摘要:

Soil water characteristic curves are a prerequisite for quantifying the field soil water balance and predicting water flow in unsaturated soils. The spatial variation of water retention in the root zone influences water availability for plants, evaporation, and fluxes of water and solutes through soils. The purpose of this study was to determine the ability of a popular model for the soil water retention function to describe the spatial variability of measured retention data and to investigate the application of a water content scaling theory to reduce the apparent spatial variation of soil water retention. Using a combination of Tempe cells and 1.5-MPa pressure plate extractors, we measured soil water retention at six pressure heads. In total, 281 undisturbed soil core samples were taken from the Ap horizon (0 to 17-cm depth increments) along an 80-m transect on a bare silt loam soil at 0.30-cm intervals. Sample statistics were calculated to identify outliers and erroneous data. A four-parameter retention model (&thetas;s, &thetas;r, α, n) was fitted to the data, and water content scale factors were also calculated. The soil water retention model was found to be extremely flexible in fitting the measured data. The parameters in the retention model showed a structured variance with a range of influence between 12 and 30. The number of parameters needed to characterize the field variability was 912 for the retention model. Scaling theory applied to the water retention data significantly reduced the apparent spatial variability. One scale factor also showed a structured variance, indicating a spatial correlation distance of greater than 30 m. Using the Akaike information criterion, we found that scaling theory could adequately represent the spatial variation in water retention with only 460 parameters. Sampling, calibration and/or experimental errors were thought to account for more than 50% of the total variability.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Rain properties (depth, drop size, and impact velocity) affect the infiltration rate (IR) curve and final IR (FIR) of soils. Because the IR is not a unique function of rain depth or rain energy, the objective of this study was to find a unique function of rain properties that determines the IR of the soil. Simulated rain of constant intensity (40 mm h−1), with 2.53− and 3.37-mm-diameter drops, was applied from heights of 0.4, 1.0, 2.0, 6.0, and 10.0 m on two soil samples: Ruppin hamra (sandy loam, mixed, Typic Rhodoxeralf), and Ruhama loess (silty loam, mixed, Calcic Haploxeralf). The FIR of the two soils decreased with increasing kinetic energy (KE) of the drops. The sandy loam was less stable than the silty loam, and seal formation in it was more susceptible to the KE of the drops. The infiltration decay process was better correlated with rain momentum than with rain depth or KE. Thus, prediction of infiltration rate decay for a given soil exposed to rains of various drop sizes and velocities is best based on drop momentum and the soil stability constant.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Repeated equipment traffic increases the bulk density and changes the pore size distribution (PSD) of soil. Spatial variability of chemical movement in soil may be partially explained by differences in PSD. The purpose of this study was to determine the relationships between soil pore size distribution and surface soil compaction on the transport of water, bromide, and atrazine (6-chloro-N-ethyl-N‘-(1-methylethyl)-1, 3,5-triazine-2,4-diamine) during multiple desaturation cycles. Undisturbed cores (8.2 cm diameter; 6.6 cm high) from a Crete silt loam (Pachic Argiustoll) were collected from wheel track (WT), nonwheel track (NWT), and row (ROW) locations in a conventionally tilled, continuous corn field. Atrazine (4.9 Kg ha−1) and KBr (66 Kg Br−1) were surface applied and equilibrated for 72 h. Effluent was collected at decreasing matric potentials between −1 and −100 kPa. The PSD indexes and bulk densities were significantly different among three locations (PSD indexes were 0.045 in WT, 0.061 in ROW, and 0.069 in NWT; bulk densities were 1.39 Mg m−3in WT, 1.30 Mg m−3in ROW, and 1.21 Mg m−3in NWT). Effluent analysis revealed more water and bromide were eluted from cores with higher PSD indexes and lower bulk densities. However, the reverse was true for atrazine. These data indicate that water and atrazine transport can be influenced differently by PSD and bulk density.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Adsorption of SO2-4and its associated metal ion by four soils from Iowa, Chile, and Costa Rica was studied. The surface charge of each soil was characterized, and the relationship between SO2-4adsorption and pH was constructed for pH ranging from 3.5 to 7 at 0.5 increments by using 1 mmol/L (2.0 mmolcL−1, or 50.0 mmolckg−1soil) each of seven SO2-4forms [Cs2SO4, K2SO4, (NH4)2SO4, CaSO4, MgSO4, Al2-(SO4)3, and In2(SO4)3] made in 1 or 10 mmol/L NaCl. Results showed that SO2-4adsorption was greatest at the lowest pH values (ca. 3.5) and decreased with increasing equilibrium solution pH and ionic strength. The amounts of SO2-4adsorbed were three to four times greater in soils containing large rather than small amounts of Fe and Al hydrous oxides, regardless of the type and valence of the metal ion. The amounts of SO2-4adsorbed from solutions containing different metal ions were affected by the charge of the metal ion and, in general, followed the order: In2(SO4)3> Al2(SO4)3> CaSO4> MgSO4> Cs2SO4> K2SO4> (NH4)2SO4. The effect of the metal ion was more pronounced at higher pH values (pH > 5), and Iowa soils (low in Fe and Al hydrous oxides) were more affected by the increase in the valence of the metal ion and ionic strength than the soils from Chile and Costa Rica. The ratios of SO2-4-/metal (M) adsorbed (SO2-4-/M) by the four soils decreased sharply with increasing pH up to 4.5 to 5.0, above which no significant change in these ratios occurred. For all soils, a relatively linear relationship was obtained between log Kd(SO2-4- distribution coefficients) and pH when the metal ions were monovalent, regardless of the ionic strength. But the Kdvalues for SO2-4- varied among the soils, depending on the SO2-4- from used.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Selenite (SeO2-3) sorption in soils has been correlated with pH, soil mineralogy, and soil solution composition, factors that are often highly variable with respect to mine soil materials. Selenite equilibrium and adsorption batch studies were conducted with four mine soil materials to determine adsorption parameters that could be used to develop a model to predict Se retention. Initial mass, Freundlich, Langmuir, and other relationships were explored to describe adsorption and retention of Se in these soils. For equilibrium and adsorption studies, 25 ml of solution was added to 2.5 g of soil in a polyethylene centrifuge tube. Time-dependent analysis consisted of duplicate treatments of two SeO2-3levels and reaction times, of 2, 6, 24, 48, 168, 336, and 504h. Adsorption studies were arranged in a 3 X 10 X 4 factorial design (three replications, 10 SeO2-3concentrations, four soils) and equilibrated for 14 d. Selenite sorption as a function of pH in each material was also examined. Selenite sorption of 10 μg Se/g soil was not greatly affected by pH between pH 4 and 8, except in one sample where sorption decreased at pH 6. Initial mass isotherms were very similar for Se additions up to 20 mg/kg for all soils and predicted Se sorption very similar to the experimental data for these and 12 additional soils. The Freundlich and Langmuir isotherms did not effectively predict Se sorption.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Applications of ammoniacal forms of N along with P in the same injection zone can enhance P availability relative to applications of P alone. The spatial and temporal variability of available P was assessed in acid soil and in alkaline soil, using ammonium polyphosphate (APP) as a P source and urea ammonium nitrate (UAN) as a N source. Either ammonium polyphosphate or APP+UAN, at a constant P application rate, was injected into soil-filled boxes using an apparatus that allowed a needle to be pulled through the soil below the surface, simulating subsurface band application. Soils boxes were sampled by sequentially removing concentric cylindric cores of increasing radii centered around the line of fertilizer injection. Sampling times were 1, 4, 12, 24, and 36 weeks. Available P was determined by either the Bray-1 or the Olsen procedure. Available Zn, Fe, Cu, and Mn were also determined with the DTPA procedure. For both soils, soil pH generally decreased in the first 12 weeks and then increased during the remaining incubation period. Treatment comparisons within rings over time showed that APP+UAN generally gave significantly higher extractable P when compared with the APP treatment. Total available P, calculated as the sum of the products of soil dry mass and extractable P for each ring, was significantly higher for APP+UAN compared with APP at all sampling times. The decline in total available P with time was best described byy=a(e−bt+c), whereyis the total available P (mg) at timet(weeks) anda,b, andcare curve-fitting parameters. The value ofbwas greater for the APP treatment for both soils, indicating that total available P declined faster for this treatment than for the APP+UAN treatment. Treatment effects on DTPA-extractable Fe and Mn generally corresponded to changes in soil pH with concentrations increasing with decreasing pH. For DTPA-extractable Zn and Cu, however, concentrations were often lower for the treatment with the lowest pH.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Many soils in Central Florida's citrus belt contain excess levels of copper (Cu) as a result of historical heavy use of Cu in citrus production. Citrus rootstocks vary considerably in their response to excess external Cu. This study was conducted to examine the effects of 0.1, 5, 10, or 20 μmol/L Cu concentrations in nutrient solution at pH 5.5 on growth, uptake, and partitioning of Cu, Zn, Fe, and Mn by seedlings ofCleopatra mandarin(CM) andSwingle citrumelo(SC) rootstock. With an increase in external Cu concentration, the shoot and root dry weights decreased significantly, whereas the concentration of Cu in both the plant parts increased. The increase in tissue Cu concentration was more marked in the root than in the shoot. Despite lack of significant difference between the two rootstocks with respect to short-term growth response to external Cu concentrations, this study demonstrated significant differences between the two rootstocks with respect to root and shoot Cu contents. Partitioning of total Cu into the shoot was significantly lower in CM than in SC seedlings. Accordingly, preferential accumulation of Cu in the roots of CM seedlings may be responsible for its increased tolerance, compared with SC rootstock, to high external Cu concentrations. Although increase in concentrations of external Cu decreased the uptake of Zn, Fe, and Mn by both rootstock seedlings, the effect of Cu was more pronounced on the uptake of Fe compared with that of Zn or Mn. The pronounced effect of Cu on Fe uptake could, in part, explain the development of Fe chlorosis symptoms, particularly, in citrus trees on Cu-sensitive rootstocks grown in high Cu soils.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

The effects of solution sodium adsorption ratio (SAR) and total electrolyte concentration (TEC) on the release of total organic carbon (TOC), total N and total P, and clay dispersion from three soils were studied in the laboratory. Solutions with high SARs and low TECs caused the greatest amount of clay dispersion, and these highly turbid solutions also had high concentrations of TOC and total P. Positive correlations were obtained between turbidity and TOC, turbidity and total P, and TOC and total P. Total N was positively correlated with turbidity and TOC for one of the soils studied, but not for the other soil for which these measurements were made. It follows from these results that SAR and TEC also have a significant influence on TOC and total P concentrations. Field data of other workers show similar relationships between these water quality factors.Decreasing the SAR and/or increasing the TEC of a solution in contact with soil will decrease the concentrations of organic carbon and total P released and decrease clay dispersion. For some soils, the concentrations of N in solution may also decrease. Increasing salt concentrations substantially is not desirable, but a decrease in SAR can be achieved through the use of calcium compounds and their application to soils in a field situation may help to improve water quality.

ISSN:0038-075X    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

The phenomenon of phosphate adsorption is, by its own nature, closely related to the mineral composition of the soils, particularly to the fine fraction. Therefore, in a paper on this subject, it is very important to have the correct characterization of the mineral components of the soils and complete understanding and use of the mineralogical concepts involved. And, finally, it is essential that the citations of previous papers in the field be accurate. This was not quite the case for the paper published by Agbenin and Tiessen in the January 1994 Issue ofSoil Science.

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