摘要:

The complex pedogenetic evolution with age is described effectively by a single multivariate model. Factor analysis of selected chemical and physical properties of four pedons representing three developmental stages of a postincisive soil chronosequence in NW Italy shows that a factorial model describes the variables adequately. Two factors, accounting for 76.9% of the overall variance, describe the evolution from the more recent Inceptisol to the older Alfisol. Factor I, linked to particle size distribution, cation exchange capacity, and the crystallinity ratio of iron oxides, was sensitive to the development of either Bt or Bx horizons and can be considered an index of soil evolution for this chronosequence. Even if age is not a direct factor in pedogenesis, the stage of evolution reached by the soils in this chronosequence is related strictly to the intensity of the pedogenetic processes over time.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Five acid forest soils of eastern Austria were used to study nickel and copper sorption at metal concentrations ranging over five orders of magnitude. Distribution coefficients were calculated, and the Langmuir equation was fitted to the experimental isotherm data.Exchange for mono- and divalent cations is considered the primary mechanism of Ni sorption, whereas complexation on organic surfaces may contribute significantly to Cu sorption in the studied soils. Organic matter is considered the most effective sorbent in topsoils, while sorption in subsoils may involve primarily Mn-oxide and clay mineral surfaces. The soils studied showed higher affinity for Cu than for Ni; however, at low metal levels, competitive complexation of Cu with soluble organic compounds counteracted sorption in topsoil horizons.Using the van Bemmelen-Freundlich equation, general sorption density isotherms were developed for the studied soils. For Ni, similar fits were obtained by using specific surface area (SSA) and cation exchange capacity (CEC) as reference quantities; however, the quality of fit was improved when only the proportion of CEC occupied by mono- and divalent cations (CEC(2+)) was used as a reference. For Cu, the surface area-based approach yielded a better fit than the charge-based isotherms. Comparison with independent datasets from the literature showed good agreement with the proposed general sorption density isotherms, suggesting general applicability for acid soils of varying origin and composition.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

To measure water pressure at any depth (including depths below 5 to 7 m) in the vadose zone and groundwater, a two-cell, omni-depth tensiometer has been developed. Water level in the lower cell in this tensiometer is maintained at a relatively constant height above the porous tip. An isolated volume of air above the water level in the lower cell changes air pressure in proportion to the water pressure changes of the soils that surround the tensiometer porous tip. The upper cell replenishes water in the lower cell when needed. Several tensiometers can be installed at different depths in boreholes. The air pressure is measured in both cells remotely above the land surface. The tensiometer can be used for long-term monitoring of negative pressure under drying and wetting cycles in the vadose zone and for monitoring of positive pressure below the water table. This paper describes a tensiometer design and the results of testing the tensiometer models.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Humic substances are the most abundant organic macromolecules in soils, and comprehension of their chemical structure is essential to understanding their role in terrestrial ecosystems. The one-dimensional nuclear magnetic resonance (NMR) spectroscopy techniques now used widely to study humic substances have provided important insight into humic structures, but the complexity of these macromolecules gives rise to resonance signals that are broad and have spectral overlap. This has prevented the definitive functional group assignments necessary for structural determination. Hence, interest has focused on more powerful two-dimensional NMR experiments, such as the homonuclear TOtal Correlation SpectroscopY (TOCSY) and Heteronuclear Multiple Quantum Coherence (HMQC), which were employed in the study of a soil humic acid standard. The purpose of this paper is to outline the potential of these techniques to the study of soil humic structures. The 2-D spectra produced were extremely encouraging, with multitudes of cross-peaks produced from both TOCSY and HMQC experiments. The identification of fatty ester/acid chains and amino acid couplings are given as examples. Results obtained with these NMR experiments indicate substantial improvements in functional group assignment capabilities and the potential for marked progress in the determination of the chemical structure of soil humic substances.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

FT-IR, FT-Raman, and1H-NMR spectroscopies were applied to investigate molecular changes in soil organic matter (SOM) treated with different biomasses. The experiment consisted of several plots of soil treated over a 22-year period (from 1972 to 1994) with different amendments: cattle manure (CM), cow slurries (CS), and crop residues (CR). Samples taken from these plots were analyzed and compared with the unamended soil (C), which was used as the control sample. The samples were analyzed for both total organic carbon (TOC) and total nitrogen (N) content, both at the beginning of the study and after 22 years of treatments. The plots amended with CS and CR and the unamended plots showed a decrease in TOC and N after 22 years when compared with the control at the beginning of the experiment. However, the amended soil with CM showed a linear increase in TOC and N in relation to the control.The above mentioned spectroscopic procedures were employed to characterize both the unfractionated SOM and the low molecular weight (LMW) fraction extracted in an acidic medium. This spectroscopic analysis revealed that the composition of the soils amended with CM varied significantly in relation to the other amendments in the sense that the more aliphatic and aromatic moieties are resistant to the degradation. This is corroborated by the spectroscopic analysis of the LMW fraction, which is richer in small aromatic and aliphatic carboxylic acids in the soil amended with CM. The results shown in this work reveal that the SOM formed during the amendment with CM might be more resistant to the process of decomposition.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Nitrate contamination of groundwater aquifers from agricultural fertilization is of growing concern. It is generally assumed that little biological activity occurs in the vadose zone and that NO−3moves through this zone unimpeded. Various N fractions and the microbial activity in the surface and vadose zone sediments from three agricultural soils in eastern Oregon were examined. Nitrate levels in the vadose zone were as high as 60 mg N kg−1soil, and fractionation showed that approximately 30% of total N was in the form of acid-insoluble N, which could be a sink for NO−3that becomes immobilized. The vadose zone also contained high concentrations of amino acid-N and amino sugar-N, suggesting that a significant amount of subsoil N is of biological origin. Significant levels of microbial biomass C and CO2respiration were found in sediments derived from the vadose zone. A 14-day lab incubation study showed that vadose zone sediments could mineralize organic N without additional C and that NO−3may be subject to biological immobilization when a high rate of glucose C (3000 mg kg−1) is present.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Sunflower (Helianthus annuus L) production has increased in the central Great Plains, but little is known regarding how this crop will affect surface biomass production, various soil quality indicators, and subsequent winter wheat (Triticum aestivum L.) yields. We hypothesized that sunflower production was reducing soil quality relative to other summer crops because of the need for tillage to incorporate herbicide, thus reducing surface residue. Our objectives were to quantify on a Weld silt loam (fine, smectitic, mesic, Aridic Argiustolls) surface crop residue levels immediately after seeding wheat, subsequent wheat grain yield, soil organic carbon (SOC), particulate organic matter-carbon (POM-C), aggregate stability, and texture in 3- or 4-year rotation. A randomized complete block design with three replications was used to compare rotations both with and without sunflower. Our data showed 13% lower SOC content and 26% lower POM-C content at the 0- to 5-cm depth in rotations with sunflower versus those without. At the 5- to 15- cm depths, differences were not significant (P< 0.05). Crop residue by mass was 5 times lower and wheat yields 33% lower in rotations with sunflower, but no differences were measured for wind erodible aggregates or texture. Tillage to incorporate herbicides for sunflower and low amounts of residue after sunflower in the 3-year rotation contributed to reduced SOC and POM-C, decreased residue at wheat planting, and reduced wheat yield. If sunflower is to be included in the central Great Plains, efforts should be made to use no-till production practices and 4-year rotations with corn.

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2000

数据来源: OVID