摘要:

We have made kinetic studies of the adsorption of oxamyl on hydrogen-, sodium-, and calcium-saturated illites. The model of Lindstrom et al. proves useful in the simultaneous evalution of adsorption (k1) and desorption (k2) rate constants. The adsorption and desorption data are in agreement with those calculated with the simple kinetic rate laws for separate sorption and desorption processes. Rate constants, activation energies, heats of activation, entropies of activation, along with the thermodynamic parameters, were calculated. The rate constant and other parameters indicated a partly physical and partly chemical type of adsorption of oxamyl on illites. Adsorption may be either by coordination or via protonation of the exchangeable clay cations to the oxygen of the amide group.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

Ionic transport in soils is commonly described by equations representing mass conservation and the rates of ion-soil interactions. The type of adsorption equation used is an important factor in solute flow predictions. Adsorption is most commonly described by either the diffuse double layer (DDL) theory, or approaches based on gas-solid interactions (GSI). Computer simulations, in the form of breakthrough curves for a goethite system, showed that DDL and GSI model predictions were similar. The GSI approach is readily adaptable to adsorption-desorption dynamics, however, and was found to be more convenient than DDL models for the simulation of ionic transport in soils.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

A two-dimensional numerical model for predicting the spatial soil temperature regime under transparent polyethylene mulch has been developed. The model takes into consideration weather conditions as well as soil characteristics. The results indicate that soil heating at the edges of the mulch is lower than at the center, and thus a narrow mulch provides less efficient heating than a wider mulch. The predicted results agree well with the observed data. This model enables us to determine the optimal size of mulch with respect to weather conditions, soil characteristics, and particular plant or agricultural requirements.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We studied the retention of arsenate by four soils of Saskatchewan, Canada, and its relation to selected soil properties and anionic environments. The data indicate that As retention by the soils at the dilute As concentration range studied does not proceed through the precipitation of sparingly soluble arsenate compounds. Arsenate retention evidently proceeds through adsorption mechanisms. The adsorption maxima of the soils are not related to acidity and the contents of inorganic C, but are linearly related to amounts of ammonium oxalate-extractable Al and, to a lesser extent, to the contents of clay and ammonium oxalate-extractable Fe. Chloride, nitrate, and sulfate present at concentrations usually present in saline soils have little effect on the adsorption of As. Phosphate substantially suppresses As adsorption by the soils, and the extent of the suppression varies from soil to soil.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We conducted this research to determine the usefulness of APDC-MIBK solvent extraction for precleaning copper and zinc from 0.05MCaCl2and 2.5 percent HOAc and for concentrating the metals from soil extracts with the two reagents. The system was effective in removing both Cu and Zn from 0.05MCaCl2, but only Cu from 2.5 percent HOAc without prior pH adjustment of the solutions. Simultaneous extraction of Cu and Zn from both 0.05MCaCl2and 2.5 percent HOAc soil extracts was carried out by adjusting the pH of the soil extracts to 5.0. The undesirable effects due to iron-APDC precipitate formation in the 2.5 percent HOAc soil extracts were overcome by using a phase separation filter paper. The metal contents in soil extracts determined by this technique were in good agreement with those determined by an evaporation-concentration technique.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We conducted quantitative point count determinations of phosphorus, potassium, calcium, and magnesium by electron microbeam analysis and scanning electron microscopy of soil-root interfaces with soil-root samples from 30-day-old peanut and soybean plants, grown in Davidson and Cecil soil. Scanning electron micrographs showed undistorted cellular details of the plant roots embedded in the soil mass. Electron microbeam counts revealed that the soil contained lower concentrations of P, K, and Ca than the root tissue. The Mg concentration showed a tendency to be higher in the soil than in the roots. An ascending ion concentration gradient was noticed in the soil from 0.40 to 0.10 mm from the root surface. Nevertheless, a slight decrease in ion concentration was observed 0.05 mm from the root, which was attributed to the presence of a mucilage layer bridging the soil with the root surface. On the basis of a sharp break in element distribution with distance to the root, we estimated the soil rhizosphere to be 0.20 mm thick. Keeping this thin layer of soil saturated was thought to be more beneficial than keeping the bulk of soil saturated with nutrients. Specific accumulation zones of K and Ca were noted in root tissue. Highest concentrations of K and Ca were measured in cortex and epidermis, respectively. Lower levels of K, Ca, and Mg were detected in soybean than in peanut roots, indicating different nutrient requirements between plant species. The results of element counts by electron microbeam analysis in peanut and soybean roots were within ranges of concentrations measured by conventional methods with dry-ashing and atomic absorption spectrophotometry.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

In subarctic woodland soils near Schefferville, Quebec, many nutrients are bound up in slowly decomposing soil organic matter. Three organic horizon samples from two soils (L and H horizons from a mature woodland and a combined L and H from a recently burned site) were incubated under laboratory conditions, and carbon dioxide evolution was measured. The major factor inhibiting decomposition is the low soil temperatures (Q10values of 2.0 to 2.3), with acidity, low N content, lack of readily available carbon, and low mesofaunal populations of secondary importance. Microorganisms, lichen extracts, water content, and other macronutrients (Ca, Mg, P, K) were relatively unimportant factors in controlling the rate of decomposition.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We used a field soil morphology rating system to evaluate a chronosequence of soils in the northeastern San Joaquin Valley, California. Relative horizon distinctness (RHD) ratings generally were less than 10. RHD ratings greater than 10 were obtained for observed and suspected parent material or soil formation discontinuities. Although monogenetic soil formation will result in high RHD ratings in some cases, the soils tested here usually had high RHD ratings at discontinuities. Relative profile development (RPD) ratings increased with age. Maximum values were in the A horizons of younger soils and in the B horizons of older soils.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We prepared sand and gravelly sand media in rigid cylinders, with different proportions and sizes of gravels and sands at various water tensions. Cores of forest topsoil were used for comparison. We measured the growth of pregerminated maize seedlings 72 hours after transplanting them into these media.Compared with growth in forest topsoil, root lengths averaged over sand and gravelly sand media were 27 percent less, depth of penetration was 65 percent less, and primary seminal root diameter was 36 percent greater. Further, primary seminal roots were significantly shorter and shallower, and penetrometer resistance was greater with the higher proportions of gravel, the smaller sizes of gravel and sand, and the lower soil water tension. Penetration resistance increased nearly sixfold as the volumetric percentage of gravel increased from 0 to 45, with a corresponding reduction in depth of root penetration below the seed of 30 percent.The resistance of close-packed sands to root penetration and the further hardening effect of gravel highlight the importance of promoting root-size pores to bypass mechanical resistance.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID

摘要:

We have developed a method for packaging large, undisturbed samples of fragile soil. Polyester resin and fiberglass cloth were used to coat a carved pedestal of soil and to affix it to a wooden pallet for handling and transport. The resin and cloth mixture dried fast and hard and weighed very little. The opened sample showed no damage or alteration due to packaging or transport to the laboratory. Measurements made at the time of sampling and the time of initial laboratory analysis showed little decrease in soil moisture for many samples stored for up to a year. Losses were drastic, however, in some duplicate samples stored for 4 years. Other samples, with more flawless coatings of resin, showed very little moisture loss even with prolonged storage.

ISSN:0038-075X    

出版商:OVID    

年代:1981

数据来源: OVID