soils underlying the ash, were examined at five sites in Califor-nia. Soil pH increased by as much as 3 pH units (to pH 10.5) immediately after burn-ing compared with unburned soil. Approx-imately 1 to 2% of each burn area was affected to a maximum observed depth of 20 cm. The major component of fresh, white wood-ash is calcite, while K and Na carbonates are present in minor amounts. The initial very high pH values of wood-ash and surface soil are caused by K and Na oxides, hydroxides, and carbonates. These compounds are very soluble and do not persist through the wet season. The calcite is much less soluble and was present in soils 3 years after burning, maintaining moderately alkaline pH in surface soils that are normally neutral to strongly acid.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID