摘要:

The molarity of ethanol droplet (MED) test is a popular rapid method for assessing soil water repellency under field and laboratory conditions. This paper reviews the theoretical basis of the MED test, discusses controllable and uncontrollable sources of error affecting its results, and proposes a detailed protocol for its standardization. Soil water repellency is a function of soil surface chemistry. More specifically, it is a function of the free energy of the solid/gas interface in soil (γSG). Because γSGis not directly measurable in the laboratory, soil water repellency must be assessed using thermodynamically related parameters such as the initial advancing contact angle (&thgr;) or the work of wetting (WW). The MED test can be used to determine &thgr;, and in turn WW, but only if some simplifications are accepted and the test is performed under standard controlled conditions. Wetting theories exclude the dissolution or swelling of the solid by the liquid or chemical reactions between the liquid, solid, and gas phases that change system composition. Consequently, for MED tests to give valid &thgr; estimates, system composition must not change measurably during 10 s of solid/liquid contact. We discuss system conditions that should be controlled before and during MED testing to improve the validity of test results. Finally, we propose a detailed MED testing protocol for possible adoption by commercial analytical laboratories and the soils research community.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The measurement of chemical concentration profiles in pore water is a starting point for the analysis of biogeochemical processes in waterlogged peat soils. Concentration patterns may be obscured when macroporosity causes preferential flow in column experiments and when pore water is retrieved from the peat by suction. To investigate the magnitude of such effects, we used LiBr as a tracer in peat columns at outflow rates of 0, 2–3, and 8 mm d−1. The results were compared with modeled advective-diffusive migration rates. Twenty to fifty percent of the tracer was recovered from depths at which the tracer would have been absent if preferential flow had not occurred. At the high flow rate, the preferential flow was stronger, and the retrieved pore-water was probably in disequilibrium with the matrix. When pore water was retrieved by suction, linear concentration gradients decreased by about 30% through the recovery of water from different depths, and the quality of fitted linear gradients decreased fromR2= 0.99 toR2= 0.82. When flow rates are low (<3 mm d−1) and pore water concentration values from samplers are aggregated or regressed, the obtained concentration profiles seem to represent the vertical distribution of chemical species reasonably well. The use and interpretation of pore water profiles in peat soils is problematic if flow rates are higher and if vertical gradients are based on individual or few data points that have been obtained by suction samplers.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Near-infrared reflectance spectroscopy (NIRS) is a rapid and nondestructive analytical technique that can be used to quantify various soil properties. The objective of this study was to evaluate the ability of NIRS to evaluate independently organic C, inorganic C, and total N content of diverse soil materials. Samples (n= 108) were prepared by mixing soil with CaCO3, humic acid, and/or compost materials. About 30% of the samples were selected randomly for the validation set, and the remaining samples were assigned to the calibration set. NIR spectra of these samples were correlated with measured values of organic C, inorganic C, total C, total N, and C:N ratios using partial least squares regression. Leave-one-out cross-validation analysis yieldedr2values between the measured and predicted soil properties higher than 0.86 for all tested properties. Similar results were obtained from analysis of the validation set (r2>0.85). The successful prediction of total N and C:N ratios for the studied samples indicates that NIRS predictions of total N for soils are based not on the strong correlation between levels of C and N but rather on an independent response to soil N. The results indicate that NIRS can be used to quantify independently and simultaneously organic C, inorganic C, and total N for soils with diverse C and N compositions.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Knowledge of exchangeable cation chemistry can provide clues about tendencies toward either soil dispersion or flocculation as exchangeable sodium accumulates. The accumulation of sodium might be influenced by soil texture and degree of salinity. The effects of clay minerals, composition, and salinity of solution on Na-Ca exchange selectivities of montmorillonite and illite were studied. Regression equations for the exchangeable sodium ratio (ESR)-sodium adsorption ratio (SAR) differed according to clay minerals, composition, and salinity of equilibrated solutions. The experimental Na-Ca exchange selectivities in this study differed from the values reported by U.S. Salinity Laboratory Staff. Our values were influenced by clay minerals, composition, and salinity of equilibrated solutions. Compared with montmorillonite, the affinity of illite for Na was high and decreased with increasing clay content. This phenomenon was obvious at the low SAR and high salinity of equilibrated solutions, based on colloidal properties. These findings suggest that the affinity of the soil for Na increases with soil salinization. In soil with low clay contents, Na adsorption/Ca release in the soil colloids was enhanced, as was soil sodicity. Therefore, the exchangeable sodium percentage of the soil increased rapidly, leading to the formation of sodic soils. Conversely, Na adsorption/Ca release in the soil colloids was comparatively suppressed in soil with high clay contents. The affinity of the soil for Na increased with increasing salinity of soil solution through the accumulation of salt in the soil. It can therefore be concluded that sodic soils are formed during the process of soil salinization in soil with high clay contents.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Cattle manure contains a high level of soluble salts, and its application to agricultural land may alter soil properties and affect crop production. The purpose of this study, conducted in Fall 1998, was to evaluate the effect of 25 annual cattle manure applications on solution and exchangeable cations in surface soil (0 to 15 cm). Cattle manure was applied at rates of 0, 30, 60, and 90 Mg ha−1yr−1(wet weight) under nonirrigated conditions and at 0, 60, 120, and 180 Mg ha−1yr−1under irrigated conditions to a Dark Brown Chernozemic clay loam soil starting in Fall 1973. The composition and concentrations of solution cations were determined in Fall 1998 using the saturated paste extraction method, whereas the composition and concentrations of exchangeable cations were determined in Fall 1998 using the 0.1MBaCl2method. Although solution and exchangeable Na, K, and Mg increased significantly with the rate of manure application, Ca response varied. Cattle manure application also led to a higher sodium adsorption ratio and potassium adsorption ratio in soil solution and higher exchangeable sodium ratio and exchangeable potassium ratio on cation exchange sites under both nonirrigated and irrigated conditions. Greater leaching and crop removal may lessen the impact of manure application on soluble and exchangeable cations in an irrigated soil.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Previous work on the estimation of soil composition has involved primarily the estimation of separate components of the composition. Because composition is a vector quantity, it is more appropriate to consider the estimation problem in terms of vectors. The estimation problem using vectors can be formulated in a single optimization programming and, by use of a decomposition method, the optimization is transformed into a conceptually simple yet powerful estimation method. The significance of our method is that ordinary kriging is performed independently for each component, and the estimation of the target composition is equivalent to a quadratic optimization with the center at these krigings. We find that there exists an upper bound (the ordinary kriging method) and a lower bound (the sample mean method) for the performance of our method. By comparing our method with ordinary kriging and sample mean methods using data from a case study that reported the fractions of sand, silt, and clay, we found that the performance of our method was very close to the upper performance bound. Furthermore, the method we proposed was used to estimate a square area containing all sample points. Spectral encoding of the soil textural data allowed the estimated soil textural fractions to be represented on a two-dimensional map, revealing detailed information about the soil distribution in the study area.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The depth distribution of137Cs (cesium-137) and its relationship with organic carbon and different particle size fractions in Haplic-Udic Ferrosols in Yujiang, Southern China, are described in this paper. Compared with other sites, the lower137Cs inventories associated with uncultivated soils on or close to the crests indicate the relatively low137Csin situretention ability of the soil. Therefore, the use of137Cs techniques in erosion studies on uncultivated Haplic-Udic Ferrosols may create some significant difficulties and limitations, including identifying the suitable137Cs reference site and its validity on and near the crests. The impact of the soil erosion process to a depth of more than 4 to 6 cm on the sloping dry farmland and dry terrace farmland indicates that the widely accepted assumption of uniform137Cs depth distribution within the plough layer may not apply in these soils, although it does basically hold true for the paddy terrace field, in the area dominated by Haplic-Udic Ferrosols. For uncultivated Haplic-Udic Ferrosols, the organic matter may not control the downward migration of137Cs because no significant relationship was found between the depth distribution of137Cs and that of organic matter. It was also demonstrated that the137Cs fallout is associated mainly with the clay fraction, whereas the organic matter is associated mainly with the silt fraction. For Haplic-Udic Ferrosols, the waterinduced erosion removes preferentially the clay associated with the relatively high concentration of137Cs and low content of organic matter.

ISSN:0038-075X    

出版商:OVID    

年代:2002

数据来源: OVID