bluuebunny/crossref_metadata_2025_split huggingface dataset:
Soil Phosphorus Desorption Kinetics and Its Relationship with Plant Growth
Authors: Raven K. P. , Hossner L. R. 
Published: July 2010

AbstractThe kinetics of P desorption in soils is important to consider from a plant nutrition perspective. This study was designed to compare the ability of several equations to describe P desorption kinetics from soils and to relate the information derived from desorption kinetic curves to plant growth and P uptake. Samples of five soils (Psammentic Paleudult, Typic Calciustoll, Udic Pellustert, Vertic Albaqualf, and Aridic Calciustoll) were treated with five P levels (0, 25, 50 75, and 100 mg kg−1) and incubated at field capacity and 24 °C for 31 d. Phosphorus desorption kinetic data for each treatment were generated by equilibrating suspensions of the incubated soil samples with mesh bags containing HCO−3‐saturated anion‐exchange resin for periods up to 96 h. Desorbed P was then determined by extraction of resin P with 0.5 M NaC1. Initial (after 0.25 h) and final (after 72 h) amounts of desorbed P and desorption rates were determined. The kinetic data were best described by the expanded form of the Elovich equation. The initial and final amounts of desorbed P were closely related to relative plant growth and P uptake. The final desorbed soil P was the best soil P availability index. Soil P desorption rates generally had soil‐specific relationships with growth of corn (Zea mays L.) and P uptake and did not seem to limit the P nutrition of plants. The parameters of the expanded Elovich equation were not satisfactory indicators of the P‐supplying capacity of the soil.
Analyzing Root Competition with Dirichlet Tessellation for Wheat on Three Landscape Positions
Authors: Van Rees K. C. J. , Hoskins J. A. , Hoskins W. D. 
Published: July 2010

AbstractThe underlying mechanisms for root competition are not completely understood; yet, it is important to accurately define the zone of influence around individual roots for nutrient or water uptake, particularly when modeling nutrient uptake processes. The objectives of this study were to investigate the use of the Dirichlet tessellation for quantifying soil polygons around roots of spring wheat (Triticum aestivum L. cv. Katepwa) grown on three landscape positions and to quantify the root spatial patterns. Roots were exposed on a horizontal soil plane at 2‐, 5‐, and 10‐cm depths and mapped on acetate sheets at 21, 45, and 88 days after planting (DAP) for shoulder, backslope, and footslope positions. Tessellation of scanned root maps showed that soil polygons decreased in size during the sampling period; however, polygon areas increased with soil depth regardless of slope position and ranged from 0.08 to 52.77 cm2. Eccentricity averaged 0.74 ± 0.01, indicating that polygons were more circular than elliptical and root displacement averaged one‐third the distance from the polygon center to the polygon edge. Root spatial patterns using R‐index values, showed that roots on shoulder positions had clumped to random patterns while roots at the footslope had random to regular patterns. Root spatial patterns and displacement for wheat violated the assumptions used in nutrient uptake modeling and should be incorporated into future modeling efforts. Dirichlet tessellation is an effective procedure for analyzing root competition and has promise for multispecies competition if different root systems can be weighted by morphological or physiological characteristics.
Spatial Patterns of Soil Organic Carbon in the Contiguous United States
Authors: Kern Jeffrey S. 
Published: July 2010

AbstractSpatial patterns and total amounts of soil organic C (SOC) are important data for studies of soil productivity, soil hydraulic properties, and the cycling of C‐based greenhouse gases. This study evaluated several approaches for characterizing SOC to determine their relative merits. The first approach entailed grouping data from a global pedon SOC database by type of ecosystem, resulting in a total of 78.0 Pg of C (Pg = 1015 g) to 1‐m depth for the contiguous USA. In a second approach, a pedon database was aggregated using soil taxonomy, resulting in a total for the contiguous USA of 80.7 ± 18.6 Pg of C when the great group SOC was spatially distributed with Major Land Resource Areas (MLRAs) using the 1982 National Resource Inventory (NRI) and the Soil Interpretation Record databases. The third approach used pedon and spatial data from a global soil map grouped by soil unit that resulted in 84.5 Pg of C for the contiguous USA. Although the ecosystem and soil taxonomic approaches resulted in similar totals, the taxonomic approaches are recommended because they gave more realistic results in areas of Histosols, shallow soils, and soils with high rock fragment content. The ecosystem approach did not give reliable spatial patterns and is only useful for very broad‐scale work where precisely georeferenced data are not needed. Grouping data by great group provided more information than grouping by order or suborder. The approach based on soil taxonomy is very useful because it is based on the NRI statistical framework and it allows stratification by other NRI items, such as land use and vegetation.
Inheritance of 2:1 Phyllosilicates in Costa Rican Andisols
Authors: Jongmans A. G. , van Oort F. , Nieuwenhuyse A. , Buurman P. , Jaunet A. M. , van Doesburg J. D. J. 
Published: July 2010

AbstractThe occurrence of 2:1 phyllosilicates in Andisols is variously ascribed to in situ pedogenic origin, aeolian addition, or the presence of hydrothermally altered rock fragments. We studied the origin of 2:1 phyllosilicates that occur in Holocene Hapludands on andesitic, sandy beach ridges in Costa Rica by micromorphological, mineralogical, and submicroscopical techniques. The 2:1 phyllosilicates also occur as pseudomorphs after primary minerals in fresh rock of the inland volcanoes, from which the parent material of the beach ridges was mainly derived. Hydrothermal processes are most likely responsible for the formation of such pseudomorphs. Rock weathering produces sand‐sized rock fragments with clay pseudomorphs and also liberates individual pseudomorphs. Subsequent erosion and alluvial transport affect their shape, but not their internal fabric. In the beach ridges, clay pseudomorphs appear as individual, sand‐sized clay bodies, and inside sand‐sized andesitic rock fragments. Submicroscopical analyses of these individual clay bodies and andesitic rock fragments with clay pseudomorphs indicate a predominance of 2:1 phyllosilicates. This implies that they are inherited from the parent material and are not due to postdepositional soil formation in the beach ridges. Weathering and biological activity affect the clay bodies and rock fragments with clay pseudomorphs, leading to the formation of clay‐sized particles consisting of 2:1 phyllosilicates. Toward the soil surface, these particles are incorporated into the allophanic groundmass resulting from actual soil formation. The geographically extensive occurrence of 2:1 phyllosilicates in Andisols suggests that the genetic processes described here may have more than regional validity.
Long‐Term Tillage and Rotation Effects on Properties of a Central Ohio Soil
Authors: Lal R. , Mahboubi A. A. , Fausey N. R. 
Published: July 2010

AbstractSustainable use of soil resources can be assessed from management‐induced changes in soil properties from long‐term experiments. Such data are scanty, especially with regard to changes in soil physical properties. Therefore, soil physical and chemical analyses were performed 28 yr after initiating a crop rotation‐tillage experiment on a well‐drained Wooster silt loam soil (fine‐loamy, mixed, mesic Typic Fragiudalf) at Wooster, OH. All combinations of three rotations (continuous corn [CC; Zea mays L.]; corn and soybean [Glycine max (L.) Merr.] in a 2‐yr rotation [CS]; and corn, oat [Avena sativa L.], and meadow in a 3‐yr rotation [COM]) and of three tillage treatments (no‐tillage [NT]; chisel plow [CP]; and moldboard plow [MP]) were maintained on the same plots for the entire length of study. All crops were grown every year. Soil properties studied for the 0‐ to 15‐cm layer were: structural stability of aggregates, bulk density, total porosity, penetration resistance, organic C, pH, cation‐exchange capacity (CEC), and exchangeable K, Ca and Mg. Mean bulk densities measured prior to tillage treatments and planting were 1.18, 1.24, and 1.28 Mg m−3 for CC, CS, and COM rotations, respectively. The lowest bulk density was observed for the CC‐NT combination. Total aggregation in CS was 26.9% greater than CC and 111.2% greater than COM. With tillage treatments, aggregation was in the order of NT>CP>MP. Rotation treatments had no effect on aggregate size. In accord with bulk density, the relative magnitude of organic C content was 100, 85, and 63 for CC, CS, and COM rotations, respectively.
Long‐Term Effects of Residue Management in Wheat‐Fallow: I. Inputs, Yield, and Soil Organic Matter
Authors: Rasmussen P. E. , Parton W. J. 
Published: July 2010

AbstractSoil organic matter (SOM) is valuable, because of both its beneficial effect on soil quality and crop productivity and its potential to sequester C. Long‐term experiments provide an opportunity to identify crop management practices that enhance or degrade soil quality. This study was initiated in 1931 to determine residue management effects on crop yield and SOM (organic C and N) in a winter wheat (Triticum aestivum L.)‐fallow system. The soil is a coarse‐silty, mixed, mesic Typic Haploxeroll. Treatments include (units ha−1 crop−1) 22.4 Mg manure, 2.24 Mg pea vine residue, 0, 45, and 90 kg N with and without spring burning of straw, and 0 kg N with fall burning of straw. Yearly C and N inputs and removals have been determined since 1976, and calculated for prior periods. Soil C and N have been determined at ≈ 11‐yr intervals. Manure, which supplies 111 kg N ha−1 crop−1, has consistently produced the highest yield and maintained the highest soil C and N contents. Other treatments initially yielded from 80 to 90% of the manure treatment, but have progressively declined in direct relation to decreasing soil N content. Low‐fertility treatments currently yield from 43 to 57% of the manure treatment. The change in soil C and N with time is nearly linear for all treatments, and highly correlated with residue input. Treatment effects on soil C and N have been confined to the top 30 cm of soil, but there has been a slow steady decline in C and N in the 30‐ to 60‐cm zone that is not related to residue management.
Preferential Transport of Nitrate through Soil Columns Containing Root Channels
Authors: Li Yimin , Ghodrati Masoud 
Published: July 2010

AbstractPreferential flow has been increasingly recognized as an important mechanism for water and solute transport. The objectives of this study were to characterize transport of NO3 through root channels in uniformly packed soil columns and to compare three commonly used solute transport models in describing NO3 transport through the soil‐root channel columns. Root channels were created by growing corn (Zea mays L.) or alfalfa (Medicago sativa L.) in 0.6‐m‐long soil columns. Transport of NO3 was then systematically studied with each of these macropore systems at a range of fluxes (from 0.042Ksm to 0.47Ksm, where Ksm is the saturated hydraulic conductivity of the macroporous system). A nonlinear least‐squares program was used to fit the convection‐dispersion equation (CDE), the physical nonequilibrium model (MIM) and a stochastic model (SM) to the experimental data. The results show that significant preferential movement of NO3 occurred in the decayed root channels at fluxes as low as 0.042Ksm. The MIM model provided a better description of the breakthrough curves than the CDE and the SM, while none of them were adequate to predict the preferential movement of the solute.
Effects of Magnesium on Cation Selectivity and Structural Stability of Sodic Soils
Authors: Curtin D. , Steppuhn H. , Selles F. 
Published: July 2010

AbstractThis study was conducted to evaluate the effects of Mg on the cation‐exchange relationships and structural stability of sodic soils. Samples of prairie soils (Haploborolls) from Saskatchewan, Canada, were equilibrated with sodic solutions [sodium adsorption ratio (SAR = Na/(Ca + Mg)0.5, where concentrations are expressed in millimoles per liter) ranging from 5 to 40] with different Ca/Mg ratios. Exchangeable Na increased as the Mg/Ca ratio increased. Averaged from all SAR treatments, the Mg‐Na systems had between 17 and 37% more exchangeable Na than did the Ca‐Na systems. The Mg‐induced increase in exchangeable Na was directly related to a preference by the soils for Ca over Mg, which makes Na more competitive against Mg than against Ca. The influence of Mg on structural stability was examined by measuring saturated hydraulic conductivity (K) using Mg‐Ca‐Na solutions (Mg/Ca ratios ranging from 0:1–1:0) with SARs of 10 and 20. The Mg‐Na system developed considerably lower K than did the Ca‐Na system when leached with solutions with total electrolyte concentration ≤ 100 mmolc L−1. Systems with intermediate Mg/Ca ratios (i.e., Mg/Ca of 1:2 and 2:1) behaved more like the Ca‐Na than the Mg‐Na system. Clay concentration in leachate from the soil columns increased as Mg/Ca ratio increased, suggesting that a major effect of exchangeable Mg was that it increased the tendency for clay dispersion. Dispersion tests confirmed that the effect of Mg was greater than could be explained by the higher exchangeable Na level in the Mg system, i.e., Mg had a specific effect on clay dispersion. Our results suggest that exchangeable Mg is about 5% as dispersive as exchangeable Na.
Soil Organic Matter Testing and Labile Carbon Identification by Carbonaceous Resin Capsules
Authors: Johns Mitchell M. , Skogley Earl O. 
Published: July 2010

AbstractAn alternative test for soil organic matter that does not produce toxic dichromate waste, as does the Walkley‐Black test, and that also allows identification of labile soil C components is currently desired. The objectives of this study were to apply carbonaceous resin capsules for measurement of soil organic C (SOC) and for identification of soluble SOC constituents. Seven carbonaceous resins, selective for nonpolar organic adsorbates, were evaluated. The resins were tightly packed as spherical capsules and placed in saturated soil pastes of 19 Montana soils. Resin capsules were desorbed with NaOH, CH3OH, CHCl3, and C6H14. Capsules extracted with the organic solvents were used in identification by nuclear magnetic resonance and infrared spectroscopy. Ultrafiltration and atomic absorption spectrophotometry of trace metals were also used. All resin capsules sorbed measurable levels of soil labile C (LC). All the resin types provided statistically significant prediction of SOC. The Ambersorb 564 resin showed the highest prediction, with a linear relationship between capsule‐extracted LC (NaOH) and SOC of r2 = 0.09 (P < 0.0001). Prediction results from these soils suggested a linear relationship between soluble SOC and solid‐phase SOC, describable as constant partitioning. Labile C was composed of mostly aliphatics and some aromatics. Carbohydrates, OH, COOH groups, and metal‐organic complexes were present. Most of the LC was composed of low molecular weight humics (<1000 daltons). The ability of LC to be desorbed by the more nonpolar solvents indicated an amphipathic character for some LC constituents. The resin capsule methodology showed good testing potential for these SOC investigations.
Soil Microbial Dynamics: Short‐ and Long‐Term Effects of Inorganic and Organic Nitrogen
Authors: Fauci Mary F. , Dick R. P. 
Published: July 2010

AbstractSoils with minimal long‐term organic inputs typically have reduced biological activity, which has implications for current interests in shifting from inorganic to organic inputs and promoting efficient nutrient cycling in agroecosystems. A greenhouse experiment was conducted to investigate the long‐ and short‐term effects of organic vs. inorganic N on microbial biomass, metabolic quotient, and key soil enzymes (protease, l‐histidine NH3‐lyase, and β‐glucosidase) involved in N and C cycles. Treatments applied factorially to four corn (Zea mays L.) crops grown for 306 d were: four soils from long‐term field plots (beef manure, pea vine [Pisum sativum L.], 0, or 90 kg N ha−1, each applied biennially for 59 yr); four greenhouse organic residues (pea vine, beef manure, poultry manure, or control); and four rates of inorganic N fertilizer (0–1600 mg NH4NO3‐N pot−1 with 2 kg soil pot−1). In the long‐term, soil microbial biomass and enzyme activity correlated with total C inputs. Recent organic inputs, regardless of long‐term management, had a large effect on soil biological response, which was controlled by residue composition (lignin content) and supported 80 to 400% greater microbial biomass C than the control. Long‐term inorganic N applications decreased organic matter and biological activity, whereas short‐term inorganic N applications had limited effects on soil enzyme activities and microbial biomass C, suggesting that inorganic N can maintain plant productivity during a transition to organic N sources without inhibiting the buildup of microbial biomass. The metabolic quotient gave mixed results as a soil biological indicator, being high with long‐term N or recent beef manure applications and low with recent N applications.
Soil Isotopically Exchangeable Phosphorus: A Comparison between E and L Values
Authors: Frossard E. , Morel J. L. , Fardeau J. C. , Brossard M. 
Published: July 2010

AbstractThis study was designed to explain the apparent discrepancies often reported in the literature between E and L values, two parameters obtained from isotopic exchange experiments and commonly used to quantify available soil phosphate. The E and L values of the surface horizons of 10 soils from tropical, mediterranean, and temperate regions were determined. The L value was measured from a 13‐wk pot experiment with common bentgrass (Agrostis capillaris L.) where the available soil P was labeled with 32PO4 ions in the presence of a carrier (25–50 mg 31P kg−1 soil). To determine the E value, the isotopic exchange kinetic experiment was carried out on each soil. Carrier‐free 32PO4 was added to the soil‐solution system at a steady state and the quantity of isotopically exchangeable soil phosphate at time t, E(t), was calculated from the kinetic equation describing the decrease of radioactivity in solution with time. Results showed that L values determined after 13 wk were not significantly different from E(t) values extrapolated to the same period (t = 131040 min). It was concluded that (i) the L value is a particular point of the kinetic equation and (ii) isotopically exchangeable phosphate is the available P for common bentgrass. A strict equality between E(13wk) and L values was not, however, reached for all samples. Possible causes for the differences were: (i) an overestimation of the water‐soluble phosphate due to the presence of silica and (ii) disturbance of the steady state following a too large uptake of phosphate by the crop or the application of too large quantities of carrier compared with the initial quantity of exchangeable soil phosphate.
Identification and Properties of Fragipan Soils in the Piemonte Region of Italy
Authors: Ajmone‐Marsan F. , Pagliai M. , Pini R. 
Published: July 2010

AbstractThe presence of a fragipan horizon in the soil profile restricts plant growth and limits nonagricultural uses. This is of special concern in the Piemonte region, in northwestern Italy, where the soil of numerous areas is reported to have a fragipan. Four sites were selected for this study with the aim of ascertaining the presence in the profile of a horizon that meets the criteria for a fragipan. In addition to standard morphological observations and physical analyses, Hg intrusion porosimetry and image analysis of thin sections were used to help in fragipan characterization. The pan of all four sites showed a suite of characteristics such as coarse prismatic primary structure, prominent vertical mottling, extremely hard dry consistence, brittleness, and absence of roots that indicated the presence of a fragipan. Other pedogenic features, e.g. clay films, mangans, ferrans, and concretions, were observed in the field. Although some of the Bx horizons had a clay content slightly higher than prescribed, in general textures were within the range prescribed for fragipans, as were bulk densities. Mercury intrusion showed a decrease in total porosity with depth, residual pores becoming dominant over storage and transmission pores in the fragipans. Image analysis of thin sections revealed a decrease of elongated pores and the presence of vesicles and compound packing voids. Also, oriented clay coatings within the pores and mangans and ferrans were observed in the fragipan. Pore‐size distribution and pore shape appeared to be useful in characterizing the fragipan.
Characterizing Changes in Aggregate Stability Subsequent to Introduction of Forages
Authors: Rasiah V. , Kay B. D. 
Published: July 2010

AbstractLimited information exists on the methods used to compute the changes in wet aggregate stability, WAS, with time subsequent to changes in management practices. The objectives of this study were to: (i) develop a model to compute the net gain in WAS, WASnet, with time subsequent to the introduction of forages, (ii) assess the model using data from different soils, and (iii) determine the influence of soil properties on the regeneration of WAS. Stability measurements were made at monthly intervals during the 1989, 1990, and 1991 growing seasons from seven different soils under continuous conventional corn (Zea mays L.) and forage treatments established in 1989. The interaction of cropping treatment, time of sampling, and gravimetric soil water content, θ, at sampling was significant for six out of seven soils at P = 0.05. Using the relation between WAS and θ and the changes in WAS with time, a semiempirical model was developed to predict WASnet. The model parameters described (i) the duration of delay before any observable changes in WAS occurred, (ii) the rate at which WAS increased from an initial to a maximum value, and (iii) the maximum potential change in WAS. The R2 for the best fit of the model ranged from 0.31 to 0.72 for the seven soils. The projected half‐life for WASnet, computed using the 3‐yr data, ranged from 4.52 yr for a clay loam to 7.75 yr for a sandy loam. Pedotransfer function analysis indicated that WASnet increased with increasing clay and organic matter contents and pH of soil. The model parameters and the associated pedotransfer functions were useful in assessing the influence of soil properties on stability following changes in management practices.