bluuebunny/crossref_metadata_2025 huggingface dataset:
Soybean Growth and Rhizosphere pH as Influenced by A Horizon Thickness
Authors: Yang J. , Blanchar R. W. , Hammer R. D. , Thompson A. L.
Published: July 2010

Crop growth and yield are known to be limited by A horizon thickness and may be related to more abundant and metabolically active roots in A than B horizon soil. The influence of A horizon thickness on root distribution and rhizosphere pH was observed in the field. Soybean [Glycine max (L.) Merr.] were grown on plots of Mexico soil (fine, montmorillonitic, mesic Mollic Endoaqualfs) with A horizon thicknesses of 0, 12.5, 25, and 37.5 cm above Bt horizons. Plant height, root and shoot growth, and rhizosphere pH (pH in soil 0.5 mm from a root surface) were determined 25, 55, and 85 d after planting. Plant height and shoot and root weight decreased significantly as A horizon thicknesses decreased from 37.5 to 0 cm, and these differences were attributed to later emergence of soybean seedlings from the thinner A horizons. Root distribution with depth in the upper 30 cm was independent of A horizon thickness. Rhizosphere pH was 0.07 to 0.65 units lower than that of the bulk soil, depending on soil horizon, root morphology, and plant age. This pH difference (ΔpH) averaged 0.36 in the A horizon and 0.18 in the Bt horizon and was independent of measurement depth within each horizon. As bulk soil pH decreased from 6 to 5, the mean ΔpH for lateral and main roots decreased 0.28, 0.21, and 0.10 units at 25, 55, and 85 d, respectively. The mean ΔpH for lateral roots was 0.34 and for main roots was 0.20. The mean ΔpH for all roots and horizons was 0.41 at 25 d, 0.28 at 55 d, and 0.11 at 85 d. The changes in ΔpH with root age, morphology, and depth suggest that ΔpH may be an indicator of root activity.
Rain Infiltration as Affected by Wheat Residue Amount and Distribution in Ridged Tillage
Authors: Baumhardt R. L. , Lascano R. J.
Published: July 2010

Texas South Plains production systems for conserving rainfall and reducing wind erosion in cotton (Gossypium hirsutum L.), a low‐residue crop, include the spring chemical termination of winter wheat (Triticum aestivum L.) overseeded post‐harvest into cotton. This practice often increases cotton lint yields under irrigation, but residues hinder weed control and increase production costs. This study characterized infiltration response to (i) residue weathering and soil consolidation with ridges, (ii) residue distribution on the ridge or in the furrow, and (iii) flat or standing architectures and residue amounts. Simulated rain was applied at 65 mm h−1 for 1 h into a bare Olton clay loam (fine, mixed, thermic Aridic Paleustoll). Mean cumulative infiltration was lowest for bare soil (28.7 mm), but increased curvilinearly with increasing residue amounts, leveling at 49.0 mm. Cumulative infiltration with residues distributed on the ridge (42 mm) or in the furrows (44 mm) were the same even though water in the furrow absorbed drop impact. A minimum amount of residue (0.7 Mg ha−1) to intercept raindrop impact was needed to increase rain infiltration, but increasing residue above a residue threshold of 2.4 Mg ha−1 had no effect because of sufficient drop impact interception. Increases in infiltration were related to the residue amount rather than to the bed or furrow location. Partial residue cover and tillage operations that lodge crop residues may increase infiltration.
Soil Heterogeneity and Root Distribution of Mature Loblolly Pine Stands in Piedmont Soils
Authors: Parker M. M. , Van Lear D. H.
Published: July 2010

Factors that influence rooting patterns in mature forest stands are poorly understood. We examined the distribution of loblolly pine (Pinus taeda L.) roots in trench profiles and related rooting to selected soil physical features along a moisture gradient on the Clemson University Experimental Forest, Clemson, SC. Root density was greater on xeric and subxeric sites than on intermediate sites. Root density declined exponentially with soil depth. Fine roots (<4 mm) accounted for 83 to 95% of all roots and averaged 17 fold higher in root channels than in the soil matrix. Root density was also higher along rock‐soil interfaces than in the soil matrix. Soil morphological and physical features, as well as the relative position of the site in the landscape, influence root growth and survival and markedly affect the distribution of roots in mature loblolly pine stands.
Soil Respiration in Pits and Mounds Following an Experimental Forest Blowdown
Authors: Millikin Catherine S. , Bowden Richard Drew
Published: July 2010

Extensive uprooting of trees by windthrow can create areas of severe soil disturbance in temperate forests. Specifically, uprooted trees leave shaded pits and mounds of exposed roots and mineral soil. To assess the contribution of pit and mound microenvironments to overall soil respiration in an experimental hurricane blowdown at the Harvard Forest Long‐Term Ecological Research site (MA), summer CO2 effluxes were measured on pit, mound, and undisturbed microsites. Mean CO2 effluxes were 45.4, 80.1, and 99.0 mgC m−2 h−1 for pit, mound, and control microsites, respectively. Although soil respiration is lower in areas of disturbed soil than in undisturbed areas, the total efflux contribution (5.3%) from pits and mounds to the overall flux rate at the site was small. The area‐weighted soil respiration estimate is 3.1% lower than the estimate obtained using flux measurements from control locations alone. Measurements taken from undisturbed plots represent a small but systematic overestimate of soil respiration across the site.
Assessment of Two Chemical Extraction Methods as Indices of Available Nitrogen
Authors: Jalil A. , Campbell C. A. , Jame Y. W. , Schoenau J. , Henry J. L. , Lafond G. P.
Published: July 2010

A soil test for estimating mineralizable N in soil is needed to improve fertilizer use efficiency. Our objectives were to: (i) test the effectiveness of two chemical indices in estimating potentially mineralizable N (N0) in soils, and (ii) determine if these indices could be used to differentiate the impact of cultural practices on the N‐supplying capacity of soils. We collected samples from the 0‐ to 0.15‐m depth of 42 soils representing all agroecological regions in Saskatchewan, Canada. We determined (i) N mineralized (Nmin), N0, and the rate constant (k) by aerobic incubation at 35°C for 24 wk, and (ii) the NH4‐N extracted by (a) 2 M KCl heated at 100°C for 4 h, and (b) a steam‐distilled phosphate‐borate solution buffered at pH 11.2. The association between N0 and the hot 2 M KCl extracted NH4‐N was close (r2 = 0.78, significant at P < 0.001); the relationship between N0 and the phosphate‐borate NH4‐N was slightly less precise (r2 = 0.73, P < 0.001). When NH4‐N extracted with cold 2 M KCl was subtracted from the NH4‐N extracted with hot extractants, the association with Nmin was weaker (r2 ≤ 0.50). The value of k for the 42 soils was generally constant (avg. 0.067 ± Sxt 0.05 = 0.040 wk−1). In a second experiment, we compared the two chemical extractants vs. the N mineralized in a 24‐wk incubation regarding their effectiveness in differentiating the effects of eight 37‐yr crop rotation treatments on N‐supplying capacity. These three indices performed effectively in this regard. For example, the 2 M KCl NH4‐N was closely associated with N mineralized in 24 wk (r2 = 0.92), as was phosphate‐borate NH4‐N (r2 = 0.88; both significant at P < 0.001). We concluded that the chemical extractants may provide a quick test for assessing N‐supplying capacity of the soil.
Soil Quality: A Concept, Definition, and Framework for Evaluation (A Guest Editorial)
Authors: Karlen D. L. , Mausbach M. J. , Doran J. W. , Cline R. G. , Harris R. F. , Schuman G. E.
Published: July 2010

This essay summarizes deliberation by the Soil Science Society of America (SSSA) Ad Hoc Committee on Soil Quality (S‐581) and was written to spur discussion among SSSA members. Varying perceptions of soil quality have emerged since the concept was suggested in the early 1990s, and dialogue among members is important because, unlike air and water quality, legislative standards for soil quality have not been and perhaps should not be defined. In simplest terms, soil quality is “the capacity (of soil) to function”. This definition, based on function, reflects the living and dynamic nature of soil. Soil quality can be conceptualized as a three‐legged stool, the function and balance of which requires an integration of three major components — sustained biological productivity, environmental quality, and plant and animal health. The concept attempts to balance multiple soil uses (e.g., for agricultural production, remediation of wastes, urban development, forest, range, or recreation) with goals for environmental quality. Assessing soil quality will require collaboration among all disciplines of science to examine and interpret their results in the context of land management strategies, interactions, and trade‐offs. Society is demanding solutions from science. Simply measuring and reporting the response of an individual soil parameter to a given perturbation or management practice is no longer sufficient. The soil resource must be recognized as a dynamic living system that emerges through a unique balance and interaction of its biological, chemical, and physical components. We encourage SSSA members to consider the concept of soil quality (perhaps as a marketing tool) and to debate how it might enable us to more effectively meet the diverse natural resource needs and concerns of our rural, urban, and suburban clientele of today and tomorrow.
Competitive Sorption of Dissolved Organic Matter Fractions to Soils and Related Mineral Phases
Authors: Kaiser Klaus , Zech Wolfgang
Published: July 2010

Experiments with soils, Al(OH)3 gel, and goethite were conducted to investigate the competitive sorption of hydrophilic and hydrophobic dissolved organic matter (DOM) fractions and inorganic anions such as SO2−4 and H2PO4−. The DOM for the experiments was extracted from a mor layer. The ratio of hydrophilic to hydrophobic dissolved organic carbon was 37/63. The sorption of the hydrophobic DOM fraction was strongly favored over the binding of the hydrophilic fractions on soils and hydrous oxides. Under conditions of a limited number of available binding sites, the preferential sorption of hydrophobic DOM suppressed the binding of hydrophilic DOM or even resulted in a displacement of indigenous hydrophilic organic substances. Favorable chemical properties were assumed to be responsible for the strong sorption of hydrophobic DOM. The SO2−4 induced little reduction of the DOM sorption, whereas H2PO4− caused a strong decrease. The effects of both inorganic anions were more pronounced for the hydrophilic than for the hydrophobic DOM fraction. As the sorption of hydrophilic DOM was strongly affected by inorganic anions and hydrophobic DOM, hydrophilic DOM seems to be the most mobile organic component in soil solutions. The results give evidence that competitive interactions among the chemically heterogeneous DOM constituents need to be considered in DOM transport process in soils.
Climatic Effects on Soil Organic Matter Composition in the Great Plains
Authors: Amelung W. , Zech W. , Flach K.W.
Published: July 2010

To examine temperature and moisture effects on the chemical composition of soil organic matter (SOM), six soil profiles were studied from a climosequence in the native prairie of the Great Plains of the USA. After the removal of plant debris, the vertical distributions (0–60 cm) of soil organic carbon (SOC), N, lignin, and cellulosic and noncellulosic polysaccharides were determined. Samples of the topsoil horizons were additionally characterized by means of 13 C and 1H‐Nuclear Magnetic Resonance (NMR) spectroscopy. As annual temperature increased from 7 to 23°C at sites with <500 mm precipitation per year, the amount of polysaccharides decreased from 605 to 422 g kg−1 SOC in the topsoil (0–15 cm) and from 516 to 278 g kg−1 SOC in the subsoil (30–40 cm). Polysaccharide contents increased with increasing precipitation, reaching 726 g kg−1 SOC in the top 15 cm and 876 g kg−1 SOC at 50‐cm soil depth (830 mm annual precipitation, 12.6°C annual temperature). At all sites, the content of lignin‐derived phenols per kilogram SOC decreased with increasing soil depth. Polysaccharides decreased much less. It is suggested that polysaccharides were resynthesized during SOM alteration within the soil profiles and thereafter preferentially to lignin protected from decay in the mineral soil. The NMR spectra suggested that both polysaccharides and alkyl compounds reflected climatic influences on the SOM composition of the Great Plains.
Long‐Term Effects of Tillage and Fertilization on Soil Organic Matter Dynamics
Authors: Salinas‐Garcia J. R. , Hons F. M. , Matocha J. E.
Published: July 2010

Understanding the effects of long‐term management practices on soil C and N pools and activities is essential for sustaining soil productivity. The objectives of this study were to evaluate long‐term and seasonal changes in soil organic C (SOC), soil microbial biomass C (SMBC) and N (SMBN), and mineralizable C and N in continuous corn (Zea mays L.) under conventional tillage (CT), moldboard (MB), chisel (CH), minimum tillage (MT), and no‐tillage (NT) with low (45 kg N, 10 P kg ha−1) and high (90 N kg, 10 P kg ha−1) N fertilization. An Orelia sandy clay loam (fine‐loamy, mixed, hyperthermic Typic Ochraqualf) in south Texas was sampled before corn planting in February, during pollination in May, and following corn harvest in July. No‐tillage and MT retained more corn residue C input as SOC and SMBC than the more intensive tillage systems. Soil organic C, SMBC, SMBN, and mineralizable C and N were greatest in the surface 0 to 50 mm with NT and MT. Seasonal distributions of SMBC and mineralizable C were consistently greater in reduced‐tillage systems (NT and MT), averaging 22 and 34% greater than plowed treatments at planting, 45 and 53% larger at pollination, and 36 and 34% higher at harvest, respectively, at a depth of 200 mm. The greater amount of crop residues remaining with MT and NT may have provided available substrate for maintenance of the larger SMB pool and the higher C and N mineralization in the 0‐ to 200‐mm depth during the growing season. Higher N fertilization increased seasonal mineralizable C and N, but did not consistently affect SOC and SMB. Reduced tillage systems that promote surface residue accumulation provide an opportunity for increasing sequestration of C and mineralizable nutrients within SMB.
Responses of Six Crop Species to Solution Zinc2+ Activities Buffered with HEDTA
Authors: Parker D. R.
Published: July 2010

Zinc contamination has long hampered the use of conventional nutrient solutions for attaining reproducible and severe Zn deficiencies. Chelator‐buffered solutions show promise for precisely imposing micronutrient deficiencies, but further studies are needed to fully evaluate the method and to develop methods to avoid Zn‐deficiency‐induced P toxicity. In a greenhouse study, seedlings of maize (Zea mays L. ‘Golden Cross Bantam’), wheat (Triticum aestivum L. ‘Yecora Rojo’), tall wheatgrass (Elytrigia pontica [Podp.] Holub ‘Orbit’), alfalfa (Medicago sativa L. ‘Germain's WL‐320’), soybean (Glycine max [L.] Merr. ‘Vinton 81’), and tomato (Lycopersicon esculentum L. ‘Jackpot’) were grown for 16 to 29 d in solutions containing 0.4 to 12 µM total Zn. Computed Zn2+ activities were buffered at 4 to 123 pmol L−1 by a 50‐µM excess of HEDTA, and solution P was maintained at 10 ± 3 µM. Zinc deficiencies ranged from mild to severe, dry matter yield minima ranged from 32 to 89% of controls, and critical Zn2+ activities for the onset of deficiency ranged from approximately 10 to 65 pmol L−1. The relative sensitivity of the six species to low Zn was maize > tomato > wheat > alfalfa ≈ tall wheatgrass > soybean. Shoot Zn concentrations were consistent with the widely reported critical range of 15 to 20 mg kg−1. Zinc deficiency in the three grass species led to hyperaccumulation of P to phytotoxic levels, and leaf symptoms largely reflected this toxicity. Leaf P concentrations in the three dicots tended to be lower, but may have been within the phytotoxic range. Thus, even with P concentrations that approach soil solution values, the P toxicity that often accompanies Zn deficiency in solution‐culture experiments was not eliminated. The effects of Zn deficiency on shoot concentrations of nutrients other than P were variable, although divalent cations tended to be elevated in Zn‐deficient shoots.
Properties and Classification of Cold Desert Soils from Antarctica
Authors: Bockheim J. G.
Published: July 2010

Eight pedons representing three climatic zones and parent materials ranging from Holocene to Pliocene were characterized from the Dry Valleys region of Antarctica. All of the soils contain abundant water‐soluble salts, including NaCl in coastal regions, NaNO3 along the polar plateau, and Na2SO4 in intermediate areas. The salts originate primarily from atmospheric deposition and accumulate linearly with time. Based on a comparison of salt input by precipitation and the salt content of the profiles, minimal leaching of salts has occurred during the past 3 million yr in soils along the polar plateau. Chemical weathering generally is restricted to oxidation of Fe‐bearing minerals and some clay authigenesis. Some of the soils contain ice‐cemented permafrost; however, many of the older soils with <5% moisture content have dry permafrost. Although the soils bear many features of Aridisols, they fail to meet the requirements of an aridic soil moisture regime because of the very cold temperatures. They could be classified as Cryids if the Aridisols suborder were expanded to include soils with temperatures that never exceed 5 or 8°C. In the proposed Gelisols order for permafrost‐affected soils, the soils are classified as Natric, Glacic, and Typic Anhyturbels (evidence of cryoturbation) and Salic and Petrosalic Anhyhaplels (no cryoturbation).
Release and Fixation of Ammonium and Potassium under Long‐Term Fertility Management
Authors: Liu Y. J. , Laird D. A. , Barak P.
Published: July 2010

Improved nutrient use efficiency in production agriculture is a research priority for both agronomic and environmental reasons. To achieve this goal, a thorough understanding is needed of both short‐term and long‐term nutrient dynamics in soils. The specific object of this study was to investigate the effect of long‐term fertility management on the dynamics of fixed and exchangeable NH4 and K in a typical Upper Midwestern agricultural soil. Soil samples (0–20 cm) were collected from long‐term (30‐yr) fertility plots near Arlington, WI. Fixed and exchangeable NH4 and K were determined for plots receiving 0 and 252 kg ha−1 K (from 1962–1982) and 0, 68, 112, 168 kg ha−1 N (from 1962–1993) as urea or NH4NO3. Levels of exchangeable NH4, fixed NH4, and fixed K were similar for all treatments. Exchangeable K was significantly higher in plots receiving 252 kg ha−1 K than in those receiving no K. Levels of exchangeable K were also higher in plots receiving no N than in plots receiving N fertilizer. Fixation capacities for both NH4 and K were significantly reduced by sustained high rates of K fertilization, but not by N fertilization. These results suggest that levels of fixed NH4 can be neither built up nor depleted through long‐term fertility management. On the other hand, levels of exchangeable K and both NH4 and K fixation capacities are influenced by long‐term fertility management.
Silicon Concentrations of Biological Standards
Authors: Bell Paul F. , Simmons Tracey F.
Published: July 2010

No NIST (National Institutes Standards Technology) standards for the Si concentration of biological materials are available, although Si has been determined for one NIST material by non‐NIST personnel. We determined the Si concentrations of NIST materials and a proposed rice‐straw (Oryza sativa L.) standard using an autoclave‐induced digestion, colorimetric method. We measured 1410 mg Si kg−1 for NIST material no. 1575, which was not significantly different from five of seven analyses reported in the literature (P < 0.05). Silicon concentrations of NIST and other materials were 2160 mg kg−1 (no. 1547), 1500 mg kg−1 (no. 1515), 1920 mg kg−1 (no. 8412), and 69 300 mg kg−1 (rice straw).
Sorption‐Desorption of Atrazine and Simazine by Model Soil Colloidal Components
Authors: Celis R. , Cornejo J. , Hermosín M. C. , Koskinen W. C.
Published: July 2010

Sorption‐desorption of atrazine and simazine on montmorillonite, ferrihydrite, and humic acid was determined using the batch equilibration procedure. Sorption of atrazine and simazine was higher on humic acid than on montmorillonite. Ferrihydrite does not sorb triazine herbicides. Enhanced sorption of atrazine and simazine on montmorillonite was measured after increasing the surface acidity of the clay. Results indicate sorption of s‐triazine herbicides on montmorillonite as protonated species must be preceded by sorption as molecular species on hydrophobic microsites of the clay unless the pH of the bulk solution is close to the pKa of the herbicide. In this latter case, cation exchange would be also operative. Sorption‐desorption of atrazine and simazine was more hysteretic for humic acid than for montmorillonite, indicating that these herbicides desorb more difficultly from organic matter than from montmorillonite because of the contribution of hydrophobic interactions with humic acid. It is suggested that, besides organic matter, smectites of low charge density and high surface acidity should increase the retention of s‐triazine herbicides in soils.
Comparison of Methods for Predicting Ternary Exchange from Binary Isotherms
Authors: Bond W. J. , Verburg K.
Published: July 2010

Methods for predicting ternary and higher order cation exchange from binary isotherms are required because it is impossible to measure isotherms for all possible combinations when there are three or more competing ions. One important use for ternary and higher order exchange predictions is for modeling cation transport in multicomponent systems. We review several existing methods for predicting ternary exchange from binary isotherm data and introduce a new method based on the Rothmund‐Kornfeld approach. Existing methods include the Valocchi and Gapon equations as well as the Wilson and subregular models used in conjunction with the Vanselow‐Argersinger exchange formulation. The methods were used with three data sets: Na‐K‐Ca exchange at 50 and 200 molc m−3 in Brucedale soil, and NH4‐Ba‐La exchange at 100 molc m−3 in montmorillonite. The resulting predictions were compared with measured ternary exchange data. It was found that all methods that account for the variation of the exchange coefficient and/or the exchanger phase cation activity coefficients performed similarly well. Their performance was much better than methods that assume that conditional exchange coefficients are constant, such as the Valocchi and Gapon methods. For the data examined, the Gaines‐Thomas formulation of the Rothmund‐Kornfeld equation consistently gave the best predictions for the least computational effort.
Kinetics of Nonexchangeable Ammonium Release from Soils
Authors: Steffens D. , Sparks D. L.
Published: July 2010

The rate of nonexchangeable NH4+ release from soils can have a significant effect on N dynamics and environmental quality. Nonexchangeable NH4+ is that N fraction which is fixed in the interlayers of clay minerals. The objective of this study was to determine the kinetics of nonexchangeable NH4+ release from two topsoils from Germany [Giessen Ap (Aqualf) and Hungen Ap (Alfisol)] and from two subsoils, one from Germany [Hungen C (Alfisol)] and one from Kentucky [Shrouts Bt (Hapludalf)]. Calcium‐saturated, freeze‐dried soils were extracted with H‐resin for 0.25 to 384 h. Sodiumethylmercurythio‐salisylate (Thimerosal) was added to the soil/H‐resin suspension to inhibit microbiological ammonification. The kinetics of nonexchangeable NH4+ release from the soils were biphasic and were best described by Elovich and heterogeneous diffusion models. The release of nonexchangeable NH4+ as a percentage of total nonexchangeable NH4+ in the soils ranged from 4 to 25% and was lower in subsoils than in topsoils. This was ascribed to the higher levels of indigenous nonexchangeable NH4+ in the subsoils, which is more tightly held than recently fixed nonexchangeable NH4+.
Quantifying Rhizosphere Respiration in a Corn Crop under Field Conditions
Authors: Rochette Philippe , Flanagan Lawrence B.
Published: July 2010

In order to quantify rhizosphere respiration (Rrh) during the growing season, we monitored the isotope ratio (δ13C) of soil CO2 in a corn (Zea mays L.) crop that was grown on a soil developed from C3 plant material. The Rrh was defined as the sum of CO2 respired by plant roots and CO2 respired by microbes that feed on organic material produced by the roots. The δ13C of soil CO2 in the corn plot changed from an early season low of approximately −20‰, to mid‐season values of approximately −14‰, before declining again at the end of the growing season. In the control plot (no C4 plants present) δ13C values of soil CO2 were significantly lower than values in the corn plot, averaging approximately −22‰ throughout most of the season. We observed no significant change in the δ13C value of soil CO2 in either the corn or control plots during a diurnal sampling period. The value of Rrh was 1.71 g CO2 m−2 d−1 27 d after planting (DAP), reached 10 g CO2 m−2 d−1 at 44 DAP, remained at about that value until 76 DAP, and gradually decreased to 2.6 g CO2 m−2 d−1 at 141 DAP. The CO2 respired by the rhizosphere was equivalent to 18 to 25% of crop net photosynthesis and 24 to 35% of crop net CO2 assimilation during most of the growing season.
Pedogenic Influence on Base Saturation and Calcium/Magnesium Ratios in Soils of Southeastern Ohio
Authors: Saif H. T. , Smeck N. E. , Bigham J. M.
Published: July 2010

Contiguous Alfisols and Ultisols occur across the unglaciated, upland landscape of southeastern Ohio. Difficulties are encountered in distinguishing and mapping these soils due to morphological similarities and base saturation differences. The soils have formed in a loess mantle of varying thickness overlying colluvium and residuum derived from sedimentary bedrocks. Four pedons were studied to evaluate the influence of the loess mantle and bedrock chemistry on base saturation and extractable Ca/Mg ratios in order to facilitate soil mapping in southeastern Ohio. Loess thickness and Cr horizon chemistry could adequately account for base saturation and extractable Ca/Mg ratios in three of the four pedons, but a pedogenic effect is essential to explain extractable Ca/Mg ratios in the other pedon. In the latter pedon, extractable Ca exceeded Mg in both the loess mantle (upper solum) and deep Cr horizons, but extractable Mg exceeded Ca in the lower solum and uppermost Cr horizons. We conclude that bases leached from the loess mantle accumulate in the underlying residuum and that Mg is preferentially retained during base recharge. We speculate that a transient Mg‐Al double hydroxide is formed in the residuum during base recharge and is responsible for preferential Mg retention.
Evaluating Soil Movement Using Cesium‐137 and the Revised Universal Soil Loss Equation
Authors: Montgomery J. A. , Busacca A. J. , Frazier B. E. , McCool D. K.
Published: July 2010

More complete information is needed on the rates and patterns of soil movement in Palouse watersheds to better guide conservation planning. Water erosion has historically been predicted from rates using the Universal Soil Loss Equation (USLE) or the Revised USLE (RUSLE). These equations, however, do not account for deposition or tillage erosion. This study was conducted to assess patterns of soil movement in an open Palouse watershed during a 27‐yr period using the 137Cs tracer technique and to statistically compare transect‐ and point‐based RUSLE soil loss rates with 137Cs‐based soil loss rates measured at 74 137Cs sampling points located on 89 landscape profiles. One hundred fifty‐eight soil samples were collected from a modified grid pattern and analyzed for 137Cs activity. Soil movement rates were interpolated at 8025 points in the sample grid using ordinary point kriging. Hillslopes were classified into geometric and geomorphic components. The kriged mean net soil movement rate for the 27‐yr period was −3.3 kg m−2 yr−1. Doubly convex landscape positions have experienced the most severe erosion, apparently due to tillage erosion. The measured 137Cs and transect‐based RUSLE median soil loss rates were both significantly higher than the point‐based RUSLE median; however, no significant difference existed between the transect‐based RUSLE and measured 137Cs median soil loss rates (α = 0.05). Meaningful comparisons between 137Cs and RUSLE soil loss rates can only be made if a tillage movement rate, history of crop management, and the accuracy of RUSLE relationships and operating files are known.
Hydroxy‐Interlayered Minerals in Japanese Soils Influenced by Eolian Deposition
Authors: Bautista‐Tulin A. T. , Inoue K.
Published: July 2010

The influence of eolian dust deposition on the development of Red‐Yellow soils and nonallophanic Andisols in Japan has been well documented. In these studies, it was reported that the clay fractions of these soils are dominated by fine‐grained quartz, 2:1 layer silicates and their intergrades, and kaolinite. However, the nature and composition of hydroxy‐interlayered minerals on these soils influenced by eolian dust addition from China is largely unknown. To address this problem, we collected and characterized 28 soil samples from seven pedons in Japan classified as Hapludalfs, Hapludults, or Melanudands, and two soil samples from a pedon in China classified as a Vermiboroll. These samples were extracted with 0.15 M acid oxalate and 0.3 M sodium citrate solutions and the amounts of Al, Fe, and Si present in the extracts were determined. This information was used in combination with x‐ray diffraction patterns of the samples obtained before and after extraction to determine the mineralogy and estimate the composition of the interlayer material. Except for the Vermiboroll samples, which contained kaolinite and highly charged smectite, the dominant minerals in these soil samples were hydroxy‐interlayered vermiculites (HIV). The citrate extracts yielded low Si/Al atomic ratios (i.e., 0.12–0.86 after 4 h and 0.39–0.90 after 24 h) suggesting that the interlayer materials of the HIV minerals were hydroxyaluminosilicate, hydroxy‐Al, and/or hydroxy‐Fe ions. Our results provide chemical and mineralogical evidence for the occurrence of hydroxy‐interlayer materials in loess‐derived Japanese soils developed under temperate, humid climates.
Error Analysis of an Evaporation Method for Determining Hydrodynamic Properties in Unsaturated Soil
Authors: Mohrath D. , Bruckler L. , Bertuzzi P. , Gaudu J. C. , Bourlet M.
Published: July 2010

Solving soil unsaturated flow problems requires knowledge of the water retention θ(h) and unsaturated hydraulic conductivity K(θ) relationships. The purpose of this study was to investigate more thoroughly the properties and accuracy of an evaporation method described by Wind (1969) for determining θ(h) and K(θ) from laboratory cores. Evaporation from a vertical column of soil was first simulated using numerical solution of Richards equation for a given set of soil hydraulic properties. The simulated data were then used to evaluate the ability of Wind's method to provide estimations of the retention and unsaturated conductivity curves when measurement errors were taken into account. The main sources of error were (i) errors due to the position of the tensiometers in the sample, (ii) errors due to the calibration of the transducers used for the pressure head measurements, and (iii) errors due to layering in the soil column. The estimated water retention curves were sensitive only to soil layering. On the other hand, small uncertainties in the position of the tensiometers (1 or 2 mm) and in the calibration curve of the transducers for the pressure head measurements (1–5%) had a great influence on the estimated hydraulic conductivity curves. A correction procedure was proposed and was satisfactory when errors of position in the tensiometers were taken into account. Results also showed that temperature corrections related to viscosity of liquid water were large. Finally, this method gives poor estimates of hydraulic conductivities when raw tensiometric data are corrupted with small errors in their position or calibration.
Inorganic Phosphorus Transformation and Transport in Soils: Mathematical Modeling in ecosys
Authors: Grant R. F. , Heaney D. J.
Published: July 2010

The movement and uptake of P in soils occur primarily in the soluble phase, so that the reliable simulation of P movement and uptake requires that the concentrations of soluble P forms be explicitly represented in mathematical models. To represent soluble P concentrations under dynamic boundary conditions, a convective‐dispersive model of P transport has been coupled to a model of P transformation in which adsorption‐desorption, precipitation‐dissolution, and ion pairing are explicitly represented as concurrent equilibrium reactions. This model is used to explain the temporal and spatial distribution of P among soluble and resin‐, NaHCO3‐, NaOH‐, and HCl‐extractable fractions in soils following amendment with KH2PO4. Simulated reductions in soil pH following different P amendments caused solid‐phase P in the model to be recovered more from resin‐ and NaOH‐extractable forms and less from HCl‐extractable forms as solution P concentration increased. These changes were consistent with those observed experimentally using a P fractionation procedure on a Malmo silt loam (Typic Cryoborall) following its equilibration with 0 to 512 mg L‐1 of KH2PO4 and following its irrigation for 205 d with 50 mg L‐1 of KH2PO4. Simulated displacement of cation coprecipitates from exchange sites allowed the model to reproduce the temporal and spatial patterns of water‐ and HCl‐extractable P in resin columns of different cation‐exchange capacities following a KH2PO4 surface amendment. The results of model testing suggest that changes in soluble P concentrations following P amendments may be represented from concurrent equilibrium reactions for adsorption‐desorption, precipitation‐dissolution, and ion pairing. However, the rate at which these reactions proceed remains uncertain.
Apparent Salt Sorption Reactions in an Unfertilized Acid Subsoil
Authors: Pearce R. C. , Sumner M. E.
Published: July 2010

The equivalent retention of Ca2+ and SO2‐4 from gypsum solutions in acid subsoils has recently been reported. The term salt sorption has been coined to describe this process, yet little is known about the nature of the reactions involved. This study was conducted to determine if other cation‐anion combinations would exhibit similar behavior and to examine the extractability of the sorbed ions. An unfertilized acid Cecil (clayey, kaolinitic, thermic Typic Kanhapludult) subsoil was equilibrated using a saturated paste technique, with solutions of six different salts at a loading rate of ≈14.0 mmolc kg‐1. The salt solutions used were CaSO4, MgSO4, Na2SO4, CaCl2, MgCl2, and a deionized water control. This soil exhibited salt sorption with all six electrolyte solutions. The SO4 salts were almost completely sorbed with both cation and anion uptake on the order 13.8 mmolc kg‐1. Calcium and magnesium chloride were sorbed at ≈11.7 mmolc kg‐1, and NaCl was sorbed at 8.2 mmolc kg‐1. The treated soils were air dried and extracted with successive portions of deionized water or 0.5 M NH4NO3. A relatively large proportion of both cations and anions were removed by repeated extraction with water, suggesting that ionic strength played an important role in the salt sorption process. Nearly all of the sorbed cations and Cl‐ were recovered by neutral salt extraction, but <100% of the SO2‐4 could be accounted for by neutral salt extraction. Neutral salt extractable Al was significantly reduced by salt treatment. It appeared that salt sorption in this soil may have resulted from several mechanisms including precipitation, specific adsorption, ionic strength induced charging, and ion pair adsorption operating concurrently.
Ionic Strength Effects on Sulfate and Phosphate Adsorption on γ‐Alumina and Kaolinite: Triple‐Layer Model
Authors: He L. M. , Zelazny L. W. , Martens D. C. , Baligar V. C. , Ritchey K. D.
Published: July 2010

It is known that PO4 is retained by soils through ligand exchange, i.e., inner sphere complexation, but the mechanism for SO4 adsorption at the mineral‐water interface has been in debate. By studying the effects of ionic strength on ion adsorption, it is possible to distinguish between inner and outer sphere ion surface complexes. This study was conducted to evaluate ionic strength effects on SO4 and PO4 adsorption on γ‐Al2O3 and kaolinite at varying solution pH (3–11), and to infer SO4 and PO4 adsorption mechanisms at the mineral‐water interface. The adsorption of SO4 on γ‐Al2O3 and kaolinite decreased monotonically with increasing solution pH and was markedly reduced by increasing the concentration of background electrolyte. On the other hand, PO4 adsorption on γ‐Al2O3 and kaolinite increased from pH 3 to 4 and decreased from pH 6 to 11, with an adsorption plateau between pH 4 and 6. Effects of change in ionic strength on PO4 adsorption varied with pH. At low pH, PO4 adsorption demonstrated a slight decrease with increasing ionic strength, whereas at high pH, PO4 adsorption increased slightly with increasing ionic strength, resulting in a crossover point where there was no ionic strength effect. The triple‐layer model (TLM) was applied to model the adsorption of SO4 and PO4 with both inner and outer sphere complexes using the FITEQL 3.1 computer program. Sulfate adsorption was better modeled by assuming outer sphere complex formation, while PO4 adsorption was better modeled by assuming inner sphere complex formation.
Combination Probe for Nitrogen‐15 Soil Labeling and Sampling of Soil Atmosphere to Measure Subsurface Denitrification Activity
Authors: Nielsen Tommy Harder , Well Reinhard , Myrold David D.
Published: July 2010

Investigations of subsoil denitrification have been hampered by the difficulty in adapting traditional methods for measuring denitrification in surface soils to subsoils. In this study, we present, and test, a combination probe constructed to detect denitrification in the vadose zone. The probe was designed to label a volume of the subsoil with 15NO‐3 and subsequently to collect gas samples from which the denitrifying activity in the surrounding soil can be estimated by isotopic analysis of N2. Gas samples were collected from the labeled soil volume by use of He‐flushed silicone tubing having high permeability for gases. No mass flow of gases through the soil was caused by the procedure. Nitrogen gas diffusing into the tubing can be collected after equilibration periods of 15 to 20 min. A combined tensiometer and sampler for dissolved ions was built into the probe to have direct estimates of soil water potential together with information about the 15N atom fraction of the dissolved NO‐3 in the surrounding soil. The probe was tested under laboratory conditions. The probe introduced 15NO‐3 into a roughly spherical volume of soil with a symmetric distribution of 15NO‐3. Estimates of the 15N atom fraction of the NO‐3 undergoing denitrification based on gas samples agreed favorably with destructive sampling of NO‐3. The accumulation of N2 derived from denitrification was consistent with expected trends and, along with computer simulations and 15N mass balance methods, was used to calculate denitrification rates. These different estimates of denitrification agreed well. This combination probe shows promise for measuring denitrification in subsoil.
Effect of Soil Water Content Variation on the Least Limiting Water Range
Authors: da Silva Alvaro Pires , Kay B. D.
Published: July 2010

The least limiting water range (LLWR), a proposed structural quality index, is the range in soil water content within which plant growth is least limited by water potential, aeration, and mechanical resistance. This study tested the hypotheses that the frequency of the soil water content falling outside the LLWR (pout) increases with decreasing LLWR and that the relation is influenced by tillage, position (row vs. interrow), and climatic conditions. Thirty‐two paired sampling sites were located along two parallel transects in a side by side comparison of no‐till and conventional tillage. The transects crossed three soil types: Aquic Hapludalf, Psammentic Hapludalf, and Typic Hapludalf. The LLWR was calculated for the 0‐ to 20‐cm depth at row and interrow positions. The site was planted to corn (Zea mays L.) and the study lasted three growing seasons. Logistic regression analysis, pout = exp(b0 + b1 LLWR)/[1 + exp(b0 + b1 LLWR)], showed that pout was negatively related to LLWR (R2 = 0.72, P > 0.01), regardless of weather, tillage, or position. Values of pout under no‐till were lower than under conventional tillage and the interrow position had a lower pout than the row position. The parameter b1 did not vary across weather, tillage, or position but b0 was influenced by these parameters. The analyses supported the hypothesis and emphasized the impact on pout of factors unrelated to structure.
Fractal Characterization of Soil Aggregation and Fragmentation as Influenced by Tillage Treatment
Authors: Perfect E. , Blevins R. L.
Published: July 2010

Parameters are needed to quantify tillage‐induced changes in soil structure. Our objective was to see if fractal parameters from ped mass‐ and number‐size relations could be applied to quantify such changes. Soil from long‐term conventional (moldboard plow, MP, plus two passes with a disk harrow, DH) and no‐till (NT) plots on a Maury silt loam (fine, mixed, mesic Typic Paleudalf) was air dried and sieved into six size classes ranging from 0.5–1 to 16–31.5 mm. The mass percentage and weight of 100 peds in each size class were used to calculate the mean mass per ped and number of peds as a function of scale. Fractal equations were then fitted to both data sets (R2 always ≥ 0.99). The resulting parameter estimates were Dm (mass fractal dimension) and km (mass of an aggregate of unit length) for the mass‐size relation, and Dt (fragmentation fractal dimension) and kf (number of fragments of unit length) for the number‐size distribution. Significant tillage effects were observed for Dm, Df, and kf. The Dm increased from 2.88 for NT to ≥ 2.94 for MP and DH, suggesting differential compaction of large aggregates by plowing and disking. The Df was always less than the Dm, as predicted by theory. Soil fragmentation was least for NT (Df = 2.02) and greatest for MP (Df = 2.55); for DH, the Df = 2.15 suggesting that disking broke up large fragments and/or coalesced small fragments following plowing. The kf, which was shown to be nonlinearly related to the Df, was least for MP and greatest for NT. Similar studies on other soils are needed to test the general applicability of these fractal relations to soil structure.
Short‐Term Effects of Cover Crop Incorporation on Soil Carbon Pools and Nitrogen Availability
Authors: Hu S. , Grunwald N. J. , van Bruggen A. H. C. , Gamble G. R. , Drinkwater L. E. , Shennan C. , Demment M. W.
Published: July 2010

Winter cover crops are increasingly used to maintain water quality and agroecosystem productivity. Cover crop incorporation influences transient soil microbial dynamics and nutrient availability at an early growth stage of subsequent crops. Short‐term (≤35 d) effects of cover crop incorporation on soil C pools and N availability were evaluated using sandy loam soils from organically and conventionally managed fields. Field and incubation experiments were designed to investigate whether cover crop incorporation had differential effects on C pools and how they were related to N mineralization. Labile C pools (soil carbohydrates and soil microbial biomass C [SMBC]) and coarse organic debris (COD) increased two‐ to threefold, whereas total organic C increased by only 20% by Day 7 after incorporation. The COD decreased faster than other C pools and best predicted SMBC (P < 0.0001). A rapid decrease in SMBC after Day 21 was accompanied by an increase in available N. Discriminant analyses revealed that organic soils were distinct from conventional soils by their higher total C, N, and SMBC, and lower available N, but cover crop incorporation obscured the distinction in the first 14 d. Residue decomposition was slightly faster in organic soils than in conventional soils at the early stage (3–4 wk), but >30% of N in cover crop residues was mineralized in both soils by Day 35 after incorporation, suggesting that manipulations of soil microbial dynamics and N mineralization in the short term can be of particular significance in synchronizing N release with the need of subsequent crops.
Accelerated Diffusion Methods for Inorganic‐Nitrogen Analysis of Soil Extracts and Water
Authors: Khan S. A. , Mulvaney R. L. , Mulvaney C. S.
Published: July 2010

The major limitation of diffusion methods for N analysis is the time required to obtain the results — typically from one to several days. Methods were developed that involve a much shorter period for diffusion. In these methods, 10‐ to 100‐mL samples of 2 or 4 M KCl soil extract or water were treated with MgO, or MgO plus Devarda's alloy, in a 473‐mL (1‐pint) wide‐mouth Mason jar to liberate NH4‐N, NO3‐N, and/or NO2‐N as NH3. The jar was placed on an electric griddle maintained at 45 to 50°C. Gaseous NH3 was collected in 5 mL of H3BO3 indicator solution in a petri dish attached to the Mason jar lid, for quantitative determination by acidimetric titration. Complete recovery of 4 mg of N was achieved from 10 or 20 mL in 1.5 to 5 h. Recovery from 50 or 100 mL was complete in 5 to 8.5 h with 1 to 2 mg of N. The methods permit 15N analysis of the diffused NH3‐N. Isotopic analyses of labeled soil extracts were accurate to within 3%, as determined by isotope‐dilution calculations. Diffusions from 10 to 50 mL were subject to very little, if any, interference from decomposition of alkali‐labile organic‐N compounds.
Nitrogen‐15 Recovery and Release by Rye and Crimson Clover Cover Crops
Authors: Ranells Noah N. , Wagger Michael G.
Published: July 2010

A grass‐legume biculture may be preferred over a legume monoculture cover crop due to the scavenging ability of a grass species, especially when high residual soil N levels are present following summer droughts in the Atlantic Coastal Plain. Rye (Secale cereale L.) and crimson clover (Trifolium incarnatum L.) were grown in monoculture and as a biculture in a 2‐yr field experiment on a Typic Kandiudult to assess cover crop recovery of fertilizer 15N and the subsequent corn (Zea mays L.) uptake of cover crop residue 15N. Potassium nitrate labeled with 10 atom % 15N was applied to microplots at 50 kg N ha‐1 1 wk after seeding the cover crops, which were monitored for recovery of fertilizer 15N. Labeled residue was placed in a new microplot to monitor release of residue 15N and its recovery by corn. Averaged across both years, rye monoculture recovered 39% of the labeled 15N fertilizer compared with 19% in the rye‐crimson clover biculture and 4% in the crimson clover monoculture. Following corn harvest and averaged across both years, total recovery of 15N fertilizer from the original microplots (cover crop, corn biomass, and soil N) was 29% for crimson clover, 75% for rye, 55% for rye‐crimson clover biculture, and 20% for the native winter weeds. In 1993, corn recovery of residue 15N was lowest in the rye monoculture (4%) compared with other treatments (20–35%). Results indicated that a rye‐crimson clover biculture was capable of recovering greater residual 15N than a crimson clover monoculture, but less than rye monoculture.