摘要:

The purpose of this study was to investigate the use of color infarared‐digital orthophoto quadrangle (CIR‐DOQ) data in differentiating among surface soils of similar properties and to identify the CIR‐DOQ spectral band most useful in estimating selected soil properties. The CIR‐DOQ data were generated by scanning four 9 × 9 in CIR aerial photographs at a uniform pixel sampling grid of 25 microns, resulting in 2 m of ground sample resolution. Correlation, regression, and discriminant analyses were used in analyzing the data. The overall accuracy of the CIR‐DOQ data in differentiating the surface soils was 62.8%. All three of the CIR‐DOQ bands were important in differentiating the surface soils. Significant correlations were found among the CIR‐DOQ data and soils variables studied; however, the amount of variance explained was quite low. The prediction equations for estimating soil properties accounted for less than 35% of the variability in the data. The low percentages can be attributed to the season of the year and climatic conditions that existed when the CIR photographs were taken. These conditions had a profound impact on the spectral quality of the photographs and, therefore, the quality of data recorded by the scanner. It was concluded that even though the spatial resolution of the CIR‐DOQ data is superior to most digital spectral data used today, the spectral quality is inadequate for differentiating among surface soils and for generating mathematical equations for predicting soil properties.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Synthetic chelates alter adsorption of metals by soil, usually rendering them more mobile and increasing the pollution potential to ground waters. The objective was to study the effects of nitrilotriacetic acid (NTA) on the adsorption of Zn, Pb, and Cd by two topsoils (Typic Hapludult and Typic Paleudult). A second objective was to test equilibrium models for their ability to predict experimental adsorption isotherms where both free and complexed metals were being adsorbed. Two soils were equilibrated with 0 to 0.96 mMZn or 0 to 0.72 mMPb or Cd in 5 mMCaCl2at pH 5.0 with or without 1.00 mMNTA. A Langmuir two‐site model was used to model the data using MINTEQA2. The finer textured, higher organic matter soil adsorbed higher amounts of metal than the sandy, lower organic matter soil. At the higher metal levels, the NTA was saturated and adsorption increased, because more free metal was available and was more strongly adsorbed than the complexed metals. When the chelate concentration was reduced to 0.7 to 0.8 mM(20‐30% reduction from the original), the adsorption model fit the observed data, indicating that some NTA was degraded and/or lost by specific adsorption. Adsorption log K values were in the order Pb > Cd > Zn when no NTA was added. The values were similar for the two soils for each metal even though the number of adsorption sites varied by a factor of about two. This result indicated that the NTA had more influence than the type of metal on adsorption. Kdvalues showed that addition of NTA would place the Zn and Pb in potentially mobile forms, but Cd would be mobilized by NTA to a smaller degree than Zn or Pb.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Urea transformation was studied under a laboratory‐simulated flooded soil condition, where the soil columns were preincubated for 3 months with 2 cm of standing water. Urea distributions in the flooded soil columns were determined under different water percolation rates and urease inhibitor treatments. The soil used in this study was a Crowley silt loam, a common rice paddy soil found in southwest Louisiana, and the urease inhibitor was N‐ (n‐butyl) thiophosphoric triamide (NBPT). Three percolation rates (0, 0.5, and 1.0‐cm d−1) and two NBPT treatments (0 and 10% of urea weight) were investigated. The experimental data showed strong effects of NBPT and percolation rates on urea distribution. More than 70% of the urea was hydrolyzed after 2 days of application without NBPT treatment, whereas only 40% was hydrolyzed with NBPT. More urea was distributed in the soil profile in NBPT treated columns. High percolation rates caused substantial urea movement downward into the soil when urea was not hydrolyzed. These results were successfully described by a convective‐dispersive transport model with equilibrium‐type adsorption and first‐order hydrolysis. First‐order hydrolysis rate constants (&mgr;m) for NBPT‐treated soil columns were 8 to 16 times lower than for soil without NBPT. However, the distribution coefficients (Kd) and diffusion coefficients (D) were similar for both NBPT treatments.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Humic and fulvic acids and other naturally derived organic compounds such as proteins and fatty acids are important constituents of soil solutions and surface waters and groundwater. The presence of both hydrophilic polar or ionic functional groups and hydrophobic structural units on these natural organic compounds can be expected to promote accumulation at the air‐water interface, which would thereby influence the solution surface tension. This study evaluated the influence of organic C concentration, pH, and temperature on the surface tension of soil solutions extracted from forest soils and solutions of International Humic Substances Society (IHSS) reference humic acids. The surface tensions of the soil solutions were substantially lower than those of IHSS humic acids at equivalent organic C concentrations and solution conditions. Differences were also observed in the temperature dependence of surface tension for the solutions. All solutions exhibited a strong dependence of surface tension on solution pH. Characterization of the soil solutions and humic acid solutions by fluorescence and absorption spectroscopy and titration analysis confirmed that the soil solutions varied markedly from the humic acid solutions. The soil solutions bore substantially higher acidity and yielded qualitatively different fluorescence spectra when compared with the humic acid solutions under equivalent conditions.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Changes in the concentrations and fluxes of CO2were monitored to a depth of 100 cm in an Andisol, under both fallow and soybean crops for a period of 1 year. Gas flux was calculated by the diffusion equation. Diel concentrations at depths less than 40 cm followed a sinusoidal pattern similar to that of the soil temperature, with the highest value being recorded in the daytime. Heavy rainfall, which closed the air pathways to the atmosphere, resulted in a higher CO2concentration in the shallow soil layers. The subsequent decrease in the concentration in the shallow layers was accompanied by an increase for a few days in concentrations in the deeper soil layers. CO2concentration under fallow increased with depth throughout the year except after heavy rainfall. CO2concentration under soybean reached maximum values at depths that increased gradually from 20 to 80 cm during the growing season, suggesting the effect of root elongation. Upward CO2fluxes decreased with depth in both fields, and the fluxes in the soil profile were high in summer and low in winter. CO2fluxes in the upper and middle parts of the profile under soybean were higher than those under fallow during the growing season. CO2fluxes from the soil surface calculated by the diffusion equation and measured by the closed chamber method showed a correlation coefficient of 0.89 except after heavy rainfall. Total CO2fluxes from the surface estimated from measurements throughout a year were 3522 g m−2under fallow and 4975 g m−2under soybean. The downward flux of CO2dissolved in the soil water was found to be negligible in comparison with the CO2flux from the soil surface.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Nitrogen availability to plants from seafood waste composts must be determined for composting to be adopted as a means of seafood waste disposal and for utilization of the compost. In a 2‐year study, the availability of N to silage corn in the year of application and the residual availability in the following year were evaluated under field conditions for four composts made from sawdust and seafood wastes. A broad range of compost rates was used to facilitate the study of the residual N availability. The composts were: HGF (groundfish waste with hemlock/fir sawdust); AGF (groundfish waste with alder sawdust); HCS (chitin sludge with hemlock/fir sawdust); and ACS (chitin sludge with alder sawdust). In the composts made with alder sawdust, the fraction of total N that was in inorganic form was smaller than that in the composts made with a hemlock/fir sawdust mixture. In the year of compost application, corn yields and N uptake were affected by the type of compost and rate of compost addition, and the rate effect varied with the compost type. The amount of inorganic N added in the composts was better than the organic N or C:N ratios of the composts at predicting corn yields and N uptake in the year of compost application. None of these compostrelated characteristics was closely correlated with residual N availability in the next year. The soil inorganic N concentration, which reflects the overall effect of composts and environmental conditions on N transformation, accounted for most of the variability in corn yield and N uptake during the 2‐year period. Although the mineralization potential of the organic N fraction in the HGF was low in a laboratory incubation, a sizable reduction of total N and organic C concentrations in the soils amended with this or other composts under field conditions suggests that considerable mineralization during the subsequent year occurred in this region, which is characterized by mild temperatures and high rainfall in the winter. Because of the limited residual N availability of the HGF, AGF, or HCS, annual addition of the composts at low rates sufficient to sustain the soil productivity is more appropriate than less frequent addition at high rates.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Given the importance of riparian areas in the western United States, knowledge about the spatial distribution, properties, and genesis of these soils is surprisingly limited. In conjunction with an interdisciplinary study of the impacts of grazing on soils and vegetation, we characterized three pedons along a hydrologic gradient on a montane meadow of the northern Sierra Nevada range. Radiocarbon dating of charcoal indicates that meadow pedogenesis began approximately 3600 years B.P., after a catastrophic valley erosional event. Since that time, nearly 1 meter of soil has accumulated over a basal glaciolacustrine unit. Critical factors and processes influencing soil genesis and morphology include: seasonal variation in soil redox status, frigid soil temperatures, additions of volcanic tephra, wildfires, and polygenesis related to Holocene climatic, hydrologic, and vegetation changes. Argillans are present on ped faces of certain soil horizons, which suggests extended dry periods at which time clay pervection occurred. Clay mineralogy is disjunct; surface horizons are dominated by kaolinite and underlying horizons by smectite. The high clay content of such youthful soils suggests rapid primary mineral weathering. Charcoal‐containing strata attest to frequent wildfires during the Holocene epoch. The spatial complexity of soil patterns and their properties infers that these riparian areas are dynamic, and their character may have been shaped by previous climatic patterns.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID