bluuebunny/crossref_metadata_2025 huggingface dataset:
Biogeochemical Cycling of Calcium and Magnesium by Ceanothus and Chamise
Authors: Quideau S. A. , Graham R. C. , Chadwick O. A. , Wood H. B.
Published: July 2010

Vegetation has long been recognized as a fundamental factor in soil formation, but vegetation and soils commonly covary in response to other environmental factors, confounding the specific effects of vegetation on soil properties. The lysimeter installation at the San Dimas Experimental Forest in southern California offers a rarely found opportunity for quantifying cation‐cycling processes in a setting where all factors except vegetation are kept constant. The lysimeters were filled in 1937 with homogenized, fine sandy loam and planted in 1946 with chamise (Adenostoma fasciculatum Hook. and Arn.) and ceanothus (Ceanothus crassifolius Torr.). Comparison of the chamise and ceanothus lysimeters was best achieved by using the Ca/Mg ratio of the different cation pools and fluxes as an index. In 1987, the ceanothus exchangeable soil pool contained proportionally more Ca than Mg compared with chamise; that is, the Ca/Mg ratio in the ceanothus exchangeable soil pool was higher than that in chamise. Strong evidence supports vegetation influence on intra‐system fluxes (weathering and biocycling) as the basis for these differences. First, more Ca than Mg was released by weathering under ceanothus than under chamise. Second, the ceanothus aboveground biomass exhibited a higher Ca/Mg ratio than the chamise. Third, differences between vegetation types widened with time since construction of the lysimeter installation in both the aboveground biomass and exchangeable soil pools. Differences in cation storage measured for the lysimeter chamise and ceanothus stands appear representative of natural chaparral communities throughout California, and may result in distinct Ca and Mg biogeochemical processes in associated ecosystems.
Selenate and Selenite Sorption on Iron Oxides An Infrared and Electrophoretic Study
Authors: Su Chunming , Suarez Donald L.
Published: July 2010

We studied selenate and selenite sorption by amorphous Fe oxide [am‐Fe(OH)3] and goethite (α‐FeOOH) as a function of time (25 min–96 h), pH (3–12), ionic strength (0.01–1.0 M NaCl), and total Se concentration (0.0001–1.0 M). We examined sorbed selenate and selenite by in situ attenuated total reflectance Fourier transform infrared (ATR–FTIR) spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and electrophoresis to deduce sorption mechanisms. Sorption of both selenate and selenite reached equilibrium in <25 min and the sorption isotherm was not reversible. Increasing ionic strength decreased selenate sorption but did not affect selenite sorption. The presence of either selenate or selenite lowered the electrophoretic mobility (EM) and decreased the point of zero charge (PZC) of both sorbents, suggesting inner‐sphere complexation for both selenate and selenite species. Both in situ ATR–FTIR and DRIFT difference spectra showed bidentate complexes of selenate with am‐Fe(OH)3 The structure of selenite complexes in am‐Fe(OH)3 –solution interface was uncertain due to insensitivity of the in situ ATR–FTIR technique. The DRIFT spectra of selenite on am‐Fe(OH)3 showed ν3 splitting as evidence of complexation. The DRIFT spectra of selenite on goethite showed bridging bidentate complex of selenite. We conclude that the influence of ionic strength on Se sorption cannot be used as a criterion for distinguishing outer‐ vs. inner‐sphere complex formation.
Acifluorfen Sorption, Degradation, and Mobility in a Mississippi Delta Soil
Authors: Gaston L. A. , Locke M. A.
Published: July 2010

Potential surface water and groundwater contaminants include herbicides that are applied postemergence. Although applied to the plant canopy, a portion of any application reaches the soil either directly or via subsequent foliar washoff. This study examined sorption, degradation, and mobility of the postemergence herbicide acifluorfen (5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoic acid) in Dundee silty clay loam (fine‐silty, mixed, thermic, Aeric Ochraqualf) taken from conventional till (CT) and no‐till (NT) field plots. Homogeneous surface and subsurface samples were used in the sorption and degradation studies; intact soil columns (30 cm long and 10 cm diam.) were used in the mobility study. Batch sorption isotherms were nonlinear (Freundlich model) and sorption paralleled organic C (OC) content. All tillage by depth combinations of soil exhibited a time‐dependent approach to sorption equilibrium that was well described by a two‐site equilibrium–kinetic model. Acifluorfen degradation followed first‐order kinetics. No more than about 6% of applied14C‐acifluorfen was mineralized by 49‐d incubation. Extracts of incubated soil gave little indication of degradation products; however,14C did accumulate in an unextractable fraction. Degradation was faster in the surface soils compared to subsurface soils and faster in CT surface soil compared to NT surface soil. Tillage did not affect acifluorfen degradation in subsurface samples. Elution of Br pulses from the intact soil columns under steady‐state, unsaturated flow indicated preferential water flow. Nonequilibrium transport of Br was well described using a two‐region, mobile–immobile water model. Inclusion of sorption kinetics in the transport model rather than assuming equilibrium sorption led to improved predictions of acifluorfen retardation. Column effluent contained negligible concentrations of acifluorfen degradation products and, as in the incubation study, an unextractable residue developed in the soil columns. However, unlike results from the incubation study, a greater fraction of applied acifluorfen was apparently bound and there was also evidence of extractable degradation products. Furthermore, first‐order rate constants obtained from the batch study underestimated acifluorfen degradation during transport. Faster acifluorfen degradation in the soil columns may have been due to poorer aeration compared to the batch systems.
Phosphorus Sorption, Desorption, and Buffering Capacity in a Biosolids‐Amended Mollisol
Authors: Sui Yaobing , Thompson Michael L.
Published: July 2010

To investigate the impact of biosolids amendments to soil on the sorption, desorption, and buffering capacity of P, laboratory experiments were conducted on soil samples collected from a field study on a Mollisol amended with three levels of biosolids. The potential for sorption of additional P and the binding intensity of P were evaluated by applying the two‐surface Langmuir model to sorption isotherms. Over the range of equilibrium P concentrations in this study, the ability of the soil to sorb added P decreased due to biosolids amendment. Addition of biosolids to the soil also decreased indices of the P‐binding intensity at both the high‐ and low‐affinity sites. The P equilibrium buffering capacity (PEBC) significantly decreased and the equilibrium P concentration (EPC) significantly increased after biosolids amendment. P desorption from soil samples with and without biosolids amendment was investigated for different equilibration periods and at various liquid/solid ratios. The amount of P that could be desorbed from the soil significantly increased after biosolids amendment. The effects of biosolids amendments on indices of soil P sorption–desorption phenomena (binding energy, PEBC, and EPC) imply a large increase in the P concentration of the soil solution. The increase of soluble forms of P in soil solution of this soil, which was heavily amended with biosolids, could enhance the loss of P in runoff and P movement below the root zone.
Surface Residue– and Root‐derived Carbon in Stable and Unstable Aggregates
Authors: Gale W.J. , Cambardella C.A. , Bailey T.B.
Published: July 2010

Stable macroaggregates are enriched in new C relative to unstable macroaggregates, but the origin and form of this new C is not known. Under simulated no‐till (NT) conditions, we used a 14C label to monitor changes in the concentration of new surface residue– and root‐derived C in aggregates of different size and stability during a 1‐yr incubation. Two water pretreatments (capillary‐wetted and slaked) were applied to the soil samples collected during the incubation. The samples were then wet sieved to obtain five aggregate size classes. Densiometric separations were used to isolate free and released particulate organic matter (frPOM) and intraaggregate POM (iPOM). Root‐derived 14C was distributed differently in the soil compared to surface residue–derived 14C. A comparison of the two water pretreatments indicated that root‐derived aggregate‐14C and iPOM‐14C concentrations were significantly higher in stable (slaking‐resistant) small macroaggregates (250–2000 μm) relative to those in the capillary‐wetted pretreatment. In contrast, there were no significant differences in the amount of surface residue–derived aggregate‐14C or iPOM‐14C in small macroaggregates (250–2000 μm) between the two pretreatments. We conclude that in relatively undisturbed systems like no‐till, new root‐derived iPOM‐C is more important than surface residue–derived C in the stabilization of small macroaggregates (250–2000 μm).
Arylamidase Activity of Soils
Authors: Acosta-Mart ı ´ nez V. , Tabatabai M. A.
Published: July 2010

The enzyme amino acid arylamidase [α‐aminoacyl‐peptide hydrolase (microsomal) EC 3.4.11.2] catalyzes the release of an N‐terminal amino acid from peptides, amides, or arylamides. Because of the presence of such substrates in soils, it is likely that this enzyme is involved in N mineralization. We report on the detection of the activity of this enzyme in soils and describe a precise and accurate method for its assay. This method involves colorimetric determination of the β‐naphthylamine produced when soil is incubated with L‐leucine β‐naphthylamide in 0.1MTHAM [tris(hydroxymethyl)aminomethane] buffer (pH 8.0) at 37°C for 1 h. The β‐naphthylamine that is produced is extracted with ethanol and converted into an azo compound by reacting withp‐dimethylaminocinnamaldehyde, and the absorbance of the color is measured at 540 nm. This enzyme has its optimal activity at pH 8.0 and is inactivated at temperatures above 60°C. Preheating soil samples for 2 h at temperatures ranging from 20 to 120°C before assay showed that this enzyme is stable up to 40°C in field‐moist soils and up to 60°C in air‐dried samples. TheKmvalues of arylamidase activity in seven surface soils ranged from 0.19 to 0.35 mMThe temperature response followed Arrhenius equation over the range from 20 to 50°C. The activation energy values ranged from 30.6 to 49.8 kJ mol−1for field‐moist soils and from 26.2 to 32.4 kJ mol−1for their air‐dried counterparts. The means of temperature coefficients (Q10) ranged fromSeveral compounds inhibited the activity of this enzyme in soils.
Organic Farming Challenge of Timing Nitrogen Availability to Crop Nitrogen Requirements
Authors: Pang X.P. , Letey J.
Published: July 2010

Groundwater has become increasingly degraded by NO3, and this degradation has been partially attributed to the use of commercial inorganic N fertilizers. Conversion from conventional fertilizer management to organic farming has been proposed as a means to reduce groundwater degradation. Matching soil inorganic N supply with crop N requirement on a temporal basis is important to achieve high yield and low water degradation. Dynamics of N mineralization from two manures and N‐uptake dynamics for two crops were derived from published data, and multi year simulations were done using the ENVIRON‐GRO computer model, which accounts for N and irrigation management effects on crop yield and N leaching. The temporal N‐mineralization and N‐uptake curves did not match well. The potential N uptake for corn (Zea mays L.) exceeded the cumulative mineralized N during a significant period that would cause reduced yield. Wheat (Triticum aestivum L.) has a low and flat N‐uptake peak, so that the cumulative mineralized N met N demand by wheat during the growing season. A crop with a very high maximum N‐uptake rate, such as corn, would be difficult to fertilize with only organic N to meet peak demands without excessive N in the soil before and after crop growth. In order to satisfy crop N demand, a large amount of manure, which would leave much N or subsequent leaching, must be applied. It took two or more years after conversion to organic sources of N to reach maximum yield because of carryover of unmineralized manure and accumulation of mineralized N after crop uptake which was not completely leached during the winter. High initial applications to build up the organic pool followed by reduced inputs in subsequent years would be appropriate.
Using Paper De‐inking Sludge to Maintain Soil Structural Form Field Measurements
Authors: Nemati M. R. , Caron J. , Gallichand J.
Published: July 2010

A high level of organic matter in soils is crucial to maintain structural stability but organic matter sources differ in their effectiveness in stabilizing structural units. Objectives of this study were, first, to determine the optimal rate of sludge and fertilizer application to improve soil physical properties, and second, to investigate a possible correlation between hydraulic conductivity and structural stability measurements. A 4‐yr field study (1994–1997) was conducted on three different soil types to evaluate the effect of different amounts of de‐inking secondary paper sludge on the soil physical properties. The soil physical properties we monitored were structural stability, water desorption characteristics, bulk density, and saturated hydraulic conductivity. Structural stability was increased by 17% in silty clay soil (SCS) and 15% in loamy soil (LS), but decreased by 35% in sandy loam soil (SLS). Results suggest that the effect of sludge application (SA) is short‐lived and that an annual application of sludge is necessary to obtain a year‐to‐year effect on structural stability. Measured bulk density dropped significantly in the SCS (4–10%) and in the LS (1–6%). A significant increase in air capacity and available water values revealed that SA increases both transmission and storage pores in the SCS. Field‐saturated hydraulic conductivity (Kfs) was increased in the SCS, but decreased in the SLS and the LS. A good correlation was observed between structural stability and hydraulic conductivity measurements in the SCS and the LS.
Triadimefon Interactions with Organoclays and Organohydrotalcites
Authors: Celis R. , Koskinen W.C. , Hermosı´n M.C. , Ulibarri M.A. , Cornejo J.
Published: July 2010

We determined the ability of several organoclays (octadecylammonium‐ and hexadecyltrimethylammonium‐exchanged montmorillonite) and organohydrotalcites (dodecylsulfate‐ and dodecylbenzenesulfonate‐exchanged hydrotalcite) to sorb the uncharged pesticide triadimefon [1‐(4‐chlorophenoxy)‐3,3‐dimethyl‐1‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone] to test the potential use of these sorbents for decontamination purposes and as slow release formulations of the pesticide. Interlayered organoclays and organohydrotalcites were at least six times more sorptive than the untreated minerals. Triadimefon sorption was higher on paraffin‐like sorbents (organohydrotalcites and organoclays prepared from high‐charge Arizona montmorillonite) than on bilayered sorbents (organoclays prepared from low‐charge Wyoming montmorillonite). The nature and amount of organic ion in the interlayer also influenced triadimefon desorption from the different sorbents. Desorption and spectroscopic studies suggested, in general, weak hydrophobic interactions between triadimefon and the interlayer organic phase of the organoclays and organohydrotalcites. However, hydrogen bonding between the carbonyl group of triadimefon and the monosubstituted amino group of octadecylammonium‐exchanged organoclays reinforced the strength of the interaction and resulted in reduced desorption from these sorbents. Selecting the interlayer ion appeared, therefore, as a good strategy to control the sorptivity and desorption of the sorbed pesticide for organoclays and organohydrotalcites. The results showed that organoclays and organohydrotalcites may find application as sorbents of pesticides similar to triadimefon.
Haying, tillage, and nitrogen fertilization influences on infiltration rates at a conservation reserve program site
Authors: Wienhold Brian J. , Tanaka Donald L.
Published: July 2010

Effect of haying (hayed or not hayed prior to tillage), tillage (no‐tillage, minimum tillage, or conventional tillage), and N fertilization (0 or 67 kg ha−1) on surface infiltration rates, Q(h), was evaluated for Conservation Research Program (CRP) site conversion. Soils included Amor loam (fine‐loamy, mixed, superactive, frigid Typic Haplustoll) and Cabba silt loam (loamy, mixed, superactive, calcareous, frigid, shallow Typic Ustorthent). In reference plots Q(h) increased from 1995 to 1997 (27.2 ± 3.2 vs. 36.4 ± 2.9 mm h−1 at 50‐mm tension, 10.9 ± 1.2 vs. 20.6 ± 1.4 mm h−1 at 100‐mm tension, and 4.1 ± 0.6 vs. 10.9 ± 1.1 mm h−1 at 150 mm‐tension) under permanent vegetation. Plots hayed prior to tillage exhibited higher Q(h) when no fertilizer was applied than plots hayed and fertilized or not hayed (31.9 ± 2.9 vs. 23.3 ± 1.3 mm h−1 at 50‐mm tension and 18.1 ± 1.3 vs. 13.5 ± 0.6 mm h−1 at 100‐mm tension). As tillage intensity increased, Q(h) at 50‐mm tension increased (20.1 ± 2.6 mm h−1 under no‐tillage, 25.5 ± 1.6 mm h−1 under minimum tillage, and 30.1 ± 2.0 mm h−1 under conventional tillage). Q(h) did not change from 1995 to 1997 in cropped plots.
Rheological Properties of Aqueous Suspensions of Palygorskite
Authors: Neaman Alexander , Singer Arieh
Published: July 2010

The rheology of aqueous suspensions of six palygorskites with different particle morphologies has been investigated as a function of clay concentration, adsorbed ion, pH, and electrolyte concentration, using a rotary viscometer. Rheological parameters (plastic viscosity, Bingham yield value, and apparent viscosity) increase with the length/width ratio of individual palygorskite fibers. The plastic viscosity increases linearly with clay concentration within the range investigated (up to 5% w/v). The rheological parameters are higher for clays saturated with divalent ions than those for clays saturated with monovalent ions. For ions of the same valency the rheological parameters tend to increase with decreasing radius of the hydrated ion. The flow of suspensions is pseudoplastic regardless of the nature of the adsorbed ion. Measurements of electrophoretic mobility in very dilute suspensions suggest that the point of zero charge of the palygorskite surface is at pH 4 to 4.5. Scanning electron microscopy indicates significant differences in fiber arrangement between low and high pH values. Face‐to‐face particle association occurs at low pH values, giving rise to close‐packed domains of fibers, while at high pH values the fibers adopt a random orientation. The flow of suspensions is pseudoplastic at pH ≤ 7 and changes to Newtonian at pH ≥ 9. At pH ≤ 7 the rheological parameters remain relatively constant even at high electrolyte concentrations, but at pH ≥ 9 they are influenced significantly by electrolyte addition. Electrolyte‐free palygorskite suspensions at pH 7 are antithixotropic. When the pH falls below 7 or when electrolyte is added, the suspensions coagulate and become thixotropic. Some rheological properties of palygorskite are similar to those of platy clay minerals such as kaolinite and montmorillonite, while other rheological properties deviate considerably. The models developed to explain the rheological behavior of platy clay minerals do not always account for the behavior of palygorskite, because of differences in particle morphology and surface structure.
Unstable Water Flow in a Layered Soil II. Effects of an Unstable Water‐Repellent Layer
Authors: Carrillo M. L. K. , Letey J. , Yates S. R.
Published: July 2010

Water repellent soils are found throughout the world and can exhibit significantly different water flow characteristics as compared to a wettable soil. The purpose of the study was to determine the significance of the stability of the water repellency on the development of unstable water flow below a water repellent layer. Unstable water‐repellent soil refers to a soil whose degree of repellency changes with time after contact with water. Experiments were conducted in a specially built rectangular chamber where wetting front patterns could be observed through a Plexiglas sheet. The experiments were done on water repellent sand layers that were treated to create water drop penetration time (WDPT) values of 1, 10, and 150 min. The WDPT of the layer and the ratio (ho + L)/hp were important in the development of fingers, where ho is the depth of ponded water at the soil surface, L is the depth of the water repellent layer and hp is the water entry pressure head of the water repellent layer. For low WDPT (1 min) no fingers formed. As the WDPT increased, the tendency for finger formation also increased. The medium WDPT (10 min) layer caused finger formation, however, the fingers broadened and converged after continued flow and an almost uniform wetting front eventually developed. The combination of a high WDPT (150 min) and (ho + L)/hp <1 produced the most dramatic and persistent fingering. The finger development across the layer and the flux through the layer was found to be a function of time. Water repellency at the soil surface has the greatest impact on infiltration because water depth may not be sufficient to overcome the water entry pressure and run‐off would decrease the time of exposure to water to overcome unstable water repellency.
Adsorption of Free Lead (Pb2+) by Pedogenic Oxides, Ferrihydrite, and Leaf Compost
Authors: Sauvé Sébastien , Mart ı ´ nez Carmen Enid , McBride Murray , Hendershot William
Published: July 2010

Iron oxides and organic matter have a high capacity to adsorb Pb and concomitantly maintain a low free Pb2+ activity in solution. It is, therefore, important to assess the adsorption capacity of naturally occurring materials and evaluate their potential to reduce toxicity. The free Pb2+ activity was measured in the solution in equilibrium with ferrihydrite (a synthetic Fe oxide), two field‐collected pedogenic amorphous oxides, and leaf compost. The experiment used a factorial design varying total Pb loading and solution pH. The results show that ferrihydrite was more efficient in lowering Pb aqueous concentration than the two pedogenic oxides. Furthermore, of the two pedogenic oxides examined, a higher Pb2+ activity was maintained in solution at equilibrium with the most crystalline phase, which also has a lower surface area relative to the other adsorbents. Leaf compost maintained a significantly higher free Pb2+ activity, relative to the various oxides. The experimental data could be fitted to a semi‐mechanistic model predicting free Pb2+ activity as a function of total Pb loadings and pH, with R2 varying from 0.77 to 0.92.
Rates of Microbially Mediated Arsenate Reduction and Solubilization
Authors: Jones C. A. , Langner H. W. , Anderson K. , McDermott T. R. , Inskeep W. P.
Published: July 2010

Reduction of arsenate [As(V)] to arsenite[As(III)] influences the mobility and toxicity of arsenic (As), yet the mechanisms controlling the rate of reduction in soils and natural waters are poorly understood. The goal of this study was to determine processes affecting reduction rates of both aqueous and sorbed phase As(V). Reduction experiments were conducted anaerobically in serum bottles with a range of glucose and As(V) concentrations. Serum bottles were inoculated with microorganisms extracted directly from an agricultural soil having naturally elevated concentrations of As (unenriched population), or with a pure culture isolate obtained from the same soil after enrichment for As(V) reduction. At As(V) concentrations ranging from 6 to 600 μM, the rate of As(V) reduction by the soil isolate was first order with respect to both As(V) concentration and microbial biomass. Reduction rates of As(V) with the soil isolate were 2 to10 fold greater than in the unenriched population, suggesting As(V) reducers represented only a subset of the unenriched population. Compiled data indicated that the pure culture isolate was fermenting glucose, and potentially reducing As(V) as a detoxification mechanism. In a parallel study, reduction rates of As(V) with the unenriched population were evaluated in the presence of goethite or ferrihydrite. When redox potential decreased from 500 to near 0 mV, aqueous As concentrations decreased by approximately 30% in a goethite suspension with a high As surface coverage, yet increased by seven fold in a goethite suspension with a low As surface coverage. In a ferrihydrite suspension, aqueous As concentrations during reduction increased approximately 100 fold faster than in a goethite suspension at similar initial aqueous As(V) concentrations, corresponding to differences in Fe oxide surface areas and reductive dissolution rates. The results indicate that rates of As mobilization during reduction in soils are highly dependent on oxide surface area and As surface coverage.
Flush of Carbon Dioxide Following Rewetting of Dried Soil Relates to Active Organic Pools
Authors: Franzluebbers A. J. , Haney R. L. , Honeycutt C. W. , Schomberg H. H. , Hons F. M.
Published: July 2010

Soil quality assessment could become more standardized with the development of a simple, rapid, and reliable method for quantifying potential soil biological activity. We evaluated the flush of CO2following rewetting of dried soil under standard laboratory conditions as a method to estimate an active organic matter fraction. The flush of CO2following rewetting of dried soil (3 d incubation at ≈50% water‐filled pore space and 25°C) was assessed for 20 soil series containing a wide range of organic C (20 ± 13 g kg−1) from Alberta–British Columbia, Maine, Texas, and Georgia. This flush of CO2explained 97% of the variability in cumulative C mineralization during, 86% of the variability in soil microbial biomass, and 67% of the variability in net N mineralization duringAccounting for geographical differences in mean annual temperature and precipitation, which could affect soil organic matter quality, further improved relationships between the flush of CO2and active, passive, and total C and N pools. Measuring the flush of CO2following rewetting of dried soil may have value for routine soil testing of biological soil quality because it (i) is an incubation procedure patterned after natural occurrences in most soils, (ii) exhibits strong overall relationships with active organic pools, (iii) shows relatively minor changes in relationships with active organic pools that may be due to climatic variables, (iv) has a simple setup with minimal equipment requirements, and (v) has rapid analysis time.
A Comparison of Strategies for Ameliorating Subsoil Acidity I. Long‐Term Growth Effects
Authors: Farina M. P. W. , Channon P. , Thibaud G. R.
Published: July 2010

Subsoil acidity is an important yield‐limiting factor. Mechanical procedures of deep lime incorporation and surface applications of gypsum have been shown to be beneficial, but no long‐term comparisons of these strategies have been published. Without such information it is difficult to make appropriate management decisions. The work reported here was conducted toward this end. In a long‐term study with maize (Zea mays L.) on a strongly acidic Plinthic Paleudult, conventional moldboard incorporation of lime (15 Mg ha−1) was compared with (i) deeper incorporation of the same quantity of lime with plowing and subsoiling operations, and (ii) treatments where large additional quantities of lime were similarly introduced below normal plow depth. The efficacy of gypsum was tested by adding 10 Mg ha−1 to conventionally limed plots. For 11 seasons, the average grain yield benefit ranged from 5 to 17% in the case of mechanical strategies and was 25% in the case of gypsum. Yields were increased only marginally by extra lime applications and segmental (slotted) amelioration proved inferior to deep‐plowing procedures. The gypsum treatment proved profitable only in the fourth season, but by the eighth season had proved more profitable than the best mechanical procedure; and by the 11th season, the gypsum treatment had resulted in a cumulative yield advantage of 3.8 Mg ha−1 Long‐term superiority of the gypsum treatment was unquestionable in this study, but gypsum is often unavailable and acidic soils are frequently unresponsive to gypsum. In such situations, deep plowing should not, as is often the case, be discarded as impractical.
A Comparison of Strategies for Ameliorating Subsoil Acidity II. Long‐Term Soil Effects
Authors: Farina M. P. W. , Channon P. , Thibaud G. R.
Published: July 2010

Acid‐subsoil amelioration is complicated by differences in the efficacy of lime and gypsum across the diverse soil environments in which the problem occurs. This study was conducted to explain long‐term growth responses to lime and gypsum on a Plinthic Paleudult of mixed clay mineralogy. In a 10‐season experiment that monitored treatment effects on profile chemical properties, we compared the effects of (i) incorporating 15 Mg ha−1 of lime to different depths, (ii) incorporating 25 Mg ha−1 of lime to about 0.5 m, and (iii) conventionally incorporating 15 Mg ha−1 of lime plus 10 Mg ha−1 of gypsum. Even at the highest application rate, lime had minimal effects on acidity below the depth of incorporation. Gypsum, however, markedly improved the rooting environment to a depth of 0.75 m. Sulfate sorption against extraction with dilute CaCl2 was accompanied by pHw increases of ≈0.4 units, by similar increases in ΔpH (pHw − pHs), by depressions in exchangeable acidity of as much as 1.5 cmolc L−1, and by decreases in acid saturation of more than 30%. The rate of subsoil amelioration was, however, much slower than that reported in more intensely weathered soils of similar texture. Only in the sixth season were benefits evident in the 0.60‐ to 0.75‐m horizon, and acidity in the 0.75‐ to 0.90‐m horizon actually increased significantly. It is speculated that this resulted from NO3 accumulation and ionic strength–induced dissolution of interlayer Al. These findings indicate that acid‐subsoil amelioration in soils with Al‐hydroxy–interlayer minerals requires greater quantities of gypsum than soils that are dominantly kaolinitic.
Preferential Flow and Pedotransfer Functions for Transport Properties in Sandy Kandiudults
Authors: Shaw J. N. , West L. T. , Radcliffe D. E. , Bosch D. D.
Published: July 2010

Soils with differences in argillic and kandic horizon clay content (12–28% clay), thickness of overlying sandy eluvial horizons (ranging from <0.50 to >1.0 m), and degree of structural development occur in upland Kandiudult soils in the Upper Coastal Plain of Georgia. Interest in agricultural site‐specific management necessitates more adequate characterization of solute transport properties between and within these soils. Undisturbed columns (15‐cm diam., ) were collected by horizon for three pedons typifying the extremes of the clay content in the argillic horizon. Breakthrough curves (BTCs) were conducted using a Br− tracer and were evaluated by fitting the single‐ and two‐region adaption of the convection–dispersion equation (CDE) to outflow measurements. Saturated hydraulic conductivity (Ks) measurements and methylene blue dye staining of conducting voids were also performed on the cores. Dye staining indicated differences in preferential flow occurred between surface (Ap), eluvial (E), and argillic and kandic (Bt) horizons. Retardation factors (R) were positively correlated with clay quantities, and horizons possessing relatively less clay (A and E horizons) possessed the highest α values (quickest solute exchange rates between mobile and immobile regions). Horizons with relatively higher clay quantities (Bts) had the lowest α and β (ratio of mobile water to the volumetric water content) values, but the highest effective dispersivity (λeff) values. Dye‐stained areas were correlated with β, which suggested β may be an approximation of the degree of preferential flow for these soils. For the three pedons studied, significant differences in α existed between the extremes, and thus they are interpreted to behave differently from a solute transport standpoint. Pedotransfer functions (PTFs) were developed for grossly estimating hydraulic and transport parameters.
Soil Structure and Organic Matter I. Distribution of Aggregate‐Size Classes and Aggregate‐Associated Carbon
Authors: Six J. , Paustian K. , Elliott E. T. , Combrink C.
Published: July 2010

Cultivation reduces soil C content and changes the distribution and stability of soil aggregates. We investigated the effect of cultivation intensity on aggregate distribution and aggregate C in three soils dominated by 2:1 clay mineralogy and one soil characterized by a mixed (2:1 and 1:1) mineralogy. Each site had native vegetation (NV), no‐tillage (NT), and conventional tillage (CT) treatments. Slaked (i.e., air‐dried and fast‐rewetted) and capillary rewetted soils were separated into four aggregate‐size classes (<53, 53–250, 250–2000, and >2000 μm) by wet sieving. In rewetted soils, the proportion of macroaggregates accounted for 85% of the dry soil weight and was similar across management treatments. In contrast, aggregate distribution from slaked soils increasingly shifted toward more microaggregates and fewer macroaggregates with increasing cultivation intensity. In soils dominated by 2:1 clay mineralogy, the C content of macroaggregates was 1.65 times greater compared to microaggregates. These observations support an aggregate hierarchy in which microaggregates are bound together into macroaggregates by organic binding agents in 2:1 clay‐dominated soils. In the soil with mixed mineralogy, aggregate C did not increase with increasing aggregate size. At all sites, rewetted macro‐ and microaggregate C and slaked microaggregate C differed in the order NV > NT > CT. In contrast, slaked macroaggregate C concentration was similar across management treatments, except in the soil with mixed clay mineralogy. We conclude that increasing cultivation intensity leads to a loss of C‐rich macroaggregates and an increase of C‐depleted microaggregates in soils that express aggregate hierarchy.
Soil Organic Matter Content as a Function of Different Land Use History
Authors: Pulleman M. M. , Bouma J. , van Essen E. A. , Meijles E. W.
Published: July 2010

A regional survey of management and crop type and soil organic matter (SOM) content was conducted in one soil series in the Netherlands (loamy, mixed, mesic, Fluventic Eutrudept). The objective was to determine the effects of land use history on SOM contents in a prime agricultural soil, using available soil survey information and statistical analyses. Soil organic matter content is a relatively stable, integrating soil characteristic that reflects long‐term land use and is an important indicator of soil quality. The SOM contents and information about past land use were obtained from 45 fields. Land use history was expressed in terms of (i) tillage; (ii) crop type; and (iii) use of chemical fertilizers, (iv) manure, and (v) biocides, for six successive periods (63–31, 31–15, 15–7, 7–3, 3–1, and 1–0 yr before sampling). Only four land use types occurred: conventional‐arable, conventional‐grass, organic‐arable, and organic‐grass. The SOM contents ranged between 17 and 88 g kg−1Regression models of the actual SOM content as a function of crop type and management in the different periods showed that SOM contents were increased under long‐term grass or, to a lesser extent, by organic farming, when compared with conventional‐arable use. The regression model depends on the nature of land use history in any particular region and on the length of the selected periods, but it provides an easy method to predict SOM content as a function of management in a given soil series. The method can be an alternative to simulation modeling in situations where detailed data records from long‐term field experiments are not available.
Irrigation with Effluent Water Effects of Rainfall Energy on Soil Infiltration
Authors: Mamedov A. I. , Shainberg I. , Levy G. J.
Published: July 2010

Seal formation at soil surfaces is significantly affected by raindrop kinetic energy (KE). We hypothesized that the deterioration in seal permeability of soils irrigated with effluents, relative to that of soils irrigated with fresh water (FW), is affected by raindrop KE. The effects of four droplet KE levels (3.6, 8.0, 12.4, and 15.9 kJ m−3) on the infiltration parameters of four Israeli smectitic soils that had been irrigated with FW or effluents, were studied with a drip‐type rain simulator. At the lowest KE (3.6 kJ m−3), final infiltration rate (IR) values for the FW‐irrigated samples were in the range of 9 to 14 mm h−1 and were significantly higher than the corresponding values for the effluent‐irrigated samples, suggesting that seals were not fully developed at this low KE and that the irrigation water type played a major role in determining soil permeability. At high KE (15.9 kJ m−3), the differences between the final IRs of FW‐irrigated and effluent‐irrigated samples of a given soil were small (<1.1 mm h−1), suggesting that at high KE, the effect of drop impact overshadowed the effects of water quality on the final IR. Rate of seal formation was faster in the effluent‐irrigated samples than in the FW‐irrigated ones, regardless of rain KE. The sensitivity of all four soils to the use of effluents was the greatest at a rain KE of 8 kJ m−3 At both lower and higher rain KE levels, the effect of effluents on the final IR, relative to that of FW, was less severe.
Cultivation Effects on Soil Carbon and Nitrogen Contents at Depth in the Russian Chernozem
Authors: Mikhailova E. A. , Bryant R. B. , Vassenev I. I. , Schwager S. J. , Post C. J.
Published: July 2010

Little is known about changes in soil organic C (SOC) and total N with depth and with land use. We conducted this study to determine the depth of changes in SOC and total N under different management regimes in the chernozem soil. Four sites were sampled: a native grassland field (not cultivated for at least 300 yr), an adjacent 50‐yr continuous‐fallow field, a yearly cut hay field in the V.V. Alekhin Central‐Chernozem Biosphere State Reserve in the Kursk region of Russia, and a continuously cropped field in the Experimental Station of the Kursk Institute of Agronomy and Soil Erosion Control. All sampled soils were classified as fine‐silty, mixed, frigid Pachic Hapludolls. Soil organic C, total N contents, and bulk densities with depth were compared. Significant reductions in SOC and total N concentrations were detected to a depth of 120 to 130 cm in the 50‐yr continuous‐fallow field and to a depth of 80 cm in the continuously cropped field. Highest reductions were observed in the top 10 cm of soil, where reduction in SOC ranged from 38 to 43% and reduction in total N ranged from 45 to 53%. Significant losses of SOC and total N per equivalent soil mass on an area basis were observed to a depth of 60 cm in the continuously cropped field and to a depth of 100 cm in the 50‐yr continuous‐fallow field.
The Effect of Slope Length on Sediment Concentrations Associated with Side‐Slope Erosion
Authors: Kinnell P. I. A.
Published: July 2010

Data from experiments where artificial rainfall was applied on side slopes associated with ridge‐tillage in the field and short inclined surfaces in the laboratory were analyzed with respect to the effect of rainfall intensity and slope length on sediment concentrations associated with the flows from the side slopes. In both the field and laboratory experiments, sediment concentrations associated with side‐slope erosion were linearly related to the intensity of the rain produced by the rainfall simulator over the range of slope length (150–600 mm) and gradient (5–30%) used in this study once the surface condition stabilized. In addition, sediment concentrations associated with flows from the side slopes were found to increase not only with slope gradient but also with slope length, particularly when side‐slope gradients exceed 10%. Increases in side‐slope erosion rate with slope length on these higher side‐slope gradients have, in the past, been associated with the development of small rills. However, increases in sediment concentrations with slope length also occurred on the higher slope gradients when rilling did not take place. In this latter case, the effect may be the result of a change from erosion dominated by raindrop detachment and raindrop‐induced flow transport (RD‐RIFT) to erosion dominated by RD and flow transport (RD‐FT).
Soil Aggregation and Glomalin under Pastures in the Southern Piedmont USA
Authors: Franzluebbers A. J. , Wright S. F. , Stuedemann J. A.
Published: July 2010

Soil aggregation is important for maintaining soil surface integrity and allowing water to infiltrate, rather than runoff and cause erosion. The effect of grazing animals on soil aggregation compared with other conservation management strategies in the Southern Piedmont USA is not well known. We tested a hypothesis that grazing animals might negatively affect soil aggregation characteristics. Water‐stable macroaggregates (>0.25 mm), mean‐weight diameter, and their stabilities were (i) similar between conservation‐tillage cropping and tall fescue (Festuca arundinacea Schreb.)–common bermudagrass (Cynodon dactylon L.) pasture; (ii) similar between 15‐ to 19‐yr‐old grazed and hayed hybrid bermudagrass; (iii) 7 to 14% greater in 30‐yr‐old than in 10‐yr‐old grazed tall fescue and hybrid bermudagrass pastures; (iv) similar among long‐term grazingland, hayland, and forestland; and (v) 5 to 11% lower under cattle grazing than under monthly haying or unharvested management during the first 4 yr following conversion of cultivated cropland to pastureland. Water‐stable aggregate distribution at a depth of 0 to 50 mm was 0.30 ± 0.07 g g−1 in the 1.0‐ to 4.75‐mm class, 0.46 ± 0.07 g g−1 in the 0.25‐ to 1.0‐mm class, 0.15 ± 0.02 g g−1 in the 0.05‐ to 0.25‐mm class, and 0.07 ± 0.01 g g−1 in the <0.05‐mm class, averaged across management systems and replications Total glomalin of the 1.0‐ to 4.75‐mm dry‐stable aggregate class was highly related to whole soil organic C content, but neither of these properties was particularly well related with water‐stable macroaggregation, mean‐weight diameter, or their stabilities. We conclude, overall, that grazing of pastures in the Southern Piedmont USA has little detrimental effect on soil aggregate distribution and stability and is comparable in soil conservation with other land conservation strategies.
Predicting Soil Albedo from Soil Color and Spectral Reflectance Data
Authors: Post D. F. , Fimbres A. , Matthias A. D. , Sano E. E. , Accioly L. , Batchily A. K. , Ferreira L.G.
Published: July 2010

The albedo of earth surface features, such as soil, is an important component of models that define land‐surface meteorological processes. If land surfaces have no vegetative cover, soil properties determine the amount of solar radiation absorbed or reflected. We evaluated the influence of two soil properties, soil color and soil moisture, on soil albedo. Two soil moisture conditions were studied, air dry and wet, defined as the condition when the water films are absorbed by the soil and no water glistens on the soil surface. The albedos for 26 U.S. soils were measured with an Eppley pyranometer, which integrates radiant energy in wavelengths between 0.3 to 2.8 μm. Soil colors were measured with a Minolta Chroma Meter and spectral reflectance curves from 0.45 to 0.9 μm (measured in 0.1‐μm increments) were determined with a multispectral radiometer. All measurements were made on <2‐mm smooth soil surfaces, and the dry and wet data were combined for statistical analyses. Soil albedos were significantly correlated with Munsell soil color value , blue , green , red , near infrared (NIR), , and sum of the four bands ; however, the slopes and intercepts for these relationships were different. The 52 spectral curves yielded nine cluster groups, which mostly related to the Munsell soil color value and soil albedo soil characteristics. The 0.3‐ to 2.8‐μm albedos of smoothed soils can be accurately estimated using the regression relationship: soil albedo (0.3–2.8 μm) = 0.069 (color value) − 0.114. Using the regression equations presented here, spectral reflectance data in selected visible and NIR bands can also be used to predict albedo.
Direct‐Diffusion Methods for Inorganic‐Nitrogen Analysis of Soil
Authors: Khan S. A. , Mulvaney R. L. , Hoeft R. G.
Published: July 2010

Determinations of exchangeable NH4, NO3, and NO2in soil normally require the preparation of an extract, which is usually obtained with a neutral salt solution such as 2MKCl. In cases where analytical speed and convenience are key factors, as in routine soil testing, a more practical approach would be to carry out the determination directly on the soil sample itself. Studies were conducted to ascertain whether this approach could be employed using Mason‐jar diffusion methods previously developed for inorganic‐N analysis of soil extracts. Direct diffusions were performed with MgO to recover NH4–N, or with MgO and Devarda's alloy to recover (NH4+ NO3+ NO2)–N, from 1‐ to 5‐g samples of a wide variety of air‐dried soils, following treatment of the soil with sufficient 2MKCl to give a 1:10 ratio of soil to solution. Up to 4 mg of inorganic N was recovered quantitatively in 18 h to 6 d at room temperature, or in 1.75 to 5.5 h with gentle heating on a hot plate (45–50°C). Analyses by direct diffusion were in close agreementwith results obtained by diffusion of soil extracts, and recoveries ranged from 97 to 102% when direct diffusions were performed on samples that had been treated with NH4–N or NO3–N. Besides being quantitative, direct diffusions were found to have potential for N‐isotope analysis. In diffusing15N‐treated samples, isotope‐ratio analyses of NH4–N or (NH4+ NO3+ NO2)–N were accurate to within 3%. The latter finding virtually precludes interference by labile organic N or nonexchangeable NH4–N; however, interference did lead to an increase in inorganic‐N analyses when diffusion was prolonged beyond the recommended period.
Estimation of the Total Amorphous Content of Hawai'i Soils by the Rietveld Method
Authors: Jones R. C. , Babcock C. J. , Knowlton W. B.
Published: July 2010

The crystalline and amorphous phases of the clay fraction of 10 agriculturally important Hawaiian surface soils were analyzed by x‐ray diffraction (XRD) and the Rietveld method. The clay fraction of these soils was also analyzed by x‐ray fluorescence (XRF). A balance sheet method was used to assign the oxide content of the clays to the crystalline phases. The remaining oxides after the crystalline phases were accounted for served as an estimate of the chemical composition of the amorphous fraction. Amorphous phase mass fractions ranged from 0.28 to 0.77. Loss of weight on ignition (LOI) was found to be an important constituent of the amorphous fraction. Acid ammonium oxalate extractions were compared with the results of the Rietveld method. Because of the differences between the results of the two methods, it was apparent that they were determining different fractions of the amorphous material. The Rietveld method determines the total amorphous content of a sample, whereas oxalate extraction determines what we refer to as the chemically active portion of the amorphous fraction. The influence of the amorphous fraction on a soil's chemical and physical properties has remained speculative because the determination of the actual percentage of the total noncrystalline component was not possible by past analytical procedures. Furthermore, because the amorphous component is not considered in the Rietveld computation of the mass fraction breakout of the crystalline phases, estimates of the actual crystalline phases' mass fractions cannot be made without a reliable estimate of the total amorphous content.