摘要:

A method is proposed for estimating the unsaturated hydraulic conductivity from observed infiltration data. Infiltration measurements are generally easier to obtain than experimental data required for in situ determination of the hydraulic conductivity. The problem was formulated in terms of a nonlinear least-squares parameter optimization method which combines Philip's two-term infiltration equation with an analytical description of the unsaturated soil hydraulic properties according to Mualem and van Genuchten. Reliable estimates for the hydraulic parameters could be obtained with an inverse procedure when independently measured water retention data were included. The results indicate that soil water content measurements at very low values of the soil water pressure head are especially important to ensure parameter uniqueness. The method provides rapid and cost-effective estimates of the hydraulic properties of field soils.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Grain size analysis is performed in many soil science laboratories using the pipet method. However, it is still troublesome and time consuming to sample a suspension at a particular depth. In this paper a method is presented in which soil suspensions (clay and silt) were sampled faster and more easily with a syringe inserted horizontally into the suspension through septa. The new syringe method was compared with the pipet method. Both methods were equally accurate but the syringe method has the advantage of being easier to handle and more time efficient. This makes it especially suitable for series analysis.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Soils and irrigation drainwaters from the west side of the San Joaquin Valley, California have elevated levels of Mo, U, B, V, As, and Se. Much of the drainwater is disposed of in evaporation ponds that may be periodically dried, resulting in cyclic changes in the redox status of the pond sediments. A laboratory incubation study was conducted to evaluate the effects of redox status on the solubility of trace elements in saline sediments and soils from the San Joaquin valley. The elements U and Mo were mobilized under oxidizing conditions, while Fe, Mn, Ni, V, and As were more soluble under reducing conditions. Reduction and precipitation of Mo, apparently as MoS2, was observed from 1 to 10 days after flooding, but when reaerated the Mo resolubilized in less than 1 day. The reductive dissolution of Fe- and Mn-oxyhydroxides released adsorbed B, which resulted in an increased solution concentration of B. Low redox conditions in drainwater ponds may reduce the solution concentrations of U, Mo, and Se, thereby reducing their chances of entering the food chain through algae uptake. However, low redox conditions favor the solubilization of As and V, which may pose an alternative threat to wildlife visiting the ponds.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

We studied depthwise distribution of B extractable by tartaric acid (TA), ammonium acetate (AA), mannitol calcium chloride (MCC) and hot calcium chloride (HCC) in some acidic Inceptisols of West Bengal. The magnitude of B extraction follows: TA > HCC > AA > MCC and showed a decrease with an increase in soil depth. The highest value (with TA) is related to its ability for complexation with boric acid and maintenance of a low soil extract pH, while the lowest value (with MCC) is explained by the unlikely possibility of the presence of B as borate at acidic pH and, thus, the formation of B-mannitol complex. The decrease in extractable B with soil depth is attributed to the decrease in organic C and the increase in the Fe- and Mn-oxide content of the soils. Implications of the influences of soil properties on the extractable B content of soils are discussed.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Soil microorganisms are capable of producing secondary metabolites such as auxins upon the addition of tryptophan (L-TRP) that may significantly influence plant growth and development. This study was conducted to determine the stability and availability of indole-3-acetic acid (IAA) and proposed intermediates in the production of auxins from the addition of L-TRP to soil. L-TRP metabolism was not observed with the addition of L-TRP to a steam-sterilized soil when incubated for up to 7 days, indicating a biotic mechanism in the production of soil auxins. Incubation of 3'-14C-L-TRP in non-sterile soil resulted in the conversion of the L-TRP label into indole-3-acetamide, indole-3-lactic acid, indole-3-acetic acid, indole-3-ethanol, and indole-3-aldehyde by the soil microbiota. The production of indole derivatives was dependent on the amount of L-TRP added to the soil. Adsorption-desorption isotherms showed a low affinity of auxin derivatives (5-hydroxy-indole-3-acetic acid, indole-3-acetamide, indole-3-lactic acid, indole-3-acetic acid, indole-3-ethanol, and indole-3-aldehyde) for the soil colloids. The persistence of L-TRP in five soils, measured in half-life (t1/2), ranged from 22.8 to 28.7 h. The t1/2measured for the intermediates of auxin production indicated that several auxin derivatives were stable in soil and may have a greater effect on plant growth and yield when compared with auxins of lower soil stability.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Nitrate is recognized as the most common agriculture-related contaminant of ground water. In Kansas, over 25% of rural drinking water wells exceed the 44 mg NO3L-1drinking water standard, and most of these wells are found in areas with fine textured soils. An experimental site near Manhattan, KS with a silty clay loam soil (fine, montmorillonitic, mesic Pachic Argiustoll) has received up to 224 kg N ha-1as ammonium nitrate since 1946. Nitrate concentrations were measured in soil and soil solution to determine the extent of leaching in this fine-textured soil. A crude N balance for these soils indicated that approximately 98 kg N ha-1yr-1were available for leaching from the plots receiving 224 kg N ha-1. Soil analyses in 1965 revealed much higher concentrations of nitrate than those measured on the same plots in 1985. Ceramic cup, vacuum, soil solution samplers were installed at 1.5 and 3.5 m in the 224-kg N ha-1plots to monitor nitrate movement with minimal disturbance of the plots. Nitrate concentrations in the 3.5-m samples usually reached a maximum in March and were at a minimum in August, indicating that the bulk of the fertilizer nitrate required approximately 12 months to leach to the 3.5-m depth. This projected time of leaching was supported by a simple piston-flow model and observations on a bromide tracer applied to the plots in 1989. Significant concentrations of nitrite (up to 7.38 mg L-1) were sporadically observed in the solution samples. Although the appearance and concentrations of nitrite in these samples did not follow a temporal trend, the occurrence of this potentially toxic anion near ground water is noteworthy.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

Spectral radiance data from Landsat's Thematic Mapper (TM) sensor were used to evaluate its effectiveness in differentiating among surface soils of similar properties and to identify the TM spectral band combination useful in estimating selected soil properties. Correlation, regression, and discriminant analyses were used in analyzing the data. The overall accuracy of the TM sensor in differentiating the surface soils was 97.2%. The order of importance of the TM bands that contributed the most in differentiating the soils was TM 6, TM 4, TM 5, TM 2, TM 7, TM 1, and TM 3, respectively. Significant correlations were found among the spectral radiance data and soil variables studied; however, the amount of variance explained was quite low. The prediction equation for estimating soil properties accounted for less than 40% of the variability in the data. The low percentages were attributed to atmospheric particles such as moisture, CO2, dust, etc. that affect the electromagnetic energy sensed from airborne and space platforms. It was concluded that even though the TM sensor is adequate for differentiating among similar soil types from the same soil order, the spatial resolution of the data (30 m) is still too coarse to be effectively used in generating equations for predicting soil properties such as clay percentages, iron oxide, and organic matter content.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

The quantity of soil material transported by wind will decrease with height above the surface. Airborne samples were obtained at five levels above four soils. Mass distribution with height differs for materials in saltation or in suspension. A technique was developed to mathematically describe the two modes of transport so the total quantity being transported could be determined by integrating the two equations. Transition height, where the transport mode changes from saltation to suspension, is termed TSS. TSS decreases as surface soil texture changes from a fine sandy loam to a loam, indicating a higher percentage of the eroded material is moving at a greater distance above the soil surface. TSS increases as roughness of the soil surface increases, indicating a decrease in the suspension component and that the majority of eroded material is moving close to the soil surface.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID

摘要:

In this paper, ammonium acetate-1,2-diaminocyclo-hexanetetracetic acid is proposed as an extractant for the determination of cation exchange properties of acidic soils. The conditions for the spectrophotometric determination of exchange acidity with ethyl red in soil extracts were studied. Results are in reasonable agreement with those obtained by routine HCl titration after extraction with BaCl2-triethanolamine. Exchangeable bases in the soil extract can be determined with atomic absorption spectroscopy or photometrically using chlorophosphonazo III xylidyl blue I, and flamephotometry. After removal of the extractant, cation exchange capacity can be determined.

ISSN:0038-075X    

出版商:OVID    

年代:1993

数据来源: OVID