摘要:

We made measurements of contact angles for glycerol, diiodomethane, and cis-de-calin drops on the surface of soil precoated with dodecylammonium hydrochloride (DDACL) film and water vapor adsorption on a natural soil. From the results obtained and on the basis of the Young equation, we calculated the dispersion and nondispersion components of the surface free energy of the soil precoated with DDACL film as well as the work of adhesion of water to the soil/DDACL film surface. On the basis of the measurements and calculations it was found that DDACL provided hydrophobization of a soil which was manifested by the decrease of the nondispersion component of the surface free energy almost to zero. The dispersion component did not practically change; this resulted from proper orientation of DDACL molecules at the soil surface. We also found that the hydrophobization of the soil surface caused a large decrease of the work of adhesion of water to its surface.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Electrofocusing could be usefully employed to characterize humic substances, but careful investigation is needed because of possible interactions of humic substances with carrier ampholytes. In the present work, three fractions of humic substances which originated bands in different parts of the pH gradient during electrofocusing were isolated by preparative electrophoresis in phosphate buffer pH7 from 0.1MNa4P2O7extracts of the A horizon of a lithic Rendoll (Fusine) and of leonardite. Infrared spectra and E4/E6ratios showed distinct compositional differences among different fractions, while corresponding fractions from humic substances of different origin displayed evident similarities. In both cases, infrared spectra showed a progressive increase in carboxyl groups and a corresponding decrease in ketonic and quinonic carbonyl groups, passing from fractions with the lowest electrophoretic mobility and highest apparent isoelectric points (H) to those with the highest electrophoretic mobility and lower apparent isoelectric points (L).Electrophoretic fractions from the protorendzina soil were also analyzed by pyrolysis gas chromatography (Py-GC). Results confirmed information obtained by spectroscopic methods and showed that the H fraction had the most complex composition with covalently linked polysaccharide and protein derived parts and was composed of poorly humidified materials.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Functional relationships to estimate the initial amount of loose abrader material present on soils crusts as influenced by rainfall amount and soil properties are needed for the continuous simulation of wind erosion. Five simulated rainfall amounts (ranging from 5 to 80 mm) were used to create soil crusts on five soils with a wide textural range. Loose material on the crust surface was collected using a vacuum method from the furrow, side slope, and top of a 0.3 m ridge. The quantity of loose material on soil crusts varied significantly among soils, rainfall amounts, and locations relative to a ridge. Soil texture had the greatest influence on the amount of material vacuumed from the soil surface; 30 times more loose materials existed on the coarsest-textured soil (0.091 kg m−2) compared with the finest-textured soil (0.003 kg m−2). Loose material generally decreased with increasing amounts of simulated rain. Sample location influenced loose material in the order: furrow > side slope > ridge top. Regression equations were developed to estimate loose erodible materials as a function of soil texture and rainfall.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

We investigated two areas of contrasting spatial variability in east-central Illinois using grid sampling to determine the composition of soil map units and the variability of significant soil properties within map units. We also evaluated the effectiveness of the modern soil survey legend and maps in addressing the soil variability in the two different landscapes. The surface characteristics of the sample sites showed extremely high variability, especially in slope and aspect with CVs of 93.5% and 83.6%, respectively. The depth of the A horizon showed high variability with CV of 35% for both areas. The depth to reducing conditions was highly variable with a CV of 34.6%, while the depth to discontinuity was 48.4%. Characteristically the degree of color variability increased in the order, hue, value, and chroma, regardless of where in the profile it occurred. The A horizon showed very high variability in sand content with a CV of 74.4%, but silt content and clay content both showed moderate variability with CVs of 22.9% and 23.6%, respectively. Organic C content showed moderate variability with CV of 15% and was more variable in the highly undulating landscape, probably due to redistribution by erosion. Soil reaction in the B horizon showed a low degree of variation with CV of 9.5%. Although the variability of each soil property within the eight map units measured by coefficient of nondetermination showed less variance than the total variance present in both sample areas, most of the variation of soil properties was still left within map units. Tolerance limits of 75% set for the various map units indicate that some of the map units contained less variation of soil properties than others. This approach should help in refining the cartographical separations by identifying potential units that need reduction in variation of selected properties. Based on evaluation of soil property variability, we found that although the existing soil survey legend and maps are good, they could be improved substantially by considering the within-map unit variability of significant soil properties. We recommend that in future soil surveys, an initial soil property variability study be conducted using grid sampling to aid in a comprehensive development of the soil survey legend which will help reduce the within-map unit variation.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Antecedent soil water content is an important variable affecting soil erosion processes and may be responsible for much of the variation in splash and wash erosion rates. The purpose of this study was to determine the effect of antecedent water content on splash detachment and on soil and hydraulic variables that control splash. Five soils ranging in texture from sandy loam to clay were exposed to simulated rainfall with an intensity of approximately 64 mm h−1for 1 h. Wash, splash, runoff, and infiltration were measured for near-saturated (-0.5 kilopascal) and air-dried soils in 0.14 m2Al erosion pans. Changes in the soil surface were monitored with a fall-cone device. Prewetting significantly reduced runoff occurring over a 60-minute rainfall period for the Heiden clay only. Prewetting reduced splash detachment rates for all soils except the Miami silt loam, with the greatest reduction for the Heiden clay. Total splash for the air-dried and prewetted Heiden clay was 770.1 and 169.4 g in 60 minutes, respectively. Prewetting increased soil shear strength following 60 minutes of rainfall for all soils. Development of a surface seal controlled the amount of soil detached from the Miami silt loam. Miami silt loam had the highest final shear strength values for air-dried and prewetted soils and the highest difference between initial and final shear strength (Δτ) among prewetted soils. Prewetted wash and splash sediment size was larger than that for air-dried sediments. Antecedent soil moisture conditions prior to rainfall influenced the amount of splash detachment and the physical processes that control amount of splash.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

There are many tephra-derived soils showing characteristic morphology and chemistry of Spodosols in humid cold climates. We reviewed ICOMOD (International Committee on the Classification of Spodosols) Proposal D by the National Soil Quality Survey Assurrance Staff (1989) using 43 tephra-derived soils from Alaska, the State of Washington, U.S.A., and Tohoku, Japan, and we propose classification of tephra-derived Spodosols including the important items as follows: 1) to recognize tephra-derived Spodosols showing characteristic morphology of Spodosols, 2) to key out Spodosols after Andisols, 3) to emphasize morphology over chemical spodic criteria, 4) to modify albic color requirement for tephra-derived Spodosols, 5) to propose a new chemical spodic criterion (oxalate A1 and a half Fe), and 6) to propose a procedure to differentiate a spodic horizon from a buried A horizon.According to our proposal, 25 of 41 pedons of tephra-derived soils which are currently classified as Spodosols will be reclassified as Spodosols, and all of them can be exactly predicted to be Spodosols by field observation.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Knowledge of cationic transport in soils is important from an agricultural and an environmental point of view. To reliably predict transport of cations that react with the soil matrix, it is necessary to know the cation exchange capacity (CEC) and the adsorption isotherms for the cations. We will present a two-step displacement method to determine exchange isotherms. The method is relatively fast and yields a complete curve using only one sample under conditions similar to those during transport. An error analysis indicates that accurate determinations of exchange isotherms can be carried out using this method. We have determined exchange isotherms for Ca-K, K-Na, and Na-Ca systems using fine-loamy and loamy soils. All exchange isotherms determined by the proposed procedure show pronounced deviations from linearity, and the soils exhibited a relatively strong preference for the mon-ovalent cations.

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1990

数据来源: OVID