摘要:

Hydraulic and chemical transport properties are the major inputs in predictive models that simulate the movement of water and chemicals through the vadose zone. However, there is a lack of field measurements of such properties to verify models describing water and chemical movement through the soil. One of the objectives of this study was to use a point source method to determine simultaneously the hydraulic and chemical transport properties at multiple field locations. A second objective was to determine the spatial distribution of such properties across a field. A total of 50 field locations within a 7 × 15-m area were rapidly and simultaneously evaluated for such properties. The hydraulic properties were the saturated hydraulic conductivity (Ks) and the macroscopic capillary length (λc). The chemical transport properties were the immobile water content, expressed as a fraction of water content (&thgr;im/&thgr;) and the mass exchange coefficient (α). The hydraulic properties were determined by applying three discharge rates from irrigation dripper lines and measuring the resultant steady-state flux densities at the soil surface beneath each emitter. The chemical transport properties were determined by applying a sequence of three conservative tracers at a steady-state infiltration rate and measuring their resident concentration in the soil. TheKsvalues ranged from 7.5 to 79.0 cm h−1, with a median of 27.4 cm h−1(± 16.8). The λcvalues ranged from 0.03 to 13.1 cm, with a median of 2.6 cm (± 3.6). The &thgr;im/&thgr; values ranged from 0.36 to 0.88, with a median of 0.57 (± 0.098). The α values ranged from 0.002 to 0.12 h−1, with a median of 0.034 h−1(± 0.027). The values of the hydraulic and chemical transport parameters were found to be comparable with values reported by studies conducted on nearby field locations on similar soil. Based on semivariogram analysis, the measured properties were not spatially correlated. Because the method required only 2 days to collect data it should prove useful for future studies that require extensive field measurements of hydraulic and chemical transport properties.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The release and migration of soil chemicals from agricultural lands is both an economic loss and a threat to the quality of surface water and groundwater. Kinetic energy from rainfall is one of the most active factors affecting soil solute transport in runoff. To determine the influence of effective raindrop kinetic energy on soil potassium transfer into runoff, a series of laboratory experiments with different raindrop falling heights and rain intensities was performed. The experimental results indicate that effective raindrop kinetic energy affects soil surface properties and infiltration processes, including infiltration volume and wetting front advance. As effective raindrop kinetic energy increased, the infiltration decreased, the wetted depth decreased, time to initiate surface runoff decreased, and the cumulative amount of runoff increased. The concentration and amount of potassium in runoff increased as effective raindrop kinetic energy increased. There appeared to be a minimum value of raindrop energy to cause splash erosion of soil. The effective depth of interaction (EDI) was calculated, and the results indicated that the EDI increased as effective raindrop kinetic energy increased. Hence effective rainfall kinetic energy influences the whole process of infiltration-runoff-potassium transport, and the amount of potassium in runoff may be decreased by controlling the effective raindrop kinetic energy that reaches the soil surface.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Heavy metal contamination from the beneficial re-use of muck sediment in agriculture is a cause for concern. Information is needed about the leachability of metals from land-applied muck sediment and the effects of muck sediment application on soil properties. For this purpose, the water solubility of metals from muck sediments at various pH values and the effects of muck sediment application on metal leachability and pH values of sandy soils were determined by leaching soil samples amended with different rates of muck sediments. The leachates and soil solutions extracted from the muck-amended soils were analyzed for pH, electrical conductivity (EC), and concentrations of heavy metals (Cd, Cr, Cu, Co, Ni, Pb, and Zn). Rapid increases in solubility of heavy metals from the muck at pH levels below 6.0 suggest that muck sediments may be most suitable for application to slightly acid to slightly alkaline soils. Soil solution pH values from soils amended with muck sediments increased with increasing muck rates. Electrical conductivity of soil solution in the muck-amended soils was higher than in soils without muck amendment. The EC values increased with increasing muck rates. Application of muck sediment increased the concentrations of Cd, Co, Ni, and Pb, and decreased the concentrations of Cu and Zn in soil solution. However, the concentrations of Cd (<40 μg L−1), Co (<44 μg L−1), Cr (<30 μg L−1), Cu (<105 μg L−1), Ni (<84 μg L−1), Pb (<128 μg L−1), and Zn (<134 μg L−1) were generally low in the soil solution from muck-amended soils. The salts in muck sediments were easily removed from the amended soils by leaching, suggesting that the added salts from muck sediments may not have long-term effects on plant growth. Relatively high EC values in the first leachates from the muck-amended soils were observed, especially for soils amended with muck at a high rate. However, application of increasing amounts of muck sediments increased soil pH. The pH increased with increasing muck rates, and was correlated positively with Na/Ca, Na, K, Na/(Ca+Mg+K), and Na/(Ca+Mg+K+Na) in the leachates and water soluble Na/Ca, Na, Na/(Ca+Mg+K), and Na/(Ca+Mg+K+Na) in the muck sediments; it was negatively correlated with Ca in leachates and water soluble Ca in the muck sediments. These results suggest that application of muck sediments does not result in a marked change in soil pH at low rates.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Land treatment of sewage sludge and the use of chemical fertilizers have resulted in cadmium (Cd) contamination of some soils. The effect of a soil’s ionic environment on the availability of heavy metals in soils and plants is of concern. In this study, we investigated the environmental availability of Cd as it is affected by the application of different sources of the phosphate anion (monopotassium phosphate (MPP) and dipotassium phosphate (DPP)), and we examined pre-application (PAP) and simultaneous application (SAP) of phosphate sources on Cd sorption in acidic and calcareous soils. The soil-solution system pH in the acidic soil decreased with additions of MPP; however, it increased with DPP applications. The pH decreased with the application of both phosphates in the calcareous soil. Values of ionic strength (I) in the acid and calcareous soils were similar after applying the Cd source (CdCl2) even though they were significantly different in the untreated control soils. TheIvalues with SAP, however, were consistently higher than those with PAP. Equilibrium Cd concentration in the soil-solution systems was also usually higher with SAP than with PAP. The value of Cd sorption capacity was the highest with PAP-DPP in both soils. The Cd sorption capacity and the bonding energy were not correlated in the acidic soil, whereas they were negatively correlated in the calcareous soil. The Cd sorption was decreased with decreasing pH in the soil-solution systems. Cadmium sorption tends to decrease with the presence of MPP and increase with the presence of DPP in both soil systems. The solution Cd concentrations with the SAP-P sources were always higher than those with the PAP-P sources in both soil-solution systems. The observed differences of Cd concentration in soil-solution systems may be attributed to (i) higher pH and lowerIwith PAP, (ii) less formation of Cd-phosphate complexes with PAP, and (iii) a larger increase in net negative charge on soil colloids with PAP than with SAP.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Studies on soil organic matter (SOM) cycling in different climate zones are an important basis for further understanding of the feedback mechanism of terrestrial carbon storage to global climatic changes and are crucial for accurate projections of future concentrations of CO2in the atmosphere. Using thin-layer methods, six soil profiles in the Dinghushan Biosphere Reserve (DHSBR), South China, and the Xiaoliang Ecological Station of the South China Institute of Botany, Chinese Academy of Sciences (CAS) were excavated and sampled for studies on the dynamics of SOM in the southern subtropical areas, based on SOM δ13C, Δ14C, soil grain size characteristics, and soil organic carbon (SOC) contents. Results indicate that the turnover of SOM occurs in three stages: (i) Rapid turnover of SOM occurs within 100 years, with SOC content decreasing sharply downwards from the ground surface and δ13C values becoming correspondingly enriched in13C as a result of carbon isotope fractionation in the process of SOM turnover; maximum till is reached at about 260–270 years; (ii) from about 260–270 years to 800–1400 years, SOM turnover rates lessen, SOC content decreases slowly downwards, and δ13C values become gradually depleted in13C due to the decomposition of SOM compartments with higher δ13C values; (iii) after about 1500 years, SOC content approaches the minimum, with slight fluctuations, and δ13C values become stable.Comparison analyses suggest that soil clay materials control existing forms and turnover processes of SOM directly, SOM in the soil sections with high clay content at DHSBR are not easily decomposed and have longer turnover periods, and soil textures are an important factor controlling SOM dynamics. Fall leaf litter generally has more negative δ13C value than the topsoil samples, which may be a result of isotope fractionation caused by rapid carbon decay prior to the penetration of carbon from the litter into the topsoils. Above-ground vegetation species and composition impact SOM turnover processes directly; δ13C analysis may be an important tool for determination of the improvement in soil quality during the restoration of degraded ecosystems. Vegetation occupation history also influences the SOM dynamics of soil profiles at different sites in one area with similar vegetation species, as shown by the soil profiles at the Xiaoliang Ecological Station of the South China Institute of Botany, CAS.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID