摘要:

We sampled the soil horizons of 40 important Belgian soil series, with textures ranging from sand to heavy clay, and measured their moisture retention characteristic (MRC). Of these horizons, the particle-size distribution in nine fractions, the dry bulk density, and the carbon content were determined as well. The Van Genuchten equation (1980), reduced to four parameters on the basis of a model comparison technique, was fitted through the measured MRCs using Marquardt's algorithm (1967) for nonlinear parameter estimation. We performed a one-dimensional sensitivity analysis on the optimized parameters of different MRCs to check their relative importance and stability. Principal factor analysis was used to reveal the structure in the data and to examine the relation between MRC parameters and measured soil properties. Regression equations were established between these MRC parameters and measured soil properties. To test the need for detailed information regarding the textural composition of the soil, two information levels were discussed. The first level contains the textural composition in three fractions (sand, silt, and clay) while the second level takes into account the textural composition in nine fractions and two distributional parameters (GMPS, GSD).We concluded that the MRC can be estimated at a reasonable level of accuracy from such simple soil properties as particle-size distribution, dry bulk density, and carbon content. Detailed information on the particle-size distribution results in a better estimation of the parameters describing the shape of the MRC (a, n). The study further shows that for the prospected horizons the Van Genuchten model gives a good description over the entire range of the MRC. In addition it has been shown that the approach is flexible enough to model the MRC for a wide range of textures.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The use of spatial distribution of effective porosity (Φϵ) to estimate the distribution of saturated hydraulic conductivity (K2) is evaluated on five new soils and on a combination of soils. TheK2is related to Φϵ by a generalized Kozeny-Carman equation. This equation is then combined with scaling theory to derive the frequency distribution ofK2scaling factors from Φ distribution. The results of fractile diagrams and variances show that the use of the generalized Kozeny-Carman equation, with exponent taken equal to 4 or 5, gives, overall, good estimates of the distribution ofK2scaling factors from Φϵ measurements. The exponent value of 4 is more generally applicable. It is interesting to find that the above method applies as well across soil types, i.e., when the data of different soils are combined. The empirical equation for combined soils may also be used directly to estimate meanK2over an area, as a first-order approximation.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The productivity of 22 soils on serpentinized peridotite, as determined by either the Dunning site index (DSI) for mixed conifers or the timber yield index (TYI), is more closely related to the surface (0 to 30 cm) soil Ca/Mg ratio in either ammonium acetate or citrate-dithionite (CD) extracts than to any combination of climatic and physical soil variables or to the Fe, Mn, Cr, Ni, or Co contents in CD extracts. The coefficient of determination of an equation for the TYI as a function of the exchangeable Ca/Mg ratio is 0.87, increasing to 0.93 upon adding a function of the plant-available-water capacity (AWC) in 1 m of soil. Manganese is the only transition element whose content in CD extracts is correlated significantly with the DSI or the TYI, and that correlation appears to be fortuitous. The soil organic carbon content in 0.6 m of soil is a function of productivity, or the TYI (r2= 0.53).

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

As a part of studies aimed at selecting reliable soil tests for Cu, Mn, Fe, and Zn in cultivated organic soils (Histosols), we grew oats, onions, and carrots, all followed by lettuce in 55 cultivated organic soils in pots in a greenhouse. The harvested crop portions were analyzed, and the uptakes of Cu, Fe, Mn, and Zn determined. The plant uptakes were statistically analyzed to determine correlations with the earlier reported sequentially extracted forms of the soil metals, with total soil contents, and with the amounts extracted by eight different extractants. The overall results suggested that the various criteria for soil tests were best met by the extractant 0.5MHCI + 0.05MAlCl3for Cu, Fe, and Zn. For Mn in the soils that contained Ca-exchangeable Mn 10 to 50 times more than the crop requirements, the uptake data pointed to 0.1MHCl as the best extractant, although it did not seem to extract significant amounts of the reserve form of soil Mn. The data also indicated that immediately available Cu can be replenished by oxidation of sulfide-associated Cu (extracted by KCN, after removal of all other extractable forms).

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

A simple and reliable device was designed for measuring soil thermal emissivity. We measured emissivity in the field for silty clay soil of different water contents under two treatments: (1) tilled (plowed and raked), and (2) tilled and compacted.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We studied the variability of soil moisture retention in space over a wide range of suctions for an Olivier soil. Soil moisture at field capacity; saturation; and 0.005-, 0.01-, 0.03-, 0.1-, and 1.5-MPa suctions was measured on undisturbed soil cores, which were sampled at 30-cm spacing from the soil surface along an 80-m transect. The soil cores were further used for laboratory measurements of saturated hydraulic conductivity (K), bulk density, and particle-size fractions. As suctions increased, the correlation coefficients (CV) for the corresponding moisture contents increased. Lowest CVs were obtained for bulk density and the silt fractions, whereas the highest CV was for measuredKalong the transect. Semivariogram analysis indicated extensive spatial structure for soil moisture data sets at most suctions, with 50% of the sample variance attributed to spatial variation. However, lack of spatial structure, i.e., pure nugget effect, was obtained for moisture data sets at low suctions (0.005 and 0.01 MPa). This semivariogram finding was consistent with results based on autocorrelation analyses. Moreover, no clear patterns were observed for the range of spatial influence or length of correlation for soil moisture with increasing suctions. We concluded that the extent of spatial structure for soil moisture was not influenced by the degree of tension in the 0− to 1.5-MPa range. In addition, cross-correlogram results indicated that optimum correlations were obtained for field capacity and &thetas; at 0.03 MPa and for field capacity and bulk density observations. Poorly defined ranges with significance but low correlations were obtained for field capacity andKand for field capacity and the silt fraction.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The presence of gypsum in soils has complicated the determination of particle-size distribution (PSD) due to the difficulty in dispersion of the soils. A technique for rapidly removing gypsum from highly gypsereous soil samples is presented here, using the resin method. A mixture of Na and Cl resins enhances the complete dissolution of appreciable amounts of gypsum in salt solutions within 6 h. The dissolved calcium and sulfate exchange with the sodium and chloride on the resins, resulting in a solution containing primarily Na and Cl ions. The increase in electrical conductivity of the gypsereous soil solution is indicative of the amount of gypsum initially present. Thus, from a calibration curve, the amount of gypsum present in a soil sample is accurately determined. After the excess soluble salt has been removed, a stable clay and silt suspension is obtained, enabling a PSD determination using the pipette method. Removing gypsum from soil samples using the resin method has no significant effect on the particle-size distribution of the soils studied.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Recommendations for using sewage sludge compost to satisfy the N requirement of crops, which resulted from greenhouse and controlled environmental growth chamber studies, have not been sufficiently validated with field trials. Studies were conducted to evaluate the effects of sewage sludge compost and complete fertilizer amendments on yields and N content of ‘Kentucky 31’ tall fescue (Festuca arundinaceaSchreb.) grown on Evesboro loamy sand (mesic, coated Typic Quartzipsamments) in different environments. Compost was applied at rates of either 0, 45, 90, or 135 Mg ha-1in greenhouse and growth chamber pot studies and 0, 60, 120, and 240 Mg ha-1in field trials. Fertilizer (N,P,K) was applied at 0 and 200 kg ha-1where indicated. Compost amendment increased the yields of fescue linearly in all three growth environments. For the second crop, yields were 50% of those for the first crop in the growth chamber and 60% of those for the first crop in the field. A conservative estimate for compost N utilization by the fescue crop was 8% for the initial cropping season and 5% for the second season (determined from the entire plant uptake in the greenhouse and growth chamber). These estimates may be low because the average utilization of compost N by the tall fescue in the field plots was 7% for the first year clippings alone (roots and stubble not analyzed). Equivalent dry matter yields were obtained for the 135 Mg ha-1compost amendment and complete fertilizer for greenhouse grown fescue; however, equivalent yields for the field-grown fescue were realized by the 60 Mg ha-1compost amendment. Model equations were derived for estimating fescue yield from compost-amended soil.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID