摘要:

Interest in anthrax has increased recently due to its use in bioterrorism attacks.Bacillus anthracis,the causative agent of anthrax, is genetically similar to otherBacillusspp. that occur in the environment, and is known to persist in soil for years in the form of spores. In many soils, naturally occurring anthrax infections tend to occur during dry periods following a wet period. The “incubator theory” suggests that spores are concentrated in low-lying areas during rainfall events and animals are subsequently exposed to contaminated soil during foraging in dry periods. It is currently believed thatB. anthracisspores require a host for germination, and thus do not undergo proliferation cycles in the soil. There is a potential forB. anthracisspores to be transported as an aerosol, but human infection due to inhalation of spores is unlikely given the high minimum infectious dose required to cause disease. Historically, naturally occurring anthrax infections in humans have most commonly occurred due to contact with diseased animals or animal products. However,B. anthracishas been developed as a biological weapon with accidental and intentional releases resulting in human death. With the development of an anthrax vaccine, anthrax outbreaks have generally been controlled in developed countries; however, anthrax is still a major problem in many parts of the world. The advent of molecular techniques has enhanced the detection ofB. anthracisspores, which is now possible in less than 1 h. However, due to the persistence of spores, it is difficult to eliminateB. anthraciscontamination from the environment. There remains a need for additional research on anthrax in several areas including evaluation of the conditions that favorB. anthracissurvival in soil, determination of whetherB. anthracisundergoes a growth cycle in soil, and determination of the potential for transfer ofB. anthracisvirulence genes to other soil microorganisms.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Humic acids were extracted from two histosols, an andosol, an inceptisol, a rice field soil, and a sludge-amended cambisol and characterized by elemental analysis, acidic groups titration, E4/E6determination, Fourier transform infrared (FTIR) and13C nuclear magnetic resonance (13C NMR) spectroscopy, viscosity and surface pressure measurements, and scanning electron microscopy. Relevant compositional differences between humic acids depending on their formation conditions were observed. Humic acids from the histosols and the andosol were largely aromatic and rich in acidic functional groups. The inceptisol humic acid contained about the same amount of aliphatic and aromatic moieties and was particularly abundant in soil, probably because it is stabilized by strong interactions with the inorganic components. The paddy soil humic acid was mainly aliphatic and poor in acidic groups because of the partial anaerobic conditions of the rice field. The sludge-amended soil humic acid was similar to humic acids from rapidly decomposed organic matter: low content of carboxylic groups and high content of proteinaceous material. The chemical composition affected, to some extent, the physical behavior of the humic acids. The surface tension was negatively correlated with the concentration of carboxylic groups. The presence of polysaccharides and proteinaceous moieties promoted elongated conformations of humic molecules in solution and directly related to the intrinsic viscosity and consequently to the molecular dimension of humic molecules. The largest aggregates in dry state were observed in humic acids with, besides a high aromaticity, a high content of carboxylic groups.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Organic phosphorus (P) can comprise a significant amount of the total P in animal wastes, yet there is little information on the potential for organic P to be transferred from soils to watercourses. We examined the adsorption of organic P compounds to soils typical of the southeastern United States, i.e., Blanton Sand (loamy, siliceous, thermic, Grossarenic Paleudult), Cecil sandy clay loam (fine, kaolinitic, thermic, Typic Kanhapludult), and a Belhaven sandy loam (loamy, mixed, dysic, thermic, Terric Medisaprist). The behavior of four organic P compounds was studied: adenosine 5′-triphosphate (ATP), adenosine 5′-diphosphate (ADP), adenosine 5′-monophosphate (AMP), and inositol hexaphosphate (IHP); while KH2PO4(ortho-P) was used as an inorganic reference. Laboratory studies were conducted to determine the effects of concentration (0–130 μg P mL−1), pH (4.6–7.6), and soil properties on P adsorption. All the organic P compounds had greater adsorption than KH2PO4on the Blanton and Cecil soils at all concentrations and ranges of pH. In the Belhaven soil, IHP had the greatest sorption followed by KH2PO4and the nucleotides (ATP, ADP, and AMP, respectively). Adsorption of organic P was positively correlated with soil organic matter and Fe and Al contents. The greater sorption of some organic P compounds over that of ortho-P suggests that these compounds may pose less of a threat to water quality, although this preferential sorption may increase soluble P in situations where there is displacement of ortho-P by organic P added in manures.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Herbicides and some heavy metals are frequently added together to agricultural crops. However, few studies on the phenomena that may take place in such systems have been carried out. We studied the adsorption of the herbicide glyphosate (GPS) and copper (Cu) on a synthetic goethite (Gt), in order to determine the relative contribution and mutual effect of both components on the availability of GPS and Cu in soils. The adsorption of GPS reached a maximum at 99 μmol g−1. In the presence of Cu, the adsorption of GPS on goethite increased about 9%. The reason for this behavior is the formation of Cu-GPS complexes and their higher tendency to be adsorbed compared with free GPS. Cu adsorption on goethite also increased in the presence of GPS. This higher Cu adsorption can be due to its adsorption through the formation of bonds with GPS previously adsorbed, and the adsorption of the Cu-GPS complexes formed in solution.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Four methods for measuring quantities of 12 plant-available nutrients were compared using three sandy soils in a series of three experiments. Three of the methods use different ion-exchange resin forms—bags, capsules, and membranes—and the fourth was conventional chemical extraction. The first experiment compared nutrient extraction data from a medium of sand saturated with a nutrient solution. The second and third experiments used Nakai and Sheppard series soils from Canyonlands National Park, which are relatively high in soil carbonates. The second experiment compared nutrient extraction data provided by the four methods from soils equilibrated at two temperatures, “warm” and “cold.” The third experiment extracted nutrients from the same soils in a field equilibration. Our results show that the four extraction techniques are not comparable. This conclusion is due to differences among the methods in the net quantities of nutrients extracted from equivalent soil volumes, in the proportional representation of nutrients within similar soils and treatments, in the measurement of nutrients that were added in known quantities, and even in the order of nutrients ranked by net abundance. We attribute the disparities in nutrient measurement among the different resin forms to interacting effects of the inherent differences in resin exchange capacity, differences among nutrients in their resin affinities, and possibly the relatively short equilibration time for laboratory trials. One constraint for measuring carbonate-related nutrients in high-carbonate soils is the conventional ammonium acetate extraction method, which we suspect of dissolving fine CaCO3particles that are more abundant in Nakai series soils, resulting in erroneously high Ca2+estimates. For study of plant-available nutrients, it is important to identify the nutrients of foremost interest and understand differences in their resin sorption dynamics to determine the most appropriate extraction method.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Spodosols are a soil order frequently exhibiting a redistribution of Al and Fe because of organic matter complexation, illuviation of these complexes, and immobilization of the Al and Fe as poorly crystalline silicates in deeper soil horizons. Little information is available concerning the organic matter complexation and migration of other elements, particularly the rare earth elements (REE). Four pedons representing the Padus series (coarse-loamy, mixed, superactive, frigid Alfic Haplorthods) from Wisconsin were selected to determine if selected transition metals and the REE are mobilized, illuviated, and then immobilized. Sequential soil extractions consisted of Na-pyrophosphate, ammonium oxalate, ammonium oxalate-ascorbic acid, and aqua-regia partitioned elements into operationally defined chemical environments. Total elemental contents of the whole soil and the whole silt fraction were determined using instrumental neutron activation analysis. Aluminum and Fe in the Napyrophosphate extraction, for the majority of the pedons, were discretely more abundant in the upper Bs horizon. The light REE were largely recovered by the aqua-regia extraction, implying that these elements are associated with apatite, whereas the heavy REE were only very slightly recovered, suggesting that the heavy REE reside in different minerals. A Na-pyrophosphate leach extracted only minor quantities of the light REE and undetectable to trace quantities of the heavy REE, suggesting that these elements have not been influenced by podzolization processes.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Interruption of flow during furrow irrigation (e.g., use of surge technique) consolidates soil near the furrow surface, causing reorientation and rearrangement of soil particles, and leads to increased surface bulk density (BD) and reduced hydraulic conductivity (HC) of this surface layer. We hypothesized that soil consolidation could be affected by irrigation water quality and soil sodicity. We studied in the laboratory changes in the BD and HC of an alfisol (Calcic Haploxeralf) and two vertisols (Chromic Haploxerert) having different exchangeable sodium percentage (ESP) levels that were subjected to five cycles of leaching and draining under matric potential of up to −5 J kg−1. Four different water qualities (electrical conductivity (EC) of 0.01, 0.95, 2.0, and 4.0 dS m−1) were tested. Final BD was significantly greater than the initial value when matric potential was applied. Conversely, for continuous leaching (i.e., no application of matric potential), differences between final and initial BD were insignificant. Water quality and sodicity did not affect BD, suggesting that for a given soil exposed to a low level of matric potential, soil consolidation was not affected by water quality or ESP. Final HC values were always lower than initial ones, with the decrease in HC after application of matric potential being by far greater than that observed when continuous leaching was used. The decrease in HC relative to initial HC depended on both water quality, and soil sodicity, was greater with the decrease in water EC and an increase in ESP. Adverse effects of low EC and high ESP on HC were less pronounced in matric potential application than in continuous leaching. Our results suggest that the quality of water available for irrigation and soil sodicity should be taken into account in cases where interrupted flow is considered for improving furrow irrigation efficiency via reducing soil infiltration rate.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID