Abstract: About 60 MT y−1 of P from agricultural runoff have flowed into an area of the northern Everglades marshes of Florida since the late 1960s, creating a nutrient enrichment gradient. The objectives of this study were to determine (i) in what forms the added and native P have been stored over the past 3

Abstract: Domestic and industrial water-softening processes are among the major contributors to the Na content of waste water. Potassium salts can replace Na salts (mainly NaCl) successfully in many water softening treatments; such replacement leads to a decrease in exchangeable Na and to an increase to −12 i

Abstract: Soils from five representative profiles and 25 additional topsoil samples from SE Nigeria were used to study physical properties and the role of some aggregating agents (such as iron and aluminum oxides, carbonates, and organic matter) on aggregate stability. The objective was to identify the major intrinsic soil constituents that influence aggregate stability as well as to evaluate the possibility of using the more easily determinable stability indices to assess the erodibility of these soils. Aggregate stability was measured at the macro level with the water stable aggregates (WSA) >0.5 mm and mean weight diameter of water stable aggregates (MWD) indices and at the micro level with the WSA, <0.2 mm and the clay aggregation indices. The topsoils were generally sandy loam to sandy clay loam, with the clay content increasing with depth. Topsoil bulk densities were high, varying between 1.34 and 1.55 Mg m -3 . Subsoil bulk densities were also high, with values reaching as high as 1.56 to 1.92 Mg m -3 in some horizons. The correlation between bulk density and organic matter (OM) was low, but the trend showed an increase in bulk density with decrease in OM content. The values of liquid and plastic limits were low to moderate. The low correlations between plastic limit (PL) and the aggregate stability indices indicate that PL is not a good predictor of the structural stability of these soils. The influence of OM on the aggregate stability indices was more pronounced within than between the soil profiles, implying that the role of OM as an aggregating agent is soil-dependent. The lowest clay content was obtained with water as the dispersant. Removal of OM and carbonates from the soil samples did not produce clay different in amount from that produced when sodium hexametaphosphate alone was used. This shows that OM and carbonates play minor roles as clay aggregating agents in these soils, probably because of their low concentrations. Removal of Fe 2 O 3 and Al 2 O 3 with sodium dithionite-citrate-bicarbonate (DCB) solution produced the highest concentrations of clay in all soils. This shows that Fe and Al oxides play the most important clay-aggregating roles in these soils. Therefore, for more reliable and reproducible soil particle size analysis, pretreatment for removal of these sesquioxides is needed. The correlations between the soil erodibility factor (K) and the aggregate stability indices were generally low (r < 0.35), implying that these aggregate stability indices are not reliable for assessing the erodibility of these soils.

Abstract: Organic matter (OM) is an important component of soils because of its influence on cation exchange capacity, water retention, soil structure, and ecology and as a source of plants nutrients. Recent attention to rising levels of atmospheric CO 2 has directed attention to the stores of organic C in soils and to changes resulting from conversion of forest to cropping. However,the spatial distribution of carbon pools in forest soils is difficult to estimate because of the unavailability of reliable data. In southwest France, thick humic acid soils have developed from Quaternary silty alluvial deposits. The area of study is characterized by textural and climatic gradients. The objective of this work was to determine if relationships between these gradients and organic matter contents could be established, in order to make a spatial prediction of organic pools in forest soils, and to simulate future evolution under corn cropping. Soil samples were collected from an oceanic zone of the French Pyrenean piedmont, ancient terraces of Pyrenean streams (southwest France), and from 11 sites. On each site, from 13 to 37 topsoil (0-30 cm) samples were collected from mature forests. A total of 194 samples were collected. Correlations between all climatic, geomorphological, and pedological data were calculated. The area of the terraces was delimited using a traditional geomorphologically based survey and stored into a geographical information system (ARC/INFO). This map was overlayed with a 1-km×1-km grid, and probability level maps of organic C amounts in forest soils down to 30 cm were produced using a multiple linear model. This study shows that relating OM contents to spatial available parameters that might influence OM distribution can provide a useful tool to improve geographical prediction of this characteristic. In this work, clay content was found to be the most important soil parameter influencing OM distribution. Another important point is the concept of probability level associated with spatial prediction. This study gives an example of a spatial model taking this variability into account

Abstract: Changes in the concentrations and fluxes of CO 2 were monitored to a depth of 100 cm in an Andisol, under both fallow and soybean crops for a period of 1 year. Gas flux was calculated by the diffusion equation. Diel concentrations at depths less than 40 cm followed a sinusoidal pattern similar to that of the soil temperature, with the highest value being recorded in the daytime. Heavy rainfall, which closed the air pathways to the atmosphere, resulted in a higher CO 2 concentration in the shallow soil layers. The subsequent decrease in the concentration in the shallow layers was accompanied by an increase for a few days in concentrations in the deeper soil layers. CO 2 concentration under fallow increased with depth throughout the year except after heavy rainfall. CO 2 concentration under soybean reached maximum values at depths that increased gradually from 20 to 80 cm during the growing season, suggesting the effect of root elongation. Upward CO 2 fluxes decreased with depth in both fields, and the fluxes in the soil profile were high in summer and low in winter. CO 2 fluxes in the upper and middle parts of the profile under soybean were higher than those under fallow during the growing season. CO 2 fluxes from the soil surface calculated by the diffusion equation and measured by the closed chamber method showed a correlation coefficient of 0.89 except after heavy rainfall. Total CO 2 fluxes from the surface estimated from measurements throughout a year were 3522 g m -2 under fallow and 4975 g m -2 under soybean. The downward flux of CO 2 dissolved in the soil water was found to be negligible in comparison with the CO 2 flux from the soil surface.

Abstract: We investigated the fate and transport of explosives in soils. Transport experiments were conducted to describe the mobility of 2, 4, 6-trinitrotoluene (TNT) and hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX) in a SWy-1 reference clay (bentonite mixed with sand) and two selected soils (Norwood an

Abstract: A low cost strategy for objective and rapid selection of soil samples from a large population was evaluated. The purpose of population was evaluated. The purpose of thestrategy was to retain a maximum of the strategy was to retain a maximum of the original variation in important soil properties with only a small selection of samples. The evaluation was made with emphasis on clay content, soil organic matter, cation exchange capacity, and base saturation, all of which are important factors for biochemical activities in the soil and, therefore, for soil fertility. The strategy involved use of near infrared (NIR) spectroscopy combined with principal component analysis (PCA). A 2-nm interval spectrum between 1300 and 2398 nm was recorded on 146 air-dried soil samples from the most important cultivated areas in Sweden. The samples were considered mainly Cambisols and Regosols. The first derivative of each NIR spectrum was used for PCA. Twenty soils were selected by visual examination of two-dimensional score-plots from PCA. Score-plots were made from NIR data alone, from NIR data combined with pH, and from the eight significant score vectors from PCA on NIR data, combined with pH. Two criteria for selection from these plots were applied: (i) one sample from each apparent group was selected and (ii) samples evenly distributed at the periphery of the total sample population, and one in the center, were selected. In all, six selections were made. The distributions in soil properties in the selections were compared with random selection and with the original population. It was clear that NIR could help to improve the diversity in sample selections compared with random selection. In general, peripheral selections generated a higher recovery of range and a more even distribution in soil parameters than cluster selections. For clay content and cation exchange capacity, PCA on NIR data alone gave the best results, but to improve the distribution in pH and the pH-dependent base saturation, pH had to be included in PCA. To select soil samples that are distributed in all five soil parameters to the best extent possible, we propose peripheral selection from a two-dimensional PCA plot calculated from score vectors and pH data. In the present study, this method would have reduced costs about 70% compared with wet chemistry analyzes

Abstract: 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 ψ o ; -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 ≤ ψ o ≤ -0.03 m and -0.24 m ≤ ψ o ≤ 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.

Abstract: Humic and fulvic acids and other naturally derived organic compounds such as proteins and fatty acids are important constituents of soil solutions and surface waters and groundwater. The presence of both hydrophilic polar or ionic functional groups and hydrophobic structural units on these natural o

Abstract: This study studied the adsorption-desorption behavior of TNT (2, 4, 6-trinitrotoluene) and RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) in a bentonite/sand reference material (Swy-1 montmorillonite clay mixed with acid-washed sand) and two selected soils (Norwood and Kolin). Release of TNT,RDX, and other compounds from a contaminated soil obtained from the Louisiana Army Ammunition Plant (AAP) site was also investigated. The kinetics of TNT and RDX retention were measured using batch methods for a range of input concentrations. For RDX, the adsorption isotherms were distinctly linear. The TNT adsorption isotherm for bentonite/sand mixture appeared linear and was described equally well using linear, Freundlich, Langmuir, and a modified Langmuir model. For the Norwood and Kolin soils, TNT adsorption isotherms exhibited distinct nonlinearity and the Freundlich model provided the best fit. As indicated by the K{sub d} values, TNT exhibited stronger retention or affinity to all soils and the bentonite/sand mixture than for RDX. The RDX retention data indicated little time-dependent behavior. The TNT retention data indicated a continued decrease in TNT concentration with time in the Norwood and Kolin soils. This was possibly caused by the formation and subsequent adsorption of transformation products because transformation products, such as amino nitro toluene compounds, were identified during batchmore » experiments. For the bentonite/sand mixture, TNT retention was rapid initially and reached apparent equilibrium within 1 day. Unlike Kolin and Norwood soils, there was no hysteretic behavior of TNT adsorption-desorption by the bentonite/sand mixture and a mass balance suggested fully reversible retention mechanisms. 15 refs., 13 figs., 2 tabs.« less

Abstract: The natural occurrence of giant sequoia (Sequoiadendron giganteum) is restricted to a mid-elevation zone on the west slope of the Sierra Nevada, California, where summer rainfall is negligible. This study measured the late summer water status of regolith (soil + weathered bedrock) profiles in the Packsaddle Grove on the Sequoia National Forest to assess the distribution of available water by geomorphic position at the end of the dry season. Soil and weathered granitic bedrock samples were collected by auger during September 7-12, 1993, at 30-cm intervals to a depth of 270 cm on triplicated sideslope, swale, and drainage positions for both giant sequoia and non-sequoia microsites throughout the grove. The samples were stored in air-tight cans and were used for water potential and water content determinations in the laboratory. Soil and weathered bedrock water potentials ranged from 0 to -2.1 MPa, generally increasing (becoming less negative ; indicating moister conditions) with depth and in drainage positions. No consistent differences between water potentials under the two vegetation types were apparent for any of the landscape positions. The Cr (weathered bedrock) horizons held a substantial Quantity of plant-available water. A representative 270-cm thick profile consisting of 90 cm of soil underlain by 180 cm of weathered bedrock is calculated to hold about 44 em of plant-available water at field capacity, 27 cm of which is stored within the weathered bedrock. Assuming 35% runoff losses, it is estimated that annual precipitation of <68 cm may fail to fully recharge the regolith profile on upland (non-drainage) sites and result in late season water stress. Such conditions of low precipitation have existed in 3 of the past 10 years. Giant sequoia growing in drainages receive additional water

Abstract: Percolation stability (PS) measured in a simple laboratory test with air-dried 1 to 2-mm aggregates correlates closely with surface roughness, decay and erosion. The processes involved in this test and the influence of soil properties on PS were studied. Air entrapment was the major cause of aggregate disintegration. Shear forces of the percolating water (10 -1 Pa), however, scarcely contributed to aggregate breakdown, although they can be one order of magnitude larger than forces of sheet flow on the soil surface. Percolation stability is a superior stability indicator for erosion studies. It is simple, needs little labor, soil, or equipment, results are highly correlated with soil loss, and, most importantly, they can be interpreted physically. The PS of 113 arable topsoils was inversely related to pH/(organic matter) or linearly to (14-pH)×(organic matter) with r 2 =0.72 in both cases. Both regressions indicate an increase in stability with increasing organic matter content and decreasing pH. The influence of pH increases with increasing organic matter content. The decrease in stability with pH argues against liming to reduce surface crusting. This result is also supported by findings of other authors

Abstract: Degradation reduces ground water contamination from soil-mobile herbicides, but degradation rates vary among soils and with depth. Alachlor and atrazine degradation were determined in Hord silt loam (fine-silty, mixed, mesic Pachic Haplustolls) surface soil (0-15 cm), subsurface soil (45-120 cm), and underlying sediment (150-240 cm) from a terrace of the Platte River near Shelton, Nebraska. Herbicide solution containing 14 C-ring-labeled alachlor or atrazine was added at 100 or 1000 ng g -1 to soil adjusted to -50 kPa water content and incubated at 22°C up to 200 days. 14 CO 2 evolution was monitored to determine mineralization with time, and soil was extracted and combusted to determine residual 14 C-labeled herbicide and bound residue formation. Respective first-order half-lives of alachlor and atrazine ranged from 8 and 11 days in surface soil to 49 and 248 days in deep soil. Soil-bound (unextractable) residue from alachlor and atrazine typically increased with time and ranged from 54 and 46% of applied 14 C in surface soil to 2 and 3% of 14 C applied in deep soil. Stepwise regression indicated that rate of degradation of both herbicides in these soils could be estimated from sorption, NH 4 + Or NO 3 - + NO 2 - , and orthophosphate content. Although atrazine is usually persistent, with little or no mineralization of the s-triazine ring, enhanced degradation was observed in two of the surface soils, where more than 60% of the herbicide was mineralized in 28 days. Lower deethylatrazine concentrations in soil exhibiting enhanced atrazine degradation suggested transformation to more labile polar degradates. A decrease in the polar degradation products and bound residue fractions as mineralization increased indicated their utilization during atrazine degradation in soil.

Abstract: Differences in microbial mineralization of added organic carbon were assessed in pristine (0.231 g total P (TP) kg -1 ) and P-polluted (1.473 g total P kg -1 ) neutral peat soils from Everglades National Park, Florida. Kinetic parameters associated with CO 2 and CH 4 evolution from glucose added to the two soils were significantly different, and the extent of evolution of both gases was greater in the high TP soil over a range of 1 to 5 mol added glucose C kg -1 soil. Carbon mineralization, measured as the sum of CO 2 and CH 4 evolved from added acetate, glucose, cellulose, or sawgrass, was significantly more extensive in the high TP soil. The lag time before the onset of CH 4 evolution was shorter and the fraction of gases evolved composed of CH 4 higher in the high TP soil for all substrates tested. Addition of PO 4 stimulated C mineralization in low TP soil amended with acetate, glucose, or sawgrass, but either had no effect or depressed mineralization of these substrates in the high TP soil. No significant differences in rates of CH 4 oxidation were observed between the two soils. Our results indicate that soil P levels may mlay a significant role in determining the relative importance of aerobic and anareobic microbial metabolism in these soils

Abstract: An approximation to an implicit infiltration formula presented earlier in this series is developed. At worst, the relative error of the approximation is always less than 1%, and it is much better than that for most cases. The approximation becomes more accurate in both the short- and long-term Limits as it becomes exact in each case. Application of the new formula is demonstrated using both laboratory and numerical experiments.

Abstract: Tillage destroys stable continuous macropores and at the same time creates unstable tillage pores within the tilled layer. The buried macropores below the tilled layer are not harmed. Flow through continuous pores is usually considered to be laminar. The objectives of this study were to determine the conditions under which water would flow into a buried macropore in a soil column, and to determine the flow regime inside a macropore. Packed columns (457 mm length, 76 mm diameter) were constructed with a sloping base to measure separately outflow from the artificial macropore (6 mm diameter) and the soil matrix. The columns were then tilled artificially by removing the top 12 cm and repacking. In addition, a study was conducted in a sloping box of soil with four macropores beneath a tilled layer. Dye was added to two 76-mm-diameter rings within the box, either immediately or 1 day before ponded infiltration into the rings. Ponded outflow rates from continuous 6-mm macropores ranged from 5 to 11 ml/s, which is equivalent to Reynolds numbers as high as 2370. Outflow also occurred from buried macropores, although the rate was reduced (0.01 to 0.3 ml/s) compared with continuous macropores. If dye was added immediately before infiltration, dye appeared in macropore outflow, but if dye was added 1 day before infiltration, no dye appeared in macropore outflow but only in matrix outflow. This indicated either preferential flow carrying the dye (if no time for binding to soil) or preferential flow of water around the dye. Even buried macropores can function as preferential flow pathways, and turbulent flow might occur through large, continuous macropores.

Abstract: 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 253- and 337-mm-diameter drops, was applied from heights of 04, 10, 20, 60, and 100 m on two soil samples: Ruppin hamra (sandy loam, mixed, Typic Rhodoxearalf), and Ruhamaa 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 formationin 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

Abstract: 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 of Cleopatra mandarin (CM) and Swingle 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, partic ularly, in citrus trees on Cu-sensitive rootstocks grown in high Cu soils

Abstract: Information about soil hydraulic properties and changes in the brought about by agricultural practices is essential in the development and use of models of catchment hydrology. The objectives of this study were to examine the extent to which different tillage practices affect the magnitude and varia

Abstract: Selenite adsorption by Mn oxides was investigated using syntheitc manganese oxides (birnessite, cryptomelane and amorphous Mn oxide), which were not expected to adsorb much selenite because of the development of a negative surface charge. Selenite adsorption by Mn oxides increased with decreasing pH

Abstract: 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.

Abstract: 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

Abstract: A soil water capacitance probe (C-probe) and a neutron probe (N-probe) were calibrated for a fine sand. Data obtained with both probes and by time domain reflectometry (TDR) were compared. Calibrations were linear for the N-probe (R 2 =0.97), and quadratic for the C-probe (R 2 =0.92), based on 30 samples varying from 0.03 to 0.30 volumetric water content. N-probe-measured water contents were better correlated with TDR-measured water contents (R 2 = 0.80). Water-content profiles were measured with both probes in 79 access tubes seven times during the summer of 1992. The C-probe gave greater soil-water estimates than the N-probe, particularly at depths less than 70 cm. Measured water depletion (in 1.5 cm profiles over 2 weeks) averaged 1.2 cm less for the C-probe than the N-probe. For dry or coarse textured soils, changes in water content are difficult to detect with the C-probe. This is partly because of the dialectric response measured by the C-probe: the calibration shows a decreasing slope with lesser water content. The C-probe also measures a smaller soil volume than the N-probe. This provides improved depth resolution, but the C-probe is more sensitive to localized conditions, including disturbance effects resulting from access tube installation