摘要:

Results obtained with a dialysis membrane technique for the study of the sorption and desorption of herbicides by a fraction of the organic matter extracted from soil are reported. The humic acid (HA) fraction of a Typic Haplumbrept soil, extracted with 0.1MNaOH plus 0.1MNa4P2O7, was cut off at 5,000 Da. The water solution of HA>5,000was transferred to a 1,000-Da dialysis tube and inserted in a shaded flask containing a water solution of the herbicides (paraquat or linuron). The sorption of herbicide by the humic acid was determined by measuring at different time intervals (0, 0.5, 1, 2, 4, and 24 h) the decreasing concentration of the herbicide in the solution external to the dialysis tube. Measurement of the herbicide concentration was carried out spectrophotometrically in the λ = 200-300 nm UV region. The results obtained indicate that the procedure adopted can be useful to study the interactions between herbicide and fractions of soil organic matter with relatively large molecular sizes (>1,000 Da).

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Solute concentration and water content profiles were measured within an area of 3 × 6 m2to a depth 1.7 m in an unsaturated soil. Spatial variabilities of soil water content and concentration were analyzed based on the field data and stochastic models. During the 33-day field experiment under constant leaching, the soil water movement showed an approximately steady-state flow. The effect of soil variability on soil water distributions was relatively small. On the other hand, the concentration distribution exhibited a profound variability in the field, especially within the zones with peak values in the vertical profiles. Immobile water content calculated from the experimental data was about one-third of the total water content. Stochastic and deterministic models were used to simulate solute transport through the vadose zone. Comparison of the simulation results with the field experimental data showed that the models described the mean concentration reasonably well without considering the pore scale dispersivity. However, the pore scale dispersivity had a significant impact on the estimation of the concentration variance.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Management of pastures in steep terrain can be expensive in terms of time, chemical inputs, and equipment requirements. Management of those portions of pasture that will yield the most for minimum inputs requires a knowledge of the spatial patterns of the soil and atmospheric environments. A steep 2.4-ha unimproved pasture in southern West Virginia was studied to determine the spatial dependency of aboveground biomass production on soil characteristics. The predominant soil of the study site was Gilpin silt loam (fine-loamy, mixed, mesic, Typic Hapludults) with an average A-horizon pH (1:1 H2O) of 4.5 (range 3.8 to 6.1). The study site was broadcast seeded with red fescue (Festuca rubraL.) in 1982, making it the major plant species. However, several other plant species, including orchardgrass (Dactylis glomerataL.), red clover (Trifolium pratenseL.), white clover (Trifolium repensL.), broomsedge (Adropogon virginicusL.), velvet grass (Holcus lanatusL.), yarrow (Achillea millegoliumL.), and wild strawberry (Fragaria virginianaL.), and others were common. Transects were laid out up and down the north-facing, south-facing, and west-facing slopes and one transect was established on the contour for measurement of soil characteristics at a 1-m spacing. Plant aboveground biomass was measured at a 2-m spacing on three of the slope transects and on the contour transect. Although correlation analysis failed to find many statistically significant relationships between biomass production and soil characteristics, cross-semivariogram analyses of biomass production and surface soil pH and extractable Al, Mn, and P indicated that a strong spatial dependency exists. Those relationships were used for identifying homogeneous areas of biomass production and associated soil characteristics by ordinary kriging.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Sewage sludge amendment of soils leads to an increase in soil fertility, but may induce heterogeneities not initially present in the soil. Spatial variation of soil organic carbon (C) and nitrogen (N) was studied in a heavy clay soil after a sewage sludge application and NPK-treatment (nitrogen, phosphorus, and potassium) using geostatistical approaches. In total, 314 soil samples were taken on two adjacent 40 m × 40 m plots (one sludge-amended and one NPK-treated) at three different scales (scale 40 m: 40 m × 40 m, scale 10 m: 10 m × 10 m, and scale 2.5 m: 2.5 m × 2.5 m). The coefficient of variation almost doubled for both C and N after sludge treatment. Because of this, more samples were needed to estimate mean values for the sludge-amended plot compared with the NPK-treated plot. To estimate the population mean at the 95% confidence level with 10% uncertainty (for all scales and all treatments), 5 to 13 samples were required for C and 4 to 7 for N. The C was spatially more structured compared to N. Semivariances of the sludge-amended plot displayed higher values compared with the NPK-treated plot, except for N at the smallest scale. This was probably due mainly to the sludge characteristics and the application technique of the sewage sludge. Constant semivariance (sill) was reached at ranges up to 15 m for C, but it was often unbounded (>40 m) for N.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Soil-solution chemistry is commonly studied in forests through the use of soil lysimeters. This approach is impractical for regional survey studies, however, because lysimeter installation and operation is expensive and time consuming. To address these problems, a new technique was developed to compare soil-solution chemistry among red spruce stands in New York, Vermont, New Hampshire, and Maine. Soil solutions were expelled by positive air pressure from soil that had been placed in a sealed cylinder. Before the air pressure was applied, a solution chemically similar to throughfall was added to the soil to bring it to approximate field capacity. After the solution sample was expelled, the soil was removed from the cylinder and chemically analyzed. The method was tested with homogenized Oa and Bs horizon soils collected from a red spruce stand in the Adirondack Mountains of New York, a red spruce stand in east-central Vermont, and a mixed hardwood stand in the Catskill Mountains of New York. Reproducibility, effects of varying the reaction time between adding throughfall and expelling soil solution (5-65 minutes) and effects of varying the chemical composition of added throughfall, were evaluated. In general, results showed that (i) the method was reproducible (coefficients of variation were generally < 15%), (ii) variations in the length of reaction-time did not affect expelled solution concentrations, and (iii) adding and expelling solution did not cause detectable changes in soil exchange chemistry. Concentrations of expelled solutions varied with the concentrations of added throughfall; the lower the CEC, the more sensitive expelled solution concentrations were to the chemical concentrations of added throughfall. Addition of a tracer (NaBr) showed that the expelled solution was a mixture of added solution and solution that preexisted in the soil. Comparisons of expelled solution concentrations with concentrations of soil solutions collected by zero-tension and tension lysimetry indicated that expelled solution concentrations were higher than those obtained with either type of lysimeter, although there was less difference with tension lysimeters than zero-tension lysimeters. The method used for collection of soil solution should be taken into consideration whenever soil solution data are being interpreted.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Red spruce ecosystems in the northeastern United States are of interest because this species is undergoing regional decline. Their underlying soils have been examined closely at only a few sites, and information available on red spruce soils throughout this region is limited. This study was conducted to examine soil and soil solution chemistry at red spruce sites in the northeastern US that encompass the range of soil conditions in which red spruce grow. Soils and soil solutions from Oa and B horizons were obtained over a 2-year period from 12 undisturbed red spruce forests (elevations of 80-975 m) in New York, Vermont, New Hampshire, and Maine. All sites had extremely acid Spodosols (Oa soil pH range 2.56 to 3.11 in 0.01MCaCl2), with generally low concentrations of base cations and high concentrations of Al on soil exchange sites. There was considerable range in exchange chemistry across the sites, however, with exchangeable Ca in Oa horizons ranging from 2.1 to 21.6 cmolckg-1and exchangeable Al from 3.6 to 18.3 cmolckg-1. Solution chemistry had high concentrations of DOC in the Oa horizons (1160 - 15200 µmol L-1), with higher concentrations in the fall than in the spring, which was probably a reflection of fresh litter inputs. Despite high concentrations of DOC in all solutions, inorganic Al was found in some Oa solutions at concentrations as high as 26 µmol L-1. Ratios of Ca2+to inorganic Al concentrations were less than 1.0 in the Oa horizon of one site, and were well below 1.0 in B horizons of all sites. That soil chemistry was related to soil solution chemistry was demonstrated by solution Al concentrations in the forest floor having significant relationships with pyrophosphate extractable Al, although it was not related in the B horizon. Soil exchangeable Ca/Al ratios in the Oa horizon explained 75% of the variation in solution Ca2+/inorganic Al ratios when mean values were used for each site. Our studies have expanded the range of soil chemical conditions measured for red spruce soils. By characterizing the regional variability, these results will enable site intensive process studies to be better applied to regional problems such as spruce decline.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Chinese soil-profile data from the 1930s through the 1980s now permit preliminary statistical tests of broad hypotheses about degradation trends for soils of given site characteristics. Given a soil-history data set, the first challenge is to devise an algorithm to detect and correct possible sampling biases in the original source materials.The soil-profile data show that South China has not had a trend toward soil acidification, as some had feared in the 1930s. Acidity abated between the 1930s and the late 1950s, though part of this improvement was reversed in some areas after the 1950s.Nor is there a clear downtrend in nutrient content, though the regional patterns in south China's soil-nutrient trends demand an explanation. Total potassium rose throughout China. In the Southwest, there was an impressive rise after the 1950s in organic matter and total nitrogen, but not in phosphorus. The trends further east were different: slight declines in organic matter and N and a slight rise in P after the 1950s. The patterns correlate over time and space with differences in cropping intensity, which outweighed the accompanying differences in fertilizer application rates. Cropping intensity abated and soil nutrients rose between the 1930s and the late 1950s. Thereafter, the rise of multiple cropping and of yields was accompanied by a slight downtrend in soil nitrogen and organic matter—except, again, in the Southwest, where cropping was always less intense.

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1996

数据来源: OVID