Showing papers in "Soil Science in 1983"

Quantitative relationships between soil color and hematite content

Abstract: We determined that the degree of redness of soils from Europe and Brazil, as given by redness ratings based on visual or spectrophotometric color measurements, was highly correlated with hematite content.For the European soils (mostly Alfisols) the pigmenting power of hematite was higher tha

Distribution and forms of copper, zinc, cadmium, iron, and manganese in soils near a copper smelter1

Abstract: We examined the contamination of soil by copper, zinc, and cadmium with respect to distance from a copper smelter. The majority of contamination was in the immediate vicinity of the smelter. Between 30 to 60 percent of total Cd was exchangeable in MgCl2 solution, and the exchangeability was much greater than that of the other elements examined, including iron and manganese. Most of the Cu, Zn, and Mn were present in an oxalate-extractable fraction, but only small amounts were extractable by citrate-dithionite-bicarbonate (CDB) solution. This suggests that Cu, Zn, and Mn were more strongly associated with amorphous iron oxides, with only small amounts being occluded in crystalline iron oxides. Only Cu was appreciably associated with the soil organic fraction. The treatment of soils with sodium hyperchlorite prior to oxalate extraction appeared to be necessary to better estimate the amounts of Cu associated with the oxalate-extractable fraction. Without this pretreatment, the oxalate extraction could overestimate the amounts of Cu associated with this particular fraction possibly due to the dispersion of organically complexed Cu in the oxalate solution. The mobility of Cu, Zn, and Cd in the soils was limited, as evidenced by a sharp reduction in concentrations of the three elements with depth. Comparing subsoil concentrations of these elements with those from areas relatively unpolluted by smelter fallout revealed that Cd was more leachable than Cu or Zn under western Washington conditions.

How many observations are needed for regional estimation of soil properties

Abstract: A common task in regional studies of soil is to determine the mean values of particular soil properties from samples. Estimates of the number of observations needed for this purpose have usually been based on classical sampling theory without regard to spatial dependence in the data. As a result they have been unduly exaggerated and have often daunted investigators from pursuing their aims. This paper demonstrates a method for determining sample size, that is, the number of observations, taking account of spatial dependence. The method depends on knowing the semivariogram for the property of interest, which is used to calculate the variances in the neighborhood of each observation point. The variances are then pooled to form the global variance from which the standard error can be calculated The pooled value is minimized for a given sample size if all neighborhoods are of the same size, i.e., if the sampling points lie on a regular grid. If variation is isotropic, then an equilateral triangular grid is slightly better than a square one, though the latter will usually be preferred for convenience. Where there is simple anisotropy, a nonsquare rectangular grid aligned with its longer intervals in the direction of least variation is practically optimal. Examples show the relations between standard errors and sample sizes when sampling on regular grids and from which sample sizes can be chosen to achieve any desired precision. In all instances the sampling effort determined this way is less, and can be very much less, than would have been judged necessary using the classical approach.

Effects of aluminum, OH: Al and P: Al molar ratios, and ionic strength on soybean root elongation in solution culture

Abstract: In a series of experiments, we studied the effects of Al concentrations, OH:Al and P:Al ratios, and ionic strength on soybean root length after 4 days’ growth in nutrient solutions approximating soil solutions. Additions of NaOH and NaH 2 PO 4 .2H 2 O solutions decreased the concentrations of monomeric Al species in solution, Al polymers being formed with Al concentrations ≤50 μM originally in solution but not at concentrations ≥100 μM Al. In nutrient solutions with ionic strengths ≤900 μM, the Al polymers formed remained in solution, but were not detected in solutions with higher ionic strengths. Soybean root elongation was reduced severely with Al concentrations of ≥10 μM. The toxic effect of Al was ameliorated by the addition of OH or P through the reduction of monomeric Al species in solution. A close curvilinear relationship was observed between relative root length (%) (y) and Σ activities (μM) of the monomeric Al species in solution (x) (y = 14.9972 + 99.163 exp(−0.130605x); R = 0.950***), irrespective of the initial Al concentration, the concentration of polymeric Al species in solution, ionic strength, solution nutrient composition, P concentration, or pH. It appeared that one or more of the monomeric Al species was responsible for the toxic effect of Al on soybean root growth, and that the ameliorating effect of OH and P resulted from the reduction in the concentration of monomeric Al in solution, either through polymerization or precipitation of Al.

A reexamination of the constant head well permeameter method for measuring saturated hydraulic conductivity above the water table1

Abstract: We describe improvements in the theory and practical application of the constant head well permeameter method for field measurement of saturated hydraulic conductivity above the water table.The theoretical improvements result in a new analytical solution and a numerical solution that produce

Carbon and nitrogen in the light fraction of a forest soil: vertical distribution and seasonal patterns

Abstract: We extracted light-fraction material densimetrically in Nal solution (specific gravity 1.65 g/cm3) from root-free soil samples from a forested site in the Oregon Cascade Mountains. We chose extraction at this density because it excluded most of the organomineral particles from the light fraction. Major components identifiable from scanning electron micrographs were dead root fragments, hyphae, charcoal, and pumice–all with adsorbed or entrapped colloidal particles. Total soil carbon (C) and nitrogen (N) at the site averaged 145 and 7.4 megagrams per hectare, respectively, to a depth of 83 centimeters. Light-fraction material accounted for 53 percent of the total C and 45 percent of the total N in the 0− to 3-cm layer; these proportions decreased abruptly in the next layer and then more gradually over the remainder of the 83-cm profile. Amounts of light-fraction material increased by 50 to 100 percent from early spring to summer and then peaked again in the fall. This large seasonal fluctuation indicates that the light fraction provides an important labile reservoir of C and nutrient elements in the forest ecosystem.

Effect Of Low Levels Of Exchangeable Sodium And Applied Phosphogypsum On The Infiltration Rate Of Various Soils 1

Abstract: The effect of exchangeable sodium percentage (ESP) on the infiltration rate (IR) and crust formation of four soils, varying in their texture, mineralogy, and CaCO 3 content was studied, using distilled water (EC ∼.05 mmho/cm) in a rain simulator. The IR of the four soils was very sensitive to low levels of ESP (5), whereas the hydraulic conductivity (HC) of these soils, as determined by Felhendler et al. (1974), was less sensitive. The presence of lime in the soils was effective in preventing HC decreases due to low levels of exchangeable Na. Conversely, lime was not effective in maintaining the IR of the calcareous soils. Phosphogypsum prevented the sharp drop in IR of the soils at all levels of ESP. The mechanical impact of the raindrops, the low concentration of electrolytes in the rain and in the surface soil solution, and the relative freedom for particle movement at the soil surface accounts for the higher susceptibility of the soil surface to exchangeable Na. The high rate of dissolution of phosogypsum, leading to the presence of electrolytes in the surface soil solution, accounts for the effectiveness of phosphogypsum in maintaining the high IR. The effect of low levels of ESP and the soil solution concentration on the IR of soils suggests that crust formation in soils is due to two mechanisms: (1) a physical dispersion of soil aggregates caused by the mechanical impact of the raindrops; and (2) a chemical dispersion caused by the soil ESP and the low electrolyte concentration in the applied water.

Effect of Fire on Hydrophobic and Cementing Substances of Soil AGGREGATES1

Abstract: Many Italian soils over which fire has passed are intensely eroded. To clarify the effect of fire on some factors associated with the soil erodibility, such as soil organic matter content, aggregate stability, and hydrophobic and cementing substances, we performed an experimental burning in

The Effect of Soil Environment and Fertilizer Modifications on the Rate of Urea Hydrolysis

Abstract: As part of an effort to model the behavior of urea by computer simulation, we studied the problems associated with modeling urea hydrolysis. Incubation experiments with a variety of soils were used to analyze the kinetics of urea hydrolysis. We studied the effects of urea disposition, mode of application, soil temperature, and moisture, as well as soil preincubation, on the hydrolysis rate. The experiments showed that hydrolysis of urea uniformly distributed throughout the soil is adequately described by zero-order equations and for some soils might even be considered instantaneous if model time steps of 24 hours are used. However, application of prilled urea creates a heterogeneous system in which urea hydrolysis was best described by first-order kinetics following a substantial lag phase. The first-order phase is followed by a rapid increase in hydrolysis rate, possibly due to a shift to zero-order kinetics. Modeling of urea hydrolysis is further complicated by the effects of the soil environment. The hydrolysis rate decreased linearly with decreasing temperature, and moisture rapidly reduced the hydrolysis rate above the permanent wilting point (PWP). Moreover, hydrolysis rates were possibly affected by waterlogging or excessive temperatures. Thus, full characterization of the behavior of urea hydrolysis in each soil used for modeling purposes seems a prerequisite to computer simulation of urea-N in soil.

Effects of Soils on Acid Phosphatase and Inorganic Pyrophosphatase of Corn Roots

Abstract: Several phosphatases are present in soils. The contribution of phosphatases in plant roots to phosphatases in soils is not well understood. This study was conducted to determine the fate of corn-root phosphatases in soils. Results showed that corn roots contain acid phosphatase (optimum pH = 4.0) and inorganic pyrophosphatase (optimum pH = 6.5), but they do not contain alkaline phosphatase. When 10 milligrams of corn-root homogenate was mixed with 1 gram of soil, the inhibition of acid phosphatase and pyrophosphatase activities of corn roots by 12 soils ranged from 43 to 63 percent (average = 52 percent) and from 11 to 62 percent (average = 44 percent), respectively. The inhibition of acid phosphatase activity of wheat germ (1 mg containing activity similar to that of 10 mg of corn-root homogenate) ranged from 88 to 95 percent (average = 92 percent). The degree of inhibition of acid phosphatase and pyrophosphatase by stream-sterilized soils was less than by unsterilized soils, indicating that the observed inhibition is, at least partly, due to soil-organic constituents. The magnitude of inhibition of these enzymes in corn roots by soil increased as the quantity of unsterilized soil added was increased from 0.1 to 1.0 g. No such increase in inhibition was observed with sterilized soils. Soil extracts (by using water or universal buffer, pH 4.0 or 6.5) inhibited acid phosphatase of corn roots and wheat germ. It is most likely that the inhibitors in the extracts are inorganic because steam-sterilized and unsterilized soil extracts showed similar degrees of inhibition. Results suggest that a major portion of phosphatases in plant roots introduced into the soil environment is rapidly degraded by soil protease or inhibited by soil constituents or both.

Competitive Adsorption During Solute Transport In Soils: 1. Mathematical Models

Abstract: One-dimensional, convective-dispersive-adsorptive flow models, in Cartesian and polar coordinates, representing flow of chemicals in soils (e.g., leaching) and toward plant roots, are generalized to competitive multispecies systems. Langmuir-type competitive adsorption models suitable for equilibrium and dynamic interactions are presented, and a few special simplified cases are discussed. Freundlich-type equilibrium adsorption models are modified to multispecies situations. An empirical approach, capable of handling most general equilibrium adsorption isotherms, suitable for multispecies systems, is also described. The empirical approach is comparable to equilibrium Langmuir and Freundlich-type competition in binary systems. Isotopic exchange, which is a form of competition between isotopes of the species for adsorption or exchange sites, may be described through a simple McKay-type equation.

Water-repellent substances and aggregate stability in hydrophobic soil.

Abstract: A hydrophobic fraction was extracted with benzene from a naturally occurring water-repellent soil. The extraction decreased the water stability of soil aggregates.Comparing this extraction with a similar one, with acetylacetone in benzene, the hydrophobic substances appear to behave as cemen

Influence Of Chloride Salinity On Cadmium Uptake By Swiss Chard

Abstract: The objective of the investigation was to determine the influence of chloride salinity on the bioavailability of cadmium in soil. The experiment consisted of treating a sandy loam soil with Cd(NO3)2 at two rates in combination with four rates of NaCl or CaCl2 and then assessing the availability of Cd in the soil with Swiss chard (Beta vulgaris ‘Cicla’). The procedure for assessing available Cd consisted of growing Swiss chard in pots containing the treated soils, harvesting, and then determining the Cd content of plant shoots. The Cd content of the shoot was taken as the measure of available Cd. Immediately after the plants were harvested, soil samples were collected for saturation extract analysis. The extracts were analyzed for all major cations, anions, and trace metals to have input data for chemically speciating Cd in the soil solution phase. The principal result showed the Cl treatment to cause a marked increase in soluble Cd, as well as an increase in leaf Cd levels; however, the distribution of estimated Cd species in the saturation extract changed with the Cl treatment. The treatment caused the percentage of estimated Cd2+ to decrease and that of estimated CdCl+ to increase. Leaf Cd was correlated better with the estimated activity of Cd2+ than with the concentration of total Cd.

Adsorption of prometryn and metolachlor by selected soil organic matter fractions

Abstract: We studied the adsorption of prometryn and metolachlor by different fractions of soil organic matter, including humic substances (humic and fulvic acids), humin, and nonoxidizable soil organic matter. As a measure for adsorption evaluation, we used a distribution coefficient (Kdfom), calcula

Physical properties of earthworm casts and surface soil as influenced by management

Abstract: We compared physical properties of worm casts with the properties of the surface 0 to 5 and 5 to 10 centimeters of soil under different management systems for an Alfisol in southwestern Nigeria. Soil management treatments consisted of comparison of notillage with conventional plowing and har

Utilization of green manure for raising soil fertility in china

Abstract: This article consists of three parts. Part 1 introduces the history and development of green manure in China, treating the utilization and evaluation of green manure in ancient times and, briefly, the development of green-manure crops after the founding of the People's Republic of China. Par

Catalytic synthesis of humic substances by natural clays, silts, and soils

Abstract: Using Warburg respirometers, we studied the oxidative power of various soils, as well as the clays and silts isolated from them. We also examined the humic substances formed through the catalytic polymerization of phenolic compounds by a soil derived from loess deposits and the silt of a Mol

Estimating Soil Moisture Storage in the Root Zone from Surface Measurements

Abstract: Numerical simulations of the dynamics of soil water in the root zone of a vegetated field show that the matric suction profile can eventually acquire the same shape as the relative root density profile. The suction at any depth is proportional to the correspond@@ ing root density raised to a power that depends on soil texture. This behavior is found only for fully grown root systems when the soil water distribution is controlled primarily by the water absorption by the roots; this becomes more likely as the soil dries out. That this power law is a solution of the continuity equation will also be demonstrated analytically. This functional relationship is used to show that, under these restrictive conditions, root zone soil moisture storage is a linear function of volumetric moisture at a particular depth, with the slope changing with depth but fixed in time. This hypothesis is supported by both laboratory and field soil moisture profile measurements, which were taken in fields with fully grown plants. No other model parameters need to be estimated, and the good agreement found constitutes an independent validation of the soil water extraction model under the plant and soil conditions described. Potential applications of these results include estimating soil moisture storage in the root zone from remotely sensed surface soil moisture and estimating the root profile from matric potential profile measurements.

Competitive adsorption during solute transport in soils: 3. a review of experimental evidence of competitive adsorption and an evaluation of simple competition models

Abstract: Experimental evidence from the literature is presented to demonstrate that adsorption of chemical substances in soils and related materials is significantly influenced by competition from other adsorbing chemicals. Both organic and inorganic ions are capable of competing for adsorption sites on soils. Potential competing chemical species include: phosphate, sulfate, selenite, molybdate, arsenate, bicarbonate, oxalate, citrate, different phenols, and polygalacturonate among anions, and calcium, lead, magnesium, sodium, and zinc among cations. Competitive adsorption occurs on a wide variety of soils, on such clay minerals as kaolinite, montmorillonite, haematite, goethite, gibbsite, pseudoboehmite, etc., and on such other materials as activated carbon. Although the diversity of experimental conditions and methods to study competitive adsorption is great, competition is clearly influenced by factors such as pH, solution concentration, and nature of the competing species. Results of some experimental studies on the effects of competition on the ion distributions between the solution and solid (adsorbed) phases are qualitatively similar to those expected from theoretical models and simulations presented in previous papers. The evaluation of the models was incomplete because the adsorption data for all the competing species were not available. Several quantitative comparisons between experimental isotherms and the theoretical predictions showed that the competitive adsorption models satisfactorily describe competition.

Comparison of the abilities of hydroxamic and other natural organic acids to chelate iron and other ions in soil

Abstract: Hydroxamate siderophores (HSs), in the form of desferrioxamine B, desferrichrome A, and an unknown mixture derived from Boletus edulis, formed stable iron (Fe) chelates in both acid and alkaline soils as determined by chelation modeling and laboratory experiments. Desferrioxamine B and the unknown mixture were more strongly adsorbed to soil than desferrichrome A. Data obtained using similar methodology indicated that citrate, oxalate, α-ketoglutarate, malate, malonate, succinate, and pyruvate did not chelate Fe effectively at alkaline soil pH, and only citrate was a reasonably effective Fe-chelating agent at acid soil pH. These data, coupled with previous work demonstrating biologically significant levels of HS in soils, indicate that HS can function as Fe mobilizers in ecosystems.

Physical Properties of Three Soils in Southern Nigeria

Abstract: To determine their physical characteristics, we studied two Alfisols and an Ultisol in southern Nigeria. The soils are formed over different parent materials. Moisture retained at saturation, 0.1, and 0.3 bar suctions was significantly correlated with available water-holding capacities. The regression models depicting the relationships between moisture equilibria and the sand, clay, and organic carbon contents had high and significant coefficients of determination and indicate that variations in soil particle size fractions and organic carbon contents accounted for over 70 percent of the variability in moisture retanined at different suctions. Significant correlation exists between organic carbon and macroporosity (r = 0.63*]) and saturated hydraulic conductivity (r = 0.88**]). Soil bulk density is negatively correlated with the organic matter content. Similarly, the percentage of clay is negatively correlated with macroporosity (r = —0.75**]) and with saturated hydraulic conductivity (r = —0.76**]), and the percentage of sand is positively correlated with these properties, with r values of 0.62**] and 0.67**], respectively.

Sorption processes in soils as influenced by pore water velocity: 2. experimental results

Abstract: We carried out experiments to measure the rate of adsorption of cadmium for static and dynamic flow conditions. The water content of samples was maintained at —12.6 kPa, corresponding to 87 percent of saturation. Adsorption rates at apparent pore water velocities of 1.3, 2.3, and 2.7 cm/h were measured. Diffusive conductance, Kd, and forward (k1) and backward (k2) rate constants were calculated using the Nelder-Mead Simplex method based on a nonlinear least-square procedure. Values of Kd and of the ratio k1/k2 increased with increasing pore water velocity. The rate of adsorption was higher in a sample with solution flowing through it than in a sample with the same solution under static conditions. The magnitude of Kd ranged from 0.07 X 10−3] at static conditions to 0.4 x 10−3] s−1] with &OV0622; = 2.7 cm/h. Results imply that the thickness of the subsurface layer decreases with &OV0622;, thus increasing the diffusion rate of ions across this layer. When the adsorption process is far from equilibrium, diffusion across the subsurface layer became a rate-limiting step in the adsorption process. Lateral diffusion cannot be ignored in studies of the kinetics of adsorption. The increase in values of k1/k2 with increasing &OV0622; indicates that the surface reaction proceeded at a more rapid rate in the presence of a continuous supply of solution. Flowing solution serves as a continuous source of the introduced ions, as well as a continuous sink for the desorbed ions of other species originally present. The accelerated rate of adsorption induced by flow of solution through the soil may be attributed both to an increase in the rate of diffusion as the thickness of the subsurface layer decreases and to an increase in the rate of the kinetic reactions at the surface as the exchange process proceeds in the presence of the continuous sink.