摘要:

This paper presents a physically based model for temperature and heat flux profiles in a homogeneous soil. It was designed to predict soil surface temperatures, which cannot usually be measured easily, from subsurface data. This is important for surface energy balance studies, including estimating evaporation. A simple but realistic surface soil heat flux model was used to calculate analytical expressions for all the coefficients and phases in the well-known Fourier series solution to the soil heat flow equations. The model depends on only four or five (depending on the application) physically realistic parameters, which may be estimated by fitting to subsurface soil temperatures or to both temperatures and fluxes. The model was tested on two bare soils and one vegetated soil. Surface temperature data were not available for comparison, but the predicted near-surface temperatures (1 cm for the bare soils and 4 cm for the vegetated soil) were accurate to about 1°C, when the soil could be considered homogeneous, and to 2 to 4°C, when variability in the thermal properties over depth and time severely violated this assumption.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

An accurate assessment of the moisture content of surface soils in arid and semiarid systems is necessary to predict the productivities of shallow-rooted plants and decomposition rates of surface and near-surface litter. Soil water loss has often been assumed to proceed in a stepwise manner, beginning at the surface and proceeding to deeper layers as the profile dries. However, recent studies suggest that plants draw water simultaneously from many or all soil layers where roots are present. We examined the potential significance of this phenomenon in a semiarid ecosystem utilizing two simulation models, one integrating soil water loss throughout the profile and the other sequentially removing water from soil horizons. Field observations indicate greater moisture retention in shallow soils than could be explained by a stepwise removal of water; a better correlation was achieved by simultaneously drawing water from all horizons.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

To investigate the contribution of organic matter to the cation exchange capacity (CEC) and the specific surface area (SSA) of organomineral complexes in soils, we studied A horizons of four soils (two Hapludalfs and two Argiudolls) in central Iowa. The effect of mineralogy on CEC and SSA was held nearly constant by sampling soils developed in the same parent material (loess) and landscape position (summit). A range of organic matter contents was obtained by variations in native vegetation, the effects of cultivation, and horizon depth. The CEC, SSA, and organic C content of unfractionated samples were determined. Soil samples were also separated into coarse silt, fine silt, coarse clay, and fine clay size fractions after dispersion by sonification. The organic C content of each fraction was determined, as were CEC and SSA, before and after peroxide treatment. Multiple linear regression equations were developed to relate CEC and SSA to organic C and peroxidized SSA. Partial regression coefficients suggested that the net contribution of organic matter to the CEC of unfractionated soil materials was 184 cmol(+) kg−1of organic C. In the coarse silt, fine silt, and coarse clay fractions, organic matter was estimated to contribute approximately 559 cmol(+) kg−1of organic C to the CEC and 7.22 x 105m2kg−1of organic C to the SSA of the fractionated materials. On average, organic matter was calculated to contribute 49% of the CEC and 19% of the SSA of the fractionated materials. Because “independent” variables were themselves highly correlated, principal components regression analysis was used to improve the precision of estimates of organic matter contributions derived from the partial regression coefficients.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We investigated the vertical profiles of 4-hydroxybenzoic (I), 4-hydroxy-3-methoxy-benzoic (II),trans-4-hydroxy-3-methoxycinnamic (III),trans-4-hydroxycinnamic acid (IV); and thecisacid of IV in a 2MNaOH-extractable fraction from a core sample of Horonobe peat soils, Japan. Amounts of compounds I, II, III, IV, and thecisacid of IV in the seven layers averaged 590, 1400, 1300, 5400, and 510 μg C/g C soil, respectively. Compound IV was dominant in amount and averaged 62% of all four phenolic acids quantified in all layers. Thecis/transratio of IV increased with the depth of the samples, with two exceptions. By dominant peat-forming plants, the samples were classified as three types of peats—low moor, transitional moor, and high moor. We found that a relationship between phenolic acids and their humification should be discussed separately in their peat environment. The amount of compound IV in a high moor environment increased with an increasing degree of humification. We also determined phenolic acids in the ethyl-acetate-extractable fraction. The ethyl-acetate-extractable forms accounted for less than 11% of 2MNaOH-extractable phenolic acids (I + II + III + IV) quantified in all layers.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Soil redox potentials are relative indicators of aeration. This study was conducted to monitor redox potentials throughout the growing season in a continuous tillage-continuous maize (Zea maysL.) field study and to determine if redox potentials reflected differences in tillage treatment. Platinized electrodes and salt bridges were installed at depths of 15, 30, and 45 cm in four replicates of no-tillage (NT), moldboard-plow (MP), chisel-plow (CH), and ridge-tillage (RT) treatments on a Tara silt loam soil (Pachic Udic Haploboroll) and monitored during the growing season. Locally weighted regression and repeated measures analysis of variance were applied to the data. Tillage affected aeration of each soil depth zone at different times during the growing season. Mean redox potential measurements ranged from about 400 to 650 mV at the 15-cm depth; only redox potentials in NT and CH treatments were depressed to 250 to 300 mV in early 1985 (after an exceptionally wet October in 1984). At the 30-cm depth, mean redox potentials ranged from about 250 to nearly 700 mV; potentials in RT and NT treatments ranged from about 400 to >650 mV throughout both growing seasons. Changes of more than ±200 mV were observed at the 450-mm depth and appeared only partially related to water content, except in late 1986 when mean potentials of all treatments declined by >100 mV. Ridge-tillage treatments tended to maintain greater redox potentials and undergo less change at the 15− and 30-cm depths than other tillage treatments. Tillage affected redox potentials below the tilled zone, and MP treatments appeared least aerated at the 45-cm depth relative to other tillage treatments.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

For convenience, most soil samples are dried, ground, and sieved prior to undergoing chemical analysis. Changes that take place in soils as they are dried and stored for extended periods could pose problems to soil scientists attempting to use the results of chemical analyses of dried soils to predict the behavior of soils under field conditions. This study was conducted to evaluate the influence of soil drying on the extractability of plant nutrients in five soil samples taken from four Florida soils and to determine if microwave-drying can be used as a rapid method of drying soils prior to chemical analyses. The soils used were the Ap horizon (0 to 15 cm) of a Malabar fs (Grossarenic Ochraqualf), a Kendrick fs (Arenic Paleudult), an Immokalee fs (Arenic Haplaquod), and a Torry muck (Typic Medisaprist), along with the Bh horizon (100− to 125-cm depth) from the Immokalee fs. The treatments imposed were airdrying for 1 wk at room temperature, oven-drying at 105°C for 24 h, microwaving to dryness, and field-moist soil. Results of this study indicate that soil drying increased levels of Mehlich-1-extractable P, Fe, and Mn by as much as 600%, oven-drying generally resulting in the largest changes from the field-moist state. In most instances, microwave-drying produced results intermediate between those given by air- and oven-drying. Soil drying also influenced soil pH and the levels of extractable Ca, Mg, K, and Zn, but the changes were not consistent among soils and were probably related to initial soil properties, such as organic matter content and clay mineralogy. Soil pH varied by as much as 0.7 pH units as a result of drying. Levels of extractable Ca, Mg, K, and Zn in the Torry muck generally increased after the soil was dried, probably due to the oxidation of organic matter. In the Malabar fs, which contains a comparatively high level of organic carbon and few clay minerals, except quartz, levels of nutrients tended to decrease upon air-drying and then to increase on further drying. Drying treatments produced variable results for the other soils used. Although drying caused definite changes in the levels of extractable plant nutrients, the concentrations of nutrients found in air-, oven-, and microwave-dried soils were highly related (r; P> 0.01) to the concentrations found in field-moist soil. This indicates that, as long as the changes that occur as a soil is dried are known and considered, useful information can still be obtained from the analysis of dried soil samples. Results of this study also suggest that microwave-drying of soil samples may represent a rapid technique for drying soils prior to chemical analysis.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

In 1888, a geologist, J. H. L. Vogt, stated that an exceptionally low apatite content in the bedrock was the reason for osteomalacia in animals in certain areas in Norway. This discovery was confirmed, for example in South Africa, soon after World War I.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

We investigated potassium exchange equilibria in 20 calcareous soils from Iraq. Soils were varied in their CEC and miner-alogical composition. The percentage of CaCO3in these soils ranged from 10 to 29. The mean (Ca) (CO3) ion activity product (IAP) was found to be 5.89 x 10−8(pIAP = 7.23) with the standard deviation of 0.391 x 10−8. The experimental data on EKR and KAR exhibited a constant Gapon exchange selectivity coefficient (KG) for EKR values less than 0.11, provided corrections for ion-pairing and complex formations have been made. However, the agreement between the data and the Temkin equation was closer than that of Gapon equation. The plot ofKGversus pIAP did not reveal a definite relationship between these quantities.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Short-term bioassay techniques that measure root development of seedlings in soil can be used to evaluate the applicability of chemical methods to predict the Al toxicity of a soil. Wheat (Triticum aestivumcv. Hart) seedlings were grown for 3 d in 20 acidic soil horizons, and root length was related to amounts and forms of Al in soil solution and Al extracted by 0.01MCaCl2, 1MKCl, 0.5MCuCl2, and 0.33MLaCl3. With the exception of Al extracted by 0.01MCaCl2, soil extraction methods were not effective in predicting root growth. Root growth was not closely related to total soil solution Al or soil solution Al reacting with 8-hydroxyquinoline, pyrocatechol violet, or aluminon. These colorimetric reagents reacted with nontoxic forms of Al, including organically bound Al, and overestimated the toxic component. Activities of Al species in soil solution were estimated from soil solution composition using the GEOCHEM program. The calculated Al3+activity ({Al3+}) ranged from 0 to 119 μMand taken alone was not a good predictor of root growth. It is likely that calculated {Al3+} overestimated actual {Al3+} due to the difficulty of measuring all Al-complexing ligands in soil solution. Root growth in these soils was best described by a multiple regression equation containing soil solution pH, Ca, and Al. The results of this study illustrate the limitations associated with the current methods used to estimate toxic Al levels. New methods are needed to directly measure the toxic Al component or components in soil solution. Until better chemical or instrumental techniques are developed, the short-term bioassay technique should serve as a useful means of assessing the potential Al toxicity of a soil.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Ethylene dibromide (EDB, or 1,2-dibromoethane) was used in the United States as a soil fumigant from 1948 until 1983, when its discovery in stored grain and in wells prompted EPA to ban further agricultural uses. Traces of EDB have also been found in some Connecticut soils up to 20 yr after their last known fumigation. This persistence in soil and water raised concern over possible contamination of vegetables or lawn grasses planted in soil previously treated with EDB. To simulate a worst case, radishes (Raphanus sativasL. cv. Champion) and perennial rye grass (Lolium perennecv. Pennfine) were planted within 7 d after fumigation, rather than waiting the usual 4 to 6 wk for the EDB to dissipate. Successive harvests during the first growing season showed that the concentrations of EDB in the tissue decreased relative to the concentrations in the soil. No EDB was taken up by radishes or grass in the second growing season after fumigation, although residues of EDB that were resistant to extraction with hexane persisted in the soil and could be removed only with hot methanol. These experiments show that the traces of EDB found to persist in soil for many years after fumigation are not taken up by plants. Also, the linearity of the dose-response curves for uptake of organic compounds by plants assumed by EPA in its proposed regulations for land application of sewage sludge should be reexamined.

ISSN:0038-075X    

出版商:OVID    

年代:1989

数据来源: OVID