摘要:

Carbon (C) sequestration in soil implies enhancing the concentrations/pools of soil organic matter and secondary carbonates. It is achieved through adoption of recommended management practices (RMPs) on soils of agricultural, grazing, and forestry ecosystems, and conversion of degraded soils and drastically disturbed lands to restorative land use. Of the 916 million hectares (Mha) comprising the total land area in the continental United States and Alaska, 157 Mha (17.1%) are under cropland, 336 Mha (36.7%) under grazing land, 236 Mha (25.8%) under forest, 14 Mha (1.5%) under Conservation Reserve Programs (CRP), and 20 Mha (2.2%) are under urban land use. Land areas affected by different soil degradative processes include 52 Mha affected by water erosion, 48 Mha by wind erosion, 0.2 Mha by secondary salinization, and more than 4 Mha affected by mining. Adoption of RMPs can lead to sequestration of soil organic carbon (SOC) at an annual rate of 45 to 98 Tg (teragram = 1 × 1012g = 1 million metric tons or MMT) in cropland, 13 to 70 Tg in grazing land, and 25 to 102 Tg in forestlands. In addition, there is an annual soil C sequestration potential of 21 to 77 Tg by land conversion, 25 to 60 Tg by land restoration, and 15 to 25 Tg by management of other land uses. Thus, the total potential of C sequestration in soils of the United States is 144 to 432 Tg/y or an average of 288 Tg C/y. With the implementation of suitable policy initiatives, this potential is realizable for up to 30 years or when the soil C sink capacity is filled. In comparison, emission by agricultural activities is estimated at 43 Tg C/y, and the current rate of SOC sequestration is reported as 17 Tg C/y. The challenge the policy makers face is to be able to develop and implement policies that are conducive to realization of this potential.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Vadose zone hydrology in the eastern Palouse Basin of northern Idaho is poorly understood because loess deposits often contain multiple hydraulically restrictive horizons that impede water flow. Valley soilscapes are of particular interest from a hydrologic perspective, because during the winter months, most of the precipitation is redistributed as runoff and throughflow into these landscape positions. Understanding the relationship between near-surface perched water table dynamics and vadose zone hydraulic processes in valley soilscapes is necessary to assess the sustainability of the groundwater resource. We implemented a combined approach to assess hydrologic processes in valley positions using hydrometric measurements, natural tracers, and stratigraphic observations. Hydrographs of near-surface monitoring wells indicate that valley positions maintain a thicker zone of saturation for longer duration compared with adjacent upland positions. Deep tensiometers demonstrate that multiple zones of seasonal saturation develop within the vadose zone of valley soilscapes in response to paleosol fragipan horizons and sediments of contrasting hydraulic conductivity. In some instances, the saturated thickness of vadose zone water tables was greater than 2.0 m and, because they are confined, displayed a positive pressure head. On adjacent uplands, seasonal saturation occurs only above the uppermost fragipan. Eluvial horizons having low Mndcorrespond to zones of saturation, whereas aquitards reflect Mndmaxima. The recharge rate calculated using natural Cl−mass balance was 2.4 mm y−1and did not correspond to measurements of saturated thickness by tensiometers. In addition, natural chloride profiles of other valley soilscapes display differences in recharge rates according to regional patterns in soil development. Together, deep tensiometer readings, secondary Mn distributions, and Cl−profiles suggest that groundwater recharge does not occur via piston flow. Detailed stratigraphic analysis illustrates that preferential flow is a possible recharge mechanism. Results suggest that valley soilscapes play an important role in both surficial and deep regolith hydrological processes in the Palouse Basin.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Soil spatial distribution, i.e. the spatial distribution of soils within landscapes, is difficult to predict because numerous processes operate simultaneously, but variably, over time. Quantifications of large areas with an acceptable degree of precision and low in cost require the development of specific methods making the best possible use of existing soil data and auxiliary information such as soil-forming factors. The quantification of the influence of soil-forming factors on soil spatial distribution is seldom performed over large areas such as regions. This study aimed to quantify the relationship between soil spatial distribution and the soil-forming factors of geology, topography, climate, and tectonic regime in order to predict soil spatial distribution over a wide region (30,000 km2). The Armorican Massif (western France), a complex basement of Proterozoic and Paleozoic rocks affected by recent tectonic activity and characterized by variations in topography and climate, was chosen as the study site. Detailed soil maps (1:25,000) were used to describe soil spatial distribution along transects. An ANOVA performed on 314 transects showed a high correlation between the occurrence of soils with particular features (namely redoximorphic, leached, glossic, and albic) and geological substrate, uplift ratio, mean slope gradient, and net rainfall. No such correlation was found with fluvic soils. These soil-forming factors seem to act through saprolite quality and erosion processes, which in turn control the development of soil features. A quantification of the relationship between soil features and soil-forming factors was performed by regression analysis in order to allow further prediction of the soil spatial distribution over the entire Armorican Massif. These results revealed and quantified the hitherto unrecognized role of tectonism on soil distribution and its relative importance in respect to other soil-forming factors. Finally, such an analysis, which is based on existing maps, can help to describe, quantify, and predict detailed soil spatial distribution at smaller scales.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

The release and transport of phosphate from manure-amended soils is detrimental to surface water because it leads to eutrophication. However, reaction rates and mechanisms of P release from manure-amended alkaline soils have not been completely characterized. The objectives of the present study were to determine the rate of P release from a manure-amended soil and to apply solubility models to predict the mineralogical phases that control soil-solution P concentrations. Phosphate release kinetics were measured on a soil that had received solid-dairy manure applications for more than a decade. To measure total P that would be released under leaching conditions, we conducted experiments in which we replenished the solution continuously until the P concentration reached a steady state (sequential desorption experiment). Measured P release kinetics indicate that 80% of the soluble P was released within 24 h, followed by a slow release that continued for up to 504 h. We applied several models, including a reversible first-order model, the Elovich model, and a modified version of the Elovich model that was empirically correlated to soil organic matter and percent clay, to describe our experimental data. The data were best fit with the Elovich model. Total P released from the manure-amended soil in the sequential desorption experiments was 29% from the surface soil (0–10 cm) and 8% from the subsurface soil (45–65 cm). Results from this study suggest that P release from manure-amended soils is controlled by rate-limited dissolution of meta-stable Ca-P mineral phases.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Humic substances are mixtures of macromolecules with varied structures and chemical compositions that are affected by differences in parental biomaterials and environmental conditions. This study used elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and solid-state13C nuclear magnetic resonance spectroscopy (NMR) to identify the chemical and structural heterogeneity of 10 humic acids (HAs) and a humin. The HAs were obtained by progressively extracting solution from a soil in western Massachusetts, eight times with 0.1 M Na4P2O7and two times with 0.1 M NaOH. The humin was the residual fraction after 10 base extractions. As indicated by solid state NMR analysis, the aliphatic carbons (0 ∼ 108 ppm) of the HAs increased gradually from 50% in fraction 1 (F-1) to 62% in fraction 9 (F-9) and 70% for the humin, but the aromatic carbons (108 ∼ 162 ppm) were highest in F-1. The band assigned to aliphatic carbon (2930 cm−1) in the DRIFTS spectra gradually increased with further extractions, and the relative intensity of this peak was the highest in humin. The atomic C/H ratio declined from 1.1 for F-1 to 0.6 for F-10 and the humin, consistent with the spectroscopic analyses. In addition, both elemental and spectroscopic data reveal that the last extracted HA and humin contained relatively lower contents of polar functional groups such as carboxylic and phenolic groups. This study shows significant chemical, structural, and molecular differences among the 10 sequentially extracted HAs and humin, even from a single soil.

ISSN:0038-075X    

出版商:OVID    

年代:2003

数据来源: OVID

摘要:

Erosion changes soil properties, especially physical properties, mainly because it removes surface soil rich in organic materials and exposes lower soil layers. In 1988, a study was established to determine the effects of soil erosion and long-term manure applications on selected soil physical properties and corn (Zea maysL.) production. After 10 years of annual manure applications, soil core samples were collected in 7.6-cm increments at three depths, 0 to 7.6, 15 to 22.6, and 30 to 37.6 cm, to determine soil bulk density (&rgr;b), hydraulic conductivity of saturated soil (Ks), and water retention. Bulk density and Ksincreased slightly with erosion level. Water retention did not change in the surface 7.6 cm, but it did decrease with increasing erosion level at deeper depths. Long-term application of manure decreased &rgr;bby 10%, whereas Kswas doubled in the top 7.6 cm of soil. Manure increased soil-water retention capacity and decreased differences in water retention between erosion levels, especially at low suctions (0 to 20 kPa). Soil carbon content correlated well with water retention and &rgr;b. Corn grain yields in 1997, 1998, and 1999 were 15, 6, and 14% less, respectively, in the severe than in the slight erosion phase. Long-term manure additions increased corn grain yields by 19% in 1998 and by 25% in 1999. Increased yield from manure additions was likely related to an enhancement in water retention. Results from this study show that long-term manure application is a possible management alternative for restoring the physical properties and crop productivity of eroded soil.

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

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