摘要:

We report here the results of laboratory and computer simulations designed to supply information on soil temperatures under forest and range fires. Measurements of temperature and water content in a soil column that was heated strongly at the surface showed a consistent pattern of warming and drying. In initially wet soil, temperature rose to around 95°C and remained there until the water content of the soil at that depth dropped below about 0.02 m3m3. When the soil was initially dry, the temperature increased more rapidly, but even the moisture present in air-dry soil was sufficient to slow the rate of temperature rise when temperatures reached 90°C. A linked-transport model, which simultaneously computes changes in temperature and water content, simulated the main features of heat and water flow in a soil column heated to high temperature. There were no consistent deviations of measured from modeled temperatures, but the water content simulations consistently showed a greater buildup of moisture ahead of the heating front than did the measurements, and less drying of the soil in the heated layers when the initial soil water content was low. Soils from sand to clay, and with differing mineralogies, water contents, and bulk densities were used to compare measurements and simulations. The model performed well in all cases. Since the temperature simulations are reasonable, the model appears suitable for predicting fire effects in the field.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Tension infiltrometers have been used to demonstrate the contribution of macropore flow to total flow by comparing measured infiltration rates at various supply water potentials. Hydraulic conductivity may be extracted from infiltration data with theoretical analyses of uniform water flow beneath the tension infiltrometer. By-pass or macropore flow, though, is nonuniform flow of water. We wished to determine whether a combination of hydraulic conductivities determined from traditional analysis of tension infiltrometer data and laboratory-determined water capacities could be used to simulate the infiltration on the soil from which the hydraulic conductivity data was collected. We observed water flow patterns beneath tension infiltrometers placed at 0.5-m depth in highly structured clay soils after infiltration with water containing a dye. The water was allowed to infiltrate under two series of increasing supply water potentials Ψ0; −0.24, −0.12, −0.06, −0.03 m and −0.24, −0.12, −0.06, −0.03, −0.02, −0.01, 0 m. Infiltration rates from the tension infiltrometers reached steady state within a few minutes after the supply water potential of the infiltrometer was adjusted. Hydraulic conductivities were calculated from traditional theory based on the steady state infiltration rates. Specific water capacities were determined in the laboratory from soil cores. Infiltration was simulated with an axisymetric finite difference model. Dye stain patterns showed that water infiltrating at both −0.24 m ≤ Ψ0≤ −0.03 m and −0.24 m ≤ Ψ0≤ 0 m passed first through fissures between slickenside surfaces and between ped surfaces, and through biopores, and then into the soil matrix. We found dye stain at much greater depths than we simulated with the finite difference model that was based on uniform flow. We conclude that models using hydraulic conductivity—water potential relationships derived from present analysis of tension infiltrometer data may not give desired results when combined with laboratory-determined capacities.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Statistical and geostatistical analyses were conducted to estimate both correlation and spatial distributions of trace elements in soils and plants within a corn field. Statistical analysis of AB-DTPA-extractable trace elements in soils and the total elemental content of plants indicated that Mo in corn leaves was negatively correlated with soil Cu and Fe. Copper aggravates Mo deficiency in plants because Cu interferes with the role of Mo in the enzymatic reduction of NO3. Geostatistical analyses of the soil trace elements, Cu, Zn, Mn, Fe, and Mo, showed that these elements were spatially interdependent. Iron, Mn, and Mo in corn leaves were spatial variables characterized by linear, spherical, and exponential variogram models, respectively. However, Cu and Zn contents in corn leaves were randomly distributed in the field. Using the relationship between soil Cu and plant Mo, and a cokriging technique, plant Mo estimation was significantly improved by incorporating the soil Cu information. Compared with kriging, cokriging reduced the mean error of the estimates by about 5 times, reduced the mean square error and the mean kriging variance up to 48%, and increased the correlation of estimates and measurements from 0.49 to 0.61.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Humic acids from a range of Italian soils and the residual suspended organic material (light fraction litter) associated with them have been studied by pyrolysis gas chromatography mass spectrometry, solid state nuclear magnetic resonance spectroscopy, and infra-red spectroscopy. Although the major vegetation types on the soils differ considerably, spectra of humic acids from soils with different major vegetation types were similar. Because no relationship between humic acid structure and major vegetation type was observed, gross assumptions about humic acid structure should not be drawn from a knowledge of macro-vegetation types on soils. Light fraction litter in the soils from minor vegetation may be more significant in affecting the eventual structure of the humic acids.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Concerns about the environmental impacts of N management in agroecosystems have increased interest in promoting N efficiency and greater utilization of animal manures, green manures, and legumes in crop rotations. Predicting N dynamics of different soil management in short-term studies is difficult because soil properties change slowly. A long-term experiment under a winter wheat-fallow system in the semi-arid region of eastern Oregon provided an opportunity to study the cumulative effects of residue management on the mineralization and plant availability of N. The treatments, established in 1931, included wheat straw burning, incorporation of straw, manure, legume plant residue, or inorganic N. To evaluate N availability to plants, a greenhouse pot study was conducted on the treated soils collected from the 0 to 20-cm depth. Ryegrass (Lolium perenneL.) was grown as an indicator plant for 120 days in 1-kg soil samples treated with different rates of inorganic N and harvested and analyzed for total N at 30-day intervals. At the control rate, ryegrass dry matter yield (DMY) and N uptake from the manure-treated soil were more than 50% higher than from other residue treatments. When adequate nutrients were applied, soil treated long-term with manure had no DMY advantage over long-term inorganic N treatments. Burning of wheat straw did not significantly influence DMY, although yields from the burned plots tended to be lower. Large accumulations of extractable nitrate (<12 mg-N kg-1) in the lower portion of the manure-treated soil suggest a potential for nitrate groundwater contamination.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

In Arkansas, the Mehlich-3 extraetant is used in the determination of soil test P for both upland and lowland crops. However, this technique does not consistently predict a response by paddy rice (Oryza sativaL.) to P fertilization. The objective of this research was to relate soil test P determined by four extractants to P uptake by paddy rice grown on two rice-producing soils. The soils in this study were a Crowley silt loam and two Hillemann silt loam samples collected from fields where P deficiencies in rice were observed the previous summer. Rice was grown on these soils in the greenhouse at fertilizer rates of 0, 5, 10, 20 and 40 mg P kg-1. Plant uptake and tissue concentrations of P were measured and related to soil test P extracted by Mehlich-3, Bray-1, Olsen, or ion exchange resin at 0, 24, 31, and 124 days after flooding (DAF). The Crowley had the highest soil test P obtained with all extractants at all flooding dates compared with the two Hillemann soil samples. Mehlich-3 and Bray-1 extractants consistently gave higher soil test P values on the Crowley soil than did Olsen and resin extractants. Only the resin showed a consistent correlation between soil test P measured at 0 DAF and % P in shoot and total P uptake measured at 24, 31, and 124 DAF. This correlation was improved when P uptake was related to soil test P measured on anaerobic soils. Although Mehlich-3 is convenient for soil test laboratories, the resin appears to be a more appropriate extractant to estimate plant available P for paddy rice.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID