摘要:

Polyenergetic, high-photon-flux X-ray absorption methods promise to make possible rapid, high-resolution measurements of phase fractions in multiphase systems. Improved statistical methods for data analysis, however, are needed. We develop a set of three new path-length estimators as alternatives to the traditional lumped-energy approach, and we compared this set of estimators for two classes of examples. The experimental comparisons were performed with clean systems to allow reliable measures of accuracy and precision of all material estimates; however, soil systems, for which X-ray attenuation methods have been routinely applied, have radiation attenuation properties similar to the systems used in this work, making these results directly applicable to soil systems. Results show that the new estimators provide more accurate and precise estimates of path length than the traditional lumped-energy approach, especially for challenging, multiple material estimation problems. The bias of estimated path lengths was reduced by at least 80% in all cases and was typically around 90% compared with the standard approach. Our sample results also demonstrate the reliable simultaneous measurement of three material path lengths, a new and desirable capability for multiphase flow experiments. Alternatively, the improved estimators developed in this work can be used to reduce measurement times compared with traditional methods for estimates of similar quality.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Determining the relationship between soil B and crop B content can help predict when crops will respond to B fertilizer and when B toxicity may be expected. Such a relationship can then be used to make fertilizer recommendations or to flag conditions of potential B toxicity. Soil samples were obtained from 65 sites located in the Broadview Water District in the San Joaquin Valley of California. A diverse set of extractants was evaluated including: hot water-soluble, 1:1 soil:distilled water and 1:2 soil:distilled water, ammonium acetate, calcium chloride-mannitol, and DTPA-sorbitol extracts. Soil extract B values were correlated significantly with various B reactive soil constituents, including aluminum and iron oxide, clay, organic matter, and calcium carbonate content. The 1:1 water extract B was highly significantly correlated (99% level) with other measures of extractable B used in the study. Extractants were compared on soil samples collected from six depths at 65 field sites in the San Joaquin Valley of California that were cropped to alfalfa, melons, and cotton. Boron concentrations of whole plants and composites of 10 leaves were determined. Plant sampling occurred at the time of soil sampling for the alfalfa. Cotton and melons were sampled at flowering and prior to fruit set, the recommended growth stages, respectively, for tissue sampling, and 6 weeks thereafter. Five weeks later the cotton was sampled a third time. Significant correlations (95% level) between extractable soil B and plant B were found for melons and cotton but not for alfalfa. Correlation coefficients for the ammonium acetate, DTPA-sorbitol, and 1:1 water extract were not statistically significantly different (95% level). Although significant correlations (95% level) were obtained, the equations provided relatively poor predictive capability. These results illustrate the difficulty of predicting plant B content based on soil B analyses from a single soil sampling.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Although Cr(III) is considered a Cr species with low mobility and toxicity, the potential oxidation of Cr(III) to Cr(VI) in soils containing Mn requires further scientific attention because of the acute toxicity of Cr(VI). This study evaluates the inhibition or enhancement of Cr(III) oxidation by Mn oxide in the presence of various organic ligands and concentrations. Batch experiments indicate that 200 μMof organic ligands inhibited 20 μMCr(III) oxidation by Mn oxide at pH 4 because of the occurrence of reductive dissolution of Mn oxide. Although oxalate did not show strong inhibition of Cr(III) oxidation at pH 10, nevertheless, citrate and N-hydroxyethyl-ethylenediamine-triacetic acid (HEDTA) ligands did retard Cr(III) oxidation. It is possible that the co-precipitation of Cr(III) and organic ligand, which has a low dissociation constant, results in low release of Cr(III) and subsequent oxidation. The current results imply that the management of Cr(III)-containing waste is very important to prevent potential oxidation of Cr(III) by Mn oxides, particularly at low pH. However, the presence of organic ligands in the field may lead to low Cr(III) oxidation where Cr(III) waste is disposed.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The humification process increases semiquinone-type free radical concentrations (SFRC) in humus. Their quantification by electron spin resonance spectroscopy (ESR) has been a good indicator of the degree of humification of soil organic matter. As an alternative to relatively complex and expensive ESR spectroscopy, fluorescence spectroscopy was used in this study to evaluate the humification degree of 18 humic acids (HA) extracted from four Brazilian soils under different land use, tillage, or cropping systems. Two fluorescence humification indexes of HA were calculated based on work done byZsolnay et al. and Kalbitz et al. in 1999, and a third new fluorescence index was proposed. Our proposal is to use the blue wavelength (465 nm) as the HA fluorescence excitation source. As this wavelength is more resonant with the humificated groups present in soil HA samples, our hypothesis is that the resultant fluorescence will provide information about these structures and, therefore, on the degree of humification of the HA. The SFRC varied from 1.90 × 1017to 14.75 × 1017spins/g HA, characterizing a wide range of the degree of humification of soil HA. The lowest SFRC occurred in native forests (1.90 × 1017to 7.50 × 1017spins/g HA) and pasture soils (2.30 × 1017to 4.64 × 1017spins/g HA). In cultivated sites, soil HAs from no-tillage soil were less humified (2.41 × 1017to 13.30 × 1017spins/g HA) than those in conventionally tilled soil (5.68 to 14.75 × 1017spins/g HA). The three fluorescence indexes show the same tendency as SFRC. Our fluorescence method was closely related to procedures found in the works of Zsolnay et al. and Kalbitz et al. (R∼0.9, P < 0.0001) and with SFRC (R∼0.85, P < 0.02), showing their potential as a simple and sensitive technique for evaluating the effect of land use and soil management systems on the humification degree of soil humic acids.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The potential of crop residue fertilization as a carbon sequestration technology was evaluated in a central Ohio Luvisol (fine, mixed, mesic Aeric Ochraqualf). Wheat (Triticum aestivum L.) straw was applied at three rates (bare: 0; low: 8 Mg; and high: 16 Mg ha−1yr−1) without (−F) and with (+F) addition of 244 kg N ha−1yr−1. The treatments were triplicated in a completely randomized block design. We report on the impact of these treatments on the total stocks and biochemical attributes of soil organic C (SOC) in the 0 to 10-cm soil layer after 4 years. Microbial biomass C (MBC) and mineralizable C (MinC), as measures of the labile C pools, were used as biochemical indices. SOC stocks, MBC and MinC were generally lowest in the bare plots, and more so with fertilization of these treatment plots. The addition of wheat straw and fertilizer had a positive and interacting effect on SOC stocks. With low mulch application, SOC stocks were similar (25.6 Mg C ha−1) in the −F and +F plots. However, when the mulch rate was high, further SOC accretion (28.2 Mg ha−1) occurred only in the +F plots. Residue-C conversion into SOC averaged 14% and 32% without and with fertilization, respectively. Positive effects of wheat straw application on MBC and MinC110 dayswere also found. Although not significant, MBC was generally lower in the fertilized compared with unfertilized treatments. Fertilization of wheat residue resulted in a 1.5-fold increase in MinC, and a 1.3 to 4 times increase in the metabolic quotient (unit of MinC per unit of MBC per day), suggesting alteration in the soil microbial community composition and less efficient C processing with fertilization. The temporal variation of these soil biochemical attributes and the fate of the labile C compounds that evolved with fertilization of residue will determine the long-term sustainability of residue fertilization practice on C sequestration in soils.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Phosphorus that accumulates in the surface of sandy soils is susceptible to leaching and surface runoff. Converting dissolved P to less soluble forms using materials containing Fe, Al, and Ca can reduce the amount of soil P released to runoff. The dredged muck of the St. Lucie Estuary has been proposed as a manufactured soil for application on local sandy soil. It is assumed that the application of the muck will enhance soil P retention. In this study, the effects of muck sediments on water-soluble P, Olsen-P, and P fractions of some Florida sandy soils were investigated. In the muck type and rate experiment, two soils (a high P soil and a low P soil) were incubated for 30 days with the mucks at 0, 5, 15, and 30%. Application of muck reduced water-soluble P and Olsen-P significantly in the high P soil, and also reduced water-soluble P and Olsen-P slightly but consistently in the low P soil. When a high rate of muck (30%) was applied, the high Fe and Al muck reduced water-soluble P by 69 to 89% and Olsen-P by 27 to 62%, whereas the low Fe and Al muck reduced water-soluble P by 23 to 61% and Olsen-P by 22 to 34%. At low rates (15%), water-soluble P was reduced by 35 to 79% for the high Fe and Al muck and 2 to 43% for the low Fe and Al muck, whereas Olsen-P was reduced by 24 to 44% for the high Fe and Al muck and 12 to 31% for the low Fe and Al muck. The decreased P solubility resulted from the conversion of readily soluble P (H2O-P and NaHCO3-P) to less soluble pools (HCl-P and residual P). Amending the high P soils with mucks has the potential to reduce P enrichment of runoff by decreasing the solubility of soil P. These data indicate that application of muck can result in significant reductions in nonpoint-source P runoff from high P soils.

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