Showing papers in "Soil Science in 1992"

Production and persistence of soil enzymes with repeated addition of organic residues

Abstract: Soil enzymes mediate biochemical transformations involving organic residue decomposition and nutrient cycling in soil. A field study was conducted to determine the activity and persistence of soil enzymes with repeated additions of different organic residues. The activities of 10 soil enzymes involv

Soil temperature and root growth

Abstract: Soil temperature affects both the rate and thoroughness with which a plant root system permeates soil. Root system expansion is a function of two temperature-dependent processes, growth and development. Growth processes, like cell elongation, increase root length and diameter. Development controls d

EFFECT OF CROPPING SYSTEMS ON ADSORPTION OF METALS BY SOILS: II. EFFECT OF pH

Abstract: The effect of pH on adsorption of Cd, Cu, Ni, Pb, and Zn by soils under different cropping systems was investigated. Plots of metal adsorption vs. pH (unadjusted) were generated for 24 soils, 12 from each of two long-term cropping systems. Two soils, one from each site, were selected to study the me

Fluorine speciation and mobility in F-contaminated soils

Abstract: Fluorine speciation and mobility were investigated in Luvisols and Regosols, contaminated during 50 years by an aluminum smelter. Fluorine solubility shows a minimum at pH 6.0–6.5 and is increasing at pH 6.5. The high solubility of fluorine under acid conditions can be explain

Controls on the Sorption of Dissolved Organic Carbon by Soils

Abstract: Dissolved organic carbon (DOC) sorption isotherms were determined for 48 soil samples derived from Humaquepts, Inceptisols, and Spodosols using a DOC solution derived from a swamp peat (Hemist). Forty-six of the samples had DOC sorption adequately represented by the linear initial mass isotherm, with initial DOC concentrations up to 81 mg L−1. Null-point DOC concentrations (DOCnp), where there is zero net DOC sorption, ranged from 6.7 to 85.4 mg L−1, with an average regression coefficient of 0.45. Distribution coefficients (Kd) averaged 1.00 × 10−2 m3 kg−1, suggesting that DOC sorption by soils is of moderate strength compared with anions such as Cl−, NO3−, PO4− and SO42−. DOCnp values were strongly related to contents of soil organic C (positive) and oxalate-extractable Al and dithionite-extractable Fe (both negative) using partial regression analysis (R2 = 0.41–0.61, P 0.001). A multiple regression with these three variables explained 70% of the variance in DOCnp. The sorption regression coefficient and reactive soil pool for DOC were also positively related to soil organic C content, with an average of 3.2% of the organic C in the soil being part of the DOC reactive pool.

Aggregate Stability and Seal Formation as Affected by DROPSʼ Impact Energy and Soil Amendments

Abstract: In soils exposed to rain, aggregate disintegration is the first process which leads to seal formation. The objective of this study was to evaluate the relative importance of aggregate stability in seal formation. The effects of raindrops' impact energy, exchangeable sodium percentage (ESP), electrol

Soil aeration and plant root metabolism

Abstract: Plant roots commonly experience temporary periods of oxygen deprivation when soil becomes flooded or waterlogged, and warm temperatures encourage rapid consumption of O2 by soil microorganisms and roots. This paper describes some of the practical situations in the field where excess soil water, part

Structural Studies on Soil Humic Acids by Curie-Point Pyrolysis-Gas Chromatography/mass Spectrometry

Abstract: Humic acids (HAs) extracted from the Ap horizon of a Haplaquoll (Bainsville) and the Bh horizon of a Haplaquod (Armadale) were investigated by Curie-point pyrolysis (Cp Py)-gas chromatography (GC)/mass spectrometry (MS). More than 300 pyrolysis products, tentatively identified by conventional electron impact (EI) and field ionization (FI) MS, were common to both samples, although very different in their intensity distributions. Whereas the Armadale HA produced predominantly alkanes and olefins, the Bainsville HA yielded large quantities of phenol derivatives. Alkanes and olefins formed homologous series up to C30 and n-alkylbenzenes up to C18. Of particular interest were the intense signals originating from aromatics and alkyl-substituted aromatics, especially phenol derivatives and methyl-substituted naphthalenes. In addition, heterocyclic compounds such as furans, pyrroles, and pyridines with and without alkyl substituents were also detected. Our data indicate the presence of aryl-alkyl structures in the HA network and contribute to a better understanding of the chemical composition and structure of soil organic matter (SOM).

N2-bet specific surface areas of some low activity clay soils and their relationships with secondary constituents and organic matter contents

Abstract: Size fractions (2000–20 μm, 20–2 μm, 2–0.2 μm, and 0.2–0 μm) were obtained after Na-resin treatment of five top horizons from low-activity clay soils. Their specific surface areas (SSA) were measured by the N2-BET method. The same method was applied after organic matter removal by H2O2 treatment to

Time-Dependent Sorption of Pesticides during Transport in Soils

Abstract: Sorption nonequilibrium of pesticides in soil is relatively less understood compared with equilibrium sorption. Furthermore, batch techniques generally used in kinetic studies do not represent field conditions. Flow techniques, on the other hand, closely represent pesticide transport and have many a

Dissolved organic carbon and sulfate sorption by spodosol mineral horizons

Abstract: Carbon cycling in soils is an important process that involves the movement of large amounts of dissolved organic carbon (DOC) within the soil profile. Recent work in a variety of soils has indicated that DOC sorption properties of mineral horizons play an important role in the retention of DOC. As part of the Watershed Manipulation Project at Bear Brook Watershed in Maine (BBWM), the solubilization and movement of carbon in terrestrial and aquatic ecosystems were evaluated. For the study, the objectives were to: (1) determine the sorption properties of mineral horizons present on the BBWM watersheds for SO4 and DOC; (2) evaluate the effect of solution pH and temperature on soil DOC sorption; and (3) examine competitive sorption effects between DOC and SO4.

Comparison of Methods to Estimate Soil Water Characteristics from Soil Texture, Bulk Density, and Limited Data

Abstract: Four approaches used to estimate the soil water characteristic (soil water content-matric potential relationship) were compared on a data set based on 366 cores of Bernow soil (Glossic Paleudalf). Regression equations based on soil texture and bulk density provided poorer estimates of soil water content, with large errors at some matric potentials, compared with other approaches examined. Regression model results were improved when one measured value of soil water content (−1500 kPa) was included as a variable in the equations, and greatly improved when two (−33 and −1500 kPa) measured values were included. A simple log-log interpolation/extrapolation approach, based on two measured values at −33 and −1500 kPa, provided results similar to the regression model with two known values. The similar-media scaling approach, utilizing one measured value at −33 kPa, displayed results similar to the log-log method, but the error was slightly higher. Estimates with the one-parameter model of Gregson, Hector and McGowan (GHM), based on one known value (−33 kPa), was similar to the log-log interpolation/extrapolation when a required generalized slope-intercept relation was calculated for the soils in the study; and the error was slightly higher when using the generalized relationship found by GHM for their data. We conclude that the models which incorporated even one known value of soil water content-matric potential relationship were much better than those based on soil texture and bulk density alone. The simple log-log interpolation/extrapolation and the one-parameter GHM model provided the best estimates of soil water content. The scaling method estimates were only slightly worse than the GHM model estimates. The soil survey data often contain at least one value of the water characteristic. These one point methods should, therefore, be the methods of choice.

Interactions Of Earthworms With Soil Physical Conditions Influencing Plant Growth

Abstract: Earthworms have been credited with creating channels that allow deeper root penetration through hardpans or unstructured soils; however, the benefit of earthworm channels decreases as the volume of alternative low resistance pathways for root growth increases. Improved root growth does not always result in increased crop growth. Some earthworm species incorporate surface residue and surface-applied lime and fertilizers. Earthworm channels can increase infiltration and reduce runoff, increasing soil water availability or, possibly, deep percolation to maintain favorable water status for crop growth. Pot studies often indicate increased plant growth in response to unrealistically high earthworm inoculation rates; however, only a few field studies indicate any plant growth increases, mainly for pastures, orchards, and small grains. The mechanisms and dynamics of plant response to earthworms needs to be more thoroughly explored, especially in field studies at realistic inoculation rates and with statistical comparisons.

Stomatal closure in oxygen-stressed plants

Abstract: Stomatal closure of plants in flooded soil, as determined by leaf gas exchange, has been recognized since 1973, and for simple hypoxia since 1975. At least 58 species have been shown to close stomata with hypoxic or flooded conditions. Various factors interact to affect the relationship between rhizosphere oxygen availability, as measured by soil oxygen diffusion rate (ODR), and degree of stomatal closure. These factors include root temperature, species, plant growth stage, plant mineral nutrition, and duration and nature of hypoxia. Soil water content, bulk density, and temperature also influence ODR. Abscisic acid accumulation in leaves appears to induce stomatal closure, as a stress response to root hypoxia, through its effect on potassium ion regulation of guard cell turgor. Stomatal closure generally persists well beyond actual soil hypoxia. Photosynthesis is reduced by root hypoxia, both by reduction of leaf gas exchange and by a lowering of the photosynthetic rate at a given leaf gas exchange rate. This phenomenon deserves greater attention in evaluating and modelling of crop response to soil hypoxia and as a sensitive indicator of severity of soil hypoxic stress.

Estimation of zero-tension pan lysimeter collection efficiency

Abstract: When using zero-tension pan lysimeters to assess the mass of solute leached, it is necessary to estimate pan collection efficiency (PCE), defined as the proportion of water draining through the root zone captured by the pan lysimeter. To evaluate PCE in a well structured Hagerstown silt loan, a stud

Effect of In-Situ Gas Accumulation on the Hydraulic Conductivity of Peat

Abstract: The in situ hydraulic conductivity of moderately decomposed, catotelm (subsurface) peat is often anomalously low (10−5 to 10−7 cm s−1) considering that the porosity (n) of this peat is often as high as 80–97%, and the dry bulk density (pb) as low as 0.05–0.25 g cm−3. It has recently been hypothesized that this is the result of a progressive occlusion of pores in the peat matrix by bubbles of gas (especially methane) which are generated in-situ by ongoing anaerobic respiration. To test this hypothesis, the change with time of hydraulic conductivity (K), volumetric water content (Θ), volumetric gas content (γ), and gaseous methane concentration (M) were measured in three, repacked laboratory columns of catotelm peat through which de-aired, temperature equilibrated water flowed continuously under positive pressure. Two of the columns contained microbially active peat which was packed to average n and pb values of 96.2% and 0.06 g cm−3, respectively. The third column was similarly packed (n = 95.5%, Pb = 0.07 g cm−3) and then sterilized using 5.5 Mrad 60Co gamma radiation to render it microbially inactive. In the two unsterilized columns, K decreased on average from 7.0 × 10−4 (±6.1 × 10−4) cms−1 to 1.8 × 10−5 (±1.7 × 10−5) cms−1; Θ decreased from 83.6% (±3.6) to 64.6% (±6.4); γ increased from 12.5% (±3.2) to 31.6% (±6.4); and M increased from 3.9 (±1.5) μmol ml−1 to 50.2 (±14.9) μmol ml−1 during four separate measurement periods (two perods per column) which varied in length from 44 to 78 days. During a 41-day measurement period, K and Θ increased in the sterilized comumn to stable, relatively high values of 5.7 × 10−3 cms−1 and 91.0%, respectively; γ decreased to a stable low value of 4.5%; and only trace levels of M were detected. The chages and eventual stabilization of K, Θ and γ in the sterilized column were due to the gradual removal by the flowing water of artifact carbon dioxide gas produced by the sterilization process. The lack of M and the low final γ value in the sterilized column indicate that no significant anaerobic respiration occurred during the measurement period. It was concluded that it is indeed possible for gas generated in situ by anaerobic respiration to cause a progressive and significant decrease in the K of moderately decomposed catotelm peat.

Moisture Effects on Visible Spectral Characteristics of Lateritic Soils

Abstract: Samples from ferralitic soils of similar texture were immersed in water, placed in a pressure chamber and subjected to different soil suction pressures (pF: 2.0, 2.5, 2.8, 3.0, and 4.2). The Cie color values (intensity, hue and saturation) were taken as the spectral signatures of these soils and calculated from the diffuse reflectance spectra. The dominant wavelength Λd (hue) increases with moisture content; as the soil becomes more “colored” by iron oxi-hydroxides, this increase becomes more pronounced. The purity Pe (saturation) decreases systematically with increasing moisture content. When the moisture content increases, i.e., from oven-dried to airdried and then to moist samples, there is a change of the refractive index, N, of the immersion medium from N = 1 (air) to N = 1.33 (water). This change causes an increase in the volumetric reflectance, especially in the weak absorption regions, and a decrease in the specular reflectance. Contrary to the generally accepted assumption, diffuse reflectance spectra of soils at different moisture contents undergo nonlinear changes leading to displacements in the spectral extrema of the absorption bands. Therefore, spectral signatures of moist soils cannot be derived simply from those of their dry equivalents.

Effect of cropping systems on adsorption of metals by soils: iii. competitive adsorption1

Abstract: Because Cd, Cu, Ni, Pb, and Zn coexist in soil solution, competitive adsorption isotherms of these metals were generated for two soils, each selected under continuous corn from different long-term cropping systems. Competitive adsorption of the metals as a function of pH was evaluated by equilibrati

Adsorption of polymers on clays as affected by clay charge and structure, polymer properties, and water quality

Abstract: The adsorption of a family of polysaccharides (guar) and a family of polyacrylamides (PAM) by clays from aqueous solutions was studied. Anionic, nonionic and cationic polymers were investigated. Silver Hill illite (IM-1) was equilibrated with two synthesized waters which represented the quality of t

Effect of cropping systems on adsorption of metals by soils: i. single-metal adsorption1

Abstract: The effect of long-term cropping systems on adsorption of metals was studied for soils obtained from two sites, Clarion-Webster Research Center (CWRC site) at Kanawha and Galva-Primghar Research Center (GPRC site) at Sutherland, under long-term rotation experiments in Iowa. Each experiment consisted of three cropping systems: continuous corn (CCCC), corn-soybean-corn-soybean (CSCS), and corn-oats-meadow-meadow (COMM), and treated with (+N) and without (0 N) ammoniacal fertilizer. In general, CSCS and COMM cropping systems did not significantly affect the metal adsorption maxima of soils obtained from both sites. Cadmium, Cu, and Pb adsorption were significantly correlated with pH and percentage base saturation for soils from both sites.

On the characterization of properties of an unripe marine clay soil: I. Shrinkage processes of an unripe marine clay soil in relation to physical ripening

Abstract: Shrinkage processes, such as volumetric shrinkage behavior, and the geometry of the volume shrinkage were studied with respect to the physical ripening naturally occurring in a marine clay soil. Three-dimensional volume shrinkage was characterized using the shrinkage characteristic curve determined

Dynamic root responses to water deficits

Abstract: Water absorption is influenced by the geometric distribution of viable roots and the availability of water at root surfaces. Utilization of additional plant energy for the extensive and localized development of root systems is a high risk investment of carbon by the plant, especially during short-te

Changes in Soil Organic Carbon and Nitrogen after Six Years of Corn Production

Abstract: Corn (Zea mays L.) production practices have significant effects on soil organic nitrogen (N) and carbon (C) levels. The effects of plant population, irrigation, and fertilization rate on soil organic C, total N, and organic N fractions after 3 and 6 years of continuous corn on a Chicot sandy clay loam soil (fine-loamy, mixed, frigid Typic Hapludalf) were studied. Soil organic C content increased by 7% after 3 years of continuous corn and by 18% after 6 years of continuous corn. The C/N ratio increased after the first 3-year period. No change in C/N ratio was found after the second 3-year period. The greater rate of fertilization (400 kg N ha−1, 132 kg P ha−1, 332 kg K ha−1) compared to the normal rate of fertilization (170 kg N ha−1, 44 kg P ha−1, 141 kg K ha−1) had a greater level of soil total N over 3 years. This increased soil total N was still found after 6 years of corn production. After 3 years of corn production, the relative amount of hydrolyzable NH4+-N and amino acid-N in acid hydrolyzates of soil organic N decreased. High rates of fertilization reduced the relative amounts of total hydrolyzable-N and unidentified-N and increased non-hydrolyzable-N compared with the normal fertilizer rate.

Salinity estimates in irrigated soils using electromagnetic induction

Abstract: Electromagnetic induction (EM) is a useful mean of assessing soil salinity in large areas, particularly after its calibration on different soils. Electromagnetic induction was used to monitor spatial and temporal changes of soil salinity within the saline irrigation district of Flumen, Spain. Soil salinity patterns in this region are entangled because of intensive land leveling and irrigation. This paper presents the EM calibrations for two different parcels. The apparent electrical conductivity (ECa), measured with EM, was compared with the electrical conductivity of soil extracts both at saturation (ECe) and at a 1:5 soil-to-water ratio on a weight basis (EC1:5). Different approaches were tested for analyzing the data. The suitability of EM in assessing soil salinity is evaluated for each entire parcel and for individual points. The calibration equation developed at one date is found to be suitable to predict the salinity for the entire parcel from EM measurements taken at another date. Furthermore, the better estimation of ECe from EM readings as compared to the estimation of EC1:5 from EM readings, lead to the recommendation of the use of the saturation extract for calibration.

Exit condition for miscible displacement experiments

Abstract: The one-dimensional solute transport is analyzed with the convection-dispersion model, including first and zeroth order irreversible reaction. A simple analytical expression is derived for the residence concentration which depends explicitly on the exit conditions at the end of the soil column or layer. The validity of the flux concentration solution ignoring the finite length of the column is also discussed by relating the exit conditions to the Peclet number.

A scaled sorption model validated at the column scale to predict cadmium contents in a spatially variable field soil.

Abstract: Sorption of Cd is described with an extended Freundlich equation, that accounts explicitly for effects of pH and organic matter content. Parameters for this scaled sorption model were estimated using batch experiments with soil taken from an arable field. The sorption model explained differences in sorption between two soil samples from the same field that differed in pH and organic matter content. For validation of the sorption model predictions, a transport model was developed for cadmium in soil. Predictions of solute breakthrough were made that were in good agreement with measurements, using sorption parameter values that were derived from batch experiments that used the same background electrolyte concentration. With the validated sorption model total soil Cd contents along a transect in the field were predicted using measured values of pH, organic carbon content, and Cd concentration in soil solution. Although spatial variability of these parameters is distinct and not identical to the spatial variability of the total Cd content of the soil, model predictions showed good agreement with the observed spatial pattern. Spatial variability of pH and of organic matter content appeared to be an important factor which explained a large proportion of the heterogeneity of Cd contents in this soil. The scaled sorption model described Cd sorption well in both batch experiments, column scale experiments, and at the field scale, when all (scale dependent) relevant processes were taken into account.

Analysis of Carbon in Calcareous Soils Using a Two Temperature Dry Combustion Infrared Instrumental Procedure

Abstract: There is increasing interest in the role the soil carbon storage plays in buffering against changes in atmospheric carbon dioxide levels and, hence, in quantifying shifts in soil carbon content as a function of changing land use. Such a task involves the analysis of numerous soil samples. The methods presently available for soil carbon analysis are costly in both time and materials, particularly where the need to differentiate between organic and inorganic carbon forms requires lengthy acid pretreatment of the samples. The authors have successfully adapted a procedure for sequential two-temperature measurement of organic and inorganic carbon in soils by dry combustion infrared instrumental analysis. Several soils representing three soil orders, with organic C contents from 4% and inorganic C from 9%, were used in method development. Results correlate highly with accepted methods. The procedure offers a greater than 10-fold reduction in time required for sample preparation, analysis, and data acquisition.