bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerobic and Anaerobic Transformations of Pentachlorophenol in Wetland Soils
Authors: D'Angelo Elisa M. , Reddy K. R.
Published: July 2010

Strategies to enhance biotransformation of pentachlorophenol (PCP) in a spectrum of wetland soils were investigated under laboratory conditions, which included manipulations of electron acceptors and donors, and PCP concentrations. Maximum transformation rates were found at PCP concentrations <10 μM (methanogenic conditions) and >6 μM to >23 μM (aerobic conditions). Differences in PCP toxicity and sorption among soils and treatments were largely governed by the activities of microbial groups. Within this concentration range, transformation was observed in soils under aerobic and methanogenic conditions, but was inhibited under denitrifying and SO2−4–reducing conditions. Aerobic PCP transformation initially produced small amounts of pentachloroanisole (PCA). However >75% of both chemicals disappeared in 30 d from five soils. Measured soil properties were not significantly correlated to aerobic transformation rates. Under methanogenic conditions, PCP was reductively dechlorinated to yield a mixture of tetra‐, tri‐, and dichlorophenols in eight soils, with rates strongly correlated to measures of electron donor supply (total C, N, organic C mineralization rates) and microbial biomass. Addition of protein‐based electron donors enhanced reductive dechlorination in a soil low in organic matter and microbial biomass. Results demonstrated the widespread occurrence of PCP transforming microorganisms in soils, which may be promoted by manipulating environmental conditions.
Soil Carbon Changes Comparing Flux Monitoring and Mass Balance in a Box Lysimeter Experiment
Authors: Nay S. M. , Bormann B. T.
Published: July 2010

Direct measures of soil‐surface respiration are needed to evaluate belowground biological processes, forest productivity, and ecosystem responses to global change. Although infra‐red gas analyzer (IRGA) methods track reference CO2flows in lab studies, questions remain for extrapolating IRGA methods to field conditions. We constructed 10 box lysimeters with homogenized mixtures of sandy loam and cattle manure and kept them free of plants to create a range of CO2fluxes. Infra‐red gas analyzer measurements, applied biweekly, were then compared to mass balance–based measures of changes in soil C over 8 mo. The CO2fluxes measured with IRGA were not significantly different (P< 0.05) from the mass balance measure in 9 of the 10 boxes. The only statistically significant difference was in the lysimeter with the highest initial C content; this box had elevated soil temperatures early in the trial, suggesting a composting effect that may have interfered with IRGA measures. Variations in the mass balance estimates were higher than expected, demonstrating how difficult establishing a true reference in field studies is. We conclude that fluxes of CO2from soils can be monitored with an IRGA‐based chamber system in the field to produce reliable estimates of cumulative C loss. Such field measures will likely be much more variable than laboratory measures, however, and thus will require extensive sampling.
Mechanism of Calcium and Phosphate Release from Hydroxy‐Apatite by Mycorrhizal Hyphae
Authors: Ness Ricardo L.Lange , Vlek Paul L.G.
Published: July 2010

The role of vesicular‐arbuscular mycorrhiza (VAM) in facilitating the uptake of sparingly soluble nutrients from the soil has been well documented. Uncertainty remains regarding the mechanism controlling the dissolution of tightly bound P such as in phosphate rock. We studied the differential Ca and P uptake by the external mycelium of VAM in maize (Zea mays L.) grown in an acid tropical soil supplied with hydroxy‐apatite (HA). Three experiments were conducted in modified double‐pot systems where Ca was adequately provided through a nutrient solution and P in the form of apatite through a compartment only accessible to the hyphae. The results showed that in this system: (i) plant uptake of the apatite P occured only with VAM formation, (ii) the P release from the apatite was accompanied by a stochiometrically equivalent buildup of exchangeable Ca in the hyphal compartment, and (iii) the released apatite P was quantitatively recovered by the maize . It appears that the hyphae drove the apatite dissolution by mass action through the selective absorption of P, thereby overcoming the counter‐ion effect due to the Ca accumulation in the soil.
Cattle Manure Amendments Can Increase the pH of Acid Soils
Authors: Whalen Joann K. , Chang Chi , Clayton George W. , Carefoot Janna P.
Published: July 2010

Crop production on acid soils can be improved greatly by adjusting the pH to near neutrality. While soil acidity is commonly corrected by liming, there is evidence that animal manure amendments can increase the pH of acid soils. The effect of fresh cattle manure on soil acidity and nutrient availability was determined in the laboratory for two acid soils from Beaverlodge and Fort Vermillion in the Peace River region of Alberta, Canada. The effect of manure on soil pH was immediate and persisted during an 8‐wk incubation. Manure‐amended soil had significantly higher pH than unamended soil, and the highest rate (40 g manure kg−1, dry weight basis) increased the pH of Beaverlodge and Fort Vermillion soils from 4.8 to 6.0 and 5.5 to 6.3, respectively. The higher pH in manure‐amended than unamended soils was attributed to buffering from bicarbonates and organic acids in cattle manure. Mineral N (NH4–N + NO3–N), available P, K, Ca, and Mg increased immediately after manure application, and available P and K remained significantly higher in manure‐amended than unamended soil after the 8‐wk incubation. Soils amended with 40 g manure kg−1 had three to four times more plant‐available P and K than unamended soils after incubation. Available S concentrations did not differ significantly in manure‐amended and unamended soils. Extractable Al and Fe declined slightly after manure application, but did not differ in manure‐amended or unamended soils after incubation. No change in the cation‐exchange capacity (CEC) of manure‐amended soils compared to unamended soils was observed in this study, and it appears that appreciable changes in Al, Fe, and CEC from manure application do not occur in the short‐term (weeks). Our results indicate that, in the short‐term, cattle manure amendments can increase the pH and the quantity of plant‐available P and K in acid soils.
Timing Effects of Deep Tillage on Penetration Resistance and Wheat and Soybean Yield
Authors: Busscher W. J. , Frederick J. R. , Bauer P. J.
Published: July 2010

In many southeastern Coastal Plain soils, subsoil pans have strengths that restrict root growth. To reduce strengths, soils are deep tilled annually, and perhaps biannually for double cropping. We evaluated the effect of deep tillage in fall, in spring, or at both times on strength of a Goldsboro loamy sand (fine loamy, siliceous, thermic Aquic Kandiudult) and on the yield of wheat (Triticum aestivum L.) and drilled soybean [Glycine max (L.) Merr.] in a double‐cropped system. Treatments consisted of all combinations of surface tillage (disked and not disked) and deep tillage (no deep tillage, paratillage before wheat planting, before soybean planting, and before both) in four replicates. Soil strengths, measured as cone indices, showed that disked, non‐deep‐tilled treatments resulted in a pan at the 20‐ to 30‐cm depth, generally associated with an E horizon. In more recently and more frequently deep‐tilled treatments, mean profile cone indices were 0.31 to 0.36 MPa lower than treatments not deep tilled or deep tilled for the previous growing season. If soil was deep tilled only once a year, it was 0.26 MPa softer when tilled only in spring than when tilled only in fall. Deep tillage at the beginning of either season reduced soil cone indices and improved wheat and soybean yields over other treatments. Deep tillage at the beginning of both seasons maintained the softest soil. For every megapascal decrease in mean profile cone index, wheat yields increased 1.5 to 1.7 Mg ha−1 and soybean yields increased 1.1 to 1.8 Mg ha−1
Unimodal and Bimodal Descriptions of Hydraulic Properties for Aggregated Soils
Authors: Coppola Antonio
Published: July 2010

This study was conducted to investigate the capability of bimodal approaches in describing water retention data and predicting hydraulic conductivity of 18 samples from an aggregated soil. In this soil, discontinuity in the shape of the water retention curve was encountered and explained by independent draining of the inter‐ and of intraaggregate pores. A single van Genuchten‐type retention curve was unable to describe the observed transition between the pore systems, especially near saturation. Such behavior occurred both when optimizing (VGopt) and when fixing at the measured value (VGfix) the volumetric water content at saturation, θs Because of the predominant effect of the shape of the retention curve near saturation upon the shape of the whole hydraulic conductivity curve, predictions of hydraulic conductivity often differed from unsaturated conductivity observations by even two orders of magnitude. To the contrary, excellent descriptions of retention data were observed when superposition of two unimodal retention curves was adopted. The first function was either a van Genuchten (VGbim) or a simple one‐parameter formulation introduced by Ross and Smettem (RSbim) for describing macroporosity, while the second was in both cases a van Genuchten formulation. The agreement was especially good for higher water content values, leading to values of the coefficient of determination, R2, very close to unity. The laboratory‐measured unsaturated conductivity values compared more closely when bimodal approaches were used, and the predictions were frequently well within one order of magnitude of the measurements.
Decrease in Humification of Organic Matter with Intensified Lowland Rice Cropping A Wet Chemical and Spectroscopic Investigation
Authors: Olk D. C. , Brunetti G. , Senesi N.
Published: July 2010

To address recent concerns of impaired nutrient cycling in intensively cropped lowland rice soils of tropical Asia, we have been investigating the effects of continuous rice cropping on the chemical nature of soil organic matter (SOM). In this study, the labile mobile humic acid (MHA) fraction and the more recalcitrant calcium humate (CaHA) fraction were extracted from soils of four long‐term field trials on the International Rice Research Institute (IRRI) farm, which varied in the number of annual irrigated rice crops and hence degree of soil submergence. The two humic acid (HA) fractions were analyzed by Fourier‐transform infrared, fluorescence, and electron spin resonance spectroscopies for elemental composition and acidic functional groups. With increasing soil submergence, the HA fractions became less oxidized or humified, with higher S and H and lower O concentrations, more amide or amino, hydroxyl, and methoxy groups, and fewer carboxyl groups and organic free radicals. The HA extracted from submerged soils appeared to have greater capacity for complexing Cu+2, Fe+3, and VO+2than did HA from aerated soils. Fertilizer treatments had little effect on HA chemical structure. The MHA was less humified than the CaHA, having fewer acidic functional groups, smaller C:N and C:H ratios, richer concentrations of amides and carbohydrates, lower concentrations of COOH, higher fluorescence intensity, and shorter wavelength of fluorescence emission maximum, and lower concentration of organic free radicals. Free radical concentrations for both HA fractions were highly correlated with other indices of humification reported here and elsewhere.
Modeling nutrient uptake using a moving boundary approach Comparison with the barber‐cushman model
Authors: Reginato Juan C. , Palumbo María C. , Moreno Inés S. , Bernardo Isabel Ch. , Tarzia Domingo A.
Published: July 2010

Single nutrient uptake by a growing root system is often estimated by the Barber‐Cushman model. The model solves the coupled equations of transport in the soil and absorption of nutrient by roots in fixed domains. This study was conducted to determine whether a moving boundary model that accounts for increasing root competition could improve predictions of nutrient uptake. Our model includes assumptions of the Barber‐Cushman model and the moving boundary approximation. The model predicts nutrient uptake by coupling nutrient flux to roots and nutrient absorption on a variable domain in time. The model output was compared with measured uptake of Mg, K, P, and S by various crops and soils using experimental data obtained from the literature. Predicted Mg, K, and P uptake by pine seedlings was close to that observed for K and P, although for Mg the predicted uptake showed deviations similar to those of the Barber‐Cushman model. Sulfur uptake by wheat in different soils was better predicted by the moving boundary model in at least 10 out of 18 measured cases. The model prediction was also compared with measured K uptake by three maize hybrids grown on typic Hapludult of Rı́o Cuarto, Argentina, in a growth chamber. The moving boundary model appears to provide a better description of coupling between transport, absorption of nutrient, and root growth than the Barber‐Cushman model, and it improves the prediction for nutrient uptake in some tests.
Lateral Podzolization in a Granite Landscape
Authors: Sommer M. , Halm D. , Weller U. , Zarei M. , Stahr K.
Published: July 2010

Analysis of soil pattern, especially the pattern of depletion and accumulation zones, is a powerful tool to decipher pedogenic processes at the landscape scale. To clarify the pedogenesis of a distinct pattern of podzolized soils in the cool, perhumid Black Forest (Germany) we performed a study in the forested upper part of a granitic catchment (B a ¨ rhalde). From detailed soil mapping we selected a typical catena of four pedons, which were analyzed for physical (bulk densities and particle‐size distribution), chemical (pH, organic C, pyrophosphate, oxalate, dithionite, and total Al, Mn, Fe), and mineralogical (clay minerals) properties. Standard mass balance calculations were modified to include a two‐component system with regard to parent material. Results showed a shift from two‐mica granite to granite–porphyry downslope. Soil pattern revealed podzolized soils with thick E horizons and thin spodic horizons developed in the upslope areas, whereas in downslope soils the reverse was found (thick spodic B and thin E horizons). Soil chemical and mineralogical properties were linked to soil morphology in that contents of organic C, pedogenic oxides, hydroxy‐interlayered vermiculites (HIV), and pH increased from eluvial to illuvial horizons as well as from up‐ to downslope soils. Mass balances of Fe and Al showed negative fluxes in upslope soils and positive fluxes in downslope soils during pedogenesis. We concluded from these results that a catenary eluvial–illuvial sequence (lateral podzolization) develops as a result of upslope mobilization followed by a (partially) lateral transport and subsequent immobilization in downslope zones, probably because the base‐richer parent material built up a geochemical barrier.
Rhizobia Inoculation Improves Nutrient Uptake and Growth of Lowland Rice
Authors: Biswas J.C. , Ladha J.K. , Dazzo F.B.
Published: July 2010

Growth‐promoting diazotrophs can enhance the growth and development of associated crops by transferring fixed N or by improving nutrient uptake through modulation of hormone‐linked phenomena in inoculated plants. Six rhizobial diazotrophs isolated from a wide range of legume hosts were investigated to determine their growth‐promoting activities in lowland rice (Oryza sativa L.) during 1997. Seeds and seedlings of rice Pankaj were inoculated with different rhizobia and grown in potted soil supplemented with varied amounts of mineral N. Inoculation with Rhizobium leguminosarum bv. trifolii E11, Rhizobium sp. IRBG74, and Bradyrhizobium sp. IRBG271 increased rice grain and straw yields by 8 to 22 and 4 to 19%, respectively, at different N rates. Nitrogen, P, and K uptake were increased by 10 to 28% due to rhizobial inoculation. Nitrogen‐15‐based studies indicated that the increased N uptake was not due to biological N2 fixation (BNF). Inoculation also increased Fe uptake in rice by 15 to 64%. Indole‐3‐acetic acid (IAA) accumulated in the external root environment of rice plants when grown gnotobiotically with rhizobia. The results indicate that certain strains of rhizobia can promote rice growth and yield, most likely through mechanisms that involve changes in growth physiology or root morphology rather than BNF.
Predicting Depressional Storage from Soil Surface Roughness
Authors: Kamphorst E. C. , Jetten V. , Guérif J. , Pitk a ¨ nen J. , Iversen B. V. , Douglas J. T. , Paz A.
Published: July 2010

Runoff may be reduced by temporal water storage in depressions at the soil surface. Depressional storage is difficult to measure and is usually estimated from some roughness index. The objective of this study was to compare the ability of selected roughness indices to describe maximum depressional storage (MDS). Height measurements were taken on 221 tilled soil surfaces across a range of roughnesses. Maximum depressional storage was determined from digital elevation models (DEMs). The MDS values ranged from 0 to 13 mm. Five roughness indices were calculated from transects across these DEMs: random roughness (RR), tortuosity (T), limiting elevation difference (LD) and slope (LS), and mean upslope depression (MUD). Regression analysis of MDS on each of five roughness indices showed that RR best described depressional storage Prediction of MDS in the field based on RR has an uncertainty of ± 3 mm (95% confidence interval). Variation was due to RR and its nonspatial nature. To improve predictions of MDS, the spatial configuration of the surface has to be taken into account.
Polyacrylamide Molecular Weight and Charge Effects on Infiltration under Simulated Rainfall
Authors: Green V. Steven , Stott D. E. , Norton L. D. , Graveel J. G.
Published: July 2010

Soil sealing is a severe problem worldwide. Increased runoff and decreased seedling emergence cause on‐ and off‐site problems affecting farmers and communities. One possible soil sealing control measure is the application of polyacrylamide (PAM). Little is known about the interaction of specific PAMs with soils of differing characteristics. This study was conducted to examine the relationship between different PAMs and soils of varying characteristics. We examined PAM charge densities (CD) of 20, 30, and 40% hydrolysis with molecular weights (MW) of 6, 12, and 18 Mg mol−1 The soils used were Heiden clay (fine, smectitic, thermic Udic Haplustert), Cecil sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult), and Fincastle silt loam (fine‐silty, mixed, mesic Aeric Epiaqualf). Polyacrylamide (20 kg ha−1) was sprayed onto the soil in liquid form. Soil material was exposed to rainfall simulation in the laboratory. Infiltration rate was used as an indicator of soil surface sealing. Polyacrylamide increased infiltration rates on all three soils relative to the control. Twenty and 30% CD PAMs performed best in maintaining high infiltration rates on Heiden clay. The 12 Mg mol−1 MW formulations worked best for Cecil sandy loam. Fincastle silt loam showed no preference for a particular PAM formulation. Polyacrylamide increased final infiltration rate by as much as 3‐ to 5‐fold for these soils. Different PAM formulations provided differing degrees of soil protection, varying between soils. Understanding the interaction of different soils with various PAM formulations will enable PAM users to select the best PAM product for their soil conditions.
Calcium Depletion in a Southeastern United States Forest Ecosystem
Authors: Huntington T. G. , Hooper R. P. , Johnson C. E. , Aulenbach B. T. , Cappellato R. , Blum A. E.
Published: July 2010

Forest soil Ca depletion through leaching and vegetation uptake may threaten long‐term sustainability of forest productivity in the southeastern USA. This study was conducted to assess Ca pools and fluxes in a representative southern Piedmont forest to determine the soil Ca depletion rate. Soil Ca storage, Ca inputs in atmospheric deposition, and outputs in soil leaching and vegetation uptake were investigated at the Panola Mountain Research Watershed (PMRW) near Atlanta, GA. Average annual outputs of 12.3 kg ha−1yr−1in uptake into merchantable wood and 2.71 kg ha−1yr−1soil leaching exceeded inputs in atmospheric deposition of 2.24 kg ha−1yr−1The annual rate of Ca uptake into merchantable wood exceeds soil leaching losses by a factor of more than five. The potential for primary mineral weathering to provide a substantial amount of Ca inputs is low. Estimates of Ca replenishment through mineral weathering in the surface 1 m of soil and saprolite was estimated to be 0.12 kg ha−1yr−1The weathering rate in saprolite and partially weathered bedrock below the surface 1 m is similarly quite low because mineral Ca is largely depleted. The soil Ca depletion rate at PMRW is estimated to be 12.7 kg ha−1yr−1At PMRW and similar hardwood‐dominated forests in the Piedmont physiographic province, Ca depletion will probably reduce soil reserves to less than the requirement for a merchantable forest stand in ≈80 yr. This assessment and comparable analyses at other southeastern USA forest sites suggests that there is a strong potential for a regional problem in forest nutrition in the long term.
Nitrogen Fertilizer Movement in the Soil as Influenced by Nitrogen Rate and Timing in Irrigated Wheat
Authors: Ottman Michael J. , Pope Nancey V.
Published: July 2010

Nitrogen fertilizer is a potential contaminant of groundwater supplies. The purpose of this study was to determine the influence of recommended N fertilizer rate and timing on N movement in the soil during the growing season. Durum wheat [Triticum turgidumL. subsp.durum(Desf.) Husn.] was grown at Maricopa, AZ, during the 1991 and 1992 growing seasons. A N rate study was conducted at two sites on a sandy loam soil [coarse loamy, mixed (calcareous), hyperthermic, Typic Natrargid (reclaimed)] and clay loam soil [fine loamy, mixed (calcareous), hyperthermic, Typic Torrifluvent] using15N‐labeled (NH4)2SO4and Br−tracer. Three N rates that ranged from 5.4 to 10.1 g N m−2for the less than recommended rate, 18.5 to 22.5 g N m−2for the recommended rate and 28.0 to 37.8 g N m−2for the greater than recommended rate were applied in split applications. The experimental design was a randomized complete block with six replications and three N rates. A N timing study was conducted on the sandy loam soil at the recommended N rate where15N and Br−were applied at only one of the application times and nonlabeled N fertilizer was applied at the other times. The experimental design for the N timing study was a randomized complete block with six replications and four (1992) or five (1991) application times. Surface flood irrigation was applied in excess of soil water depletion (top 1.5 m), varying with year, soil type, and N rate. After harvest, the soil was sampled to a depth of 2.4 m and analyzed for15N and Br−Nitrogen rate had no influence on15N fertilizer or Br−movement in the soil. Nitrogen rate increased the N content of the surface soil, but most of this N was not in NO3form. In most cases, the median depth of movement of recovered15N for all N rates was 0.23 m compared to 1.13 m for Br−Timing of applications did not influence N fertilizer movement. Bromide overestimated the depth of15N movement recovered in the soil possibly due to plant uptake and immobilization of N in the surface soil. We found that for irrigated wheat in Arizona, most of the N fertilizer recovered in the top 2.4 m of soil was in the surface soil, regardless of N fertilizer practices.
Propensity of Soils to Develop Redoximorphic Color Changes
Authors: Rabenhorst M. C. , Parikh S.
Published: July 2010

Most soils with seasonally high water tables exhibit redoximorphic features, such as Fe depletions and concentrations. Some soils formed from red parent materials apparently are less typical in their behavior and have in this sense been described as problematic. Regulatory guidelines have mentioned such problematic red soils, and the Field Indicators of Hydric Soils in the United States attempts to address the issue by using test indicator TF2. This study was undertaken in an attempt to develop an approach for quantifying the inherent tendency of soils to form redoximorphic features under reducing conditions. Thirty soils from diverse parent materials in the Mid‐Atlantic region was studied, including 13 thought to be problematic soils formed from red parent materials. Samples were treated using a citrate‐buffer and Na dithionite at room temperature (25°C) for periods of time ranging from 0.5 to 72 h, and also at 80°C for 4 h. Colors were measured using a digital colorimeter to document changes in Munsell hue, value, and chroma. By comparing initial soil colors with those measured under the treatments of 25°C for 1 h and at 80°C for 4 h, a color change propensity index (CCPI) was developed that effectively discriminated between soils which were and were not thought to be problematic. The utility of the CCPI was tested using 14 additional soil samples, six of which came from outside the Mid‐Atlantic region. Recommendations are made to differentiate between problematic and nonproblematic soils based on values of CCPI.
Using Surface Crack Spacing to Predict Crack Network Geometry in Swelling Soils
Authors: Chertkov V. Y.
Published: July 2010

Prediction of the geometrical characteristics of steady crack networks in swelling soils is possible using a previously published model based on concepts of multiple cracking and fragmentation. Applications of the model require estimation of the model parameters: the thickness of the upper intensive‐cracking layer, zo, and maximum depth of the cracks, zm A technique of such an estimation is proposed based on the correlation of these parameters with the mean spacing between the shrinkage cracks at the soil surface. The data from three previously published papers are used for validation of the correlation. The data are related to 10 different soil profiles and different geographical areas. Estimates of standard deviations of comparable values show their overlap within the limits of measurement errors.
Soil Physical Properties and Moisture Content Affected by Site Preparation in the Afforestation of a Semiarid Rangeland
Authors: Querejeta José Ignacio , Rolda´n Antonio , Albaladejo Juan , Castillo Vı´ctor
Published: July 2010

Revegetation of arid regions is primarily water‐limited. To test the impact of several afforestation site preparation methods on the physical properties and the moisture content of the soil, a factorial experiment was conducted in a degraded semiarid rangeland of southeastern Spain. The land preparation treatments evaluated were terracing (mechanical or manual) and organic amendment (with or without urban solid refuse, USR). Terracing negatively affected some of the physical characteristics of the surface soil, such as the proportion of stable aggregates (21–33% decrease). Mechanical terracing increased soil water storage up to 40% more than manual terracing. The addition of USR counteracted many of the negative effects of terracing on soil physical properties and significantly increased soil moisture, particularly in the mechanical terraces (up to 40% increase compared with the nonamended treatment). The beneficial effects of the organic amendment on soil water content in the mechanical terraces persisted 4 yr after the single addition of the USR. The combination of mechanical terracing and USR addition significantly enhanced soil water availability, which is the most likely factor for the enhanced plant survival and growth seen in this study.
Nonsingularity of Naphthalene Sorption in Soil
Authors: Gamst Jesper , Olesen Torben , De Jonge Hubert , Moldrup Per , Rolston Dennis E.
Published: July 2010

Realistic models for transport of organic chemicals in soil require accurate predictions of the adsorption‐desorption kinetics. In this study, a physically based two‐compartment one‐rate (TCOR) sorption model was evaluated by comparison of model simulations to measured adsorption‐desorption isotherms of naphthalene (C10H8) for five different soils on a short‐term (48 h) and a longer‐term (504 h) time scale. Two soils exhibited minor adsorption‐desorption nonsingularity (labeled Type I soils), two soils pronounced nonsingularity (Type II soils), and the fifth soil pronounced nonsingularity only on the longer‐term time scale (Type I/II soil). The TCOR sorption model fitted, measured adsorption‐desorption isotherms well on both short‐term and longer‐term time scales. However, the TCOR sorption model parameters varied for each soil between short‐term and longer‐term data, especially for Type II soils. The uniqueness of the TCOR model fit was tested by varying the number of desorption data used, resulting in markedly changed parameter values. The TCOR sorption model was evaluated by using model parameters obtained from short‐term data to predict longer‐term sorption results. The TCOR prediction of adsorption‐desorption behavior was good for Type I soils, satisfactory for the Type I/II soil, and poor for Type II soils. Model parameters obtained from short‐term and longer‐term experiments were used to predict independently measured adsorption kinetics, showing decreasing prediction accuracy with increasing sorption nonsingularity. The results imply that the TCOR sorption model description of the diffusion process at the grain scale is oversimplified, and that sorption nonsingularity is not well explained by kinetic factors alone.
Soil Water Characteristic Determination from Concurrent Water Content Measurements in Reference Porous Media
Authors: Wraith Jon M. , Or Dani
Published: July 2010

We introduce and verify the use of calibrated reference soils or other porous media having known and reproducible water retention characteristics as a means to determine the unknown water retention properties of soils in situ. Pockets of the reference soil may be buried at experimental soil locations, with embedded time domain reflectometry (TDR) probes in both the target and adjacent reference media. Monitoring changes in water content by TDR allows inference of the soil water characteristic (SWC) properties of surrounding soil in hydraulic equilibrium via the known reference media SWC relationship. An expression relating the van Genuchten retention coefficients of any two paired porous media is used to estimate the unknown coefficients. Advantages include in situ measurements across the entire soil wetness range, an ability to closely match pore‐size distributions (hence hydraulic continuity) with a wide range of porous media, and measurement efficiency based on using the same instrumentation for all measurements. Seven different soils were used in experiments conducted in a laboratory pressure plate apparatus, a greenhouse, and the field. Soil water characteristic relationships obtained using the reference soils approach were generally similar to those measured using pressure plate apparatus. Potential operational concerns include realizing consistent bulk densities for the buried reference soil pockets, and ensuring that water content (θ) measurements are obtained near effective saturation in field applications. Practical utility of the proposed method may be enhanced by identification or manufacture of a range of reference porous media having reproducible SWCs, e.g., that are invariant under different packing conditions.
Effect of Exogenous Carbon on Movement of Simazine and 2,4‐D in Soils
Authors: Cox L. , Cecchi A. , Celis R. , Hermosín M. C. , Koskinen W. C. , Cornejo J.
Published: July 2010

Organic amendment (OA) addition is an agricultural practice that can greatly affect pesticide behavior in soil. The influence of three OAs, consisting of a liquid amendment (LOA), solid (SOA) humic amendment, and a solid urban waste (SUW), on sorption, persistence, and leaching potential of simazine (2‐chloro‐4,6‐bis (ethylamino)‐s‐triazine) and 2,4‐D (2,4‐dichlorophenoxyacetic acid) in a sandy soil (P2) has been investigated. The OAs were added to P2 at a rate of 5% (w/w). Sorption was studied using the batch equilibration technique, degradation by incubations at 20°C and −0.33 kPa moisture content, and leaching using handpacked soil columns. Simazine sorption increased in the order of P2 ≤ P2 + LOA < P2 + SUW < P2 +S OA. The herbicide, 2,4‐D, did not sorb on P2 soil, but in amended soils sorption increased in the same order as simazine. The lower sorption of both herbicides in P2 + LOA as compared with P2 + SOA and P2 + SUW is attributed to higher dissolved organic matter (DOM) content of LOA. Simazine's half‐life was reduced upon amendment. Degradation of 2,4‐D followed a sigmoidal rate in P2, P2 + SOA, and P2 + SUW, but not in P2 + LOA, in which 2,4‐D persistence was much higher. The higher stability of 2,4‐D in P2 + LOA has been attributed to 2,4‐D‐dissoved organic C interactions. Leaching studies indicate that degradation affects movement to a higher extent than sorption, specially in the case of 2,4‐D in P2 + LOA soil, in which the amounts leached are much higher than those in unamended soil. In the case of simazine and P2 + SUW soil, greater reduction in large‐size conducting pores upon amendment, as revealed in Hg porosimetry studies, resulted in a greater reduction of leaching than that suggested from the small differences in sorption and degradation between P2 and P2 + SUW soil.
A Simple Soil Test for Detecting Sites that are Nonresponsive to Nitrogen Fertilization
Authors: Khan S. A. , Mulvaney R. L. , Hoeft R. G.
Published: July 2010

Recent work indicates that accumulation of amino sugar N in soil reduces the yield response of corn (Zea maysL.) to N fertilization, and that nonresponsive sites are detectable by determination of amino sugar N in soil hydrolysates. Unfortunately, the hydrolysis process is too complicated and time‐consuming for use in routine soil testing. A much simpler technique was developed to estimate amino sugar N without the need for acid hydrolysis. In this test, 1 g of air‐dried soil is treated with 10 mL of 2MNaOH in a 473‐mL (1‐pint) wide‐mouth Mason jar, and the sample is heated for 5 h at 48 to 50°C on a hot plate to liberate (NH4+ amino sugar)‐N as gaseous NH3The NH3is collected in H3BO3–indicator solution, and subsequently determined by acidimetric titration. Recovery ranged from 97 to 102% when analyses were performed after treating samples with15N‐labeled (NH4)2SO4or glucosamine, but did not exceed 6.5% with labeled glycine and was undetectable with labeled NO3or NO2Comparative studies using 12 nonresponsive and 13 responsive soils showed a very high correlation between soil‐test N and hydrolyzable amino sugar N (r= 0.90***). Test values were significantly higher (P< 0.001) for nonresponsive (237–435 mg N kg−1) than for responsive (72–223 mg N kg−1) soils. The soil test described has important economic implications for production agriculture, and also should be of value for controlling NO3pollution of ground and surface water.
Heterotrophic Microbial Activity in Northern Everglades Wetland Soils
Authors: Wright A. L. , Reddy K. R.
Published: July 2010

Phosphorus loading to the northern Florida Everglades has been implicated in causing changes in vegetation, peat accretion rates, and other soil physical‐chemical properties. Our study focused on determining the influence of P loading on aerobic and anaerobic heterotrophic microbial activities (measured as CO2and CH4production) in detritus and soil collected from the Water Conservation Area 2a (WCA‐2a) of the Everglades. Heterotrophic microbial activities measured under both field and laboratory conditions were higher in areas impacted by P loading as compared to the unimpacted interior marsh. Microbial heterotrophic activities were higher in detritus and surface soils and decreased with depth. In field studies, CO2production rates in anaerobic soils were approximately 64% of those observed in aerobic soils. Additions of substrates containing C, N, and P generally enhanced heterotrophic microbial activity. In laboratory studies involving addition of various inorganic electron acceptors, increased microbial activities in the order ofwere observed. Microbial CO2production rates under denitrifying and sulfate reducing conditions ranged from 30–42% and 29–44%, respectively, of aerobic rates. Methane production rates were only up to 9% of aerobic CO2production rates. Both CO2and CH4production rates were significantly correlated with soil P parameters and microbial biomass. Enhanced heterotrophic microbial activities resulting from P loading has the potential to increase turnover of organic matter which may lead to increased supply of bioavailable nutrients to emergent macrophytes and periphyton and higher nutrient concentrations in the water column.
Carbonate Adsorption Mechanism on Goethite Studied with ATR–FTIR, DRIFT, and Proton Coadsorption Measurements
Authors: Wijnja H. , Schulthess C.P.
Published: July 2010

The adsorption reaction of bicarbonate at the goethite–water interface was investigated by determining the speciation and coordination of adsorbed carbonate species using in situ attenuated total reflectance (ATR)–Fourier transformed infrared (FTIR) and diffuse reflectance infrared Fourier transformed (DRIFT) spectroscopies, and the proton coadsorption by pH‐stat measurements. The spectra of the adsorbed carbonate species indicated monodentate inner‐sphere surface complexes. Only the carbonate anion species was detected as the adsorbed species in the pH range of 4.8 to 7.0. The DRIFT spectra indicated the existence of additional protonated surface groups associated with adsorbed carbonate. The proton‐to‐bicarbonate coadsorption stoichiometry was 0.54:1 in 0.011 M NaCl and 0.86:1 at very low ionic strength. These proton stoichiometry values appear to be higher than stoichiometry that have been reported for other bivalent oxyanions. The adsorption reaction of carbonate and the concurrent proton adsorption reactions on goethite are proposed.
Creation and Interpolation of Continuous Soil Layer Classes in the Lower Namoi Valley
Authors: Triantafilis J. , Ward W.T. , Odeh I.O.A. , McBratney A.B.
Published: July 2010

The major errors associated with soil classification and mapping are due to subjective allocation of individuals to classes and incongruities between the classification system and the natural continuous variability of the soil mantle. Fuzzy clustering algorithms can be applied to resolve both errors. In this study we numerically classified 1419 soil horizon samples using fuzzy k‐means (FKM) and fuzzy k‐means with extragrade (FKME) analysis. Each sample was characterized by 12 chemical and textural attributes that were used for the numerical classification. The fuzzy classes produced were mapped at various depths using a method that considered the unity of class membership and local kriging. The use of a confusion index enabled the representation of the continuous nature of membership between the classes mapped and highlighted areas where the collection of additional information may be appropriate. The resulting classes reflect sensible and practical groupings that are easily related to the natural structure of the landscape. Silt and clay contents were the most distinguishing attributes in identifying the various geological and geomorphic components. Differences in soil‐forming process were well highlighted by organic C (Org. C), P, electrical conductivity (EC1:5), pH, and Cl− content. We concluded that the fuzzy clustering algorithms and geostatistical techniques provide a worthwhile approach to soil classification and representation of the soil continuum.
An Assessment of Environmental and Solution Parameter Impact on Trace‐Metal Sorption by Soils
Authors: Harter Robert D. , Naidu Ravendra
Published: July 2010

When studying metal sorption by soils, the potential influence of environmental and solution parameters on the experimental systems cannot be ignored. Characteristics of the soil mineral surfaces are the final determinative factors in whether a metal ion will be sorbed, but soil‐solution composition affects both mineral surface properties and whether the metal ions will be in forms that can react with the surfaces. Examples of factors affecting sorption of metals by soil surfaces include ionic strength, cations, anions, and/or organic ligands present in solution, solution pH, and solution metal concentration. In addition, sorption will be affected by external factors such as pressure, temperature, soil/solution ratio, and the manner in which soils to be studied are sampled and stored before investigation. To date, there has been little attempt to standardize experimental protocol, so results obtained using varied systems in different laboratories cannot be readily compared. An initial suggestion that all sorption studies include at least one treatment meeting minimal standards of ionic strength (0.01), background electrolyte (NaNO3), pH (between 5.5 and 6.0), and temperature (25 ± 3°C) is presented as a first step toward enabling improved ability to make interlaboratory comparisons.
Estimating Surface Soil Organic Carbon Content at a Regional Scale Using the National Resource Inventory
Authors: Brejda John J. , Mausbach Maurice J. , Goebel Jeffrey J. , Allan Deborah L. , Dao Thanh H. , Karlen Douglas L. , Moorman Thomas B. , Smith Jeffrey L.
Published: July 2010

The National Resource Inventory (NRI) may be used to estimate soil organic C (SOC) levels at a regional scale if accurate and precise estimates can be made across a wide range of soils, land uses, and topographic positions. The objectives of this study were (i) to identify important sources of variation in SOC content at a regional scale and (ii) to determine the precision with which SOC content can be estimated. Surface soil samples (0–10 cm) were collected in four Major Land Resource Areas (MLRAs) and analyzed for SOC, sand, silt, and clay content. Land use, hillslope position, and slope aspect effects on SOC levels were evaluated by analysis of covariance with sand or clay content as a covariate to adjust for textural differences at each sample point. Land use was a significant source of variation in all four regions. Hillslope position and slope aspect were significant sources of variation in only one of the four regions and there were no significant interactions between land use and hillslope position or aspect. The SOC content ranged from 26 to 55 Mg ha 10 cm−1 in the Northern Mississippi Valley Loess Hills, 22 to 50 Mg ha 10 cm−1 in the Palouse and Nez Perce Prairies, 9 to 26 Mg ha 10 cm−1 in the Central High Plains, and 5 to 8 Mg ha 10 cm−1 in the Southern High Plains. Standard errors ranged from 0.5 to 5.0 Mg ha−1 and were lowest in regions where SOC levels were also lowest. Results indicate the NRI can be an effective tool for estimating SOC levels under different land use and conservation practices on a regional scale.
Influence of Selected Inorganic Electron Acceptors on Organic Nitrogen Mineralization in Everglades Soils
Authors: White J.R. , Reddy K.R.
Published: July 2010

Organic N mineralization can regulate the bioavailability of N in wetland soils and be controlled by the availability of inorganic electron acceptors. During the past 40 yr, the northern Everglades has been affected by nutrient loading as a consequence of the diversion of surface water runoff from agricultural lands. The greatest hydraulic loading occurs in the summer season when precipitation is highest. Fluctuations in water levels and loading of alternate electron acceptors (NO−3and SO2−4) could result in variable N turnover rates. The effect of aerobic, NO−3reducing, SO2−4reducing, and methanogenic conditions on potential organic N mineralization rate was investigated. Soil at 0‐ to 10‐ and 10‐ to 30‐cm depths and overlying plant detritus were collected from eight stations along a 10‐km eutrophic gradient in the northern Everglades, Florida. Selected soil characteristics including microbial biomass C and N (MBC and MBN), total P, and extractable NH+4were measured. Significantly (P< 0.05) higher rates of N mineralization were observed in the detritus, lower rates in the 0‐ to 10‐cm depth, and lowest rates in the 10‐ to 30‐cm depth under each of aerobic, NO−3reducing, SO2−4reducing, and methanogenic conditions. Organic N mineralization rates decreased sequentially from aerobic to NO−3and SO2−4reducing conditions to methanogenic conditions. Total P, MBC, and MBN were all significantly correlated (P< 0.05) to the N mineralization rates under dominance of each electron acceptor. Of all the measured soil characteristics, extractable NH+4was the most strongly correlated (P< 0.01;r= 0.62–0.92) indicator of potential N mineralization rates. Results of this research have important implications for the biogeochemical cycling of N and ecosystem productivity in wetland systems.
A field method for determing percentage of coated sand grains
Authors: Lindbo D.L. , Vepraskas M.J. , Rhoton F.E.
Published: July 2010

Several USDA‐NRCS hydric soil field indicators require estimation of the percentage of organic‐coated sand grains (black grains). For example, to meet the Dark Surface field indicator the soil layer must contain at least 70% coated (black) grains. Field experience has shown that the estimation of the percentage of coated sand grains is often subjective and highly variable from one soil scientist to another. In order to overcome this variability a set of standards was created using a mixture of black and light gray (representing uncoated grains) sand grains. Weighing out each component for the desired ratio and mixing them in a 47‐mm‐diam. petri dish we made a set of three standards consisting of 50, 70, and 90% black grains. To test the effectiveness of these standards, soil scientists estimated the percentage of coated grains from similarly prepared samples first without the use of the standards and then with the use of the standards for comparison. Individuals improved the accuracy of their estimates by 10 to 60% and their hydric soil identification by 16%. The standards are easily prepared, easy to use, and portable.
Calibration of a Two‐Dimensional Root Water Uptake Model
Authors: Vrugt J. A. , Hopmans J. W. , Šimunek J.
Published: July 2010

Although solutions of multidimensional transient water flow can be obtained by numerical modeling, their application may be limited in part as root water uptake is generally considered to be one‐dimensional only. The objective of this study was to develop and test a two‐dimensional root water uptake model, which can be incorporated into numerical multidimensional flow models. The two‐dimensional uptake model is based on the model by Raats, but is extended with a radial component. Subsequently, the root water uptake model was incorporated into a two‐dimensional flow model, and root water uptake parameters were optimized, minimizing the residuals between measured and simulated water content data. Water content was measured around a sprinkler‐irrigated almond tree (Prunus laurocerasus M.J.Roem) for a 16‐d period at 25 locations, following irrigation. To calibrate the flow and root water uptake model, a genetic algorithm (GA) was used to find the approximate global minimum of the optimized parameter space. The final fitting parameters were determined using the Simplex algorithm (SA). With the optimized root water uptake parameters, simulated and measured water contents during the 16‐d period were in excellent agreement, with R2 values generally ranging between 0.94 and 0.99 and a root mean squared error (RMSE) of 0.015 m3 m−3 The developed root water uptake model is extremely flexible and allows spatial variations of water uptake as influenced by nonuniform (drip irrigation) and uniform water application patterns.