ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The flux-concentration relation [F(&thetas;)] expresses in reduced form the dependence of flux density on moisture content during various unsteady flow phenomena in unsaturated soils. In this first paper of a series, the general properties ofF(&thetas;) are established for various phenomena: one-dimensional sorption and infiltration with constant concentration conditions and one-dimensional sorption (for the ‘linear’ soil only) with constant and variable flux and variable concentration conditions. These studies provide a guide to the properties ofF(&thetas;) in more complicated phenomena in one-, two-, and three-dimensional systems.F(&thetas;) is independent of time for some phenomena and it varies only mildly with time for some others; and, for some phenomena, the dependence ofF(&thetas;) on the ‘shape’ of the moisture diffusivity function lies within fairly narrow bounds, which are fixed by reference to the extreme cases of the ‘delta-function’ and the ‘linear’ soil. This relative stability ofF(&thetas;) makes it a useful aid to the study of methods of solving the unsaturated flow equation. It is employed in later papers in a critique of Parlange's method and in the development of a new quasi-analytical technique.An appendix demonstrates that the approximation of step-function moisture profiles implies a delta-function moisture diffusivity function.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Equilibration was studied between water and four profile samples of the Mexico silt loam: (1) grass-covered alley between plots; (2) fallow control plot; (3) fallow plot with initial sodium bicarbonate addition in the 4–12-in. layer; and (4) fallow plot with initial calcium carbonate addition in the 4–12-in. layer. After equilibration, the soil solutions from 1:1 soil-water mixtures were extracted through ultrafilters at 16 atm pressure and chemically analyzed.Equilibration required reaction periods longer than 10 days; 36-day periods gave only slightly different results from 12 days. pH variations were studied through additions of HC1 or Ca(OH)2. pCation-pH curves were obtained, as were pAl-pH and pSi-pH curves. The pAl-pH curves all showed a straight line portion between pH values 6.9 and 8.4 whose slope corresponds to an ionic composition (Al6…)−. The pSi-pH curves showed a sharp rise in pSi on the alkaline side; the solubility of Si may become less than that of quartz.Results were plotted on Garrels and Christ diagrams; that is, log [Cation+]/[H+] or log [Cation2++]/[H+] against log [Si(OH)4] both for the acid-alkali treatments and for the depth samples. The slope of the beidellite-kaolinite boundary is given by (2 — 4/n) wherenis the extent of substitution of Al + Na for Si in a unit of 24 O. Examination of data involving pH variation indicates that the dominant weathering reaction is beidellite → kaolinite. However, it has proceeded only slightly in this soil.Study of variations with depth shows that K varies most in relation to profile features. Calcium and Mg show weaker variations with the same character. Sodium shows entirely different variation with depth. These differences may arise from strong plant uptake of K, Ca, and Mg from the root zone, with subsequent release at or near the surface. Sodium is not appreciably taken up by prairie species.Selectivity numbers for Na/K and Ca/Mg were calculated. Those for Na/K sensitively reflect profile differences.Results are discussed (1) in light of Donnan hydrolysis effects as affected by CO2and (2) through the weathering reaction beidellite → kaolinite.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Less than 10 percent of the Mg added to soils at the rates of 0.5, 1.0, 5.0, and 10.0 symmetry concentrations was retained in forms not extractable with neutralNNH4OAc. There was no evidence of Mg fixation by either the clay or organic fractions of the soils. The sample of commercial vermiculite also failed to fix Mg. Magnesium retained remained fairly constant for both the short-term (7 days) and the long-term (30 days) incubation periods, suggesting a tendency towards an equilibrium situation. Calculations made using equilibrium exchange equation showed that a substantial portion of the Mg adsorbed on the soils was held on exchange sites. Mg adsorbed could be described in terms of a Freundlich isotherm but failed to conform to the Langmuir equation.The quantities of Mg released from nonexchangeable forms were very small as compared to critical exchangeable Mg levels for agronomic and commerical crops.There did not appear to be an equilibrium between the nonexchangeable and exchangeable Mg in the soils studied. The results of the fixation and release studies suggested the impracticality of improving the long-term Mg-supplying power of soils and indicated the importance of repeated application of Mg fertilizers, especially in highly weathered soils.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Morphological, chemical, and mineralogical properties of a Gray Brown Podzolic soil, derived from granite in Greece, are presented and discussed. Certain analytical data concerning this soil, namely the CEC and clay content, are incompatible, and this incompatibility could not, for some time, be explained. Thus, the clay content and the CEC of the B22t, B3, and C horizons were 20.8, 11.0, and 5.4 percent and 47.7, 50.5, and 47.8 me/100 g of soil, respectively, while the organic matter content was lower than 1 percent. This incompatibility has been explained and the observed high CEC values accounted for with accuracy, when it was found that not only the clay but also the coarse fractions of this soil contained high CEC material, namely a trioctahedral vermiculite and montmorillonite, the latter being present in small quantities only. The trioctahedral vermiculite was found in percentages ranging from 2.7 to 28.8 in the sand and 10.4 to 29.6 in the silt, and dominated the clay fraction (26.6 to 31.3 percent).

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Fluometuron is partitioned between a soil and a solvent in accord with its chemical structure and that of the soil and solvent. Direction of approach (i.e., adsorption or desorption), soil/solvent ratio, type of soil and type of solvent affect the equilibrium distribution. In the presence of an “infinite” number of soil sites and an “infinite” number of solvent sites the partition is approximately linear. As soil sites become limiting, the partition becomes curvilinear. The curvilinear response can be translated to “monolayer” concentration and amount of covered surface area. Fluometuron adsorbed by Cecil B2t soil from dichloromethane solution covers only a small fraction of the total surface area of the soil.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Segments of onion roots infected with the endomycorrhizal fungiEndogone mosseaeandE. fasciculatahad high levels of radioactivity when32P-labeled phosphate was incorporated in soil 27 mm from the root surface. Autoradiography indicated diffusion of 7.5 mm or less from the point of application. Nonmycorrhizal roots had little radioactivity. When hyphae growing from mycorrhizae were severed, mycorrhizal roots did not differ significantly in32P-labeled phosphate content from nonmycorrhizal roots. Our evidence indicates that the mycelial network of endomycorrhizal fungi enables plants to remove phosphate from a larger soil volume, extending beyond the immediate vicinity of the root surface.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The nitrate electrode was adapted for use in soils and plant extracts. The effect of interferences and depressions of the nitrate ion activity by other ions in the sample and variations in total ion strength were minimized by making standards and samples of 0.01Min sodium citrate. The electrode method was found to be accurate and rapid for soil and plant analysis.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID