ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Infiltration characteristics of frozen soils are of prime interest for a variety of concerns, including water conservation, runoff, flooding, and erosion. Although frozen soil infiltration is typically not associated with irrigation practices, winter and spring irrigation in northern and north-western China is conducted mostly during the freeze-thaw period when water is available. The shortage of water resources is an important factor affecting and restricting development of crop and livestock in northern and northwestern parts of China. Therefore, improving irrigation efficiency and determining irrigation parameters have become key problems for agricultural management. This paper examines the infiltration characteristics during different freeze-thaw stages through the winter based on water infiltration in a green bean standing stubble field. The variation in 90-minute cumulative infiltration capacity and final infiltration rate were examined for the transient freeze-thaw stage, the steady freezing stage, and the thawing stage. Results showed that during the transient freezing stage, the effect of the frozen layer on infiltration characteristics was limited only at the beginning of infiltration. During the steady freezing stage, cumulative infiltration and final infiltration rates decreased as soil frost depth increased. During the thawing stage, cumulative infiltration and final infiltration rates increased with the increase in thaw depth. The exchanges of water and heat between surface soil and atmosphere and the phase change of soil water were the main reasons for the variation in infiltration characteristics. Results from this study have practical significance for directing the winter and spring irrigation in seasonally frozen soil areas and also have hydrologic implications for predicting runoff and flooding associated with rainfall and snowmelt on frozen soil.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Recent studies have shown that aging or increased residence time can reduce the availability of trace element cations sorbed to common soil minerals. Numerous explanations have been given to explain the observed residence time effect. However, most of these studies begin only with sorbed species and not surface precipitates. The formation of Ni2+surface precipitates on common soil minerals has been observed in the laboratory by a number of researchers. Accordingly, the influence of residence time on the sorption/desorption kinetics of Ni2+on kaolinite was examined. Nickel sorption kinetics were conducted at three aqueous concentrations (0.10, 0.50, 0.75 mM) of Ni2+in the presence of 25 g L−1kaolinite at pH 7.5. More than 99% of the Ni2+was sorbed to the kaolinite surface at the end of 14 days for all aqueous concentrations of Ni2+. Adsorption was characterized by an initial fast reaction followed by a slower reaction. Both reactions followed first order kinetics. Based on previous spectroscopic studies, the fast reaction was attributed to chemisorption, whereas the slow reaction was attributed to nucleation and surface precipitation of a Ni-Al layered double-hydroxide (LDH). Desorption experiments were conducted on kaolinite samples after 14 days (short-term) and 20 weeks (long-term) in the presence of 1 mM oxalate at pH 6.0. Similar to adsorption kinetics, desorption kinetics were characterized by an initial rapid reaction followed by a slower reaction, both of which followed first order kinetics. For all surface coverages the total quantity of Ni2+desorbed and the desorption rate coefficients (k1and k2) were greater for the short-term than for the long-term experiments. It is suggested that the residence time effect observed for the slow desorption/dissolution reaction was caused by an increase in crystallinity of the LDH surface precipitate and, to a lesser extent, phase transformation into a Ni-Al phyllosilciate. In contrast, several processes may be responsible for the residence time effect observed for the fast desorption/dissolution reaction, including movement of weakly bound Ni2+to a more strongly bound phase (eg, change in the type of surface complex), diffusion into micropores or intraparticle spaces, or an increase in crystallinity (eg, Ostwald ripening) of weakly precipitated Ni2+. The above results demonstrate and suggest potential mechanisms for the long-term natural attenuation of trace metal cations such as Ni2+adsorbed to mineral surfaces.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Bioavailability, toxicity, and mobility of heavy metals in soils are determined by their partitioning between solution and solid-phase and their further redistribution among solid-phase components. The wetting-drying moisture regime is one of the most important factors in controlling the physical, chemical, and biological properties of irrigated soils. Solid-phase redistribution of Cu, Cr, Ni, and Zn, added as soluble salts to two arid-zone soils incubated under a wetting-drying cycle moisture regime, was studied for 1 year. The heavy metals were fractionated into six operationally defined fractions. During the long-term process in the two soils, Cr was transferred from the carbonate fraction (CARB) into the organic matter fraction (OM), and Cu, Ni, and Zn moved from the exchangeable (EXC) and CARB fractions into the reducible oxide (RO), OM, easily reducible oxide (ERO), and residual fractions (RES) with time. The soil moisture regime strongly affects metal redistribution. Compared with a field capacity regime, soils at the wetting-drying cycle and saturated paste regimes had higher metal reactivity, resulting in the more complete movement of metals toward stable fractions, especially in the loessial soil and for Ni, Zn, and Cu.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Minable quantities of heavy minerals occur in prime agricultural lands of the Atlantic Coastal Plain. We evaluated the use of yard waste compost to reclaim tailings mined from these lands. A 30 × 60-m area was excavated to a depth of 5 m to establish a reclamation study site. Soils were removed, treated in a manner simulating the separation of the mineral sands, and returned in a slurry form. Undisturbed natural soils, Hapludults and Paleudults, have sand and loamy sand surface horizons. Mining these soils and redistributing the tailings as a slurry resulted in sandy loam and sandy clay loam textures. Treatments established in the tailings were: unamended tailings; tailings amended with 23 to 270 t/ha compost; and tailings capped with 45 cm of topsoil. Selected treatments were sampled and analyzed to test for differences in the physical properties related to treatment. Gravimetric water contents of tailings amended with 135 t/ha compost were significantly higher (at the 0.05 level) than unamended tailings, tailings capped with top soil, or the natural soil. Mechanical resistance values recorded in the Fall for tailings amended with 135 t/ha of compost were lower than the unamended tailings and tailings capped with topsoil. Mean hydraulic conductivity (Ksat) and porosity values for tailings amended with 135 t/ha compost were higher than the natural soil surface horizons. Tailings amended with as little as 45 t/ha compost had higher porosity (48%) and lower bulk density (1.38 g/cm3) values than the natural soil surface (45% and 1.43 g/cm3). Tailings capped with topsoil had the highest bulk density (1.64 g/cm3) and lowest porosity (38%) and Ksat (0.13 cm/hr), suggesting that this reclamation approach may not be the best way to try to reclaim the tailings. Average corn yields for tailings amended with compost were higher than those for tailings capped with topsoil or unamended tailings. Results suggest that mine soils can be constructed with excellent physical properties with regard to plant growth by amending tailings with yardwaste compost.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Soil and plant tissues were used to examine the effect on the release of dissolved organic carbon (DOC) of rinsing over time at two temperatures and under oxic and anoxic conditions in a laboratory incubation. The release of DOC over 60 days of incubation ranged from 0.5 to 189 mg DOC g−1oven-dry material and was correlated inversely with the degree of decomposition of the material: fresh maple leaves > old maple leaves >Sphagnummoss > fibric peat > hemic peat = sapric peat > Inceptisol A horizon. Rates of DOC release were similar through the duration of the experiment, except for the fresh maple leaves, where release rates fell after 3 day. Rinsing, by the replacement of water in the incubating samples after 20 day, produced slower rates of DOC release, except in the Inceptisol A and sapric peat samples. There was no significant difference between DOC release under oxic and anoxic conditions, except for the Inceptisol A soil, where DOC release was greater under anoxic than under oxic conditions. The rate of DOC release at 22 °C was an average of 2.4 times greater than at 4 °C, translating into Q10values of about 1.6. At 22 °C under oxic conditions, DOC production accounted for 14 to 58% (average 24%) of the total C released as DOC + CO2, with the highest proportion in the maple leaves. Under anoxic conditions, DOC production accounted for 63 to 95% (average 82%) of the total C released as DOC + CO2+ CH4. Production of CH4under anoxic conditions was minor, accounting for <1% of the total C released. Under oxic conditions at 22 °C, the incubations released between 2 and 107% of the organic C contained in the samples, the largest proportion of which was released from the plant tissues. Microbial utilization of DOC meant that some C was double-counted, both as DOC and as subsequently emitted CO2. Under anoxic conditions, 0.0 to 49% of the sample organic C was mineralized. The release of DOC represents the balance between production, adsorption, and desorption and microbial utilization. This release differs clearly among samples and among treatment effects.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Because soils are both a source and a sink for atmospheric CO2, there is an increasing need to characterize the spatial distribution of soil C pools. Large amounts of organic carbon (OC) accumulate in hydric bottom-lands soils. In the Armorican Massif (Western France) where these soils represent 20% of the total surface area, the spatial characterization of OC pools is difficult to assess due to methodological problems such as high spatial variability. Soil color indexes, which combine various characteristics of soil horizons or profiles, are an alternative approach for quantifying the differences in OC storage. In addition, terrain attributes derived from Digital Elevation Models (DEM) may be useful in characterizing the distribution of soil color indexes over large areas. Thus, the overall goal of this work was the development and application of a model for use in predicting the organic carbon (OC) content of soil areas. To accomplish this, extensive examination of soil morphology combined with selected terrain attributes measured in the field and calculated from a digital elevation model (DEM) were used. Soil samples were collected in Western France from a 2-ha agricultural parcel that forms the major part of a hillslope. The results indicate that OC stocks of the entire profile were correlated highly to a soil hydromorphic index (HI) (r2= 0.80). HI is a function of the percent of the total soil profile depth constituted by horizons with some degree of hydromorphic feature development and the moist color of the surface A horizon. Using a stepwise regression technique, we constructed a prediction model of HI distribution by using the relations between HI and (i) the elevation above the stream bank (ES) (r2= 0.80); (ii) the downslope gradient (DG) (r2= 0.55); and (iii) the upslope contributing area (AMU) (r2= 0.60). Validation of this model on a second site showed that topographical attributes explained up to 75% of the profile OC stock variability. These results confirmed that the integration of a soil index and topographical information is a useful tool for prediction of OC distribution. In addition, the use of soil morphologic indexes could significantly improved the construction and the validation of soil-landscape models because it would minimize laboratory measurements of OC reservoirs.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

To compare the effectiveness of different pasture species in restoring soil quality, changes in concentration and quality of soil organic carbon (C) were measured in the surface 10 cm of an Oxic Paleustalf (red earth) in the semiarid area of New South Wales, Australia, at the end of 4 years under lucerne (Medicago sativa cv. Trifecta), Consol lovegrass (Eragrostis curvula), and barrel medic (Medicago truncutulata cv sephi). Before the investigation, the soil had been degraded by 50 years of cropping. Soil samples were analyzed for water stable aggregation, mineralizable N, and C by three procedures: Total carbon (C) by dry combustion, oxidizible C by potassium permanganate, and oxidizible C by potassium dichromate/sulphuric acid with varying concentrations of acid.Higher dry matter production caused lucerne to be was more effective than barrel medic in increasing soil organic carbon concentration. Compared with fallow plots, total soil organic carbon concentration increased by 16, 26, and 11%, respectively, in the Consol lovegrass, lucerne, and barrel medic treatments. Nevertheless, even in the case of lucerne, the 26% increase in organic carbon in the 0-10-cm layer at the end of 4 years (7.87 vs. 9.88 g/kg) represented only 15% of the total loss in organic carbon after 50 years of cropping.Most (78-92%) of the organic carbon increases under the various pastures were of the more labile forms, as indicated by their removal under much milder oxidizing conditions than those recommended in the standard methods for organic carbon determination. Significant improvements in structural stability and nitrogen availability were detected in the perennial pasture soils. Our results suggested that the amount of organic carbon oxidizible by a modified Walkley-Black method, which involves using only half the amount of sulphuric acid, is a more sensitive indicator of the improvement in soil quality parameters under investigation, namely increases in mineralizable nitrogen and water stable aggregation. Further research is needed to verify these findings over a range of soil types and agroecosystems.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID

摘要:

Considering the soil as a heterogeneous bioreactor, a method is developed that permits a quantitative evaluation of O2and CO2levels in the soil atmosphere. Mathematical modeling allowed us to quantitate the rate at which soil consumes O2or produces CO2under close-to-field conditions. Values of qCO2and qO2ranging between 0.2 and 8 kmol CO2-C ha−1day−1, and 0.4 to 35 kmol O2ha−1day−1, respectively, were measured in a soil recently subjected to agriculture in the El Salado river basin (Buenos Aires, Argentina). The mathematical model discriminates between purely physical (diffusion, advection) and biological (e.g., microbial activity) processes. The gas measurements were sensitive to the crop stage in a soil recently subjected to agriculture. We conclude that qO2reflects more accurately than qCO2the contribution of microbial activity to the rate of gas exchanges in soil. Results are discussed in terms of soil biogeochemical processes.

ISSN:0038-075X    

出版商:OVID    

年代:2001

数据来源: OVID