摘要:

This paper describes a modification of the standard procedure for preparing saturated extracts of salt-affected soils whereby soil saturation is approached from the wet, rather than from the dry, side. This new method offers considerable saving in time and labor of preparting saturated soil pastes for extraction and analysis. An effective test for the end point of saturation and modern extraction equipment are also described.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Boron adsorption characteristics of “allophanic” soils derived from volcanic ash were studied in samples collected in central-southern Chile.he general technique for boron adsorption was based on the use of selected parameters such as 2.50 g of moist soil equilibrated with 25.0 ml of solution, pH 6.0, room temperature, and 24 hr of reaction. In addition, the effects of equilibration time, pH, concentration of boron, and competition with S and P were studied.The equilibrium time for boron adsorption was about 24 hr, though approximately 60 percent was adsorbed in a very short time. Boron adsorption under acid conditions appears to be the result of molecular adsorption of B (OH)3, whereas the adsorption in the alkaline range, reflects in addition, adsorption of B (OH)4-on activated sites by either alkalinization or protons dissociated from boric acid.Competition experiments showed that there was possibly an effect due to the presence of K2SO4, but little or no effect was noted when boron adsorption was studied in the presence of KH2PO4.The high amounts of boron adsorbed by these soils are due to the affinity of boron for amorphous alumino-silicates, as shown by the significant correlation found between boron adsorption and “allophane” content, and not with other amorphous components of the soils such as organic matter and free iron oxides.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

An Entic Haplorthod, cropped for many years to potatoes, was used for plant pot and chemical studies involving the effects of pH increases by liming on the availability of B and P toZea maysL. andMedicago sativaL.Increasing amounts of B added to the soil increased yields and B contents of alfalfa but caused increased toxicity symptoms in corn. Boron toxicity in corn was prevented by pH values above 6. When only the standard rate of P was applied, best growth of both crops was in soil at pH values from 5 to 5.7. When pH values were above 6, growth was retarded by deficiency of P. At pH values above 6, the addition of the high rate of P practically doubled dry-weight yields of corn and produced more than 20-fold increases in alfalfa yields. Deficiency of P induced by liming decreased with time.Parallel behavior of B and P in this study supports the hypothesis that both elements may be bound in podzolized soils by similar pH-dependent mechanisms, probably precipitation or adsorption by hydroxy Al.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

To obtain more information about the K exchange behavior of naturally fine-grained micaceous minerals, and especially the reasons for part of the K in these minerals being nonexchangeable, samples of Grundite illite were subdivided on a particle-size basis or ground in various ways and characterized in regard to their NaTPB-extractable K.Various illite fractions that were prepared by mechanically disperising the material in water, released K at nearly the same rate and to the same degree (66 percent). These data emphasize the difficulties encountered in isolating particle-size effects in naturally fine-grained micaceous minerals, show the limited exchange of interlayer K in small particles is not confined to ground or chemically dispersed samples, and establish the level of K exchange to be used in assessing the effects of particle size in this mineral. Since these fractions appeared to be made up of aggregates, portions of the illite were dispersed by chemical treatments that were shown to not alter the K-release behavior of the mineral. With these chemically dispersed size-fractions, the rate of K exchange increased and the degree of exchange decreased as the particle size decreased. While this K-release behavior of illite fractions is similar to that observed with ground micas, the limitations on K exchange imposed by particle size is far greater with illite (only 48 percent of the K in <0.08 μ illite particles being exchangeable) and no illite fraction released all its K.The effects of grinding illite by wet and dry procedures were evaluated in terms of the changes induced in both the nonoxidizable N (by NaOBr) and the nonextractable K. The wet procedure had little effect on the mineral but a simulataneous increase in N oxidation and K exchange was achieved by dry grinding. Part of the K and N in this mineral seem to occur together in contracted interlayers and are rendered inaccessible by the same small particle-size effect. Unlike the results obtained with ground micas, a net increase in the accessibility of the interlayer components was achieved by fracturing illite particles. However, even dry grinding failed to expose 9 me K per 100 g and 147 ppm N.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The acid-resistant humic residue resulting from a proximate analysis of forest raw humus was oxidized with potassium permanganate. The methylated residue was oxidized at pH 9–10, and nonmethylated residue at pH 7–8, pH 9–10, and pH 11–12.Twenty-six phenolic and benzenecarboxylic acids and eleven straight-chain dicar-boxylic acids were identified as methyl ethers and esters. Identity was established after preparative thin-layer and gas chromatography, followed by micro-I.R. spectroscopy and mass spectrometry.The highest amount of dicarboxylic acids was recovered from nonmethylated residue oxidized at pH 7–8, and the highest yield of benzenepolycarboxylic acids was found by oxidation at pH 11–12. These oxydations gave only small amounts of methoxy- and none of dimethoxy-benzenecarboxylic acids.Oxidation of methylated residue demonstrated that 1,2-dihydroxy (or 1-hydroxy-2-methoxy) substitution of aromatic structures contributes significantly to the organic matter. Hydroxy-substituted aromatic rings contribute one-third of the dihydroxy structures. The amounts of benzenepolycarboxylic acids and dicarboxylic acids produced from this oxidation were smaller than those produced from oxidation of nonmethylated residue.The differences in yields indicate that condensed ring structures are of significant importance in the residue. These structures are possibly linked together by aliphatic chains of different lengths. The aliphatic part of the humic structure consists of straight chains or cycloaliphatic rings, where 6 CH2units are most abundant.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Soil salinity can frequently be reduced and controlled under dryland conditions of the Northern Plains by proper use of dryland cultural practices that promote soil water conservation. Summer fallow significantly reduced salinity in the root zone, whereas salinity increased under a small grain crop. Soil salinity reductions attributed to fallow were greater under a deeper water table regime compared to more shallow water table conditions. A straw cover or small grain stubble mulch during the winter, in conjunction with summer fallow, led to further salinity reductions. The straw mulch was more effective in reducing salinity at a more severely saline and higher water table site than at a more moderate location. Summer fallow was more effective at the more moderate site compared to the severe location. Under the combination of summer fallow and winter vegetative mulch, precipitation in excess of evapotranspiration losses supplied water for leaching. Growing a crop, except during high rainfall periods, did not leave excess water.Our findings suggest that summer fallow with winter vegetative residue management can be effectively utilized in the cultural rotation for reducing soil salinity under dryland conditions.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Humic acid is readily available from leonardite, a naturally occurring oxidized form of lignite coal. Humic materials have been found to greatly promote root initiation ofPelargonium hortorumcuttings. Sodium humate, humic acid, fulvic acid, and leonardite produced a proliferation of roots at optimum concentrations of 0.05%, 0.05%, 0.05%, and 0.5%, respectively. Pea root tip elongation measurements indicated that the humic materials possess auxin activity.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Particulate opaline silica accounted for 0.01 to 3.79 percent of the dry weight of leaves from 36 deciduous angiosperm tree and shrub species. Silicification was noted in all cellular elements of the leaves of some species, and the pattern of silica deposition varied widely between taxa. Morphological variations were minimal among silica particles from mesophyll cells, stomata, vascular elements, crystalloids, and bundle sheath parenchyma. Siliceous epidermal cells, epidermal hairs, and hair bases exhibited sufficient variation to warrant further study toward the development of opal phytolith groupings of different taxonomic order. Morphological groupings appear possible in some cases, while separations to families, genera, or species appear possible in other cases.

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1973

数据来源: OVID