ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Phosplate solutions were added to samples of a soil and the samples were then incubated at a range of temperatures between 4° and 42°C for periods of up to 320 days. After various intervals, the proportion of the added phosphate which exchanged with P32was measured by shaking the soil with solutions which were 0.01 M with respect to calcium chloride and which contained appropriate concentrations of labeled phosphate.The proportion of the added phosphate which exchanged was found to be independent of the quantity of phosphate added. It decreased with increasing periods of incubation at a rate which depended on the temperature. The effects of time and temperature of incubation were comparable with previously observed effects on the concentration of phosphate in the soil solution and on the decrease in effectiveness of phosphate for plant growth.For a given period and temperature of prior incubation, the proportion of the added phosphate which exchanged was related to a fractional power of the period of equilibration with P32. The effects of level of application, period and temperature of incubation, and period of equilibration could be described by a single equation.It is suggested that the effects observed in this and in preceding papers can be explained if it is assumed that the initial adsorption reaction of phosphate is followed by a further reaction in which a second hydroxyl group of the phosphate reacts with the surface. It is postulated that there is a range of reaction velocities at individual sites. A distribution of reaction velocities which is compatible with the results is presented.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The extent of irreversible adsorption of cobalt and zinc ions in sodium montmorillonite is shown to depend upon the composition of the solid phase and the pH. At low and intermediate occupancy of the divalent cation, the adsorption is perfectly reversible up to a pH value of about 6. At very high occupancies, approaching saturation, a significant portion of the adsorbed divalent cations become irreversibly fixed, but can be desorbed by a pH decrease. The consequences of the irreversible and nonstoichiometric uptake of these ions are analyzed and the phenomenon is discussed in terms of an adsorption process, involving either structural hydroxylgroups of the clay or hydroxyaluminum compounds.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A simple and precise colorimetric method of determining phosphate in ethylenediaminetetraacetic acid (EDTA) or nitrilotriacetic acid (NTA) extracts of soils is described. It involved extraction of the phosphate in soil with EDTA or NTA solution, titration of the extract with dilute hydrochloric acid to pH 1.5, filtration (to remove the slightly soluble, H-EDTA or H-NTA and mimic acid precipitates formed), and colorimetric determination of the phosphate in the filtrate by an ascorbic acid method. The method is sensitive and accurate', and it permits determination of phosphate extracted from soils by using up to 300 mM EDTA and NTA solutions.Studies of the factors affecting the release of phosphate from soils by EDTA or NTA solution showed that the release of phosphate from soils is affected by the pH, time of extraction, soil: solution ratio, and concentration of the chelating solution used, and that the organic phosphate extracted from soils by these reagents is stable at room temperature for several days.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Characterization of the metal-complexing ability of polyfunctional macromolecules through the determination of stability constants of their metalic complexes is discussed along with the validity of ascribing a relationship between the metal-ion complexing properties of organic matter extracted from the soil and the role of naturally occurring organic matter in soil in the processes of plant nutrition and soil genesis.The type of complex obtained when mixing metal-ion and complexant solutions will be a function of the molar ratio metal-ion/complexant. If Schubert's original experimental conditions (e.g., complexant concentration ≫ metal-ion one) are used, the MCh- or MChb-type complexes will always be formed regardless of the polyfunctional character of the organic macromolecule (Ch). It is suggested that the overall stability constant of the saturated complex MaCh would describe in a comprehensive way the metal-complexing properties of such complexants.No reliable information about the role of soil organic matter in plant nutrition or soil genesis processes can be obtained by studying the metal-complexing ability of extracted soil organic matter. This is due to the fact that the metal-complexing properties of these materials—or the number of active anionic group on the extracted molecules—will depend on the extent of depolymerization suffered by the naturally occurring soil organic matter during extraction.The methodology used up to the present to study the involvement of soil organic matter in plant nutrition or soil genesis processes through its metal-complexing ability urgently needs reevaluation.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The stability of heavy metal sulfides (MnS, FeS, ZnS, CuS, and HgS tagged with35S) in aerobic and anaerobic soil was studied. The sulfides are listed in decreasing order of solubility. Water extracts of each treated soil were made regularly during a 75-day incubation period. The radioactivity of the extracts was indicative of the stability of the water-soluble salts. For the aerobic soils, H2O-extractable35S decreased with a decrease in solubility of the sulfide. The metal-sulfides were relatively stable in the anaerobic soil. The least soluble salt was the most stable.To study the oxidative capacity of rice (Oryza sativa L.) roots the35S tagged metalsulfides were mixed with anaerobic soil to which rice was transplanted. The tagged soil was placed in the lower rooting zone and covered to a depth of 8 cm with unlabeled soil. The transplanted rice plants were grown for specific times and the aerial portions harvested. The uptake of35S from the respective sulfide salt was determined. The apparent degree of stability and subsequent uptake of35S was directly related to the solubility of the sulfide salt. No35S was taken up from the Hg35S.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Different sequences of temperature fluctuations between 5° and 35°C imposed upon three soils during incubations of 52 days had no effect upon the amount of N mineralized. Over the first 32 days, the results agreed with calculated mineralization rates in all three soils, but only one soil (Barnes) showed agreement for the whole 52-day period. The failure to obtain agreement in Cecil and Kranzburg soils beyond 32 days may be due to the effects of extreme temperature changes upon the ammonifying organisms. The results, however, justify continued efforts to improve means for predicting soil nitrogen mineralization rates in the field.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Alfalfameal, sucrose, and peat moss were added in large amounts to very acid soil to find their effects on yields of barley and alfalfa grown in the greenhouse. Alfalfameal was found to be the most effective. Its action was attributed primarily to complexing of exchangeable Al and, in consequence, decreasing toxic quantities of Al in the soil. The Al-organic matter complexes formed by the nonincubated alfalfameal were mostly soluble in water, but those formed by the incubated (4 weeks) alfalfameal were insoluble in water. In both cases, complexing was caused mainly by the water-soluble component of the original, i.e., nonincubated alfalfameal. Release of NH3from the decomposing alfalfa meal was not considered a major cause of decrease in exchangeable Al, since most of that decrease had taken place before there was an increase in exchangeable NH4.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

A simple technique for the production of low-Na peanut (Arachis hypogea L., variety Virginia Jumbo) seedlings is described. In the construction of the growth chamber only plastic or low-Na material was used. Peanut seedlings grown by the technique for as long as 7.3 days picked up only 2 μg of extraneous Na on a per seedling basis.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The number of earthworm channels ranging from 2 to 11 mm in diameter were counted to 80 cm depth in tilled and untilled grey-brown podzolic soil derived from loess. Number and percentage volume of earthworm channels in the Aphorizon approximately doubled during 4 years of no-tillage practice as compared to the tilled plot. Almost all the channels of the Aphorizon in the untilled plot had ports at the soil surface and were capable of taking in tension-free irrigation water and transmitting free water to a maximum depth of 180 cm, where the channels end at the transition to unweathered loess. The channels in the Aphorizon of the tilled plot were not effective in water transmission. The same is true for a large number of channels in the subsoil of tilled and untilled plots, which could not contribute to water infiltration because they were not connected with the soil surface. The maximum infiltrability of conducting channels in the untilled soil was computed as more than 1 mm (1 liter per m2) per minute, although the volume of these channels amounted to only 0.2 vol. %.

ISSN:0038-075X    

出版商:OVID    

年代:1975

数据来源: OVID