摘要:

Plastic film mulch technology is a cropping system feature for water saving that is used extensively in arid and semiarid areas of northwest China. When evaporative demand is fairly strong, film mulching can greatly reduce soil water evaporation. However, research on water flow beneath and through various open hole ratios of the perforated film mulches is limited, and questions concerning soil water flow and soil heat transfer for this type of water-saving system remain unanswered. It is, therefore, very important to perform research on soil water evaporation and soil temperature distribution with various open hole ratios of the perforated plastic mulches. A series of soil water evaporation experiments using different open hole ratios of perforated plastic mulches was conducted. The columns received mulches with various open hole ratios: 0% (covered with a solid plastic mulch), 1.39%, 2.84%, 7.24%, 30.5%, and 100% (nonmulched bare surface). In conjunction with the water movement of evaporation from film hole studies, soil temperature distributions were also analyzed. Our measurements indicated that film hole mulch had a restraining effect on evaporation and that the restraining effect decreased with the increase in open hole ratios. Compared with bare soil evaporation, the percentage of evaporation reduction rates for open hole ratios of 0%, 1.39%, 2.84%, 7.24%, and 30.5% were 69.26%, 33.09%, 22.80%, 20.05%, and 11.82%, respectively. The results showed a linear relationship between cumulative water evaporation and square root of time for the different open hole ratios of the perforated plastic mulches, and the coefficients of the linear function, i.e., the C parameters, were fitted well with the open hole ratios—u(C = 0.0101u0.1019+ 0.0075). On this basis, mathematical relations of relative evaporation rate and evaporation based on hole areas of perforated plastic mulches were analyzed and discussed. These results extend the Gardner evaporation equation to bare soils to include water evaporation from soils covered by various perforated plastic mulches. The resulting equations presented in this paper provide an approach for describing evaporation from plastic mulch-covered soil.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The advent of Geographic Information Systems (GIS) is bringing about the expansion of soil survey data into interdisciplinary research projects. A GIS database was developed for the Palouse Basin in northern Idaho and eastern Washington to identify areas where soil and geologic features are likely to impact ground-water recharge. Using GeoProcessing operations in ArcView, 1:24,000 soil survey data and surficial geology were combined. The resulting ArcView-based GIS coverage was used to delineate recharge mechanisms and classify recharge potential in the Palouse Basin. A database was developed using binary weighting and index overlay modeling methods to assign values to soil map units based on selected soil characteristics, including permeability rates, depth to bedrock, and the presence of perched water tables. These data were then linked to Basin recharge mechanisms to produce maps indicating the potential for deep percolation through soil and subsequent recharge to the local aquifer system. Results indicate that recharge through loess is the most spatially extensive recharge mechanism, operating over 71% of the total study area. Of this, approximately 2300 ha have high potential for recharge. Recharge through stream loss operates over 16% of the total study area, whereas percolation through localized fractures in bedrock is the least extensive recharge mechanism, operating over just 13% of the total study area. Although stream loss and infiltration along Basin margins occupy a limited spatial extent they have more land area rated as ‘high potential’ for recharge. There is lower recharge potential in the eastern portion of the Basin because of the presence of extensive hydraulically restrictive subsoil horizons.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The spatial variability of soil variables is a critical component of modeling, estimation, prediction and risk assessment in soil science. On one hand, spatial variability must be taken into account for optimal spatial interpolation (e.g., kriging) and risk assessment (e.g., evaluating the probability that the value of a given property is higher than an established threshold); on the other, spatial variability influences the output of physically based models (e.g., rainfall-runoff). As soil variables are usually known at only a small number of experimental locations, their spatial variability must be evaluated using statistical tools such as the spatial covariance (or the semivariogram), which, in turn, are modeled by a few parameters (e.g., nugget variance, sill, range). These covariance parameters, however, can only be inferred with an associated statistical uncertainty. The main objective of this paper is to show that this uncertainty can be assessed by a maximum likelihood approach to inference. Three different methods for obtaining joint confidence intervals of spatial covariance parameters are considered: (i) the Fisher information matrix, (ii) likelihood intervals, and (iii) the likelihood ratio statistic. The authors show that, when expressed as likelihood intervals, the confidence regions provided by the likelihood ratio statistic are especially suitable for applications because of its straightforward calculation. A second objective of the paper is to demonstrate how the uncertainty of the spatial covariance parameters can be included in applications. The interpolation uncertainty is included by Bayesian kriging whereas it is included in risk assessment and physically based models by geostatistical simulation. A case study of the zinc content of soils of the Swiss Jura is used to illustrate the methodology.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The calcareous prairies of Louisiana are among the most endangered and the least understood ecosystems in North America. The major threat to this ecosystem is the invasion of woody plants, primarily eastern red cedar (Juniperus virginianaL.). We studied the vertical profile of soil organic C (SOC) and the stable carbon isotope (δ13C) from soil organic matter (SOM) to infer the vegetation history and to understand the C dynamics of these prairies. SOC decreased with depth (0–100 cm), but variation due to vegetation type (prairie, transition, forest) and landscape position were not statistically significant. The mean total SOC stock within the 0–30 cm depth from three sites, three vegetation types, and two landscape positions was 7.6 ± 0.4 kg/m2(mean ± SE,n= 18). The SOM δ13C values within the 0–10 cm depth showed that although the forest vegetation was exclusively C3, the transition and the prairie vegetation were composed of a mixture of C3 and C4 plant functional forms. Statistical comparison of SOM δ13C values from the forest, transition, and prairie with depth showed that the SOM δ13C from the prairie and transition are significantly different from that of the forest up to the 30–40 cm depth. SOM δ13C values of the prairie and transition were not significantly different at all depths, suggesting that the invasion of C3 trees and shrubs observed within the transition may be a recent phenomenon coinciding with fire suppression. SOM δ13C below 30–40 cm indicated that in the past, a C4 community might have dominated the entire site.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Changes in concentrations and properties of dissolved organic matter (DOM) caused by oxygen deficiency are poorly understood. We estimated the influence of redox conditions on DOM dynamics in the field, sampling soil solutions at different depths of three soils (Humic and Histic Gleysol, Chromic Cambisol) along a soil catena in the cool-humid Black Forest (Germany) over a period of 2 years. We measured dissolved organic carbon (DOC) and determined the specific absorbance at 280 nm and two humification indices derived from fluorescence spectra to describe the aromaticity and complexity of DOM. Redox potential (Eh) was monitored continuouslyin situ.In the forest floor, DOC concentrations ranged independent of soil organic matter content and redox regime between 40 and 60 mg C L−1. DOC concentrations in all soils decreased with depth, accompanied by a decrease in DOM aromaticity and complexity. In the mineral subsoil, DOC concentrations, aromaticity, and DOM complexity were smallest in the aerobic soil (Chromic Cambisol; Eh > 500 mV) and largest in the most anaerobic soil (Histic Gleysol; Eh < 100 mV). Large DOM retention in the aerobic soil could be related to high contents of Fe oxides, highlighting their importance for DOM adsorption. Despite significantly reduced DOM retention under anaerobic conditions, it remains relatively large because the main DOM adsorbents changed from Fe oxides under oxic conditions to clay minerals, which were about 100 times more abundant under anaerobic conditions than Fe oxides. We found indications that biodegradation of DOM contributes more to DOM retention under anaerobic conditions, and we conclude that large DOM fluxes from anaerobic forest soils are the result of limited DOM adsorption in the subsoil rather than large DOM release from the topsoil.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

No-till management is generally preferred over conventional tillage, especially in fine-textured soils where tillage can increase soil compaction, disrupt the natural structure formation process, and have long lasting effects on soil quality. The objective of this project was to quantify the interactive and residual effects of different tillage systems on the water transmission and structural properties of Kokomo silty clay loam (fine, mixed, superactive, mesic Typic Argiaquoll). Soil physical properties were assessed at the Don Scott experimental farm of the Ohio State University, Columbus, Ohio, 9 years after initiating the study and 20 months after the last tillage operation. Three tillage treatments were replicated four times: moldboard plow (MB), chisel plow (CP), and no-till (NT). Tillage operations took place during the fall of each year between 1993 and 2000, and soil samples for physical property assessment were obtained during summer 2002 for 0–10- and 10–20-cm depths. The water infiltration tests conducted on each of the 12 experimental plot showed that the highest cumulative infiltration (I, 90 cm) and steady state infiltration (ic, 27 cm h−1) were for the NT treatment and varied in the order NT > CP ∼ MB. Soil bulk density (&rgr;b) varied in the order MB > NT ∼ CP, available water capacity (AWC) and air filled porosity (fa) NT > MB ∼ CP. The water stable aggregation (WSA) (943 g kg−1) and the volume of transmission (TrP) (0.10 cm3cm−3) and storage pores (StP) (0.31 cm3cm−3) were the highest for the NT plots for 0–10-cm depth. For the 10–20-cm depth, the WSA and MWD were in the order NT > MB ∼ CP; AWC-NT (2.00 cm) ∼ CP (1.71 cm) > MB (1.36 cm). Tillage effects on soil properties between MB and CP seemed to diminish at the end of the growing season, and the infiltration rate after 5 min, ic, I, WSA, and soil &rgr;bvalues were similar. Canonical correlation analysis indicated strong association between volumes of StP and I, icand soil &rgr;b, and SOC and soil &rgr;b.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

About 1000 years ago, Mississippian Indians built what are now designated Mounds 69 and 70 at Cahokia near Collinsville, Illinois. Loamy soil materials were placed on the mounds by Mississippian Indians before A.D. 1100, and the site was inhabited until approximately A.D. 1300. The general objective of this study was to determine the potential of using archaeological mounds or sites to obtain information on soil development and erosion processes. Our specific objectives were to determine: (i) the extent of soil formation during the past 900 years, (ii) the time period and extent of disturbance by human activities, including tillage and digging by treasure hunters and looters, and (iii) the erosion phase of soils on mound sideslopes and the amount of soil loss from accelerated erosion. The vegetation and distribution of organic C in soil profiles suggests there has been no tillage since the 1970s and little soil erosion of either the summit or the sideslope of Mound 69. The adjacent alluvial plain is still being cultivated. Fly ash, particulate matter resulting from high-temperature coal combustion, was used as a time marker in soil and sediment. Fly-ash distributions in the upper 20 cm of Mound 69 support the theory that cultivation occurred between the 1850s and the 1970s. Based on the fly ash data, approximately 55% of the original surface soil layer remains on the sideslope of Mound 69 (compared with the uncultivated sideslope of Mound 70). There has been substantial deposition of sediment rich in fly ash onto the footslope of Mound 69 (from the cultivated sideslope) and the toeslope of Mound 70 (from the cultivated footslope). The fly ash and organic C data for the summit soil profile on Mound 70 suggest treasure hunters and looters disarranged the soil profile completely. The uncultivated sideslope with a 23% slope had a 40-cm surface layer rich in fly ash. The fly-ash content and thickness of the footslope soil surface layer was reduced as a result of tillage and erosion from the 1850s to the 1970s. Fly ash-enriched sediment accumulated on the toeslope and created a 60-cm surface layer. The current vegetation and the decrease in organic C with depth on the footslope and toeslope of Mound 70 suggest that no tillage has occurred since the 1970s. Fly ash presence within soil layers indicates which layers have been exposed at the soil surface since the 1850s and the extent of soil mixing. Archaeological mounds with known dates of construction can be used to obtain information on soil development and erosion processes.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID