摘要:

Soil and root resistances were studied in two stands of a Douglas fir forest, Soil water potential was measured with a tensiometer-pressure transducer system in the 0 to −1− bar range, and with Wescor HR-33T dew point microvolmeter and hygrometers at values less than −1 bar. Root xylem water potential was measured with hygrometers, and twig xylem pressure potential was measured by the pressure-chamber technique. Transpiration rates were calculated from energy balance and stomatal diffusion resistance measurements. Total bulk-soil-to-root-xylem resistances were calculated from the water potential differences and transpiration fluxes. Root density was determined from intensive sampling. Root xylem water potential, like twig xylem pressure potential, showed a definite diurnal trend. Soil water potential approached toe root water potential as the soil dried. Assuming the absence of contact resistance between roots and soil, the soil resistance remained very small in comparison with root resistance, even at a soil water potential of −11 bars. An analysis using a contact resistance model suggested that contact resistance could account for one-half the total bulk-soil-to-root-xylem resistance when the soil was moist (-0.3 bar) and almost three-quarters when dry (-11 bars. Analysis of midday data during the drying period showed that the rate of water uptake was linearly related to the difference between soil and root xylem water potentials, and that total soil-to-root-xylem resistance remained relatively constant with decreasing soil water potential.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

A derivation is given for the equation of thermodynamic equilibrium between ice and water in porous media. The equation accounts for a difference between the pressure of the ice phase and the total potential (in pressure units) of the water phase. Emphasis is laid on the distinction between the total potential and the hydrostatic pressure and osmotic pressure of the unfrozen soil solution. The difference between the hydrostatic pressure of the solution and the ice pressure is accounted for by the ice-water interfacial tension, as expressed by the generalized form of Laplace's equation. The resulting generalized form of the Clausius-Clapeyron equation is an equilibrium expression, whereas the Laplace equation only expresses a definition, valid under any circumstances. It is emphasized that all influences of the pore wall, which may or may not work via the diffuse double layer, and which cause the liquid to have lower Gibbs free energy than the equilibrium liquid at the same temperature, are collected in the osmotic pressure term.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

Twelve phenolic compounds and glycine were mixed in two different formulations, designated asAandB,and dissolved in adequate amounts of very dilute NH4OH. FormulationAcontained fewer trihydroxyphenolic compounds and more dihydroxypenolic compounds than formulationB. They were added separately to two portions of a neutralized latosol low in organic matter content at five separate times. The polymerization of the compounds was catalyzed by the soil and traced by paper chromatography. At the end of this part of the experiment, the two portions of the soil were extracted with (1) benzene-95 percent alcohol: 1–1, (2) 0.1NHC1, (3) 0.1MNa4P2O7at pH 7.0, and (4) 0.5NNaOH in sequence. The model humins were also extracted after treating the soils with HC1-HF Solution. The model HAs and FAs extracted resemble the natural ones in color, solubility in acid and alkali, infrared spectra, etc. In the benzene-95 percent alcohol extract of the soil treated with formulationA,aromatic polymer was the main component, while in that treated with formulationB,aliphatic polymer predominated. The percentage of conversion of the total compounds added to the soil in the two formulations into polymers was a little over 63 percent. The nitrogen found in model HAs was 1.51–3.03 percent and in the model FAs 0.59–1.23 percent.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

An agricultural soil containing approximately 3.7 ppm residual toxaphene was collected from a cotton-growing area of Mississippi and used to study toxaphene disappearance under several laboratory conditions. The soil was incubated in the laboratory for 4 weeks, either unamended or amended with alfalfa meal, moist (-0.3-bar water potential) or flooded (unstirred or stirred continuously), and under CO2-free air or nitrogen. Extensive toxaphene disappearance, based on percent recovery, occurred in both the unamended and amended anaerobic environments, and may be the result of a microbiological enrichment effect. In amended soil, the percent of toxaphene recovery and degree of anaerobiosis (Eh) followed the order: flooded, stirred (N2) < flooded, unstirred (N2) < flooded, unstirred (air) moist (N2) < flooded, stirred (air) < moist (air). Percent recovery of toxaphene (y) was related to Eh (x) by the equation y = 22.815 + 0.72x+ 0.00005277x2

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

Sands and loamy sands within the Glacial Lake Souris basin in North Dakota vary considerably from one area to another in their particle size distribution. The objective was to relate water retention of these sandy soil textural classes to particle size percentage.Water retention percentages, on an oven-dry basis, were determined for samples at field capacity under field conditions and also at 1/10-, 1/15-, and 1/20-bar soil water section for air-dried, < 2-mm samples in conventional porous ceramic plate-pressure pot equipment. No single soil water suction produced water retention values adequately representing field capacity for all textures. In most instances the percentage of very fine sand alone and in combinations with the percentages of silt and clay were significantly correlated with soil water values.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

Several phosphatases are present in soils. This study was conducted to determine the distribution of phosphomonoesterases (acid and alkaline phosphatases). Results showed that the activities of these enzymes were associated with surface soils and that they decrease with depth. Acid phosphatase was predominat in acid soils, and alkaline phosphatase was predominant in alkaline soils. The activites of these enzymes were significantly correlated with organic C. The log of acid phosphatase activity was significantly but negatively correlated with the pH of 38 samples of 5 soil profiles examined. Regression analysis showed that acid phosphatase activity was significantly but negatively correlated, while alkaline phophatase activity was significantly and positively correlated, with the pH of 11 surface soils studied.Orthophosphate inhibited phosphomonoesterases in soils. At 10 μmole PO43-/g of soil, inhibition of acid phosphatase activity ranged from 21 to 42 percent, and the inhibition of alkaline phosphatase activity ranged from 17 to 51 percent, in 6 surface soils. The inhibition of these enzymes by orthophosphate decreased when the amount of orthophosphate added decreased from 10 μmole to 1 μmole/g of soils. The inhibition by orthophosphate showed competitive kinetics. The results explain the variation of Kmvalues ofp-nitrophenyl phosphate for acid and alkaline phosphatases and the observed decrease in phosphatase activity with organic P mineralization in soils.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

Ion exchange equilibria have been investigated in mineral soils, but little information is available for organic soils. This investigation was undertaken to characterize the cation selectivity of differing histosols and to determine a suitable cation exchange equation to express the ion selectivity in these soils. Four histosols were incubated for 3 weeks with 5 levels of K and Rb. At the end of incubation, ions in soil solution and on the adsorbed phase were determined. All soils had a greater fraction of Ca in the exchange phase than in solution, whereas with Mg, Na, K, and Rb, the reverse occurred. Increasing K and Rb saturation was related to an increase inkRb/K. On the Pahokee muck soils, Rb was adsorbed more tightly than K, where the amount of Rb added exceeded 1.0me/100g of soil. On the Edwards muck soil, Rb was adsorbed preferentially to K at all levels. Magnesium was adsorbed preferentially to Ca on the Edwards muck soil, but not on the Pahokee soils. Selectivity coefficients for K-Ca were calculated using the Kerr, Gapon, Krishnamoorthy and Overstreet, Vanselow, and Scheffer and Ulrich equations. In all but the Scheffer and Ulrich equation, the selectivity coefficient decreased as K and Rb were increased. In the latter it increased. No equation satisfactorily described the system.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

This investigation was carried out because of a need to monitor soil moisture content periodically in the field. The neutron probe equipment (Troxler, model 104 A) was therefore calibrated in the field on four soil profiles of contrasting soil physical properties. The effects of gravel content and gravel mineralogical composition on the thermalization of neutrons were also investigated in the laboratory. An oil drum was filled with mixtures of gravel and a subsoil fine earth fraction. Gravel concentrations of 0, 50, and 75 percent were used. Quartz gravel and iron/manganese concretions were used separately. The correlation coefficient of the regression equation,Y = a + bx,whereYis the count ratio andxis the moisture content, which was obtained for the different soil layers in the field ranged between 0.84**and 0.98**. The lower correlation coefficient, obtained mostly in the gravelly layers, was attributed to both spatial variability of the soil physical properties and the inherent problem associated with gravimetric moisture determination in gravelly soils. Although gravel concentration, gravel mineralogical composition, and total bulk density increased the thermalization of neutrons, the slopebof the calibration curve was not significantly affected. Sandy soils had lower interceptsathan clayey soils. For a soil-gravel mixture made in the laboratory that has a gravel concentration of 50 percent (g/100g) and a moisture content of 0.15 cm3cm-3, the count ratio was 0.50 and 0.67 for quartz gravel and iron/manganese concretionary gravel, respectively. Unlike the field calibration curves, the slopebof the laboratory calibration curve was identical to the factory calibration curve. Although it was possible to establish one single calibration curve for all soils and depths (r= 0.89**), the use of the curve to infer absolute moisture content would lead to an appreciable error. Also, the factory calibration curve will find its best use only in interpreting relative changes in moisture content.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID

摘要:

Calcium-45 and32P were injected into soil 4.5 cm from onion root surfaces at rates designed to label available pools of Ca and P at equivalent specific activities. Both tracers were detected in mycorrhizal but not anonmycorrhizal plants after 5 days. Calcium-45 was detected less frequently and in much lower amounts than32P, indicating that Ca is not translocated to roots through mycorrhizal hyphae as readily as P.

ISSN:0038-075X    

出版商:OVID    

年代:1978

数据来源: OVID