摘要:

A scaling technique is presented for estimating the hydraulic conductivity based on experiments of horizontal infiltration of water into an air-dry soil. From plots of the distance from the water source to the wetting front as a function of the square root of time, a scaling factor is obtained that permits the estimation of the hydraulic conductivity as a function of soil water content.The method has been established experimentally using five Brazilian tropical soils and seven California temperate soils, with one of them being taken as a standard soil. Bulk density measurements used to verify the homogeneity of each soil column and volumetric soil water content measurements were made by gamma-attenuation using137Cs.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

This study deals with the derivation of the diffusion equation by considering the displacement of a fluid particle through an unsaturated porous medium as a Markov's stochastic process.The comparison of this equation with that obtained from the combination of Darcy's generalized equation and the equation of continuity allows us to find the physical significance of the diffusivity coefficient D as well as its partial derivative (ð D)/(ðx).The physical interpretation of these parameters may be related to the boundary conditions of the flow phenomenon and enables us to determine the field of application and the validity limits of the diffusion theory.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Two proteins, lysozyme and ovalbumin, were adsorbed to smectite homoionic to first five elements of the alkali and the alkali earth series, hydrogen, aluminum, and lanthanum. Lysozyme was also adsorbed to Na-smectite in the presence of 10−3to 2.0 N NaCl solutions. Lysozyme adsorption by all clays was of the high affinity type, with 93 percent of the variance in the adsorption maximum being accounted for by the equation Amax= 290.2–5.5 (valence) - 96.8 (ionic radius) - 114.3 (Pauling electronegativity) - 6.5 (ionization potential). Adsorption of lysozyme by Na-smectite was decreased when the reaction occurred in solution with NaCl concentrations of 0.5 N or above. Adsorption of ovalbumin by the smectites was of the constant partition type and pH dependent. All homoionic clays except those saturated with H and Be adsorbed similar amounts of ovalbumin. Attempts to desorb the two proteins were generally unsuccessful, indicating that stabile complexes had been formed.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Calcite solubility is of major importance to geologists and soil scientists, and yet attempts to characterize the system in terms of basic chemical relationships have met with limited success. The model reported herein adequately describes calcite equilibria in aqueous solutions open to the air that have practical significance to both geologists and soil scientists. Equations accounting for activity coefficients and various ion-pair formations were sufficient to describe calcite equilibrium in solutions of widely varying ionic characteristics. Sixty out of 73 solutions selected from the literature yielded calculated Kisp values for calcite ranging from 2.6 to 4.0 x 10−9with an average of 3.3 x 10−9.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Complex formation between kaolinite and the clay fractions of Ultisols and humic-fulvic acids extracted from a Paleudult was investigated by Sephadex gel filtration and infrared spectroscopy.Humic acid remaining in solution after complex formation exhibited infrared spectrograms with increased absorption in the 1050, 1400, and 1600 cm−1regions for Si-O and carboxyl vibrations, respectively, coupled with the appearance of new peaks at 940–840 cm−1for O-A1-OH vibrations. Gel filtration of the humic acid above resulted in the separation of HA/I (high molecular weight) with strong infrared Si-O absorption, and of HA/II (low molecular weight) with spectrograms revealing the O-A1-OH absorption. Admixture with clay particles was eliminated by Sephadex, since clay was not eluted through the column. Infrared analysis of the clay material before and after reaction with humic acid, showed spectrograms indicating the presence of possible structural changes. After reaction with humic acid, kaolinite and soil clays had spectrograms with decreased absorption for Si-O vibrations. These observations suggested the possibility of a gradual decomposition of the Si-O-Si linkages in the clay structure by acidolytic attack of humic acid. Increased amounts of Si and Al contents found in the remaining supernatant humic acid solution were supporting evidence for the release of these elements by clay.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

New fixation procedures for soft tissue and scanning electron microscopy (SEM) examination of yellow poplar root material with intact fungi were investigated. The applicability of an x-ray fluorescent system for elemental analyses of fixed materials under observation was also examined. Roots were prepared for SEM viewing by use of chemical fixatives followed by freeze-drying. Results of this study demonstrated that large-volume, soft-bodied plant tissue (roots) and related components (fungi) can be fixed to withstand the high vacuum stress of the SEM with no apparent distortion, and it is possible to preserve components of associations (root-fungi) and contact agents (soil) intact for microprobe analysis as well as SEM viewing.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A simple device for measuring emergence force of seedlings was developed. In this, the emerging seedling was directed to a groove in the gypsum block adhering to the lower side of a cantilever beam. The growing seedling pushed the beam upwards and produced flexure stress in it. Emergence force was computed from the strain measured by gauges cemented on the beam.Effect of seed size, depth of planting, seed orientation and bulk density of the soil below the seed on the emergence force/pressure of corn was studied with this device. Emergence force increased significantly with increasing bulk density of soil below the seed. Differences due to seed orientation were more pronounced in emergence pressure than in the emergence force. Seed size and depth of planting had no effect on emergence force. In a field experiment, compaction below the seed and D (proximal end down) orientation of planting produced faster and greater emergence.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

This column study indicates that, when plant amendments are added to soil, Mn and Fe are released at moisture contents below field capacity. Soluble Mn and Fe were released from the soil columns in the order: alfalfa > wheat straw > soil alone. Release was greater at 0.3-bar than at 0.5-bar moisture tension, and the effect was more noticeable for Mn than for Fe. When the easily reducible Mn in the soil was compared with total Mn elution at 0.3 bar, 6.6 and 16.1 times more total Mn than the amount of easily reducible Mn in the soil was eluted from the 2 and 5 percent straw treatments, respectively. The results suggest a potential for soluble Mn accumulations where large amounts of plant residues are incorporated into a normally well-drained soil.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The phosphorus status of twenty-one selected soils from various parts of Nigeria was studied. Total P content in the surface soils studied ranged widely from 120 to 1880 ppm. In most cases, the relative abundance of the various fractions of inorganic P was in the order of occluded P ≫ Fe-P > Al-P ≥ Ca-P. The distribution of various P forms was related to the parent material, degree of weathering, and drainage conditions of the soils. Organic P constituted more than half of the total P in most of the forest soils. Multiple correlation showed that organic P content was significantly correlated with soil pH, organic carbon content and total P content in the soils.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The magnetic susceptibility of lateritic soils and clays has been determined. A linear relationship between specific magnetic susceptibility and iron oxide content of kaolinitic and allophanic soils and clays has been observed. Montmorillonite and magnetite-bearing soils have shown high magnetic susceptibilities which were not related linearly to their iron oxide contents. Fe+++and Fe++ ion substitutions in the octahedral position of 2:1 types of clays were thought to be the probable cause of high magnetic susceptibility of such soils. The high values obtained for the latter may be attributed solely to the ferromagnetic property of magnetite. The type of bonding of Fe+++ion in octahedral coordination was investigated through spin-only moment (u. eff.) determinations. It was found that substitution of less than half a mole of Fe+++ion per unit cell in 2:1 types of clays appears to form electrostatic bonding (i.e., spin-free, sp3d2bonding), while more than half a mole of Fe+++ion per unit cell shows the covalent type of bonding (i.e., spin-paired, d2sp3bonding). The diamagnetic, paramagnetic, and ferromagnetic nature of kaolinite, montmorillonite, hematite, and magnetite, respectively, has been evidenced.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID