摘要:

A dynamic simulation model describing diffusion of gases in multinary gas mixtures was developed to calculate the inter-diffusion of gases in complex systems where respiration and denitrification take place. The model is based on the Stefan-Maxwell equations for concentration diffusion of isothermal, isobaric ideal-gas mixtures and applies to a one-phase system in one dimension. To test the correct implementation of the theory in the model, it was used to calculate the mole fraction distribution in a gas layer for some ternary diffusion problems for which analytical solutions to the steady-state situation are known. Agreement between numerical and analytical solutions was within 1%. Subsequently, the model was used to calculate the dynamic behavior of a gas system in which denitrification takes place and acetylene is used to prevent the conversion of nitrous oxide into molecular nitrogen. When a 2% concentration of acetylene was maintained at the surface of the gas layer, and biological activity was positioned at a depth of 0.25 m, these calculations showed the acetylene concentration to reach 1.8%. This value is sufficiently high to inhibit nitrous oxide conversion into molecular nitrogen, but would be equal to 2% when calculated on the basis of Fick's law. A simplified approach to calculate diffusion in multinary gas mixtures is proposed and tested for the case study of denitrification. It turns out that results of the simplified approach approximate those of the Stefan-Maxwell equations to within 10%. The objectives of this paper are to discuss the model, to compare the results of the numerical and analytical solutions of two ternary diffusion problems, to report the results of the case study of denitrification, and to compare these results with those obtained from simplified diffusion theory.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

For predicting ionic strength from specific conductance, a saline soil, an alkali soil, and a normal typical rice soil amended with different levels of salt (NaCl) and alkali (NAHCO3) were kept submerged with deionized water for 12 wk. Despite wide variations in the ionic composition and ionic strength of the soil solutions, a close relationship (r= 0.98) was found between the actual ionic strength (total concentrations corrected for the presence of ion pairs) and specific conductance of equilibrium soil solutions collected by gravity every other week up to 12 wk. The ionic strength (moles/L) was approximately 11.62 times the specific conductance (mhos/cm, 25°C).Higher values were found for ionic strengths measured from stoichiometric concentrations compared with values of actual ionic strengths measured after incorporating the corrections due to the presence of ion pairs. The variations were more in NAHCO3-amended soil (25 to 51 %) than when the same soil was amended with NaCl (3 to 32%). Very good agreement was found between the ionic activities calculated from actual ionic strength and ionic strength predicted from specific conductance.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

We investigated the effect of 17 soil properties on hydrolysis of seven linear oligophosphates ranging from P2to P65and a cyclic polyphosphate (trimetaphosphate). Each of 29 Iowa surface soils was treated with 500 μg of polyphosphate P/g of soil and incubated under aerobic conditions at 25°C for 7 d, and the amount of orthophosphate (Pi) produced was determined. Results showed that polyphosphate hydrolysis varied with the oligophosphates and soils used. Statistical analysis of paired relationships showed that, with the exception of P2, the amounts of Pi produced from the individual polyphosphates were significantly correlated with soil pH and negatively correlated with dithionite-extractable Al3+and Fe3+. The amounts of Pi produced from certain polyphosphates, but not the others, were significantly correlated with water-soluble Ca2+, but negatively correlated with pyrophosphatase activity (buffered and nonbuffered systems). Multiple-regression analyses showed that polyphosphate hydrolysis is affected by pH, water-soluble Ca2+and nonbuffered pyrophosphatase activity, all of which had significant positive partial-regression coefficients. Soil properties that showed significant negative partial-regression coefficients were percentage of clay (all P compounds studied), water-soluble Mg2+(P2, P3, TMP, P5, P15, and P25), and dithionite-extractable Al3+(P2, P5, P15, P25, P35, and P65). TheR2values of these regression equations ranged from 0.66***to 0.88***.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

We incubated samples of five unfertilized Argentinian soils with phosphate at 4, 25, 40, and 60°C and measured the change in the null-point phosphate concentration through time. There was an initial decrease in this phosphate concentration, but, in some cases, it was followed by an increase in concentration. The increases were most marked after long periods or high temperatures and especially at low levels of added phosphate. The increases in concentration appeared to be due to release of phosphate already present in the soil. The amount released increased with both time and temperature of incubation. Functions to describe this release were included in equations to describe the continuing reaction between added phosphate and the soil. This produced a close description of the changes in concentration through time. We argue that it is consistent with mechanistic models of phosphate reaction with soils to subdivide phosphate added at different times into separate “pulses.” The net outcome is then the algebraic sum of the trend for each “pulse.”

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

The objective of this study was to evaluate the effectiveness of sludge P in comparison with inorganic P, as a fertilizer for P-deficient sesquioxic soils.Municipal sewage sludge and monocalcium phosphate (MCP) were applied to two soils—Griffin clay (Typic Haplorthox) and Clovelly sandy clay loam (Tropeptic Haplorthox)—at rates equivalent to 200, 500, and 1,000 kg ha−1P. Italian ryegrass (Lolium multiflorum) was grown in the soils using a split pot technique, and tops were harvested at 14, 35, 63, 97, 125, 153, 181, and 209 d after commencement of root:soil contact. Yield and concentration of P, N, Ca, Mg, K, and Na in the plant tissue were determined.Both soils exhibited large responses to applied P, with P uptake from sludge treatments being significantly greater (P< 0.05) than MCP treatments in the Griffin soil, and significantly lower than MCP treatments in the Clovelly soil. Rates of P uptake declined rapidly with time in MCP-treated soils, and in sludge-treated soils rates of P uptake increased or declined only slowly. The relative efficiency of sludge P compared with MCP increased from 44 to 90% and 64 to over 100% with time in the Clovelly and Griffin soils, respectively.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Sodium content of utricles, utricle bracts, testa, and embryo was determined forSarcobatus vermiculatus. Immediately after germination, seedlins were grown in H2O, 330 mM NaCl, or 225 mM Na2SO4solutions, and Na+content was determined. Sodium content of utricles averaged 38 900 μg·g−1, with highest concentrations in bracts (53 100 μg·g−1), and lowest concentrations (1843 μg·g−1) in embryos. Sodium concentration of washed embryos averaged 954 μg·g−1. Seedlings germinated from debracted utricles and grown 24 h in distilled H2O contained 2965 μg·g−1Na+. The Na+content of seedlings germinated and grown 24 h in NaCl or Na2SO4solutions averaged approximately 24 000 μg·g−1. Rapid uptake of Na+by the germinating embryos and seedlings is postulated to be an adaptive mechanism for developing and maintaining a favorable water balance in soils with low osmotic potentials.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Sewage sludges were incorporated annually into the surface 20 cm of Dublin loam over a period of 8 yr. Sludge rates varied from 0 to 225 metric tons per hectare (t/ha) in increments of 45 t. Data presented cover a 9-yr period, which includes a final year in which no sludge was added to the soil. Metal concentrations found by analysis were higher in the surface soil only when the concentration of metal in the added sludge exceeded that found in the untreated soil. Metal availability, expressed as DTPA/HNO3ratios, was greater in the acid Oakland-sludge-treated soils for Cd, Zn, Ni, Co, Fe, and Mn than in the neutral to alkaline Pacheco-sludge-treated soils. The increased soil acidity and the high percentage availability of metals in the Oakland plots did not result in an increased metal movement within the soil profile. Metals tended to remain in the zone of soil incorporation over the 9-yr period in spite of sludge additions amounting to 1800 t/ha for Pacheco and 1440 t/ha for Oakland sludge. The apparent movement of Zn and Cd5 cm below the area of sludge incorporation may be an artifact resulting from inaccurate depth measurements due to the decrease in bulk densities. Rototilling of the field resulted in a lateral movement of soil and sludge particles downlope from the plot areas. This soil movement made it impossible to balance metals added in sludge with metal contents of the soil. No significant movement of metals occurred in the year following termination of sludge additions.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Two soil samplers—a soil core sampler and a test-tube sampler—and the related techniques for vertical and horizontal quantitative determinations of soil rhizosphere microorganisms are described: both are easily constructed, require no special maintenance, and were successful in field trials. The tools may be adapted to other types of soil research, such as root distribution.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Palmelloid, unicellular green microalgae in the genusChlamydomonaswere inoculated onto replicated plots at rates calculated to approximate feasibility through sprinklers (5 x 1011log phase cells ha−1yr−1) and with an airplane (5 x 107ha−1yr−1) to test their value as soil-conditioning agents. Applications were made to the same parcels of a Quincy loamy sand for three consecutive growing seasons. Highrate plots consistently showed significantly greater (5% level) stability to slaking of 0.92− to 1.68-mm sized aggregates from the surface (2 to 3 mm) algal veneer compared with low-rate and control plots, which were not different. This ranged from about 11 to 27% increased stability at the end of each season. After the 3rd yr, a significant difference of almost 12% was measured for wet aggregate stability of high-rate plot samples from the first 30 cm. Low-rate and control plots were never different. Dry aggregate stability to disruption by a Chepil-style rotary sieve was significantly greater (by 37%) for veneer samples from the high-rate plots after the second and third seasons. Low rate and control plots were not different. Similarly, dry stability of aggregates from the first 30 cm of the high-rate plots was significantly greater than comparable samples from the low-rate and control plots after the 2nd and 3rd yr (by 13%). Low-rate and control plots were not significantly different, suggesting a commercial potential for microalgal soil conditioners on light soils to which large inocula can be applied.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID

摘要:

Environmental conditions are important in determining the potential for ammonia volatilization from surface-applied urea. This study evaluated the influence of soil water potential and air relative humidity on ammonia volatilized from surface-applied urea. A laboratory study was conducted to evaluate the importance of moisture on ammonia volatilization from prilled, granular, and solution urea, which were surface-applied to a Captina silt Ioam (Typic Fragiudult). Treatments included air at 25 and 85% relative humidity and soil water potentials of −0.033 and <-1.5 MPa. The temperature was 25 ± 2°C, and the air-flow rate was 8.4 cm2cm−2min−1, which was equivalent to 2 volume exchanges min−1. At a constant soil water potential of −0.033 MPa and air at 25% relative humidity, ammonia volatilized from the three urea sources averaged 46.4% after 257 h, and no significant source effect was observed. When an initial water potential of −0.033 MPa was allowed to decrease immediately after urea application, by passing 25% relative humidity air across the soil surface and not replenishing soil water, average ammonia volatilization was reduced to 10.8%. The mechanism for this reduction in ammonia loss was inhibition of urea hydrolysis as the soil dried. Delaying the onset of drying by 120 h resulted in nearly complete urea hydrolysis, and volatilization losses averaged 45.2% of applied N. An initial moisture of <-1.5 MPa subjected to air at 85% relative humidity resulted in ammonia losses at a more variable and generally slower rate than from a moist soil, but ammonia losses reached levels similar to those from an initially moist soil by 290 h. These data indicated that soil water potential, air relative humidity, and time before the soil surface dried were important in determining ammonia volatilization from urea.

ISSN:0038-075X    

出版商:OVID    

年代:1987

数据来源: OVID