Showing papers in "Soil Science in 1990"
TL;DR: Soil acidity and plant growth, Soil acids and plants growth, the authors, Soil acidities and plant growing, مرکز فناوری اطلاعات و اسلاز رسانی, ک-شاوρزی
Abstract: Soil acidity and plant growth , Soil acidity and plant growth , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی
272 citations
TL;DR: In this paper, the authors measured hydraulic conductivity (saturated and unsaturated) on 127 soil cores, which were taken in different horizons of a wide variety of Belgian soil series.
Abstract: We measured hydraulic conductivity (saturated and unsaturated) on 127 soil cores, which were taken in different horizons of a wide variety of Belgian soil series. The hot air method (Arya et al. 1975) and the crust method (Bouma et al. 1983) were combined to obtain the complete range of hydraulic conductivity from saturation to air-dry. The textural composition in nine fractions, the organic carbon content, and the dry bulk density were determined for each of the sample horizons as well. Four different empirical models were evaluated on their performance in describing the measured hydraulic conductivity curves. The model parameters were estimated by linear and nonlinear regression techniques. It is concluded that the Gardner equation (1958) with three parameters best described the hydraulic conductivity for the given soils. Regression equations for estimating the Gardner parameters were established from simple soil properties, such as soil texture, carbon content, bulk density, and saturated hydraulic conductivity. We found that the three parameters can reasonably well be estimated from the textural composition and the saturated hydraulic conductivity. A one-dimensional sensitivity analysis indicates that the n parameter, representing the slope of the hydraulic conductivity pressure head relation in log-log scale, is most sensitive.
256 citations
TL;DR: In this paper, the effects of forest fire on organic matter from a Dystric Xerochrept under Quercus rotundifolia was simulated in laboratory experiments.
Abstract: This study is about the effects of forest fire on the organic matter from a Dystric Xerochrept under Quercus rotundifolia. In laboratory experiments carried out to simulate the effects of fire on isolated humic fractions, several physicochemical characteristics were described in the heated samples,
238 citations
TL;DR: A biomantle is a differentiated zone in the upper part of soils produced largely by bioturbation, but often aided by subsidiary processes as mentioned in this paper, such as loss of fine particles and redistribution of coarse ones from evolving biomantles.
Abstract: A biomantle is a differentiated zone in the upper part of soils produced largely by bioturbation, but often aided by subsidiary processes. One such process is loss of fine particles and redistribution of coarse ones from evolving biomantles. This is accomplished by rainwash and wind sorting of unpro
197 citations
TL;DR: For example, most studies comparing duration of cultivation to organic matter changes are usually confounded by differences in soil type and/or management practices or are restricted to comparisons of a single long-te
Abstract: Cultivation of native rangeland generally leads to a reduction in its organic C and N. However, most studies comparing duration of cultivation to organic matter changes are usually confounded by differences in soil type and/or management practices or are restricted to comparisons of a single long-te
183 citations
TL;DR: In this article, the effect of surface application of anionic polyacrylamide (PAM) at rates of 10, 20, and 40 kg on the infiltration rate (IR) of two soils, a loess (Calcic Haploxeralf) and a grumusol (Typic Chromoxerert), during simulated rainstorms was studied.
Abstract: Seals formed at the soil surface during rainstorms reduce rain penetration and cause runoff and erosion. We studied the effect of surface application of an anionic polyacrylamide (PAM) at rates of 10, 20, and 40 kg.ha-1 on the infiltration rate (IR) of two soils, a loess (Calcic Haploxeralf) and a grumusol (Typic Chromoxerert), during simulated rainstorms. We determined the interaction between PAM and electrolyte concentration at the soil surface under a simulated rainfall of distilled water or tap water and by spreading gypsum. Electrolytes in the soil solutions that flocculated the soil clay enhanced the beneficial effect of the polymer on aggregate stability and greatly reduced water losses. Complete drying of the polymer-soil surfaces improved the binding action of the polymer. Treatments with PAM under optimal conditions increased the final IR of the loess from 2.0 to 23.5 mm.h-1 and increased rain intake of an 80-mm rainstorm from 12.3 to 64.2 mm. PAM treatment of the grumusol increased the final IR from 3.0 in the control to 20.5 mm.h-1 and the rain intake from 21.3 to 62.3 mm. As soils from semiarid regions are unstable, form crusts, and produce much runoff (80%) during rainstorms, the use of PAM to reduce runoff should be considered.
168 citations
TL;DR: In this paper, the authors studied adsorption of copper and zinc on three different soils: a brown silty soil, an Oxisol, and a Podzol, and determined the amounts adsorbed and the shapes of adsorbing isotherms as a function of the pH of the adsorbbing medium at a constant ionic strength.
Abstract: The authors studied adsorption of copper and zinc on three different soils: a brown silty soil, an Oxisol, and a Podzol. They determined the amounts adsorbed and the shapes of adsorption isotherms as a function of the pH of the adsorbing medium at a constant ionic strength. The adsorbed amount-pH relationship depended strongly on the natures of the metallic cation and of the soil. The pH greatly influenced the characteristics of adsorption isotherms. They based interpretation on the variations with the pH of both adsorbent affinity for the metal in relation to the surface electric charge and chemical speciation in solution. The adsorption mechanism in the Oxisol probably involves monohydroxylated cations but is more determined by bivalent cations in the brown silty soil and the Podzol. From a general point of view, adsorption of copper and zinc cannot be represented with a single adsorption constant, but should be described by adsorption isotherms obtained at various pH values.
149 citations
TL;DR: In this article, the authors derived a new infiltration equation that takes into account the possibility of an infinite diffusivity near saturation, using the example of two soils (clay and coarse sand).
Abstract: We derived a new infiltration equation that takes into account the possibility of an infinite diffusivity near saturation. Using the example of two soils (clay and coarse sand), we showed that this new infiltration equation has a sound physical basis. In particular, all parameters used are true soil properties that are constant with time and independent of the water depth imposed as a surface boundary condition. Compared with analytical, numerical, and experimental results, the equation shows a great precision (σ2 The present law introduces a significant improvement over the law obtained in part 1 of this series dealing with ponded infiltration by introducing the physical effect of an infinite diffusivity at saturation.
139 citations
TL;DR: In this article, the effect of the heat wave that accompanies the passage of a fire on some chemical parameters related to soil fertility and plant growth was investigated, and two soils, classified as a sandy loam and a silty clay, were subjected to artificial heating under controlled conditions.
Abstract: To clarify the effect of the heat wave that accompanies the passage of a fire on some chemical parameters related to soil fertility and plant growth, we subjected two soils, classified as a sandy loam and a silty clay, respectively, to artificial heating under controlled conditions We arranged the
131 citations
TL;DR: In this article, the structural stabilities of eight arid zone soils using percent optical transmittance as a measure of flocculation dispersion behavior were investigated and their stabilities determined in sodium chloride solutions of varying concentrations.
Abstract: We investigated the structural stabilities of eight arid zone soils using percent optical transmittance as a measure of flocculation-dispersion behavior. The soils were sodium saturated and their stabilities determined in sodium chloride solutions of varying concentrations. We treated the soils with
124 citations
TL;DR: Using first-order kinetics, this paper described the release of nutrients by coated slow-release fertilizer (SRF) using first order kinetics and calculated the logarithm of the concentration of intact fertilizer in the soil.
Abstract: Using first-order kinetics we describe the release of nutrients by coated slow-release fertilizer (SRF). Plotting the logarithm of the concentration of intact fertilizer in the soil [log(Q0 - Qt), where Qt, is the amount applied and Qt, is the amount released at time t] versus the time yielded a str
TL;DR: Several different extractants may be used to estimate plant-available soil P. Each laboratory utilizes the extractant that best predicts yields on its range of soils as determined by soil test correlations as mentioned in this paper.
Abstract: Several different extractants may be used to estimate plant-available soil P. Each laboratory utilizes the extractant that best predicts yields on its range of soils as determined by soil test correlations. The Agricultural Extension Service Soil Testing Laboratory of Texas A&M University is the onl
TL;DR: In this paper, Humic acid extracted from sewage sludges, manure, and worm compost have been characterized by chemical and spectroscopic methods, revealing meaningful differences in the composition of the products.
Abstract: Humic acids extracted from sewage sludges, manure, and worm compost have been characterized by chemical and spectroscopic methods. Meaningful differences in the composition were revealed by FTIR, {sup 1}H, {sup 13}C NMR, and visible spectroscopies. These differences allow a differentiation among the products depending on the source from which they were obtained. Humic acid extracted from sewage sludges contains the highest percentage of aliphatic carbon, associated with polysaccharides and proteinaceous structures, and has characteristics close to those of aquatic humic acids. On the other hand, humic acids from manure and worm compost are similar to the humic acids originating from soil.
TL;DR: In this article, the microscopic approach thin section description sediments anthropogenic features postdepositional processes and relevant features are used for soil science and current methods field strategies field strategies.
Abstract: Basic concepts in soil science and current methods field strategies the microscopic approach thin section description sediments anthropogenic features post-depositional processes and relevant features. Case studies: the cave of Vaufrey, Perigard, France Kebara cave, Israel the cave of the pigeons at Taforalt, Eastern Morocco the Acheulean site of Berekhat Ram, Israel the neolithic site of Netiv Hagdud and the Salibya depression, Lower Jordan Valley, Israel the bronze age/neolithic site of Fort Harrouard, France dark earth, England human settlement patterns and holocene environments in the Shaggar Plain, Northwest India rural settlement at Castellaro di Uscio, Liguria, Italy chalcolithic land-use in Italian Appennines and Alps.
TL;DR: In this paper, a low-power HeNe (helium-neon) laser source and a matrix-array detector are used to measure in situ soil surface roughness profiles using a laser profile meter, which leads to 1001 sampled values (volt, range 0 to 10 V) at a constant increment of 0.002 m, registered automatically on a microcomputer.
Abstract: This paper describes a new optical technique for measuring in situ soil surface roughness profiles using a laser profile meter. The described method uses a low-power HeNe (helium-neon) laser as a laser source and a matrix-array detector, as the laser image. The matrix-array detector gives a defect-of-focus laser image of the soil. Soil elevation is measured by projecting a laser beam normally onto the soil surface and measuring the ratio (Ir/It) on the matrix-array detector between the referenced intensity of the return Laser beam (Ir), measured by the central cell of the detector and the total intensity (It), measured by all the cells of the detector. The measured profile leads to 1001 sampled values (volt, range 0 to 10 V) of the surface height profile, at a constant increment of 0.002 m, registered automatically on a microcomputer. A calibration is made in the laboratory in order to convert the electrical measurements into elevation data. The method is universal and can be adapted to different scales of soil surface roughness. Changing the scale is done by changing the lens. Tests were carried out to improve this method for field use and to compare this technique with a method of reference. This technique is considerably quicker and causes no disturbance to the soil. The accuracy on height measurement depends on the choice of the lens. The small focal lens is convenient for smooth soil surfaces. The accuracy on height measurement is less than 0.75 mm. The wide focal lens is convenient for rough soil surfaces. The accuracy on height measurement is estimated at about 1.0 to 1.5 mm.
TL;DR: In this article, three fractions of humic substances which originated bands in different parts of the pH were characterized using electrofocusing, and they were used to characterize humic compounds with carrier ampholytes.
Abstract: Electrofocusing could be usefully employed to characterize humic substances, but careful investigation is needed because of possible interactions of humic substances with carrier ampholytes. In the present work, three fractions of humic substances which originated bands in different parts of the pH
TL;DR: Manganese and copper were found in the iron oxide plaque on roots of Phragmites australis collected at six sampling sites in southern Quebec and Ontario, Canada as mentioned in this paper.
Abstract: Manganese and copper were found in the iron oxide plaque on roots of Phragmites australis collected at six sampling sites in southern Quebec and Ontario, Canada. Manganese concentration in the plaque, like that of Fe, is correlated with Mn-bound-to-carbonates fraction of the soil/sediment. The Fe:Mn ratio of the plaque resemble the same ratio of Fe:Mn-bound-to-carbonates in the substrate. The ratio changes with environmental conditions, increasing with percentage of water and decreasing with pH. Plants located near flowing water accumulate more Mn (and Fe) in the plaque than plants in other habitats through the summer. Copper concentration in the plaque than plants in other habitats through the summer. Copper concentration in the plaque is pH-dependent and is positively correlated with the amount of Fe and Mn of the plaque, but appears to be related more closely to Mn.
TL;DR: In this article, a pasture soil with up to 224 kg of ammonium nitrate and 45 kg of superphosphate was analyzed for soil test values as a function of depth, and significant changes in soil pH, lime requirement, organic matter, Bray and Kurtz no. 1 P, and DTPA-extractable micronutrients were observed.
Abstract: Continuous fertilization for 40 years with N and P resulted in significant changes in soil pH, lime requirement, organic matter, Bray and Kurtz no. 1 P, and DTPA-extractable micronutrients. A pasture soil receiving up to 224 kg N.ha-1 as ammonium nitrate and 45 kg.ha-1 as superphosphate since 1946 was analyzed for soil test values as a function of depth. Soil pH values were observed to decrease when N applications exceeded plant requirements. In plots receiving continuous additions of 224 kg.ha-1, the pH decreased from 6.5 to 4.1. The lime requirement of the soils reflected pH changes. Organic matter was found to be unaffected by P fertilization, but increased with increasing N rate. Bray and Kurtz no. 1 P concentrations were extremely high in the surface 10 cm of P-fertilized plots, and increased concentrations were observed to a depth of 60 cm. DTPA-extractable Fe was negatively correlated with pH, and increased DTPA-Fe was observed to a depth of 20 cm. DTPA-Mn also tended to increase in soils with lower pH, and both total and DTPA-extractable Mn appeared to have leached from the 0− to 10-cm to the 10− to 20-cm increment in soils receiving the highest rate of N application. A strong interaction of N, P, and depth was observed for DTPA-Zn, but DTPA-Cu was unaffected by fertilization. In 1965, the plots were split, with one-half of each plot continuing to receive fertilizer and the other half having the fertilization permanently discontinued. The soil pH, lime requirement, Bray and Kurtz no. 1 P, and DTPA-extractable Fe and Mn all showed a significant response to discontinuation of fertilizer additions. The pH tended to increase, whereas the lime requirement, Bray and Kurtz no. 1 P, and DTPA micronutrients decreased during the 20 yr without fertilizer.
TL;DR: The authors conducted a field study in 1984 and 1985 on a Gilpin silt loam soil association in Preston County, West Virginia, to determine soil and environmental factors controlling corn yield differences among landscape positions.
Abstract: The topography of the Appalachian region strongly influences the environment for plant growth. We conducted a field study in 1984 and 1985 on a Gilpin silt loam soil association in Preston County, West Virginia, to determine soil and environmental factors controlling corn (Zea mays L.) yield differences among landscape positions. Four plots were established at each of nine locations including summit, shoulder (N, E, S, W aspects), and backslope (N, E, S, W aspects). Athough common management practices were used throughout the field, silage, yields (65% moisture) were 15.3 to 43.0 Mg/ha in 1984 and 22.2 to 36.6 Mg/ha in 1985. Grain yields (15% moisture) were 3.1 to 8.2 Mg/ ha in 1984 and 4.0 to 7.6 Mg/ha in 1985. Poor silage and grain yields were associated with higher clay content and lower organic C in the A horizon, lower plant “available water” in the 0− to 15-cm depth interval, and possible subsoil acidity problems. Mean “available water” as represented by the difference between gravimetric water determined over time and water retained at 1500 kPa was a good predictor of silage yield. Soil water was apparently the most important factor controlling corn production differences in this study. The ability to predict soil water relationships on the landscape would hasten the development of successful agronomic management practices for the hilly Appalachian region.
TL;DR: The spatial distribution of soil loss and gain in agricultural fields was examined at twenty-one sites in the Boroll soil zone of southern Saskatchewan as mentioned in this paper, where the rates of soil redistribution and gain were assessed using cesium-137 redistribution techniques.
Abstract: The spatial distribution of soil loss and gain in agricultural fields was examined at twenty-one sites in the Boroll soil zone of southern Saskatchewan. The rates of soil loss and gain are assessed using cesium-137 redistribution techniques. The correlations between the rates of soil redistribution and individual slope variables (e.g., gradient and length) are very low. Statistically distinct rates of soil redistribution are, however, associated with three-dimensional landform elements of the slope systems examined. In the aridic and ustic Boroll soil regions the highest rates of soil loss are associated with divergent back-slopes and shoulders; in the udic Boroll zone the highest losses occur on the convergent backslope sites. In all three zones soil gain is concentrated in the convergent footslope elements. The differences in the observed spatial pattern of soil redistribution between the udic Boroll region and the aridic and ustic Boroll regions is attributed to differences in the dominant detachment and transport process in the landscape.
TL;DR: In this paper, the effect of antecedent water content on splash detachment and on soil and hydraulic variables that control splash was investigated in simulated rainfall with an intensity of approximately 64 mm h−1 for 1 h.
Abstract: Antecedent soil water content is an important variable affecting soil erosion processes and may be responsible for much of the variation in splash and wash erosion rates. The purpose of this study was to determine the effect of antecedent water content on splash detachment and on soil and hydraulic variables that control splash. Five soils ranging in texture from sandy loam to clay were exposed to simulated rainfall with an intensity of approximately 64 mm h−1 for 1 h. Wash, splash, runoff, and infiltration were measured for near-saturated (-0.5 kilopascal) and air-dried soils in 0.14 m2 Al erosion pans. Changes in the soil surface were monitored with a fall-cone device. Prewetting significantly reduced runoff occurring over a 60-minute rainfall period for the Heiden clay only. Prewetting reduced splash detachment rates for all soils except the Miami silt loam, with the greatest reduction for the Heiden clay. Total splash for the air-dried and prewetted Heiden clay was 770.1 and 169.4 g in 60 minutes, respectively. Prewetting increased soil shear strength following 60 minutes of rainfall for all soils. Development of a surface seal controlled the amount of soil detached from the Miami silt loam. Miami silt loam had the highest final shear strength values for air-dried and prewetted soils and the highest difference between initial and final shear strength (Δτ) among prewetted soils. Prewetted wash and splash sediment size was larger than that for air-dried sediments. Antecedent soil moisture conditions prior to rainfall influenced the amount of splash detachment and the physical processes that control amount of splash.
TL;DR: In this article, the authors explored the empirical distribution of the standard error for several soil properties (total carbon pools, exchangeable cation pools, and forest floor element pools) using data collected from a northern hardwood forest site in central New Hampshire.
Abstract: In long-term field studies, the number of soil samples required to detect a specified change is often determined by using the standard error of a soil property from a pilot study. When a soil property is highly variable, estimates of its standard error will also be highly variable. Therefore, it is useful to have confidence limits for the standard error in sample size calculations. We explored the empirical distribution of the standard error for several soil properties (total carbon pools, exchangeable cation pools, and forest floor element pools) using data collected from a northern hardwood forest site in central New Hampshire. We used a bootstrapping routine to simulate data sets for sample sizes ranging from 6 to 60 soil pits and computed the mean, 95%, and 98% confidence limits for the percentage change detectable by a specified number of sample observations. Using the 95% confidence limit for standard error resulted in as much as a twofold increase in the sample size requirement compared with the average standard error. For normally distributed data, the bootstrap confidence limits of standard error agree with those computed analytically. In the presence of modest nonnormality in the data, however, the analytic confidence limits do not agree with the bootstrap limits. Since the bootstrap procedure is free of parametric assumptions, it is a useful tool for general application in soil science.
TL;DR: In this article, the authors collected soil solutions during the spring snowmelt at two depths using tension-free lysimeters in two Humic Cryorthods located in forested catchments.
Abstract: The authors collected soil solutions during the spring snowmelt at two depths using tension-free lysimeters in two Humic Cryorthods located in forested catchments. They also extracted soil solutions by centrifugation from the B and the C horizons of these soils. Although most data points cluster around the solubility line of natural gibbsite, the relationship between Al{sup 3+} activity and solution pH showed a marked departure from Al(OH){sub 3} solubility with a slope of {minus}1.91. Moreover, at pH values below 4.6, solutions were slightly undersaturated with respect to natural gibbsite. Results from thermodynamic calculations suggested that the Hermine B, and probably the Coniferous B, horizons have attained chemical conditions sufficient to enter the stability field of a basic aluminum sulfate mineral formed in the presence of Al(OH){sub 3}. Mineral stability relationships indicated that the solid phase of concern could be alunite (pK{sub s} = 85.4) and that the apparent saturation status of the soil solutions with respect to alunite increased with increasing reaction time. However, physical evidence for the presence of alunite in these horizons is still lacking. Solutions from the C horizons were all clearly undersaturated with respect to any Al{sub x}(OH){sub y}(SO{sub 4}){sub z} mineral. While the possible formationmore » of alunite could be affecting sulfate retention in these acid soils, the results do not exclude the pH-dependent sulfate adsorption mechanism proposed by a number of investigators.« less
TL;DR: In this article, a method of evaluation of nutrient release from membrane-coated slow-release fertilizers is presented based on the gravimetric measurement of water-vapor uptake by individual fertilizer granules placed in a saturated water vapor chamber.
Abstract: A method of evaluation of nutrient release from membrane-coated slow-release fertilizers is presented. The method is based on the gravimetric measurement of water-vapor uptake by individual fertilizer granules placed in a saturated water vapor chamber. The nutrient release from such fertilizer consists of two stages. In the first stage, water vapor infiltrates into the granule and condenses on the soluble fertilizer salt, leading to the development of pressure within the particle. The elevated pressure leads to swelling of the granule and the outward leakage of the fertilizer solution. The method yields results characterizing both the average rate of nutrient release and the release rate distribution among the population of fertilizer granules. The results are consistent with measurements of nutrient release rates in soil-fertilizer mixtures.
TL;DR: In this paper, the authors investigated the effect of annual tillage on soil organic carbon (C) stored in the surface meter of soil, mainly by altering plant species composition, and found that root C in untilled plots constituted only one-quarter of the total loss of C below ground.
Abstract: Seven years of annual tillage of a fine-textured Hapludalf, cleared of forest about 160 yr ago and more recently cropped for hay, caused grasses to be replaced by annual herbs Tillage decreased carbon (C) stored in the surface meter of soil, mainly by altering plant species composition Carbon storage in the surface 15 cm of soil was reduced by 24%, ie, by 679 g C/m{sup 2}, 76% of which was due to a reduction in root biomass Relatively small changes were found in mineral soil organic C from annual tillage, ie, about 1 mg C/g soil Results illustrate a dual-component cycle of soil organic C that appears especially pronounced in these fine-textured soils: (1) a rapidly cycling, plant-dominated C pool, and (2) a much more slowly cycling resistant C pool at least partly bound to clay-mineral surfaces The dynamics of root C can be a dominant factor to the C balance of tilled and cropped soils In the present study, root C in untilled plots totaled only about one-quarter of the total C in the 0- to 15-cm depth of soil, yet reductions in root C accounted for three-quarters of the total loss of C below ground To determine effectsmore » of land use on soil C, soil samplings must distinguish clearly between effects on plant roots from those on mineral-soil organic matter« less
TL;DR: In this paper, the effect of exchangeable K on hydraulic conductivity and infiltration rate of three South African soils and compared it to exchangeable Ca and Na, using K-Ca and Na-Ca systems with different levels of exchangeability K or Na.
Abstract: The authors studied the effect of exchangeable K on the hydraulic conductivity (HC) and infiltration rate (IR) of three South African soils and compared it to the effects of exchangeable Ca and Na, using K-Ca and Na-Ca systems with different levels of exchangeable K or Na. Increasing the amount of K in the exchangeable phase resulted in a decrease in both the HC and IR of the soils. It was found that, relative to Ca and Na, exchangeable K had an intermediate effect on the HC and IR of the soils. These observations support previous findings insofar as HC measurements are concerned and confirm the view that exchangeable K cannot be grouped together with either Ca or Na as ions having similar effects on the hydraulic properties of soils.
TL;DR: In this paper, the authors use a model soil consisting of spherical, cylindrical, or flat aggregates to measure the shortest distance from a randomly chosen point to the interaggregate space.
Abstract: In models on diffusive transport it is necessary to make use of a simplifying description of the geometry of an aggregated soil. It is proposed to use a (hypothetical) model soil consisting of spherical, cylindrical, or flat aggregates. The model aggregates are of different sizes, and each size class occupies a certain fraction of the total volume. These volume fractions can be calculated in such a way that diffusive transports take place in approximately the same way in soil and model soil. The method is operational. The quantity to be measured is the shortest distance from a randomly chosen point to the inter-aggregate space. The desired volume fractions can be derived from the probability distribution of this distance. The procedure does not require the existence of individual aggregates and may be applied, for instance, to a cracked clay soil. The use of a simple model soil is based on the shape independence of diffusion processes. That shape independence has been verified by means of theoretical calculations for both a single aggregate and an aggregated soil.
TL;DR: In this paper, the authors studied the morphology, mineralogy, and isotope chemistry of pedogenic calcite at Harappa, Pakistan, to determine the process by which they form and the climatic conditions under which they developed.
Abstract: In the Punjab territory of the Indo-Gangetic plains, calcite nodules commonly are found in soils on older stream terraces composed of calcareous silt. For this paper, we studied the morphology, mineralogy, and isotope chemistry of pedogenic calcite at Harappa, Pakistan, to determine the process by which they form and the climatic conditions under which they developed. A well-developed soil (fine-silty, mixed, hyperthermic Aridic Haplustalf) showed greatest nodule complexity in the calcic horizon by x-ray diffraction and thin section analysis; inner portions of these nodules had a radiocarbon age of 7080 +/- 120 yr BP Inner portions of nodules, which are presumed to have formed in equilibrium with soil CO2, reflect a large influence of atmospheric CO2 and a very low soil respiration rate. Delta 13C values indicated that a maximum of 71% of the disseminated calcite was pedogenic in origin. Oxygen isotope ratios of disseminated and nodular calcite indicate calcite precipitation in equilibrium with soil water, with δ 18O values similar to that of modern precipitation. A shallower water table at some time in the past may have influenced calcite deposition deep in the profile.
TL;DR: In this paper, the authors studied the release of NH4+ from soils when cropped with ryegrass, and found that nonex-changeable NH 4+ was released only in the immediate vicinity of the roots where, it is sugge
Abstract: We studied the release of nonexchangeable NH4+ from soils when cropped with ryegrass. The plants were grown in special soil containers in which part of the soil was not in direct contact with the roots. Nonex-changeable NH4+ was released only in the immediate vicinity of the roots where, it is sugge
TL;DR: The distribution of added potassium (K) in soil K forms (water-soluble, exchangeable, and nonexchangeable) as a function of clay mineralogy and taxonomy was determined using 102 soils from the continental United States and Puerto Rico, representing 10 soil orders as discussed by the authors.
Abstract: The distribution of added potassium (K) in soil K forms (water-soluble, exchangeable, and nonexchangeable) as a function of clay mineralogy and taxonomy was determined using 102 soils from the continental United States and Puerto Rico, representing 10 soil orders. The soils were divided into three groups (kaolinitic, mixed, and smectitic) based on dominant clay mineralogy. A linear increase in water-soluble, exchangeable, and nonexchangeable K content of each soil was obtained after a 25-wk incubation with K (0 to 250 mg K kg-1). Slopes of these relationships represent water solubility (S), exchangeability (E), and fixation (F) indexes, with a significant decrease in S and increase in E and F observed from kaolinitic to mixed to smectitic soils. The indexes were closely related (r2 = 0.75 to 0.96) to clay content for each group of soils. The K buffer capacity (KBC) was significantly greater for smectitic than mixed and kaolinitic soils and was closely related to clay, CEC, and K saturation for each group of soils. Using the relationship between clay content and S, E, F, and KBC, the distribution of fertilizer K in an independent set of 60 kaolinitic, mixed, and smectitic soils and published data was closely estimated. Differences in these relationships between each group of soils were consistent with K reaction mechanisms of the dominant clay minerals. Use of these relationships may allow prediction of fertilizer K disposition in soils of differing taxonomic and mineralogical properties and, thus, aid fertilizer K recommendations for certain soils.