摘要:

Soil carbohydrates are a mixture of a variety of different polysaccharides, all of unknown structure. They may originate from soil bacteria, fungi and algae, or soil animals. Of the 27 mono- and di-O-methyl monosaccharides detected in a raw humus hydrolyzate, 10 have not been found in nature before. These are 2,3-di-O-methyl-arabinose; 4-O-methyl-rhamnose; 2,6-di-O-methyl-galactose; 2,6,-di-O-methyl-glucose; 2,4-di-O-methyl-glucose; 2,4-di-O-methyl-mannose; 3,6-di-O-methyl-glucose or mannose; 6-O-methyl-mannose; 2-O-methyl-mannose; and 2-O-methyl-glucose.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Decomposition of primary minerals by humic and fulvic acids was investigated by shaking microcline, biotite, or muscovite with soil humic solutions at pH 7.0 and 2.5 for 0 to 1000 hours. Silica, aluminum, and potassium released by the primary minerals were determined in the extracts by atomic absorption spectrophotometry, and changes in mineral structure supporting possible decomposition were studied by X-ray diffraction analysis. At pH 7.0, humic and fulvic acids were capable of dissolving very small amounts of silica, aluminum, and potassium from the minerals by chelation, complex reactions, or both. The amounts released increased with time and reached a maximum at 800 to 1000 hours. At the termination of the experiment, the cumulative recovery of silica, aluminum, and potassium did not exceed 5 milligrams (or 0.2 millimoles) per gram of mineral, which was far less than that reported by other workers. The present findings conform better with natural conditions. The ease of mineral decomposition occurred in the following order: biotite > microcline > muscovite. The dissolution of the elements was enhanced considerably at pH 2.5. Fulvic acid extracted 10 times more silica and 6 times more aluminum at pH 2.5 than at pH 7.0. Statistical analysis indicated that this large increase in dissolution was the effect of an interaction between low pH and type of organic acid. X-ray diffraction analysis revealed the microcline to be a mixture of orthoclase and microcline. The X-ray curves yielded evidence that humic and fulvic acids had dissolved more readily the orthoclase component, the less resistant form of potash feldspar, leaving the stable form, or microcline, to accumulate in the residue.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Calculations performed using a Gapon-type exchange equation agreed with experimental observations of the influence of lime on solution potassium levels in a soil with a high pH-dependent cation exchange capacity (CEC). As lime additions increase the pH and the CEC, solution potassium decreases. Amounts of potassium that must be added to the soil to reach solution pK-1/2p(Ca + Mg) = 2 were calculated to increase from 84 parts per 2 million at no lime to 1150 parts per 2 million for the high-lime level.The influence of lime on potassium availability could be even more severe if not for the decrease in potassium selectivity relative to calcium with increasing charge density.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Reduction of pedogenic iron oxides by the activity ofClostridium butyricumwas studied in model experiments under controlled conditions of pH, particle size (63 to 125 μm), glucose (2 percent), and anaerobic conditions. Three horizons—from a gley, pseudogley, and red clay soil, respectively—with different Feo:Fedratios were selected as test material. Except for Fe(II) formation, pH and Eh were measured at regular intervals. In all soils the total amount of free iron oxides (Fed), as well as the crystalline Fe (Fed- Feo), decreased while Fe(II) increased. The amount of amorphous Fe (Feo) remained relatively constant in those soils low in Feo:Fed(0.1 to 0.19), but diminished in the sample with a relatively high amount of amorphous Fe (Feo:Fed= 0.78). This suggests that crystalline rather than amorphous Fe forms are dissolved preferentially by acting as terminal electron acceptors. Nevertheless, the reduction of crystalline59Fe-labeled oxides (hematite and goethite) mixed with Fe-amorphous gley soil material (Feo:Fed= 0.78) clearly showed that oxalate-soluble Fe was attacked in preference to59Fe-labeled crystalline Fe.The processes of Fe(III) reduction in a microsite are discussed in relation to the mechanism of Fe(II) formation in flooded soils.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Laboratory incubation studies of a Norfolk sandy loam (Typic Paleudult), a soil typical of the southeastern Coastal Plains, were conducted to assess factors affecting ethylene accumulation. Soil from the Ap horizon accumulated more ethylene than soil from either the A2 or B horizon. In the presence of initially high oxygen and methionine, the Ap soil accumulated 35 nanograms of ethylene per gram of soil in 14 days. The same soil with methionine incubated under initial oxygen levels less than 10 percent, however, accumulated less than 5 nanograms per gram of ethylene in 14 days. When incubated under low (< 1 percent) initial oxygen concentrations, ethylene accumulation from soils from all three horizons was unaffected by the addition of methionine. Since methionine did not increase the ethylene concentration in soil with low oxygen concentrations, significant methionine-induced ethylene accumulation in the fields of Norfolk sandy loam does not appear probable. Unamended Ap soil incubated under high oxygen levels did not accumulate significant ethylene unless the water content was near saturation (> 28 percent water by weight). Adding finely ground Bermudagrass residue (0.5 to 2.0 percent) induced an increase in ethylene accumulation. The time required for peak ethylene accumulation decreased with increasing amounts of added plant residue. Nitrate, particularly at concentrations greater than 75 milligrams per kilogram, suppressed the accumulation of ethylene. The research suggests that ethylene accumulation in Norfolk sandy loam is enhanced by high moisture, low oxygen, and added organic matter, and is suppressed by high nitrate concentrations.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Four acid, low-phosphate soils from the southeastern United States were limed at four levels and amended with phosphorus (P) at five levels. Barley was grown for 60 days on these amended soils in the greenhouse. Plant yields and P uptake were measured.With these same amended soils, 24-hour equilibration P adsorption curves and equilibrium phosphate concentrations (the P concentration supported in solution by a soil at near field moisture capacity) were determined. The greenhouse and laboratory data were used to develop a two-point adsorption-curve method for estimating soil P additions to correct P deficiencies. The method is simple and includes the use of a correction factor that relates the amount of fertilizer P a soil adsorbs during the first 24 hours of addition to the amount the soil adsorbs during a growing season. Correction factors were estimated for the four soils, each at four different pH levels, on the basis of the lowest equilibrium phosphate concentration that supported 0.25 percent P in barley tissue.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

Comparisons of the effectiveness of the various zinc sources have, in past research, produced conflicting results. Therefore, this study was conducted to evaluate the effect of zinc source, zinc rate, and phosphorus carrier on corn production in the western corn belt of the United States. Three sites were selected representing a wide range of soil pH and other soil properties.The zinc sources were mixed with a suspension fertilizer (8–8.8–4.8) to supply four rates of zinc. The fertilizer was placed below and to the side of the seed at planting. Whole plant samples collected at two stages of growth and ear leaf samples collected at silking were used to evaluate the influence of zinc source, zinc rate, and phosphorus carrier on zinc uptake by corn.Zinc uptake by plants sampled three weeks after emergence was influenced by zinc source, zinc rate, and phosphorus carrier. Differences among sources were related to soil properties. Phosphorus carrier had no effect on zinc uptake at a later growth stage. Differences in zinc uptake brought about by the different zinc sources and phosphorus carriers were not reflected in yield. Application of zinc increased yield at one of the three sites, 1.7 kilograms of zinc per hectare being adequate for maximum yield. Neither zinc source nor carrier had any effect on yield throughout the study. The data showed no advantage of the chelated forms of zinc over inorganic forms when they were applied in a suspension fertilizer to the side of and below the seed at planting.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

The quality of irrigation water of selected rivers in Natal is characterized in terms of chemical components related to salinity and sodicity. Using rainfall and evapotranspiration data for each sampling site, and assuming certain management practices, we calculated the anticipated soil water salinity and sodicity values for poorly drained soils, obtaining four variables to assess water quality: water salinity and sodicity and soil salinity and sodicity. Grouping the data according to crop salt tolerance and soil sodicity limitations confirms the evaluation of water quality obtained using recently published schemes for assessing irrigation water. The general agreement between schemes for classifying irrigation water indicates the feasibility of using a system of evaluation of water quality based on crop, soil, and climatic characteristics of the area under consideration. Comparing the saturation extract salinity and sodicity of poorly drained soils with salinity and sodicity calculated from this environmental model showed reasonably good agreement, which did not invalidate the general qualitative usefulness of this approach.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

In a study on the effect of hexachlorocyclohexane (HCH) on soil transformations in flooded soils, 5 percent granules of HCH were added to three soils to provide final concentrations of 5 to 100 parts per million of active ingredient, and the soils were flooded. Addition of HCH even at the 5-ppm level led to a remarkable decrease in the formation of Fe2+and, to a lesser extent, soluble manganese and prevented the drop in redox potentials in all soils. These effects of HCH were well pronounced also in the presence of added rice straw (0.5 percent), although rice straw alone hastened soil reduction. The inhibitory effect of HCH on soil reduction lasted even after 50 days of flooding.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID

摘要:

We describe a new instrument developed to measure moisture movements as a result of condensation and evaporation processes in the upper soil layers in laboratory and field experiments. It is based on the well-known method of relating the moisture content of a soil to its electrical conductance. The high spatial resolution of 2 millimeters and the high sensitivity, especially in the dry range, make it a valuable tool for condensation and evaporation studies during the dry season of arid and semiarid climates, as well as for soil physical investigations of water vapor diffusion. A number of laboratory tests demonstrate the performance of the instrument.

ISSN:0038-075X    

出版商:OVID    

年代:1980

数据来源: OVID