摘要:

We present a new quasi-analytical technique for solving the flow equation. It has affinities with Parlange's method, but offers the following advantages: freedom to choose an initial assumed flux-concentration relation,F1, greatly improves the possible accuracy of the first approximation, and the higher approximations preserve integral continuity and therefore behave more stably. The first of these advantages is of practical importance, but the second is more basic. This paper treats only solutions subject to concentration conditions; the related technique for solutions subject to flux conditions will be developed in a later paper.The technique is studied analytically and numerically forone-dimensional sorptionsubject to constant concentration conditions. It is found to be convergent for a wide range of shapes of the diffusivity function. For the unfavorable case of the ‘linear’ soil, the mean error is 3 percent after two iterations and 1 percent after three. For absorption in Yolo light clay the corresponding figures are 0.57 percent and 0.07 percent.The general iterative scheme forone-dimensional infiltrationsubject to constant con—centration conditions is presented. Three choices ofF1should yield useful first approximations: (A)F1A= limt→oF(t is time) =Fabs, theFfor the analogous absorption process; (B)F1B= limt→∞F= &thetas;; and (C)F1c, an interpolation function which is exact in the limits ast→ 0 andt→ ∞.F1Ashould lead to a goodlower boundfor the infiltration rate functionq(t),F1Banupper bound, andF1Caclose upper boundfor all except very larget, and the quality of the estimates of moisture profiles should be comparable. Detailed calculations for Yolo light clay bear out these expectations; the three estimates are wholly consistent with the power series solution of Philip (1957b). The error of the approximation based onF1Cincreases from 0 percent att= 0 to about 1 percent att= 106sec. This first approximation is accurate enough to render iteration unnecessary for most purposes. Parallel calculations confirm the nonconvergence of Parlange's method when applied to infiltration.General iterative schemes are given also fortwo- and three-dimensional sorptionsubject to constant concentration conditions.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The agar method and the cell diffusion method were used to measure the self-diffusion coefficients of45Ca in CaCI2solution and14C-labelled 2,4-Dichlorophenoxyacetic acid. Both methods gave results that were in agreement with theoretical considerations. Problems were experienced with the agar method. Difficulties encountered were preparation of stable media of low agar concentration and inability to properly account for physical properties of the matrix through which diffusion occurred, such as tortuosity, adsorption by the agar, and density gradients with associated viscosity gradients in the agar.The cell diffusion method was simple to use and gave results that were in agreement with values calculated from ionic mobilities. The diffusivities measured with the cell diffusion method were: for45Ca in CaCl2solution,K= 0.70 cm2/day and for14C-labelled 2,4-D,K= 0.69 cm2/day.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Analysis of seven spodosols from southeast Alaska formed on contrasting parent materials show that the soils have similar chemical properties in upper horizons in spite of some wide differences in parent materials. With soils formed on basalt and limestone, influences of parent materials on chemical properties are evident only in the lowest horizons.Considerable accumulation of organic matter is found in these soils in surface layers and within the mineral profile. Also, nitrogen and mineral element contents of the surface organic layers are relatively high. Upper layers of the soil remain moist throughout the season and rooting is largely limited to the surface organic layers and the top few inches of mineral soil. The shallow rooting with the high rainfall of the area apparently limits the influence of lower horizons and parent materials on chemical properties of the upper soil.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The ability of solutions of arsenate to displace previously adsorbed phosphate from soil was investigated. Displacement increased with concentration of arsenate, with time of shaking, and with pH. There was a marked change in slope of the pH-displacement curve near the pK2of arsenic acid. This was taken to indicate that arsenate was competitively displacing specifically adsorbed phosphate. At equivalent concentration the effectiveness of arsenate decreased in the sequence: lithium, sodium, potassium. These differences may be associated with differences between the cations in their average distance of approach to a negatively charged surface.With increasing time of contact between soil and phosphate, the proportion of the added phosphate which was not displaceable by arsenate slowly increased. The rate of conversion to a nondisplaceable form increased with temperature. The conversion occurred over a wide range of soil moisture levels. The proportion converted was not affected by level of addition within the range tested, and it was argued that this indicates that conversion does not involve diffusion of phosphate from one site to another through the solution phase.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Heating preformed KBr pellets effectively eliminated interference arising from hygroscopic moisture in infrared studies of humic acids. Structural changes in humic acid during heating were confined to the formation of cyclic anhydrides from carboxy1 groups. The use of thallous bromide as a nonhygroscopic pelleting matrix and perfluorokerosene as a mulling agent can be recommended in infrared investigations of humic substances.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Studies were conducted to evaluate the interactions of P, K, and S applied to alfalfa grown on a calcareous silt loam. Phosphorus fertilization increased alfalfa yields. The application of K and S had no significant influence. In each of 2 years, the highest yields were obtained at the highest rate of P used. There was residual response to P applied in the previous cropping year. The P content of the alfalfa tissue was increased by P fertilization. The use of K and S had no influence on the tissue content of the respective nutrient. Soil P as measured by the bicarbonate extractant was related to previous P fertilization. This was not true for soil P extracted by the Bray procedure. The data in this study support the choice of the bicarbonate method for describing the P levels in calcareous soils.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The results of an investigation of the soil algal flora from three different sites on a farm in Pike County, Pennsylvania, are presented. Representatives of 29 genera were recorded of whichChlamydomonas, Hormidium, Chlorococcum, andTetracystiswere most frequently encountered, and in that order of frequency. Only four blue-green algae,Anabaena, Lyngbya, Nostoc, andSchizothrizwere present in these soils. The diversity and frequency of occurrence increased between late winter and early summer. Species ofNannochloris, Stichococcus, andChlamydomonasdeveloped in soils inoculated into sea water enrichment medium (35% salinity).

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Parlange's approximate analytical solution for the horizontal infiltration of water into soil is numerically tested for the case of two-step diffusivity function and also for the Yolo Light Clay diffusivity of Philip (1957). It is shown that Parlange's second approximation for the Boltzman variable &phis; =x·t1/2as a function of moisture content gives in both cases too high values, as compared to the analytical solution for two-step diffusivity, or Philip's solution for the soil-water case. The error decreases as the diffusivity function approaches more closely to the delta-function type of diffusivity. The improved second approximation of Parlange is, however, very precise, even for the diffusivities, which are not of delta-function type. The increase of labor for this improved approximation is very small. A recurrence formula for the successive &phis;'s is also examined, but it is found, however, that this formula does not give convergent values and the computational effort is larger than the improved second approximation.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID