摘要:

The problem of axisymmetric diffusion from a line source under constant flux in a soil is discussed. Earlier results are greatly simplified and made more accurate as well. An exact solution for power law diffusivities agrees remarkably well with a general analytical approximation for powers that cover the range from clay to sand. The latter could be used to predict the saturated front position, thereby simplifying the numerical prediction of the profile, or to predict the whole profile with a lesser accuracy

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The soil water characteristic and hydraulic conductivity curves of Shonai sand dune soil were measured from saturation to 25-MPa matric suction. The hydraulic conductivity was measured using a steady-state flux control and an instantaneous profile method in two different matric suction ranges. The determined hydraulic conductivity varies from 10−2to 10−13cm/s, with change in volumetric water content from saturation to 1.0%. An empirical equation relating hydraulic conductivity with volumetric water content was developed, which fits the measured data very well. The vapor and the liquid components of hydraulic conductivity were estimated. The estimated vapor component exceeds the liquid component below 2.1% (5-MPa matric suction) water content. The measured values of hydraulic conductivity were used to test the Mualem and the Burdine predictive equations. Both equations estimate the hydraulic conductivity fairly well at water contents higher than 18%, but overestimate the conductivity at medium water contents from 5 to 18%

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The updated versions of the SLIM and MACRO computer simulation models were evaluated using 3 years of bromide leaching data from a field experiment conducted on Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalf) with a well developed structure in central Pennsylvania. An application of potassium bromide (KBr) tracer was broadcast to 18 plots at 100 kg ha−1at planting on May 13, 1988. Eighteen zero-tension pan lysimeters (0.456 m2) were placed at a depth of 1.2-m below the soil surface to collect gravitational water samples. Average pan collection efficiency was 52%, with a CV of 44%. Model simulations of Br−leaching for 1988, 1989, and 1990 were compared with the mean of pan efficiency-corrected measured data. There were no statistical differences between the SLIM and MACRO model predictions and, the experimental data for 1988 except for 1 or 2 months for each model. The SLIM model accurately predicted Br−leaching in 1989 but significantly underestimated Br−leaching from October 1990 through February 1991. The MACRO model significantly underestimated Br−leaching from May to November 1989 and performed well in 8 of 12 months in 1990. The overall simulations for 3 years of each model were compared with the overall field measurements of Br−leaching. The statistical evaluation criteria indicated that the SLIM model performed somewhat better than the MACRO model through the 3-year period. The results given in this study indicate that both models have good potential for conservative tracer simulation

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Water infiltration and movement into soil are important factors for cropping systems in texture contrast soils subject to runoff and erosion under unsteady rainfall. This study considers the effects of 10 years of direct drilled (with stubble retained) wheat, in a duplex soil (luvisolic type soil with sandy clay loam A horizon and clay subsoil) in southeastern Australia, on water penetration into both dry and wet soil profiles, in comparison with conventional tillage (soil cultivated 100 mm after stubble burnt). Earthworm populations, biomass, and species diversity were determined under each tillage system. Surface-applied bromide in solution was used in the field, under ponded conditions, to trace water movement into the soil profile and to detect differences in leaching patterns between tillage systems. In dry soil conditions, conventional tillage retarded the movement of water, and the soil surface quickly became saturated. Bromide penetration and movement was increased below 100 mm by direct drilling, in comparison with conventional tillage. Bromide added to a wet soil tended to concentrate at the surface 50 mm under conventional tillage, compared with direct drilling. Preferential flow, where a proportion of infiltrating water bypassed the soil matrix, apparently occurred in the 0 to 100-mm depth under direct drilling. Unsaturated flow and impeded water movement were evident near the surface of the conventional tillage. It is suggested that different soil structures and soil stabilities directly influenced water infiltration, although antecedent moisture conditions appeared to strongly influence leaching patterns. Characterization of earthworm abundance and species indicated that conservation tillage increased the presence ofAporrectodea trapezoidesandAporrectodea rosea, which forms extensive, vertical burrows. Overall, direct drilling improved the movement of water into the A horizon of duplex soils

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Brief drying times for soil samples are sometimes necessary, e.g., to halt microbial activity quickly or to estimate the fresh weight of soil needed to provide a particular dry weight for incubation or other experiments. Soil samples ranging from high to low organic content can be dried successfully in microwave ovens within a few minutes, thus achieving the same &thetas; values as when measured by conventional drying techniques. In this study we compared the effects of air, conventional, and microwave drying on soil chemical propertiesSamples of 20 forest soil horizons from New Hampshire were air-dried, dried in a forced draft laboratory oven, or dried in a rotary microwave oven. Levels of exchangeable Ca2+, Mg2+, K+, and Na+and pH of dried soils were compared with values for field moist controls. There were no significant differences between mean values determined for levels of the exchangeable cations or pH for field moist or any of the drying methods. Nor were cation values obtained from samples dried in the microwave oven significantly different from those obtained by drying in a conventional laboratory even

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

A better understanding of organic- inorganic phosphorus transformations is needed to improve management of phosphorus fertilization of cultivated soils. This study was conducted to determine if the mineralization of organic phosphorus compounds in a soil could be induced enzymatically and observed using31Phosphorus Nuclear Magnetic Resonance Spectroscopy (31P NMR). Sampler, of an Osorno series (Typic Dystrandept) soil were sterilized using gamma radiation, then incubated with alkaline phosphatase, acid phosphatase, phosphodiesterase, and phytase. Soil extracts were prepared using 1.0MKOH, then treated with a cation exchange resin to remove interfering paramagnetics.31P NMR analysis of untreated and treated soil extracts showed a decrease in phytic acid and a corresponding increase in orthophosphate for the phytase-treated sample. Results indicate that soil organic P is mineralized enzymatically and that the NMR technique is useful for studying mineralization in soils having sufficiently high levels of organic P

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Studies were conducted to investigate loess rejuvenation effects on the morphological, physicochemical and mineralogical characteristics of some intensely weathered soils in south-central Kentucky without evident lithological discontinuities. Soils were classified as clayey, mixed, thermic Typic Paleudults; Hapludults; Haplohumults; and fine, mixed, thermic Typic Paleudalfs. They showed higher than expected clay activities, base saturations, and weatherable minerals in the upper sola, apparently caused by the influence of variable eolian depositions. Because a major part of the control section is within the upper solum, the soils lack kandic horizons or kaolinitic mineralogy but have lower sola with relatively low clay activities, large amounts of kaolinite and free Fe oxides, and lower concentrations of weatherable minerals. In spite of the apparent advanced past development of these soils, their classification contradicts the nature and properties of the rejuvenated upper solum materials

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

On the Great Hungarian Plain, the correlation between soil variables and plant data was studied in a heterogeneous solonetzic grassland. A 21-in transect was sampled to identify the basic features of the soil-plant correlations. The abrupt change from nonsaline meadow to salt-affected grassland vegetation was explained by the sharp increase in the sodium concentration of the groundwater. Two 50-m transects were sampled, and the relationship between soil variables and plant data was used to predict soil variables. The observed data of the 50-m long transects were divided into two groups of plants, one used for the multiple regression equations and the other used as a check. When comparing the efficiency of various groups of variables for estimation, plant cover data was only half as precise as the soil data.

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1994

数据来源: OVID