Showing papers in "Soil Science in 1976"

The Biology of Nitrogen Fixation

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The accumulation in soil of cadmium residues from phosphate fertilizers and their effect on the cadmium content of plants

Abstract: The accumulation of Cd and Zn in soils through the application of fertilizer and the effects of this and other cultural practices (e.g. liming) on the Cd content of crop plants has been investigated. At least 80% of the Cd impurities in phosphate fertilizers applied during cropping practices could be accounted for in the cultivated layers of soil examined with the exception of a very light textured siliceous sand from which 50% of the Cd had been lost, possibly by leaching. The Cd uptake from the soil was found to be affected by the pH of the soil, the application of Zn, and the level of soil phosphorus.

Trace element movement in soils: influence of soil physical and chemical properties

Abstract: A natural leachate individually spiked with 11 trace elements (As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Se, V, Zn) was used to leach 11 soils from the seven most prominent orders. Soil column effluents were continuously analyzed for the various elements and these data were correlated with soil physic

A macroscopic-scale model of water uptake by a nonuniform root system and of water and salt movement in the soil profile

Abstract: A dynamic numerical model, based on the transport equations for water and noninteracting solutes in a porous medium and written in IBM S/360 CSMP language, was designed to compute the movement of water and salts in a soil profile in the presence of an active root system. The inputs are: soil

The Influence of Soils and Microclimate on Vegetation of Forested Slopes in Eastern Kentucky

Abstract: Soils, microclimate, and vegetation differed greatly between two contrasting northeast- and southwest-facing slopes in the Appalachian Mountains of eastern Kentucky. Silt loam Shelocta soils had developed on the northeast slopes, while sandy loam Rigley soils had developed on the southwest slopes. Air temperature, through-fall, soil temperature, and the annual cycle of soil temperature fluctuations were all significantly greater on the southwest than on the northeast slope. Available soil moisture and relative humidity were greater on the northeast slope. Vegetation of the northeast slope was more diversified in numbers of species and tended towards the mixed mesophytic type including yellow poplar, basswood, and cucumber magnolia. The southwest slope supported a less diverse plant community with mixed oak and hickory as the dominant trees.

Isotope geochemistry of carbonate dissolution and reprecipitation in soils

Abstract: The processes of dissolution and reprecipitation of carbonates in soils developed on carbonate rocks, loess-derived soils, and marine clay soils were studied with the methods of stable isotope geochemistry. Between 10 and 50 percent of the carbonates present in the upper part of soils developed on carbonate rocks are newly formed. In loess-derived soils and in marine clay soils, up to 100 percent of the carbonates present may be newly formed. The efficiency of the dissolution-reprecipitation process varies between 10 and 30 percent. In the salt marsh investigated the dissolution is caused by the action of biogenic carbon dioxide.

Organic phosphorus as a predictor of plant-available phosphorus in soils of southern nigeria

Abstract: Phosphorus mineralized during four periods of cropping with maize in the greenhouse Was the factor which correlated best (r = 0.90) with P uptake from 21 surface and four subsoil samples from southern Nigeria. Over the cropping periods the organic P decreased an average of 27 percent and the

Kinetics of phosphate release from a desert soil

Abstract: The kinetics of indigenous phosphorus release from the surface and subsoil of Thiokol silt loam, a typic calciorthid, was studied at 11°, 25°, and 40°C. The anion-resin technique was used to obtain the P-release data. The P-release data from the two samples over a period of 5 days could be d

Aluminum and Silica Solubility in Soils

Abstract: The applicability of equilibrium relationships to the mobility of Al and Si in open systems (soil columns) was examined in nine soils representing six soil orders. Gibbsite, halloysite, kaolinite, and montmorillonite appeared to control the solubility of Al and Si. X-ray diffraction measurements confirmed their presence in the soils. A model for describing soluble Al as a series of Al(OH)3−zz (z = 0–5) monomers was evaluated. The monomer model was in agreement with the electrophorectic properties of aqueous Al and the solubility of solid phase Al.

Extraction and Colorimetric Determination of Thiosulfate and Tetrathionate in Soils

Abstract: Thiosulfate and tetrathionate are two intermediate forms of S produced during oxidation of elemental S to sulfate in soils, but no simple and specific method is available for determination of microgram quantities of these S forms in soil extracts.A simple and precise colorimetric method of d

Estimating Potentially Mineralizable Soil Nitrogen from a Chemical Index of Soil Nitrogen AVAILABILITY1

Abstract: The feasibility of estimating potentially mineralizable soil nitrogen, N0, from direct on indirect measurements of NH4+–N produced by hydrolysis of soil organic nitrogen during 16-hr autoclaving (121°C), Ni, was investigated for 13 groups of soils comprising 475 surface and subsurface samples representing 54 soil types. The regressions of N0 on Ni for different soil groups were pooled, and the resulting equation was N0 = 4.1 (±1.0) Ni + 6.6. Apparently, therefore, the coefficient, 4.1, provides a means of reasonably estimating N0 from the chemical index, Ni, for a broad range of soils, with certain specified exceptions. Estimates of N0 from Ni together with measurements of residual mineral, plant-available N may provide a basis for developing improved N fertilizer recommendations.

Some effects of cadmium on coniferous forest soil and litter microcosms

Abstract: Description and criticism is given of preliminary design and use of a soil/litter microcosm in which oxygen, temperature, and humidity are kept constant, and oxygen generation and carbon dioxide and heat evolution rates are monitored. Using four microcosms, one acting as a dead control, experiments were performed giving the following results: For ''identically'' prepared and incubated microcosms, the coefficient of variation was as small as 3.8 percent for carbon dioxide evolution rate and as large as 9.9 percent for oxygen consumption rates. It was also found that an adjustment period of 7 to 10 days after microcosm preparation was necessary to approach relatively constant production rates. For microcosms adjusted to 10, 30, and 60 percent of field water holding capacity, oxygen and carbon dioxide rates and bacterial densities vary directly whereas the fungi and actinomycetes varied inversely; while for cadmium-amended microcosms, 0.01 ppM and initial stages in the 10 ppM Cd/sup 12/C unit, oxygen consumption was stimulated suggesting respiratory enzyme uncoupling while in the later stages the 10 ppM cadmium-amended soils reduced both O/sub 2/ and CO/sub 2/ respiration by 40 percent. No organismal density changes due to cadmium were detected indicating the cadmium initially affects respiration, possibly by uncouplingmore » respiratory phosphorylation, and that longer experiments might be necessary to detect population density changes.« less

A statistical approach to define soil, aeration in respect to denitrification1

Abstract: Interpretation of aeration measurements made in soils with restricted aeration may lead to contradictory conclusions. One reason for this difficulty is the high spatial variability of soil factors which affect aeration such as structural properties of the gaseous diffusion paths, distribution and intensity of gaseous sinks and sources and hence partial pressures of gaseous components. The variability pattern of aeration parameters is a meaningful expression of soil aeration status. The objective of this paper is to discuss and illustrate the concept that aeration may be understood as a statistical expression of microscale heterogeneity. The significance of space resolution of aeration sensors and ways of interpreting aeration measurements are discussed with respect to the relative importance of anoxic microsites. The range of soil aeration variabilities is illustrated with oxygen diffusion constants measured on soil samples and with field-measured nitrous oxide concentrations.

Spatial variability of in situ unsaturated hydraulic conductivity of maddock sandy loam

Abstract: Unsaturated soil hydraulic conductivity (K) versus depth was measured in situ in five infiltration plots within a 0.01 hectare area on a soil developed from lacustrine materials in a glacial lake bed. Sufficient water was allowed to infiltrate each plot to wet the soil profile to 152 cm. The soil surface was covered to prevent evaporation and during the ensuing drainage period, soil water pressure was monitored with triplicate tensiometers at each depth of 15, 30, 45, 61, 91, 122, and 152 cm. Soil water characteristic data determined on triplicate cores taken from the same depth as the tensiometer cups, were used in conjunction with the soil water pressure head data to compute the hydraulic conductivity. Significant spatial variability of hydraulic conductivity at the 1 percent level was found. In addition, K significantly varied with depth, at the 1 percent level, generally increasing, due to the heterogeneous nature of soil in the vertical direction. Hydraulic conductivity as a function of porosity was computed for each site by the modified Green and Corey method. Agreement of these theoretical K values with those measured in situ depended on the soil water content at which the matching factor was selected. Agreement between methods was best when the matching factor was selected at the lowest water content at which K was measured in the field for that particular soil depth.

EFFECT OF SALINITY, SAR, Ca: Mg RATIO IN IRRIGATION WATER, AND SOIL TEXTURE ON THE PREDICTABILITY OF EXCHANGEABLE SODIUM PERCENTAGE

Abstract: Effects of salinity, SAR, Ca:Mg ratio in irrigation water, and soil texture were studied using 50 different solutions and three type of soils to predict the ESP of soils by ESR-SAR relationship. Adsorption of sodium slightly increased with the increase of salinity, and more with the SAR, and

EFFECT OF 2450 MHz MICROWAVE RADIATION ON SOME SOIL MICROORGANISMS IN SITU

Abstract: Different soils were exposed to 2450 MHz microwaves in the laboratory and in the field. The effect of microwave radiation on soil microorganisms was assessed by classical microbiological techniques. It was found that soil bacteria, bacterial spores, actinomycetes, fungi, nitrogen-fixing bacteria, and nitrifying bacteria were resistant to 40,000 joules of microwave energy applied to each cm2 of soil surface. Weed seeds exposed to much lower levels of radiation were uniformly inactivated in laboratory and field experiments. Bacteria became susceptible to microwaves when removed from their natural habitat but they were not affected by soil moisture. There appear to be no residual effects of microwaves in the soil and the effects on microorganisms seem to be nonselective except that fungi, as a class, were more susceptible. A “heat shock” activation of bacterial and fungal spores was observed. From the data presented, it is reasonable to assume that microwaves can be used to control field weeds without damage to the soil microorganisms.

Note Simulation of Root Growth and its Effect on the Pattern of Soil Water Uptake by a Nonuniform Root System

Abstract: ABSTRACT An approach is described toward evaluation of the effect of root growth on soil-water-plant relations in the context of a dynamic simulation model of moisture extraction by a nonuniform root system. The method accounts for root proliferation in each layer and of root extension into deeper layers, the rates of which are assumed to depend on soil moisture potential. The death rate of roots in each layer is also taken into account. The results demonstrate the overriding importance of root extension as a factor prolonging the period of time a plant can continue to thrive on the unreplenished reserve of moisture contained in an initially-wet soil profile.

Altitudinally Coordinated Patterns of Soils and Vegetation In-The San Jacinto Mountains, California

Abstract: Soils and vegetation were sampled in eleven ecosystem types along the elevation gradient of 3000 m on the inland slope of the mountains, from subalpine and montane pine forest through woodlands and chaparral to desert. All soils were on granite or granite-derived materials, so that soil differences reflected effects of climate directly or by way of vegetation. Gradients of soils characteristics were observed: (1) Soil organic content increased with elevation, but soil litter cover was maximal at upper-middle elevations where plant cover and productivity were highest. (2) Other characteristics related to organic matter—water-holding capacity, and cation exchange capacity—increased with elevation; bulk density and particle density decreased with elevation. (3) Water movement shifted from moderate leaching at higher elevations, through relative balance, to the evaporative climate of the deserts and surface salinization in the lowest-elevation soil sampled, a solonchak. (4) Soil pH and percent base saturation decreased with increasing elevation. (5) Clay production was maximal in the combination of temperature and precipitation conditions of middle elevations. Although these are relatively young soils of mountain slopes, they suggest a geographic sequence from a cool (and relatively dry) northern woodland to a warm desert climate.

Adsorption of Picloram by Humic Acids and Humin

Abstract: ABSTRACT More picloram (4-amino-3,5,6,-trichloropicolinic acid) was adsorbed by humin than by the organic low-moor peat soil humus from which the humin was prepared. However, less picloram was adsorbed by the humic acids extracted from the organic material. The pH-dependent adsorption found for all four preparations agreed with the concept that the adsorption of picloram is largely that of uncharged (or dipolar) molecules. The effects of salt concentration on adsorption are largely those due to exchange of hydrogen into solution, shifting the equilibrium toward the molecular form. Anion exchange apparently did not occur with the organic matter preparations. Salting out occurred with 0.1 molar salt solutions. A slight decrease in adsorption took place at pH values below 1 and this is explained by the fact that picloram becomes diprotonated in this pH region, forming cations, which cannot compete with H+ for adsorption sites.

Influence of Soil Temperature and Water Tension on the Decomposition Rate of CARBON-14 Labeled Herbage

Abstract: The relation of decomposition rate of carbon-14 labeled blue grama (Bouteloua gracilis) to soil water content and temperature was examined in laboratory studies. Soil samples amended with ground herbage were incubated at various temperatures (3, 10, 25, 40, 50, and 60/sup 0/C and water contents (.009, .03, .06, .60, 5.8, and 113 atm water tension). The oxygen concentrations in the decomposition vessels were determined to evaluate the possibility that oxygen became limiting in the experiments. Radiocarbon losses were assessed and the results used to develop a multiple regression equation, which predicted percent carbon loss per hour as an exponential function of water tension, time, temperature, and the inverse of temperature.