Showing papers in "Soil Science Society of America Journal in 1972"

Nitrogen Mineralization Potentials of Soils

Abstract: Net mineralization of N in 39 widely differing soils was determined over a 30-week period at 35C, using incubation intervals of 2, 2, 4, 4, 4, 6, and 8 weeks. Mineral N was leached from the soils before the first incubation and following each of seven incubations by means of 0.01M CaCl₂ and a minus-N nutrient solution. Soil water contents were adjusted by applying suction (60 cm Hg), and losses of water during incubation under aerobic conditions were negligible. With most soils, cumulative net N mineralized was linearly related to the square root of time, t½. The pH of soils changed very little in the course of 30 weeks' incubation. Because of the generally consistent results, the data were employed in calculating the N mineralization potential, Nₒ, of each soil, based on the hypothesis that rate of N mineralization was proportional to the quantity of N comprising the mineralizable substrate. Values of Nₒ ranged from about 20 to over 300 ppm of air-dry soil. The fraction of total N comprising Nₒ varied widely (5 to 40%) among soils. Mineralization rate constants did not differ significantly among most of the soils. The most reliable estimate of the rate constant, k was .054 ± .009 week⁻¹. The time required to mineralize one-half of Nₒ, t½, was estimated to be 12.8 ± 2.2 weeks. Results suggest that the forms of organic N contributing to Nₒ were similar for most of the soils.

Selective Dissolution of Manganese Oxides from Soils and Sediments with Acidified Hydroxylamine Hydrochloride

Abstract: Hydrous manganese and iron oxides of soils and sediments are strong scavenging agents for heavy metal ions. Information on heavy metals extracted along with manganese and iron oxides has been used in mineral exploration. But currently used methods do not differentiate metal ions associated with manganese oxides and those associated with iron oxides. Manganese oxides differ from iron oxides in solubility in response to oxidation-reduction conditions, charge characteristics, and the quantity and kind of metal ions scavenged. This paper reports the development of an extraction method for the selective dissolution of manganese oxides from soils and sediments with minimal attack on the coexisting iron oxides, based on the difference in behavior of manganese oxides and iron oxides toward reduction under various conditions. By dissolving manganese oxides and iron oxides separately and determining respective metal ions which are released in the process, the geochemical significance of interelement relationships may be established. Manganese oxides in soils and sediments are found to be readily dissolved by a hydroxylamine hydrochloride (NH₂OH · HCl) solution, leaving the major part of iron oxides in the residue. Although dissolution of manganese oxides is relatively independent of pH (pH 1, 2, and 3) and concentration of the NH₂OH · HCl solution (0.025 to 0.25M), and time of equilibration (15 to 60 min), progressively greater amounts of iron oxides are released with lower pH and higher concentration of NH₂OH · HCl solution, and with longer time of equilibration. A 0.1M NH₂OH · HCl solution prepared in 0.01M HNO₃ (pH 2) dissolves, on the average, 85% of manganese oxides and about 5% of iron oxides from various sediments after equilibrating for 30 min. Dissolution of manganese oxides and of iron oxides from four highly weathered soils by this solution amounts, respectively, to 50% and less than 1%. At pH 2, most heavy metal ions released during the dissolution of manganese oxides will be prevented from forming insoluble hydroxides or basic salts through hydrolysis, and then they can be determined in solution by appropriate analytical methods.

A simple titrimetric method for determination of inorganic carbon in soils

Abstract: A simple method of determining inorganic carbon in soils is described. The soil sample is treated with 2M HCl at room temperature for 16–24 hours in a stoppered bottle containing 2M KOH in a small beaker, and the CO₂ released from carbonates by this treatment is determined by titration of the KOH solution with standard HCl. The method is accurate and precise, and tests reported indicate that it is not subject to interference by organic soil consituents. It gives quantitative results with carbonate standards, and its results with soils agree closely with those obtained by the methods proposed by Allison and by Anderson and Harris.

Salt and water movement in unsaturated frozen soil

Abstract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

Concerning the Location and Persistence of Soil Urease

Abstract: Urease activity in soil is persistent for long periods under low water, low temperature, and sterile regimes, and it has been suggested that some form of enzyme-protective mechanism exists in soil.Dublin soil was sonicated in water and extracted by adding a mixture of salts. Urease activity is associated with the organomineral complex thus obtained and is resistant to the activities of proteolytic enzymes. Clay-free soil organic matter prepared subsequently by filtration also exhibits urease activity which is resistant to proteolysis. Models consisting of enzymes with bentonite and lignin were found to mimic this resistance to proteolysis. Models consisting of enzymes with bentonite and lignin were found to mimic this resistance to proteolysis.A model system is presented which suggests both the origin and location of soil ureases and a reason for their persistence in nature.

Influence of water content on electrical conductivity of the soil

Abstract: MEASUREMENT OF DYNAMIC SALINITY AND WATER CONTENT PROFILES UNDER LABORATORY CONDITIONS WERE NEEDED TO TEST A MODEL DEVELOPED TO CHARACTERIZE THE SIMULTANEOUS FLOW OF WATER AND SALTS IN SOILS. METHODS WERE NEEDED FOR MEASURING SALINITY IN PLACE IN A SYSTEM WHERE RAPID WATER MOVEMENT OCCURRED. BECAUSE OF THE TIME LAG IN SALINITY SENSORS, OTHER METHODS WERE CONSIDERED FOR EVALUATING SALINITY. THE FOUR-PROBE SYSTEM OF MEASURING ELECTRICAL CONDUCTIVITY OF SOIL ELIMINATES THE TIME LAG ERROR, BUT INTRODUCES THE PROBLEM OF CORRECTING THE CHANGES IN CONDUCTIVITY CAUSED BY WATER CONTENT. UNITS WERE CONSTRUCTED AND SAMPLES PREPARED TO EVALUATE THE INFLUENCE OF WATER CONTENT, AND SALT CONCENTRATIONS OF THE FOUR-PROBE CONDUCTIVITY. TWO SOILS WERE STUDIED. REGRESSION EQUATIONS DEVELOPED TO ESTIMATE SATURATION OR 1:5 EXTRACT ELECTRICAL CONDUCTIVITY FROM FOUR- PROBE CONDUCTIVITY AND WATER CONTENT GAVE CORRELATION COEFFICIENTS OF 0.75 AND 0.90, RESPECTIVELY. CORRELATIONS FOR INDIVIDUAL SOILS WERE GENERALLY HIGHER THAN THE COMBINED SOILS.

Water Movement in Undisturbed Swelling Clay Soil

Abstract: Hydraulic conductivities of Houston Black clay were measured in two field basins, in 73-cm and 21-cm diameter undisturbed cores, and in small cores prepared from sieved soil. Conductivities averaged about 2.5 cm/day for the field basins, about 0.3 cm/day for the undisturbed cores, and 0.1 cm/day for the disturbed soil cores. After steady-state flow through the larger, undisturbed cores was obtained, water tagged with fluorescein was used to displace water in the cores until tagged water first appeared in the effluent. Examination of cross sections of the cores at different depths showed distinctive isolated areas where tagged water was present in the soil pores. The results imply that most water contained within structural units was inactive in the flow process compared to water flow around the units. The core walls apparently cut off some large pores associated with the soil structure, causing the decreased conductivities. Therefore, only field-determined hydraulic conductivities are appropriate for use when predicting water flow in natural profiles of a swelling clay soil.

Potentiometric Determination of Soil Organic Matter

Abstract: THE DICHROMATE-WET COMBUSTION DETERMINATION OF SOIL ORGANIC MATTER INVOLVES A TITRATION OF THE EXCESSIVE DICHROMATE. A POTENTIOMETRIC TITRATION IS PROPOSED. THIS MODIFICATION ENABLES A FAST AND ACCURATE END POINT DETERMINATION. MOREOVER, THE METHOD CAN BE EASILY ADAPTED FOR AUTOMATIC TITRATIONS.