摘要:

An241Am and a137Cs source with two single amplifier/discriminator systems are used simultaneously. Special attention is paid to a negligible influence of the Cs source in the Am channel, resulting in a cross-source-position layout. A residual Cs contribution of about 10 c.p.s. remains in the Am channel, which can easily be corrected. A soil column scanner is described in detail.Punch tape output permits fast data assimilation. The results of a number of calibration studies are presented. Variation in mass attenuation coefficients for soil seriously limits the use of this technique in natural soil columns.Statistical accuracy is low compared to a single moisture determination. In spite of both heavy sources a counting time of at least 1 min is preferable.Finally, an experiment with a swelling clay soil clearly demonstrates the possibilities of the simultaneous use of both radioisotopes.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

An approximate analytical solution for the lateral movement at the periphery of a one-dimensional flow of water without gravity is derived for a source that is a semi-infinite plane. The solution is shown to be valid experimentally for relatively long times for a source with finite length. The theory can be utilized to calculate, and correct for, the additional infiltration due to lateral movement in measurements of water intake in the field; when gravity is present, however, the correction is valid only for short times.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The concentration of atmospheric O2over a flooded soil is a factor in determining the amount of N lost by denitrification. Large increases in N loss occurred from the first few increments of oxygen with little further loss occurring above 20 percent O2. The thickness of the aerobic layer was also governed by the amount of O2in the air. Nitrogen loss was generally related to the thickness of the aerobic layer, even though appreciable loss occurred at 5 and 10 percent O2where the aerobic layer was relatively thin.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Phosphate, at several levels of application, was incubated with four soils for 12 months at 25°C or was left in contact with soil in the field for three years. The capacity of the soils to adsorb further phosphate and the proportion of the phosphate remaining isotopically exchangeable were then measured.Previous additions of phosphate reduced the capacity of the soils to adsorb further phosphate. Not only were the adsorption curves displaced but they were also of lower slope; that is, the buffering capacity for phosphate was decreased. Only a small proportion of the previously added phosphate remained isotopically exchangeable within 24 hr. The results indicated that some of the phosphate had been converted into a form which was occupying phosphate adsorption sites, blocking them from further reaction, and thus reducing the buffering capacity for phosphate. The reduction was not linearly related to level of application. Low levels of application produced a proportionately larger effect than high levels.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

A laboratory study of the rate of hydrolysis of pyrophosphate in three soils at six temperatures over the range 5° to 40°C showed that the hydrolysis rate is dependent on both the temperature and the properties of the soil. The time required for hydrolysis of 50 percent of the pyrophosphate to orthophosphate was 25 to 60 days at 5°C and 4 to 13 days at 25°C, and at temperatures between 25° and 40°C there was a moderate decrease in the rate of hydrolysis. The results are in agreement with those reported in a similar study with English soils. An almost uniform uptake of heavy metals by corn fertilized with two polyphosphates and three other sources of phosphorus in a greenhouse experiment indicated that the rate of hydrolysis was sufficient to preclude an observable effect of polyphosphates on heavy-metal uptake through sequestration phenomena.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Samples (5 g) of Pembroke soil were incubated at 40°C in 12.5 ml of salt solution (0, 1 × 10−3, 1 × 10−2, 2.5 × 10−2, and 1 × 10−1Mof KH2PO4, NaH2PO4, KCl, and NaCl) for varying time periods up to 35 days in order to determine salt effects on biological and chemical changes in flooded soil.For all salts, carbon dioxide evolution increased with time of incubation and generally decreased with concentration of salt at the 7-day incubation. However, at longer incubations P salts stimulated CO2evolution while Cl salts had little effect. Although theoretically possible, NH4precipitated with P as ammonium taranakites in these soil systems was rejected since added NH4was recovered from sterile soil systems. The data suggest that P salts increase microbial activity resulting in greater amounts of N being immobilized in microbial tissue.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The hydrometer method usually has been tested against the pipet method for determination of total silt and clay (50–2μ < 2μ in diameter). For analysis of more silt and clay size fractions (i.e., 50–20, 20–10, 10–5, 5–2, 2–1, <1μ), this study showed no difference between the two methods. The hydrometer method also gave, by substraction, results comparable to the wet sieve method for particles >43 and 53μ. Frequent insertion and removal of the hydrometer from suspension, as needed in detailed particle-size analysis, did not affect the accuracy of the hydrometer method.Hydrometer specifications were used to calculate and plot hydrometer readings versus particle diameter at different time intervals after initiation of sedimentation. The procedure facilitiated calculation of particle size distribution.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Two Vertisols, Gezira clay from Sudan, Africa, and Houston Black clay from Texas, USA, were studied relative to the effects of concentration and ratio of NaCl and CaCl2solutions on their hydraulic conductivity and structure stability.In both soils hydraulic conductivity, degree of structure stability, and flow rates through clods generally increased with increasing electrolyte concentration but decreased with increasing SAR and decreasing electrolyte concentration. These effects usually were more pronounced in the Gezira soil than in the Houston Black soil. Drying increased water-stable aggregates in some samples and decreased them in some others.The Gezira soil, formed in clayey Nile River alluvium, seems to have less-stable aggregates that are more readily disrupted by Na than the Houston Black soil formed from calcareous clays, marls, or limy shales older than the Nile alluvium. Contrasting soil genesis, levels of organic matter, and particle size distribution in the soils likely account for these differences. Both soils are classified Vertisols. Additional research is needed that compares soil and water management effects on complete profiles of alluvial clay soils classified as Vertisols with profiles of older Vertisols in uplands.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Dispersion profiles of 2,4-dichlorophenoxyacetic acid were measured experimentally to evaluate a theoretical dispersion model previously developed by the investigators and to evaluate the effect of pore size on dispersion. The chemical being dispersed along a column made up of glass beads was initially present only in the pore water of a 1 cm long section at the front of the column. After leaching for a period of time, the column was sectioned and the concentration in each section was obtained and compared with a predicted concentration.Four porous media systems consisting of glass beads with particle diameters of <30, 28–53, 105–149, and 149–210 μm obtained by dry sieving were used. Corresponding predominant pore radii were 4.5, 8.2, 19.5, and 36.2 μm. The corresponding dispersion coefficients were found to be 0.53, 0.69, 1.41, and 2.05 cm2/day, repectively. Using these values, theoretical dispersion profiles were calculated. The theoretical distributions of the chemical in the columns were found to be in good agreement with the experimentally determined distributions. The values of the dispersion coefficients were in agreement with values reported in the literature and could be related to pore size, diffusion coefficient, and flow rate.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Measurement of dibromochloropropane (DBCP) by gas chromatography showed that an injection of DBCP at a depth of 20 cm resulted in higher concentrations and deeper penetration in sandy clay loam and silt loam than when it was applied in water. Application of the same amount to the soil surface in 15 cm of water showed DBCP is trapped near the surface in these soils. Persistence is longer in these two soils and in loamy sand after injection. The most rapid penetration after application in water occurred in loamy sand where the rate and depth of penetration were greater than those measured after injection.

ISSN:0038-075X    

出版商:OVID    

年代:1974

数据来源: OVID