bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical Distribution of Roots and Soil Nitrate: Tree Species and Phosphorus Effects
Authors: Jama Bashir , Ndufa J. K. , Buresh R. J. , Shepherd K. D.
Published: July 2010

We hypothesized that trees can rapidly root into subsoil and capture NO3, which can accumulate in the subsoil of agricultural soils with high anion sorption. The vertical distribution of root length and inorganic N (NO3 and NH4) to 3.95‐m soil depth was compared for 11‐mo‐old stands of eucalyptus (Eucalyptus grandis W. Hill ex Maiden), sesbania [Sesbania sesban (L.) Merr.], calliandra (Calliandra calothyrsus Meissner), markhamia [Markhamia lutea (Benth.) Schumann], and grevillea (Grevillea robusta A. Cunn. ex R. Br.) grown at two P levels (no added P and 500 kg added P ha−1) on a Kandiudalfic Eutrudox in Kenya. The trees were planted at a 1 by 1 m spacing in a randomized complete block with three replications. Added P had no effect on root length, soil NO3, and soil NH4 even though the soil was low in available P. Total root length was greater for calliandra (15.5 km m−2) than other trees (1.2–5.6 km m−2). The slope for the model of natural logarithm root length density (cm cm−3) as a function of soil depth was affected by tree species (P < 0.01), indicating differences among trees in the tendency for deep rooting. Root length densities, averaged for the two P levels, were ≥0.1 cm cm−3 to depths of 2.2 m with calliandra, 1.8 m with sesbania, 1.2 m with eucalyptus, 0.45 m with grevillea, and 0.3 m with markhamia. Calliandra and sesbania reduced soil NO3 in the top 2 m by about 150 to 200 kg N ha−1 within 11 mo after establishment and effectively captured subsoil NO3. Fast‐growing trees with high root length densities can rapidly reduce subsoil NO3.
Modeling Moisture Retention in Peat Soils
Authors: Weiss R. , Alm J. , Laiho R. , Laine J.
Published: July 2010

Soil moisture governs many biogeochemical processes in peatlands. Modeling of those processes relative to climate and anthropogenic influences requires knowledge of the basic hydraulic properties of different peat soils in a function form. Water retention of undisturbed surface peat samples, collected at four depths at each of 38 undrained and drained pine (Pinus sylvestris L.) mire sites, was measured for suction pressures of −0.98, −3.10, −6.19, −9.81, −98.1, and −1554.25 kPa. The obtained data were used to test several well‐known water retention models commonly applied to mineral soils. The most suitable model was found to be van Genuchten's model if the residual water content was omitted. Peat characteristics were used to explain the variation in the model's shape parameters. Accounting for the remains of Sphagnum, Carex, Eriophorum, and lignin and the distinction between shallow and deep peat layers considerably improved the moisture retention predictions compared with using bulk density only. The different behavior of the shallow vs. the deep peat layers was mainly attributed to the Sphagnum and lignin residues, but not to the Carex residues. We developed a semiempirical model with only one shape parameter, which was clearly better explained by the peat characteristics than the two shape parameters of the van Genuchten model. We recommend that for statistical investigations or investigations requiring a robust model, the semiempirical model be used. The van Genuchten model is to be preferred in predicting the moisture conditions near saturation.
Characterization of Dissolved Organic Matter Extracted from Composted Municipal Solid Waste
Authors: Chefetz Benny , Chen Yona , Hadar Yitzhak , Hatcher Patrick G.
Published: July 2010

The properties and transformation of dissolved organic matter (DOM) extracted from municipal solid waste compost at five stages of composting were studied using a chemical fractionation scheme. We fractionated the DOM into hydrophobic or hydrophilic neutrals, acids, and bases, and obtained solid‐state cross polarization magic angle spinning (CPMAS) 13C‐nuclear magnetic resonance (NMR) spectra of the unfractionated DOM and of the different fractions. The hydrophobic acid (HoA) fraction was the dominant hydrophobic fraction, exhibiting a moderate increase during composting. The hydrophobic neutral (HoN) fraction increased sharply while the hydrophobic bases (HoB) fraction decreased during composting. The hydrophilic neutrals (HiN) represented the major fraction of the hydrophiles until 120 d of composting, decreasing thereafter by 38%. The 13C‐NMR spectra of the unfractionated DOM revealed an increasing level of aromatic structures in the residual DOM with composting time. The 13C‐NMR spectra of the HoA fraction suggested a polyphenol‐humic structure, whereas the HoN spectra exhibited strong aliphatic features. The spectra of the HiN fraction confirmed its polysaccharide nature and the hydrophilic bases (HiB) fraction contained mainly proteins and carbohydrate‐amino complexes. A comparison between the 13C‐NMR spectra of HoA and fulvic acid (FA) indicated the former to be the most soluble FA fraction. The steady DOM concentration and the relative decrease of HiN as the HoA and HoN fractions increased indicates that DOM at the final stage of composting contained less bioavailable organic matter and more macromolecules related to humic substances. The constant level of DOM observed during the curing and maturation stages represents a steady‐state situation during which the chemical composition is continually changing.
Comparison of Methods to Estimate Occluded and Resistant Soil Phosphorus
Authors: Bowman R. A. , Rodriguez J. B. , Self J. R.
Published: July 2010

Weathering, pH changes, and biotic interactions through geologic times have created a gradation of easily released (labile) to strongly stabilized (resistant) P pools. While methodologies for fertility indices and labile P are well established, methods for quantifying less labile P, such as the occluded and resistant or residual P, are less well established. We reexamined existing methods for these pools, and suggested new procedures to improve their precision and timeliness. Specifically, we compared two methods for reductant‐soluble (occluded) P, and two existing and a new procedure for the resistant P. Occluded P was difficult to reproduce from a sequential extraction procedure because of problems associated with molybdate blue reaction, which required extra molybdate or persulfate oxidation to minimize citrate interference. However, use of inductively coupled plasma (ICP) spectroscopy eliminated this problem. Measurement of P by ICP for surface and occluded P in the total free Fe oxide pool was more quantitative and reproducible [average coefficient of variation (CV) = 5%] than in the sequential extraction (average CV = 7%) procedure. Results for the proposed resistant P method (total soil P minus acid‐extractable P in an ignited sample) approximated the two sequential extraction procedures (total soil P — total acid‐ and base‐extractable organic and inorganic P) and is easier, and more reproducible. Both procedures for all soils except the Molokai showed essentially the same amounts of occluded P. An average of about 26% of the total soil P (TP) was resistant, with the more weathered Cecil soil containing about 50% resistant P.
Loessial Soils of Delaware: Taxonomy and Map‐Unit Assessment
Authors: Rebertus R. A.
Published: July 2010

Map units named for the Matapeake series (fine‐silty, mixed, mesic Typic Hapludults) comprise one‐third of the Coastal Plain in the soil survey of northern Delaware. The concept was one of well‐drained soils formed in thin loess over coarse‐textured fluvial sediments. This study uses characterization data from pedons within the loess‐blanketed terrain of northern Delaware to assess the taxonomy and composition of Matapeake map units. All pedons are Alfisols rather than Ultisols, and this status has not been influenced by liming. Fine‐loamy rather than fine‐silty soils typically occur where loess is <80 cm thick. Much soil variability exists on interfluves where thin loess discontinuously blankets the irregular surface of the sandy Pensauken Formation. This results in an inability to map specific consociations, even for large‐scale, detailed surveys. The existing soil survey used specific map units — consociations named for phases of soil series — that do not adequately depict the diversity on mappable landscapes. The Matapeake and associated series used in this area are too narrowly defined in ranges of characteristics, are too general in geographic setting, have loess thickness limits that are not concordant with particle‐size classes, and leave gaps in the lithologic‐hydrologic continuum. They therefore provide little utility for organizing knowledge, understanding relationships, or as objects for research. Soil survey in this area requires more generalized map units, greater emphasis on stratigraphy and geomorphology and their interaction to influence hydrology and lithology, and less emphasis on artificial conceptual groupings at the lowest taxonomic category, the series.
Sediment Regimes under Different Slope and Surface Hydrologic Conditions
Authors: Huang Chi‐hua
Published: July 2010

During rainfall events, many physical processes occur simultaneously. Conceptual frameworks for infiltration, runoff, surface sealing, sediment detachment, transport, and deposition processes have long been recognized. Nevertheless, interactions between hydrologic and sediment regimes and how they are affected by changes in slope steepness, soil erodibility, and rainfall erosivity have not been evaluated. A laboratory study on the Glynwood clay loam (fine, illitic, mesic Aquic Hapludalf) was designed to demonstrate interactions between hydrologic and sediment regimes. Four rainfall intensities, from 30 to 120 mm h−1, and two inflows, equivalent to 30 and 60 mm h−1 rainfall, were applied to create different combinations of rainfall detachment and shallow flow transport. Sediment delivery was quantified from two rainfall events: first on freshly packed soil under free drainage and later on the eroded surface under seepage. During the first rainfall event, average sediment deliveries from 30 to 100 mm h−1 runoff were 1.8, 3.4, and 3.3 kg m−2 h−1 for slopes of 5, 10, and 15%, respectively. The lack of slope effects from 10 to 15% slope indicates the shift from a transport‐limiting sediment regime at low slopes to a detachment‐limiting sediment regime at high slopes. Under the potentially more erodible seepage condition, the second rainfall event produced only 1.3, 1.8, and 1.5 kg m−2 h−1 sediment from the same range of slopes and runoff rates. Reduction in sediment delivery during the second run was caused by removal of the easily erodible fraction during the first run. Increased profile drainage at the 15% slope further limited sediment detachment. These results show interactions between surface hydrologic conditions and erosion processes and the importance of understanding dominant sediment regimes in developing erosion prediction models.
Characterizing Interrill Sediment Size by Partitioning Splash and Wash Processes
Authors: Wan Y. , El‐Swaify S. A.
Published: July 2010

Sediment transported from interrill areas is generally finer than the in situ soil matrix. We hypothesized that sediment size depends on the processes dominating interrill sediment transport, i.e., splash or wash, which, in turn, are influenced by rainfall intensity and slope gradient. Aggregate size distribution of directional splash and wash sediment from a Rhodic Eutrustox (Wahiawa silty clay) was measured at 4, 9, 18, 27, and 36% slopes under simulated rainfall with 45, 65, 90, and 135 mm h−1 intensities. Mean sediment geometric mean diameter (GMD) was 0.74 mm for downslope splash, 0.67 mm for lateral splash, 0.59 mm for upslope splash, and 0.40 mm for wash. Both splash and wash preferentially transported aggregates <0.063 mm. However, mean enrichment ratios (ER) for this fraction were <2 for splash and ≈12 for wash. Wash sediment GMD significantly increased with increasing rainfall intensity and slope, and was thus positively correlated with the erosion rate of wash (r = 0.95). In contrast, splash sediment GMD was much less influenced by rainfall intensity and slope, and was weakly correlated with the corresponding splash rate (r = −0.17 for total splash). Splash tended to generate sediment with similar size to the in situ soil and the size sorting process was in a matrix‐limited regime. Wash appeared to be in a force‐limited regime and produced sediment that was much finer than the in situ soil.
Modeling Interrill Sediment Delivery
Authors: Zhang X. C. , Nearing M. A. , Norton L. D. , Miller W. P. , West L. T.
Published: July 2010

Shallow surface runoff is a primary transport agent for interrill sediment delivery. Runoff, rainfall intensity, and slope interactively affect interrill erosion. We hypothesized that the inclusion of a runoff factor in an interrill erosion model can reduce the dependence of the interrill soil erodibility (Ki) on soil infiltration characteristics as well as improve model predictability. A complete factorial rainfall simulation experiment with two soils (Cecil sandy loam, a clayey, kaolinitic, thermic Typic Kanhapludult, and Dyke clay, a clayey, mixed, mesic Typic Rhodudult), four rainfall intensities, four slopes, and two replicates was conducted under prewetted conditions to measure runoff and sediment delivery rates. Tap water with electrical conductivity <0.2 dS m−1 was used in all the runs. Rainfall intensity I, unit discharge q, slope S, soil type, and their interactions significantly affected sediment delivery per unit area (Di). Sediment delivery had the greatest correlation (r = 0.68) with unit discharge; however, neither discharge nor rainfall alone adequately predicted sediment delivery. The equation Di = KiIq1/2S2/3 was proposed. The linear intensity term (I) represents detachment of soil by raindrop impact and enhancement of transport capacity of sheet flow, while the product of q1/2S2/3 describes sediment transport by sheet flow. Validation with independent data showed that the model predicted soil erodibilities well. The mean r2 for four validation soils was 0.93 when the proposed model was fitted to validation data to predict interrill erodibility (Ki). The better estimation of Ki indicates that interrill erosion processes were adequately described by the model.
Aluminum in Soil Solutions of Forest Soils: Influence of Water Flow and Soil Aluminum Pools
Authors: Matzner E. , Pijpers M. , Holland W. , Manderscheid B.
Published: July 2010

The Al3+ saturation of soil solutions of acid forest soils (defined as pAl3+‐3pH) is highly variable with time and soil depth under field conditions. We hypothesized that the release of Al from soil solids into the soil solution is kinetically restricted. This hypothesis was tested by evaluating soil solution data from a field site and in an experiment with large undisturbed soil columns from two acid forest soils. Soil columns of 40‐cm diameter and 90‐cm height were established in six replicates at 10°C and irrigated in a steady‐state flow with an artificial acid throughfall (pH 3.5 and 2.8) at rates of 1, 4, and 12 mm d−1. Soil solutions from the columns as well as in the field were taken by suction lysimeters from various depths and the Al3+ saturation of the soil solutions was related to the extractable soil Al pools and water flow rates. Under field conditions, undersaturation was related to high water flow rates through the soil profile at both the 20‐ and 90‐cm depths. This was attributed to preferential flow in the soil profile. In contrast with the field results, Al3+ saturation of soil solutions from the column experiments was not affected by flow rate despite a large variation in flow rate, acid input, and ionic background. In the column study, the Al3+ saturation differed between soils, soil horizons, and replicates; increased with soil depth; and was undersaturated with respect to gibbsite in the upper soil profile. The Al3+ saturation of soil solutions was spatially highly variable both in the field and in the column experiment corresponding to the heterogeneity of soil extractable Al pools. The relation of soil extractable Al to the Al3+ saturation was different for the two soils. The modeling of soil solution Al and pH under equilibrium assumptions and without kinetic constraints is rather uncertain when short‐term variations and different soil horizons are considered.
Recovery of Leucaena and Dactyladenia Residue Nitrogen‐15 in Alley Cropping Systems
Authors: Vanlauwe B. , Sanginga N. , Merckx R.
Published: July 2010

Quantification of the fate of residue N is essential in low‐input tropical cropping systems for the development of management practices that optimize N‐use efficiency. The recovery of N from 15N‐labeled leucaena [Leucaena leucocephala (Lam.) de Wit] and dactyladenia [Dactyladenia barteri (Hook fex Oliv.) Engl.] leaf residues was followed in the soil, crop, and hedgerow of the respective alley cropping systems during three maize (Zea mays L.) and two cowpea (Vigna unguiculata L. Walp. subsp. unguiculata) seasons. More residue N was recovered in the top 5 cm of soil in the leucaena than in the dactyladenia microplot during the first 471 d after residue application (DAA). The first maize crop recovered 8.6 and 5.2% of the N from leucaena and dactyladenia, respectively, while the two subsequent crops recovered <1%. The cowpea plants in the leucaena and dactyladenia microplots contained 0.5 and 1.1% of the residue N in the first harvest. Sixteen and 9% of the residue N was recovered by the leucaena hedgerow in the first and second pruning following residue application. The dactyladenia hedges recovered maximally 3.1% of the residue N in a single pruning. The total N recovery in the leucaena microplots was ≈90% at 120 and 471 DAA, compared with 56 and 35% in the dactyladenia microplots. At 858 DAA, 62% of the added leucaena N was accounted for, compared with 25% of the dactyladenia N. Residue quality was shown to have a major impact on the dynamics of applied residue N in alley cropping systems and will be an important factor in deciding which residue‐supplying plant species to integrate into similar cropping systems.
Process‐Based Analysis of Aggregate Stability Effects on Sealing, Infiltration, and Interrill Erosion
Authors: Fox D. M. , Le Bissonnais Y.
Published: July 2010

Aggregate stability indices are correlated with soil erosion rates. Although aggregate stability influences soil erodibility and aggregate breakdown product size distributions, these indices are usually unsatisfactory because of interacting physicochemical considerations affecting infiltration and erosion. We examined the spatial variability in structural and depositional seal composition, and the influence of breakdown fragment size distribution on seal hydraulic resistance and interrill erosion. Two Alfisols, Villamblain clay loam and Blosseville silt loam, were sieved to retain <2.0‐cm aggregates and packed in 0.25‐m2 soil trays. Soil trays were rained upon for 4 h at 23 mm h−1. Infiltration, runoff, and subseal pressure head were measured throughout the experiment, and surface roughness and depositional seal area were measured at selected times during the event. Aggregate stability, hydraulic resistance, and fragment size distribution of the seal matrix were also determined. Mean weight diameter (MWD) of aggregates after mechanical breakdown by stirring was greater for Villamblain (1.70 mm) than for Blosseville (0.92 mm) (r2 = 0.94, P < 0.001). Blosseville seals had finer fragments than those of Villamblain (r2 = 0.82, P < 0.001): fewer than 28% of fragments >1 mm and more than 40% <0.1 mm, compared with 60 and 15% for Villamblain. Depositional seals had finer fragments than structural seals for both soils. For the same runoff rate (15 mm h−1), soil loss was greater for Blosseville (2 g m2 min−1) than for Villamblain (0.4 g m2 min−1) since breakdown products were finer and more transportable. Seal hydraulic resistance was correlated (r2 = 0.53, P < 0.01) with MWD of seal fragments.
Bulk Densities of Brazilian Amazon Soils Related to Other Soil Properties
Authors: Bernoux Martial , Cerri Carlos , Arrouays Dominique , Jolivet Claudy , Volkoff Boris
Published: July 2010

The results of this study provide the first baseline for predicting Db from soil properties for soils across the Amazon basin. Bulk density values are needed to convert nutrient content and organic carbon (OC) content to weight of nutrient and OC per unit area; unfortunately, common field methods to measure Db are limited with regard to reliable, complete, and uniform soil data. Much effort has been made in finding alternative solutions to predict Db from soil properties. We hypothesized that Db could be reliably estimated by multiple regression of OC, soil textural properties, and some chemical properties. Using the data of 323 soil horizons from the Brazilian Amazon basin, a stepwise multiple regression (SMR) procedure was developed to predict Db from other soil properties. Multiple regression relationships were obtained for all the data, which were also partitioned by layer and then by main soil order: Latossolos (Oxisols, 62 horizons) and Podzólicos (Alfisols and Ultisols, 212 horizons). The SMR on all the data showed that clay content is the best predictor of Db, accounting for 37% of the variation. Adding OC content increased the explained variance up to nearly 50%. Predictions of the models were improved when the data were partitioned by order and by horizon type. In the case of Latossolos (Oxisols), the use of OC and clay content as predictors increased the percentage of explained variation, reaching 71% using all layers and 79% for A horizons. The results of this study will provide a basis for estimating OC stocks in the Amazon basin.
Statistical Distributions of Soil Loss from Runoff Plots and WEPP Model Simulations
Authors: Baffaut Claire , Nearing M. A. , Govers Gerard
Published: July 2010

Soil conservation measures may be better designed with the knowledge of daily distributions of erosion. Collecting reliable data to determine daily erosion distributions is costly; however, new process‐based soil erosion models have the potential to simulate extended records. The objectives of this study were to analyze frequency distributions of measured daily soil loss values and to determine if the Water Erosion Prediction Project (WEPP) model accurately reproduced statistical distributions of the measured daily erosion series. A Log‐Pearson Type III (LP III) distribution was fitted to measured and WEPP‐predicted soil loss values from six sites for periods ranging from 6 to 10 yr. Cumulative soil loss as a function of storm recurrence interval was used to show the relative contributions of large and small storms to total soil loss at each site. Results showed that both measured and predicted frequency curves fell within the 95% confidence range of the LP III distributions. This was true both using weather data from the site for the period of monitoring as well as when using synthetic weather series generated with the CLIGEN model. Thus the results were encouraging in terms of using WEPP in conjunction with CLIGEN to generate long‐term daily soil loss frequency distributions, which can contribute toward alleviating the problem of having only a short monitoring period for measured erosion. Cumulative soil loss results indicated that large storms contributed a major portion of the erosion under conditions where cover was high, but not necessarily under conditions of low cover.
Spatial and Temporal Variability of Corn Grain Yield on a Hillslope
Authors: Timlin D. J. , Pachepsky Ya. , Snyder V. A. , Bryant R. B.
Published: July 2010

The purpose of this study was to relate the temporal and spatial variability of corn (Zea mays L.) grain yield on a Typic Fragiochrept soil on a hillslope to soil properties and topographic features. Corn grain yields were sampled from a field that measured 280 by 150 m using a grid and five transects. One‐hundred forty yield measurements were taken on the grid (1983–1985) and 190 measurements on the transects (1984 and 1985) from plots 5.3 m long and two corn rows wide. Measurements of soil surface elevation, soil organic matter (OM), P, and K contents were also taken at the grid plot locations. These data were analyzed using the methods of spectral analysis. Yield spatial and temporal variability was strongly related to surface undulations and the value of surface curvature was found to be a useful parameter to quantify variations in topography. The intra‐annual differences in weather had the largest effect on grain yield at locations where the magnitude of curvature was large. Where the magnitude of curvature was small, the correlations of yield for the wet (1984) and dry (1985) years were highly significant. Yields correlated with soil P, K, and OM only in the dry year, 1985. Yields in the relatively dry years (1983 and 1985) correlated with depth to fragipan. Elevation data helped us interpret the spatial and temporal variability of grain yield by separation of areas with convex curvature from areas with concave curvature.
Regional Soil Organic Carbon Storage Estimates for Western Oregon by Multiple Approaches
Authors: Homann P. S. , Sollins P. , Fiorella M. , Thorson T. , Kern J. S.
Published: July 2010

Soil is an important factor in regional and global C budgets because it serves as a reservoir of large amounts of organic C. In our study, we compared six approaches of estimating soil organic C (kg C m−2, not including the surface organic horizon, hereafter called soil C) and its spatial pattern in the mountainous, largely forested western Oregon region. The approaches were (i) USDA NRCS pedons, (ii) other pedons, (iii) the State Soil Geographic Data Base (STATSGO), (iv) the United Nations Soil Map of the World, (v) the National Soil Geographic Data Base (NATSGO), and (vi) an ecosystem‐complex map. Agreement between approaches varied with scale. For the entire region (105 km2), estimates of average soil C varied from 4.3 to 6.8 kg C m−2 for the 0‐ to 20‐cm depth and from 12.1 to 16.9 kg C m−2 for the 0‐ to 100‐cm depth. At the subregional scale (≈104 km2), all approaches indicated higher soil C in the coastal area than in the inland southern area, but relative amounts in other subregions varied among the approaches. At the subsubregional scale (≈103 km2), soil C was consistent between individual STATSGO map units and NRCS pedons within those map units, but there was less agreement with other pedons. Rigorous testing of soil‐C maps requires data from pedons that are located by objective criteria, in contrast to the subjectively located pedons now available. The uncertainty associated with regional soil‐C amounts and spatial patterns should be considered when soil‐C maps are integrated into regional or global assessments of physical and biotic processes because simulation‐model outputs may be sensitive to soil C.
Neural Network Analysis for Hierarchical Prediction of Soil Hydraulic Properties
Authors: Schaap Marcel G. , Leij Feike J. , van Genuchten Martinus Th.
Published: July 2010

The solution of many field‐scale flow and transport problems requires estimates of unsaturated soil hydraulic properties. The objective of this study was to calibrate neural network models for prediction of water retention parameters and saturated hydraulic conductivity, Ks, from basic soil properties. Twelve neural network models were developed to predict water retention parameters using a data set of 1209 samples containing sand, silt, and clay contents, bulk density, porosity, gravel content, and soil horizon as well as water retention data. A subset of 620 samples was used to develop 19 neural network models to predict Ks. Prediction of water retention parameters and Ks generally improved if more input data were used. In a more detailed investigation, four models with the following levels of input data were selected: (i) soil textural class, (ii) sand, silt, and clay contents, (iii) sand, silt, and clay contents and bulk density, and (iv) the previous variables and water content at a pressure head of 33 kPa. For water retention, the root mean square residuals decreased from 0.107 for the first to 0.060 m3 m‐3 for the fourth model while the root mean square residual Ks decreased from 0.627 to 0.451 log(cm d‐1). The neural network models performed better on our data set than four published pedotransfer functions for water retention (by ≈0.01–0.05 m3 m‐3) and better than six published functions for Ks (by ≈0.1–0.9 order of magnitude). Use of the developed hierarchical neural network models is attractive because of improved accuracy and because it permits a considerable degree of flexibility toward available input data.
Retention of Phosphate by Hydroxyaluminosilicate‐ and Hydroxyaluminum‐Montmorillonite Complexes
Authors: Saha U.K. , Inoue K. , Hiradate S.
Published: July 2010

Hydroxyaluminosilicate (HAS) ions were prepared from solutions containing hydroxyaluminum (HyA) ions and orthosilicic acids at an Al concentration of ≈4 mM; Si/Al molar ratios of 0, 0.25, 0.5, and 1.0; and NaOH/Al molar ratios of 1.0, 2.0, and 2.5. Phosphate retention behavior of montmorillonite (Mt) carrying nonexchangeably adsorbed HyA, HAS ions, or both (HyA/HAS‐Mt complexes) was studied at equilibrating solution pH of ≈5.0. The HyA/HAS‐Mt complexes showed larger phosphate retention capacities than untreated Mt. Retention of phosphate by these complexes at 0.5 to 50 mM initial P concentrations decreased with increasing NaOH/Al and Si/Al ratios of the hydroxy materials adsorbed on Mt. Phosphate, probably retained initially through surface complexation and ligand exchange reactions principally with OH or OH2 groups, coordinated with Al atoms at the broken edges of HyA or HAS polymers adsorbed on the external planar surfaces and in the interlayer spaces of Mt. This was followed by expulsion of the phosphated hydroxy materials from the Mt interlayers to the ambient solution, and finally, precipitation as amorphous Al‐phosphate solid phases. Results of this study thus merit attention in P‐fertility management as well as indicate a probable P‐induced weathering process in acidic nonallophanic Andisols and in Red‐Yellow soils (Hapludalfs and Hapludults) with a predominance of hydroxy‐interlayered minerals.
Carbon and Nitrogen Mineralization in Tallgrass Prairie and Agricultural Soil Profiles
Authors: Ajwa H. A. , Rice C. W. , Sotomayor D.
Published: July 2010

In situ mineralization of N may contribute significantly to total inorganic‐N pools deep in the soil profile. We conducted long‐term laboratory incubation experiments to evaluate the net C and N mineralization in soils collected from various depths in tallgrass prairie and agricultural fields of the same geological materials and soil type. Samples were packed to a bulk density of 1.4 g cm‐3 in 5‐cm‐diameter by 10‐cm‐long cores. The cores were incubated at 35°C for 40 wk in sealed containers. Net C mineralization was measured by evolved CO2, and N mineralized was measured by periodic leaching with NH+4 and NO‐3 measured in the leachate. Carbon and N mineralization in the surface horizon were greater in the tallgrass prairie than in the agricultural soil. In both the tallgrass prairie and agricultural soil profiles, C mineralization was least at the water‐table depth. Carbon mineralization was described by a first‐order kinetic model, but N mineralization was described better by a consecutive (sigmoidal) reaction model. At most depths, the ratios of potentially mineralizable organic C (C0) to total organic C (C0/TOC) and potentially mineralizable organic N (N0) to total N (N0/TN) were greater in the agricultural soil profile than in the tallgrass prairie soil profile. The C0 and N0 in the surface soil (0–0.2 m) represented 11.6 and 12.2% of the total organic C and N pools for the tallgrass prairie soil profile, respectively, and 21.0 and 10.2% of the total organic C and N pools for the agricultural soil profile. Management practices affected the mineralization potentials and rates of both the surface and subsurface soils.
Fall Contour Ripping Increases Water Infiltration into Frozen Soil
Authors: Pikul J. L. , Aase J. K.
Published: July 2010

Crop residue management to trap snow and soil management to improve water infiltration into frozen soil might reduce spring runoff and increase soil water storage. We hypothesized that soil macropores created by tillage would improve water infiltration when the soil was frozen. This hypothesis was tested by ripping a Dooley sandy loam (fine‐loamy, mixed Typic Argiboroll) in the fall of the year and then measuring water infiltration when the soil was frozen. A single subsoiling shank was used to rip soil to a depth of 0.3 m at 6‐m contour intervals. Ripping was compared with no ripping using a randomized experimental design having three replications. Studies were conducted during 4 yr near Culbertson, MT, on plots seeded annually to spring wheat (Triticum aestivum L.). Soil water was measured with neutron attenuation and gravimetric methods. We used a constant‐head (100 mm) method to measure water infiltration into frozen soil and a rainfall simulator for unfrozen soil. Final infiltration rate on frozen, ripped soil averaged 16 vs. 2 mm h‐1 without ripping. Final unfrozen infiltration rate in spring was 34 mm h‐1 with ripping vs. 15 mm h‐1 without ripping. Average spring water content of the top 1.2 m of soil, to a distance 1.5 m downslope from a rip, was 32 mm greater with ripping than without ripping at comparable slope positions. There were no wheat yield differences between treatments. Contour ripping can decrease water runoff, and seems best suited where spring runoff and soil erosion caused by heavy winter snows is a problem.
Restoration and Canopy‐Type Effects on Soil Respiration in a Ponderosa Pine‐Bunchgrass Ecosystem
Authors: Kaye Jason P. , Hart Stephen C.
Published: July 2010

In ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & Lawson)‐bunchgrass ecosystems of the western USA, fire exclusion by Euro‐American settlers facilitated pine invasion of grassy openings, increased forest floor detritus, and shifted the disturbance regime toward stand‐replacing fires, motivating ecological restoration through thinning and prescribed burning. We used in situ soil respiration over a 2‐yr period to assess belowground responses to pine invasion and restoration in a ponderosa pine‐bunchgrass ecosystem near Flagstaff, AZ. Replicated restoration treatments were: (i) partial restoration — thinning to presettlement conditions; (ii) complete restoration — removing trees and forest floor material to presettlement conditions, native grass litter addition, and prescribed burning; and (iii) control. Within treatments, we sampled beneath different canopy types to assess the effects of pine invasion into grassy openings on soil respiration. Growing season soil respiration was greater in the complete restoration (346 ± 24 g CO2‐C m‐2) and control (350 ± 8 g CO2‐C m‐2) than the partial restoration (301 ± 5 g CO2‐C m‐2) in 1995. In 1996, the complete (364 ± 17 g CO2‐C m‐2) and partial (328 ± 7 g CO2‐C m‐2) restoration treatments had greater growing season respiration rates than the control (302 ± 13 g CO2‐C m‐2). Results suggest that restoration effects on soil respiration depend on interannual soil water patterns and may not significantly alter regional C cycles. Soil respiration from grassy openings was 15% greater than from soil beneath presettlement or postsettlement pines in 1995 and 1996. A lack of active management will decrease belowground catabolism if pines continue to expand at the expense of grassy openings.
A Simple Spectrophotometric Determination of Nitrate in Water, Resin, and Soil Extracts
Authors: Yang J. E. , Kim J. J. , Skogley E. O. , Schaff B. E.
Published: July 2010

Nitrate is one of the most important chemicals in agricultural and environmental management. Most methods for NO3 analysis, however, require expensive equipment or complicated procedures. The objective of this study was to develop a simple, rapid, accurate procedure for NO3 analysis that can be conducted in laboratories worldwide, without the need for specialized equipment. We based our studies on a colorimetric method that involves electrophilic aromatic substitution (nitration) between nitronium and salicylate. The simplified procedure was tested for NO3 analysis of water, soil, and resin extracts. Only 1 mL of sample containing 0 to 4 mg NO3‐N L‐1 is required, and a single solution (TRI solution made as a mixture of sodium salicylate [2‐hydroxybenzoic acid monosodium salt], NaCl, and ammonium sulfamate [sulfamic acid monoammonium salt]) is used for color development. The detection limit is 0.1 µg NO3‐N, with linearity up to 4 µg NO3‐N in a final volume of 11 mL. Evaporation of the sample may be done in several ways to remove water from reactants, as long as the temperature for activiation of nitration is attained. Resin extracts from 2 M HCl required neutralization with 2 M NaOH prior to analysis, and soil extracts from 1 M KCl provided more uniform results than from 2 M KCl. Results from all types of solution samples were highly significantly correlated with those by the automated Cd‐reduction method. This simplified sodium salicylate procedure (SSP) for NO3 analysis is simple, reproducible, and it requires only inexpensive equipment.
Forms of Soil Phosphorus in Selected Hydrologic Units of the Florida Everglades
Authors: Reddy K. R. , Wang Y. , DeBusk W. F. , Fisher M. M. , Newman S.
Published: July 2010

The Florida Everglades wetland ecosystem is subject to changes in hydroperiod and nutrient loading, resulting in soil P enrichment and changes in vegetation communities. The objectives of this study were to: (i) quantify the forms of inorganic and organic P in soils from four hydrologic units of the Everglades, and (ii) develop empirical relationships among various soil P forms. Soil samples from selected hydrologic units, including the Water Conservation Areas (WCAs) and the Holey Land Wildlife Management Area (HWMA), were obtained at various locations along transects perpendicular to each nutrient input source, while selected field sites were sampled in the Everglades Agricultural Area (EAA). Spatial distribution of total P in the surface 0‐ to 10‐cm soil depth showed distinct gradients in the WCAs and HWMA soils, with high total P in soils closer to sources (canals and inflow structures) than in interior, unimpacted areas. Soil ash content and bulk density were also altered as a result of soil subsidence (for EAA soils), hydrology, and nutrient loading (for the WCAs and the HWMA soils). Influence of P loading was primarily confined to the top 30‐cm soil depth, with about one‐third of the P stored in the inorganic pool (primarily as Ca‐ and Mg‐bound P), and the remainder present as organic P. Inorganic P content was higher in surface soils and decreased with depth. Soil P enrichment indicated that for approximately 5 km from the inflow structures or canals, soils have been impacted by nutrient loading. Empirical relationships developed in this study should be useful for estimating soil P forms at the landscape level, using total P data available for a large number of sites throughout the Everglades region.
Measurement of Field Soil Hydraulic and Solute Transport Parameters
Authors: Casey Francis X. M. , Horton Robert , Logsdon Sally D. , Jaynes Dan B.
Published: July 2010

Agricultural chemical presence in groundwater has drawn attention toward transport processes occurring in soil. Hydraulic conductivity (K) and water‐holding capacity of a soil have great influence on water flow and solute transport. However, much of the chemical transport to groundwater can occur through preferential flow pathways. The simplified, preferential flow, mobile‐immobile model partitions the water content (θ) into mobile (θm) and immobile (θim) domains, with solute exchange between the domains characterized by the mass‐exchange coefficient (α). In this study a sequential tracer application technique was used and K, θ, θim, and α were estimated for a series of pressure heads (H = 10, −30, −60, and −150 mm). This method uses a tension infiltrometer to measure both hydraulic and solute transport parameters in situ. The study took place in a no‐till corn (Zea mays L.) field mapped as a Harps series soil (fine‐loamy, mixed, mesic Typic Calciaquoll). Unsaturated values of θ and K were distinct from the saturated values. Similarly, though less clear cut, distinctions between saturated and unsaturated values of θim, immobile water fraction (θim/θ), and α were observed. The medians of θ for the sequence of decreasing H values were 0.40, 0.34, 0.34, and 0.33 m3 m‐3. The median K values for the same sequence of H were 108, 1.69, 1.51, and 0.72 µm s‐1. The median θim/θ values for the H sequence were 0.40, 0.28, 0.25, and 0.39. The median values of α for the H sequence were 0.59, 0.015, 0.0028, and 0.0029 h‐1. A strong correlation between α and H suggests a velocity dependence of α.
Sensitivity of Soil Enzyme Activities to Conservation Practices
Authors: Bergstrom D. W. , Monreal C. M. , King D. J.
Published: July 2010

There is a need to assess changes in soil quality resulting from introduction of conservation practices. This study tested for an effect of tillage practice and crop rotation on activity of six soil enzymes (dehydrogenase, urease, glutaminase, phosphatase, arylsulfatase, and β‐glucosidase). Samples of the Ap horizon were collected from adjacent no‐till and tilled fields. At one site, fields were located on a simple, single slope averaging 4%, and differed in previous cropping history. The second site included coarse‐ and fine‐textured soils at lower and upper slope positions, respectively. Enzyme activities of field‐moist samples were measured during two growing seasons, and maximum reaction velocity (Vmax) values were estimated for three enzymes on a subset of air‐dry samples. At the first site, implementation of no‐till and previous cropping to forages increased activity of all enzymes. At the second site, there was no consistent response of enzyme activities to tillage practice in the coarse‐textured soils, which had relatively large total C content. In the fine‐textured soil, activity of phosphatase and arylsulfatase, and dehydrogenase in the surface (0–8 cm) layer, was greater in the no‐till field. At this location, these enzyme activities were more sensitive than total C (TC) concentration to tillage practice. Slope position and time and depth of sampling influenced enzyme activities and affected management comparisons.
Soil Aggregate and Texture Effects on Suspension Components from Wind Erosion
Authors: Mirzamostafa N. , Stone L. R. , Hagen L. J. , Skidmore E. L.
Published: July 2010

Many detrimental impacts are caused by the suspension‐size (<0.10‐mm) dust (SSD) generated during wind erosion. Prediction models of SSD are needed to assess SSD magnitudes and also aid in design of controls. Current models tend to lump together all sources of SSD from the soil surface, and their overall structure is best suited for use on large, uniform source areas. We reviewed equations developed to simulate generation of SSD on a subfield scale from individual structural components of the soil. These sources include direct emission of loose SSD, abrasion of SSD from surface clods by impacting saltating aggregates, and breakdown of saltating soil aggregates to SSD. The main objective of this study was to experimentally determine the effects of aggregate structure and soil texture on the individual SSD sources for a range of Kansas soils. Periodic sampling of 11 soils showed that the fraction of loose SSD in the upper 20 mm available for emission ranged from 0.7 to 80% of soil mass. However, variation in the mean SSD fraction in these soils was directly related to soil texture (r2 = 0.87). Content of SSD in the total mass abraded from clods in a wind tunnel ranged from 14 to 27%. This range was relatively narrow, but related to parent soil clay content (r2 = 0.69). Saltation‐size aggregates were about nine times more stable than target clods of the same soils. However, the production of SSD based on breakage coefficients of saltating aggregates was also related to clay content of the parent soils (r2 = 0.96).
Aggregation and Soil Organic Matter Accumulation in Cultivated and Native Grassland Soils
Authors: Six J. , Elliott E.T. , Paustian K. , Doran J. W.
Published: July 2010

Tillage intensity affects soil structure and the loss of soil organic C and N. We hypothesized that no‐tillage (NT) and conventional tillage (CT) differentially affect three physically defined particulate organic matter (POM) fractions. A grassland‐derived Haplustoll was separated into aggregates by wet sieving. Free light fraction (LF) and intra‐aggregate POM (iPOM) were isolated. Natural abundance 13C was measured for whole soil C, free LF C, and iPOM C. The mean residence time of soil C under CT (44 yr) was 1.7 times less than in NT (73 yr). The amount of free LF C was 174, 196, and 474 g C m‐2 for CT, NT, and NS, respectively. Total iPOM C amounts in CT, NT, and NS were 193, 337, and 503 g C m‐2, respectively. The level of fine iPOM C (53–250 µm) level in macroaggregates (250–2000 µm) obtained after slaking was five times greater in NT vs. CT and accounted for 47.3% of the difference in total POM C between NT and CT. The amount of coarse iPOM C (250–2000 µm) was only 2.4 times greater and accounted for only 21% of the difference in total POM C. Sequestration of iPOM was observed in NT vs. CT, but free LF was not influenced by differential tillage. We conclude that differences in aggregate turnover largely control the difference in fine iPOM in CT vs. NT and consequently SOM loss is affected by both the amount of aggregation and aggregate turnover.
Residual Effects of Crop Residues on Grain Production and Selected Soil Properties
Authors: Power J. F. , Koerner P. T. , Doran J. W. , Wilhelm W. W.
Published: July 2010

Returning crop residue improves water conservation and storage, nutrient availability, and crop yields. We have little knowledge, however, of the residual impacts of crop residues on soil properties and crop production. We hypothesized that residual impacts of crop residues vary with the amount of residues used. A 10‐yr study near Lincoln, NE, evaluated the residual effects of an earlier 8‐yr study of various crop residue amounts on crop growth and selected soil properties. From 1978 through 1985, crop residues were returned at 0, 50, 100, and 150% of the quantity produced by the previous crop (averaging 0 to ≈6 Mg ha‐1 yr‐1). Continuous corn (Zea mays L.) was produced 1986 through 1995 on these plots, except sorghum [Sorghum bicolor (L.) Moench] was substituted in several years. To study management effects on residual responses, plots were subdivided with or without tillage, N fertilizer (60 kg N ha‐1), and hairy vetch (Vicia villosa L.) cover crop. Residual effects of the 150% residue amount increased grain production 16% compared with the 0% amount (4900 vs. 4250 kg ha‐1, respectively), and were not affected by time or other management practices. Increasing previous residue amount did enhance soil N availability (from 73.0 to 82.3 kg autoclave‐mineralizable N ha‐1) and Bray soil P (16.7 to 20.3 kg ka‐1). These results are among the first to show that residual effects of crop residue are prolonged (half‐life of ≈10 yr) and probably result from changes in soil properties that enhance soil nutrient availability.