摘要:

A bare-soil surface resistance parameter significantly improved the fit of a numerical model of heat and moisture flow in soils to 3 days of field measurements. The resistance removed a positive bias from the model estimates of daily cumulative evaporation on days with minimum surface soil moisture (0 to 0.5 cm) less than about 10% by volume. The model calibration was also made more stable. Saturated hydraulic conductivity and surface roughness were estimated by fitting the model to daily maximum surface temperature and minimum soil moisture. Without the surface resistance parameter, their values had to be changed from day to day to fit the surface measurements, though their day-today changes were minimal when surface resistance was included. A procedure is outlined to estimate the resistance as a function of soil moisture when independent measurements of the latent heat flux are available.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Calcic plagioclase (An69Ab30), albite (An6Ab94), and microcline (An2Ab31Or67) were leached over a 10-wk period at 13°C with 10−4Msolutions of a number of low-molecular-weight organic acids. The effectiveness of the organic acids in dissolving the feldspars was found to be citric ≈ oxalic > salicylic > protocatechuic ≈ gallic >p-hydroxybenzoic > vanillic ≈ caffeic, and the ease of weathering of the minerals was calcic plagioclase > microcline > albite. Because of the conditions under which the experiments were performed, the amount of aluminum released on dissolution of the feldspars by the organic acids appeared to be related more to the strength of the acid than to its ability to form complexes with aluminum.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Interactions between nonhydrolyzed polyacrylamide and aluminosilicates are governed by hydrogen bonding: the isolated hydroxyl group plays the role of the surface active site. The most interesting observation concerns the opposing behavior of the two faces of kaolinite: whereas the basal faces act as nonadsorbing surfaces, the edge faces modulate the adsortive capacity. Variations in polymer adsorption closely follow the modification of the surface electrochemical properties. The structure of the aqueous solution near the clay surface also affects the clay-polymer affinity. Results concerning the variation of the surface coverage and the kinetics of the adsorption process are discussed in terms of the local environment of the active site.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We applied isotopically labeled (15N-depleted) ammonium sulfate (115 kg N ha−1) to a Spodosol in a citrus grove, to determine the fate and subsequent distributions of NO3-N and NH4-N in the soil profile. The soil was tile-drained, and citrus trees were located on soil beds. We examined three soil management treatments: (1) the original A1 horizon (ST): (2) deep mixing of A1 and A2 horizons with the underlying Spodic horizon (DT); and (3) incorporation of 56 Mg ha−1of dolomitic limestone, along with deep mixing (DTL) of the profile. Soil samples were taken to the 70-cm depth in ST and to the 95-cm depth in DT and DTL soils and were extracted with 1MKCl. Extracts were chemically analyzed for NH4-N and NO3-N concentrations, and isotopic analysis was performed by mass spectroscopy. At 12 d after fertilization, both NH4-N and NO3-N values in the ST soil profile exceeded corresponding values for DT and DTL soils. This N was derived primarily from the fertilizer. With time, concentrations of both NH4-N and NO3-N decreased in profiles for all three soils; however, N concentrations in the ST soil consistently exceeded corresponding values for DT and DTL profiles. The shallow root system in the ST soil was observed to be less efficient for uptake of available N than was the deeper root system in DT or DTL soils. Labeled, as well as unlabeled, forms of plant-available N decreased rapidly during the first few weeks after application of fertilizer to these soils. Rapid uptake of fertilizer N by plant roots resulted in low levels of available soil N throughout the profile and small quantities of fertilizer discharged in drainage effluent.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Several numerical classification methods can be used to distinguish classes of soil. We used principal component analysis, cluster analysis, discriminant analysis, and a graph-theoretical method (minimum spanning tree).These methods divided 30 forest soil profiles from southwestern China into six groups based on their chemical and physical properties. The numerical classifications corresponded to a traditional soil classification. The groups formed by the numerical methods also corresponded to different forest vegetation types. In the high-mountain forest region of southwestern China, trees and shrubs are important in soil formation. The major soil-forming processes are eluviation (acid leaching) and humification. A sequence of soil Great Groups are recognized that identify these processes.In this analysis by numerical classification, not only can the soil profiles be divided into different groups, but the delimitation indexes of various soil properties can be established by discriminant functions.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

In this paper, we report on the interaction of the cationic pesticide chlordimeform with the clay fraction of a soil of variable charge. The soil used was classified as an Alfic Dystric Eutrocrept, with the following mineralogical composition: illite, talc, chlorite, vermiculite, goethite, maghemite, hematite, and lepidocrocite. Iron components dominate the clay fraction and silicates are present in lesser proportion, but the results show that the silicates have an important influence on the adsorption process. The variation of the electric surface charge with pH produces the rise in adsorption as pH increases, and changes in surface area produced by heating also cause an increase of pesticide adsorption.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

It has been suggested that different tillage methods create soil physical conditions that persist for various lengths of time in the easily compacted soils of the Southeastern Coastal Plain. To test this hypothesis, plots that had been subsoiled and chiseled were conventionally treated (disk-harrowed) for 1 to 3 yr to observe the residual effect of deeper tillage. In the final season, penetration resistances of all plots were measured at field capacity over a 1.90− x 0.55-m cross-sectional cut of soil perpendicular to the rows. This allowed plotting the isostrength patterns of the soil profile of each treatment. Although some residual subsoil tillage effect could still be identified 2 yr after subsoiling, the increase in soil strength (cone index) to 1.5 to 2.5 MPa even after a single year and the inability to position planters precisely over the previous year's subsoiled rows negated any benefit from the previous year's tillage.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

In this study we compared the ability of porous ceramic cups and a newly developed pan sampler to monitor chloride movement through the following three soils of diverse texture: a Grossarenic Paleustalf, a Typic Udifluvent, and a Udic Chromustert. Two pan samplers and three suction cups were installed at a depth of 0.6 m in three locations of each soil. Chloride was applied to the soil surface at 305 kg ha−1. Samples were collected weekly from the samplers and porous cups and analyzed for chloride.Both samplers collected sufficient volume to detect and describe the leaching of chloride through the loamy sand and silt loam soils. The pan samplers generally gave larger and more consistent samples than the porous cups at high soil moisture potentials.Porous cup samplers were ineffective in sampling well-structured clay soils, but samples were collected by the pan samplers in the soil. We think this difference is due to rapidly leaching water and chemicals moving through large pores; it bypassed the porous cups, but was intercepted by the larger surface area of the pan samplers.The initial chloride concentration applied to the soil was 500 mg L−1, but the highest measured concentrations in the samplers were 70, 53, and 170 mg L−1in the loamy sand, silt loam, and clay soils, respectively.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

Field inoculation of groundnut (Arachis HypogaeaL.) with effective strains ofRhizobiumis complicated because many tropical soils contain indigenous cowpea rhizobia capable of forming nodules on this host. We evaluated inoculation in an attempt to improve nitrogen fixation in a sub-Sahara soil of Sudan. Greenhouse screening of rhizobia on two Sudanese groundnut cultivars, Barberton (Spanish type) and Ashford (Virginia type), indicated significant differences among the 10 strains tested, mainly in host-plant color ratings and nodule numbers. Two strains, 8A11 (from the Nitragin Co.) and TAL 309 (from NifTAL), were selected for testing in the field. The strains were applied as single or mixed inoculants, formulated (a) in peat and placed with the seed or 5 and 10 cm below the seed, and (b) in oil and applied to the seed. The soil (Entic Pellusterts) at the test site contained 2.1 x 104cowpea rhizobia g−1. When inoculants were added in a peat carrier at seedling depth, the only nitrogen-fixing trait significantly improved (P< 0.01), compared with the uninoculated controls, was nodule mass. The TAL 309 strain was serologically distinct from the indigenous cowpea rhizobia, and agglutination reactions indicated that approximately 40% of the main- and lateral-root nodules were occupied by this strain where applied. Unfortunately, this did not result in improved yields. With inoculation in an oil carrier, both nodule mass and pod yield of Barberton were significantly reduced (P< 0.01). The Barberton cultivar evidently was sensitive to the presence of oil. As peat inoculant was placed deeper into the soil, both the linear and quadratic terms were significant (P< 0.06) for improved top dry weights, whereas other traits were unaffected. The nitrogen control (120 kg N ha−1as ammonium sulfate) significantly depressed nodule numbers and nodule mass and improved top dry weights and tissue nitrogen. The Ashford and Barberton cultivars were significantly different in nodule numbers, top dry weights, pod yields, and nodule mass.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID

摘要:

We report the development of a nondestructive experimental method that is capable of measuring changing solution contents and tracer salt concentrations in unsaturated soils. The method utilizes a dual-source, gamma-attenuation system. We develop and discuss a probable-error analysis of solution content and salt concentration determinations from the dualsource gamma system. Results from fluxcontrolled absorption of SrCl2and NaI solution into two dry soils are presented. We observed substantial water movement apart from the liquid phase via vapor transport and adsorption mechanisms in the fine-textured silt loam, but not in the coarser sandy loam. Analyses of distributions of solution content and salt concentration during absorption provide insight into the complex interactions of multiphase transport mechanisms during solution movement in soils at low solution contents.

ISSN:0038-075X    

出版商:OVID    

年代:1986

数据来源: OVID