bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tillage‐Induced Horizontal Periodicity of Preferential Flow in the Root Zone
Authors: Petersen C. T. , Hansen S. , Jensen H. E. 
Published: July 2010

AbstractFlow patterns for water and solutes in the root zone are often heterogeneous. Understanding the spatial variability of flow is essential in solute‐transport studies and for management of chemical movement. We hypothesized the occurrence of effects of past tillage operations (plowing and seed bed preparation with and without rotovation) on flow patterns and that such effects could be determined from dye tracing. High‐resolution, digitized images of flow patterns on 221 vertical soil profiles (1 m2) perpendicular to the direction of plowing in two sandy loam soils (Typic Agrudalfs) were analyzed using time series analysis. Significant (P < 0.01) horizontal periodicity with a characteristic length equal to the furrow width for the plow (35 cm) was found for the degree of dye coverage in the 0‐ to 25‐cm topsoil layer (12 out of 15 plots) and for the number of stained channels in the 25‐ to 100‐cm subsoil layer (11 out of 15 plots) after plowing and conventional seed bed preparation (harrowing). The 35‐cm‐scale periodic variability of flow patterns in the subsoil was linearly related to the variability of patterns in the topsoil in three out of 17 plots (P < 0.01). Significant (P < 0.05) linear trends with horizontal distance were found for the degree of dye coverage in the topsoil (11 out of 20 plots), and for the number of stained channels in the subsoil (10 out of 17 plots). Rotovating after seedbed harrowing (five plots) reduced the number of stained flow pathways in the subsoil.
Light Fraction Soil Organic Matter and Available Nitrogen following Trees and Maize
Authors: Barrios E. , Buresh R. J. , Kwesiga F. , Sprent J. I. 
Published: July 2010

AbstractTrees grown for 2 to 3 yr in rotation with crops (tree fallows) are a potential technology for increasing soil fertility in maize‐based cropping systems in sub‐Saharan Africa. The objective of our study was to determine the effect of contrasting fallow options, compared with continuous maize (Zea mays L.), on light fraction soil organic matter (SOM), inorganic N (NO3 and NH4), and N mineralization. Soil was collected 2 and 3 yr after the establishment of fallow and maize systems on a sandy clay loam (Ustic Rhodustalf) in Zambia. Total soil C, N, and P were not different among the fallow and maize systems. Soil inorganic N and amount of light fraction N (150–2000 µm, <1.13 Mg m‐3) were higher for the mean of five N2‐fixing trees than the one non‐fixing tree. Inorganic N, anaerobic and aerobic N mineralization, and light fraction N were (i) higher for the mean of the two trees with lowest (lignin + polyphenol)/N ratios in leaf litter than the two trees with highest ratios in leaf litter and (ii) higher for Sesbania sesban (L.) Merr. than the mean of other trees. Sesbania and fertilized maize monoculture resulted in similar soil inorganic N, but N mineralization and light fraction N were greater after sesbania. Comparable effects of the systems on light (<1.13 Mg m‐3) and light + intermediate fraction (<1.37 Mg m‐3) SOM suggest that light and intermediate fractions can be combined to simplify the fractionation procedure. Tree species vary greatly in effect on N availability and hence their suitability for soil fertility replenishment.
Wind Erosion Control with Crop Residues in the Sahel
Authors: Sterk G. , Spaan W. P. 
Published: July 2010

AbstractMulching for wind erosion control in Sahelian farming systems is limited by low biomass production and use of crop residues for other purposes. The aim of this study was to test the effectiveness in soil protection created by two low amounts of crop residues. A field experiment was conducted in southwest Niger, on a Psammentic Paleustalf (sandy, siliceous, isohyperthermic) during the early rainy seasons of 1994 and 1995. Particle mass transport was quantified in two plots of 55 by 70 m. During the first storms of both seasons, the plots were without a mulch cover. Afterward, one plot was covered with flat pearl millet [Pennisetum glaucum (L.) R. Br.] stalks. The application rates were 1500 and 1000 kg ha‐1 during the first and second seasons, respectively. To quantify the mulch effect, mass transport rate differences between the two bare plots were quantified with a multiple linear regression model (R2 = 0.89), using wind speed (7.4–12.3 m s‐1), wind direction, and storm duration (464–3835 s). Total mass transport rates were reduced from 365.2 to 132.9 g m‐1 s‐1 (63.6%) with 1500 kg ha‐1, and from 325.1 to 188.0 g m‐1 s‐1 (42.2%) with 1000 kg ha‐1 of crop residues. Soil protection tended to decrease with increasing wind speed. Linear regression indicated that the reduction in mass transport becomes zero at wind speeds of 11.1 and 16.0 m s‐1 for the 1000 and 1500 kg ha‐1 covers, respectively. The 1000 kg ha‐1 cover even enhanced sediment transport by 6.5% during one storm with a wind speed of 11.3 m s‐1. The 1500 kg ha‐1 mulch cover reduced sediment transport from 49.7 to 80.2% during five storms with wind speeds varying from 8.3 to 10.6 m s‐1, and is therefore recommended as the better application rate for wind erosion control in the Sahel.
A Single, Continuous Function for Slope Steepness Influence on Soil Loss
Authors: Nearing M. A. 
Published: July 2010

AbstractRecently proposed relationships for the effect of slope steepness on soil loss by water are linear functions of the sine of the slope angle. The Revised Universal Soil Loss Equation (RUSLE) uses two such functions: one for slopes <9% and another for slopes >9%. Recent research indicates that yet a different linear function is necessary for slopes greater than approximately 22%. The objective of this study was to develop a single slope steepness function that is representative of the data for all slopes. The resultant equation takes the form of a logistic function. It closely follows the RUSLE relationships for the slope steepness factor for slopes up to 22%, and also fits existing data for slopes greater than those from which the RUSLE relationships were derived.
Seasonally Precipitated Iron Oxides in a Vertisol of Southeast Texas
Authors: Golden D. C. , Turner F. T. , Sittertz‐Bhatkar H. , Dixon J. B. 
Published: July 2010

AbstractThe composition and crystallinity of Fe oxides in soils determines the reactivity and toxicity of Fe through redox and solubility reactions. The mineralogy and crystallinity of Fe oxides seasonally precipitating on ped surfaces and within soil pores and those forming around rice (Oryza sativa L.) roots were investigated by x‐ray diffraction, electron microscopy, and electron microprobe analyses. Iron oxides precipitated on exposed surfaces of the League soil (fine, montmorillonitic, hyperthermic Oxyaquic Dystrudert), which is flooded during rice production, differed from Fe phases precipitated around rice roots. Iron oxides precipitated on ped surfaces and within soil pores were relatively poorly crystallized while those precipitated on rice‐root surfaces were well crystallized. The presence of soluble Si and P during flooding may be responsible for precipitation of the less crystalline Fe oxides. Infrared and electron‐diffraction data on the precipitate suggest the presence of PO4 groups either adsorbed or coprecipitated with Fe oxide. Depletion of Si and P from the rhizosphere is believed to contribute to the formation of well‐crystallized lepidocrocite on root surfaces. The poorly crystalline Fe‐oxide precipitate that forms on ped surfaces upon draining and oxidation of the League soil has adsorbed or occluded Si and P. Thus, Fe oxides may influence the mobility of Si and P in alternately flooded and drained soils. Electron‐diffraction data suggests that some of the Fe may be precipitated as strengite. Upon reduction and dissolution, these oxides release Fe, Si, and P into the soil solution and influence the nutrient dynamics in the rhizosphere of the rice plant.
Aggregation and Aggregate Size Effects on Extractable Iron and Aluminum in Two Hapludoxs
Authors: Lima Jose M. , Anderson Sharon J. 
Published: July 2010

AbstractOxisols contain stable aggregates, and sorption and desorption kinetics for aggregates typically are slower than for disaggregated samples. The objectives of this research were to determine whether aggregation inhibits Fe and Al extraction more in large than small aggregates, and to determine whether aggregate composition differs between large and small Oxisol aggregates. Water‐stable 1‐ to 2‐ and 0.125‐ to 0.25‐mm aggregates were separated from two Oxisols that have similar total Fe contents but different goethite/hematite and kaolinite/gibbsite ratios. To assess the effect of aggregation on extractable Fe and Al, subsamples were disaggregated by sonication. Disaggregated samples and intact aggregates were then reacted with oxalate and dithionite‐citrate‐bicarbonate (DCB). In the larger aggregates, oxalate and DCB extracted 10 to 20% less Fe and Al from intact aggregates than from disaggregated samples. In the smaller aggregates, aggregation only caused a 5 to 10% decrease. Aggregation generally inhibited Fe and Al extraction by DCB more in B than A horizons. There also were small compositional differences between large and small aggregates. In A horizon samples, large aggregates contained more clay and had correspondingly greater extractable Fe and Al than did small aggregates, although the extractable Fe and Al in the clays themselves did not differ between large and small aggregates. Goethite/hematite ratios were 10 to 20% greater in clay from large than small aggregates. Thus, the rate and extent of sorption‐desorption reactions may differ between large and small aggregates not only because of physical differences, but also because of slight compositional differences.
Tikhonov Regularization of Electrical Conductivity Depth Profiles in Field Soils
Authors: Borchers Brian , Uram Tom , Hendrickx Jan M. H. 
Published: July 2010

AbstractElectromagneetic induction is an established, noninvasive technique for measuring the apparent electrical conductivity of soils and contaminants in soils and aquifers. Nevertheless, the noninvasive determination of electrical conductivity depth profiles using only aboveground electromagnetic induction measurements remains difficult since it involves ill‐posed inverse problems. Tikhonov regularization is an established technique for the solution of ill‐posed linear inverse problems. We used Tikhonov regularization for estimating the electrical conductivity depth profile of the soil from aboveground electromagnetic induction measurements. Results from the inversion of sets of Geonics EM‐38 measurements are reported. It was found that this technique is superior to other inverse techniques previously reported in the literature.
Spatial Variability of Water Fluxes in Soil: A Field Study
Authors: Heuvelman W. J. , McInnes K. J. 
Published: July 2010

AbstractKnowledge of spatial variability of soil properties is important for soil sampling and modeling water and solute transport through soil. A field study was conducted on a Silawa‐variant loamy fine sand (fine, mixed, thermic Udic Paleustalf) in Brazos County, Texas, to evaluate spatial variability and convergence and divergence of water fluxes through the soil profile. A 7 by 14 grid of interception cells (each 25 by 25 mm) was built to collect surface‐applied water at 0.3‐, 0.9‐, and 1.2‐m depth. The interception cells were installed on the ceilings of tunnels that had been hand dug horizontally into the walls of a large backhoe‐dug pit. Water was applied under a positive head of ≈50 mm in a 1.2 by 1.2 m infiltration square. Normal and lognormal probability functions were fitted to frequency distributions of intercepted fluxes from topsoil and subsoil, respectively, with correlation coefficients of 0.95 and higher. Most nonmatrix flow was found at 0.9 m in the Bt2 horizon. We speculate that fluxes were most heterogeneous in this horizon because of associated soil texture and structure. Compared with soil at 0.3 and 1.2 m, texture was finer, peds were larger, and clay films were more abundant at 0.9 m. This relationship with pedologic development suggests that descriptions of texture and structure might be used to predict spatial distributions of fluxes and design sampling schemes. Convergence of water flowpaths was observed from 0.3 to 0.9 m while divergence occurred from 0.9 to 1.2 m.
Miniature Rain Simulator for Field Measurement of Soil Infiltration
Authors: Ogden C. B. , van Es H. M. , Schindelbeck R. R. 
Published: July 2010

AbstractIn studies of erosion, runoff, and infiltration, high soil variability may demand many replicate measurements and rapid, inexpensive methodology. We developed a drop‐forming rainfall simulator in which flow through long, coiled capillary drip tubes is controlled by an adjustable Mariotte‐type bubbling tube. These rain simulators are inexpensive, rugged, simple to operate, easily transported, and require minimal maintenance. Responses to pressure head and water temperature changes were determined for two simulators using tap water. Flow response to pressure head changes corresponded closely to that predicted by Poiseuille's Law. Response to increasing water temperatures was somewhat less than predicted, due to formation of bubbles in the capillary tubes. Simulators incorporating long, coiled capillary tubes can provide combinations of low flow rates and large drop sizes, or a desired range of flow rates when appropriate drip tube diameters, lengths, and numbers of tubes per unit area are combined.
Organic Matter, Sodicity, and Clay Type: Influence on Soil Aggregation
Authors: Barzegar A. Rahman , Nelson Paul N. , Oades J. Malcolm , Rengasamy Pichu 
Published: July 2010

AbstractOrganic matter influences aggregation in non‐sodic soils, but less is known about its role in sodic soils. The purpose of this study was to examine the role of organic matter in aggregation and clay dispersion in soils with different levels of sodicity. Prepared soils with 15% clay (smectitic or illitic) and natural soil aggregates (from a smectitic clay soil [Pellustert] with 25 g kg−1 organic C and a pair of illitic loams [Rhodoxeralfs] with 15 and 29 g kg−1 organic C) were equilibrated with solutions having sodium adsorption ratios (SAR) of 0, 5, 15, and 30. Pea (Pisum sativum L.) straw was added at 50 g kg−1 to the prepared soils, which were then incubated. Changes in aggregation during incubation were similar irrespective of clay type. After 7 d incubation with no added straw at SAR 0 and 30, the amounts of spontaneously dispersible clay were 5.9 and 23.7 g kg−1 soil, and mechanically dispersible clay was 11.9 and 23.3 g kg−1 soil. Macroaggregation (>250 µm) was 125 and 41 g kg−1 soil at SAR 0 and 30. After 67 d incubation with pea straw, spontaneously dispersible clay contents were 2.1 and 5.4 g kg−1, mechanically dispersible clay contents were 9.0 and 17.7 g kg−1 soil, and macroaggregation was 533 and 416 g kg−1 soil at SAR 0 and 30. The effects of sodicity and organic matter on structural stability of the natural soil aggregates were similar to those in the prepared soils, but macroaggregation was less, and the smectitie clay soil was more sensitive to sodicity than the illitic loams. This work showed that organic matter has at least as great a role in aggregation in sodic soils as in non‐sodic soils.
A Landscape‐Scale Study of Soil Quality in Three Prairie Farming Systems
Authors: Boehm M. M. , Anderson D. W. 
Published: July 2010

AbstractThe relationship between farming practices and the quality or function of agricultural soils is difficult to characterize because of the complexity of soils and spatial variability within the landscape. This study in Saskatchewan, Canada, tested the hypothesis that soil quality differed among farming systems that varied in fallow intensity (crop‐fallow [fallow every second year], extended rotation [fallow every 3–5 yr], and continuous cropping [no fallow]) and that differences could be assessed using soil properties as indicators of soil quality. In 20 fields with coarse to fine loamy, glaciolacustrine soils (Typic Haploborolls), major landform elements were sampled. As years of continuous cropping and related fertilizer inputs increased, increases in organic C (by weight [Cw] 22%, by volume [Cv] 3%), aggregate size (24%) and stability (45%), microbial biomass (50%), resin‐sorbed N (503%) and P (227%), and nitrification potential (≈25%), decreases in bulk density (8%) and infiltration time (19%), and greater solum thickness (26%) were measured. We postulate that the changes in soil properties indicate an improvement in soil quality under the continuous cropping system and that the observed changes were caused by more frequent additions of crop residues (organic C), especially near the soil surface, which resulted in lower bulk density, more microbial biomass, and greater soil aggregation. It seems that the annual inputs of crop residues in conjunction with nutrients, such as N and P, resulted in the formation of an active and labile soil organic matter, increased availability of soil N and P, and a comparatively large pool of microbial C.
Carbon to Organic Matter Ratios for Soils in Rocky Mountain Coniferous Forests
Authors: Jain Theresa B. , Graham Russell T. , Adams David L. 
Published: July 2010

AbstractVegetation type, soils, climate, and conversion ratios influence estimates of terrestrial C. Our objectives were to (i) determine carbon to organic matter (C/OM) ratios for brown cubical rotten wood, litter, surface humus, soil wood, and mineral soils; (ii) evaluate the validity of using 0.58 and 0.50 ratios for estimating C in mineral and organic soil components, respectively; and (iii) determine if C/OM relationships were applicable across broad geographic areas. The study sites were located from the southern to northern Rocky Mountains. They differed in vegetation, soil parent material, and climate. The C/OM regression slopes we developed for organic components were quite consistent and relatively constant across vegetation types ranging from 0.43 to 0.51 and were similar to the 0.50 traditional ratio. The C/OM regression slopes for mineral soils ranged from 0.16 to 0.48 depending on vegetation type. These slopes were lower than the 0.58 ratio often applied. The reliability of simple ratios when used in estimating C as a function of organic matter is often overestimated. Error and bias can be introduced into C estimates when using simple ratios. This study refined C/OM regressions for mineral soils and provided regressions for organic soil components. Information developed in this study can be applied to improve regional and global C assessments.
Spatial Variability of Nitrogen Mineralization at the Field Scale
Authors: Mahmoudjafari M. , Kluitenberg G. J. , Havlin J. L. , Schwab A. P. , Sisson J. B. 
Published: July 2010

AbstractSpatial variability of N mineralization represents a potential problem in predicting the quantity of N mineralized under field conditions. An understanding of mineralization variability is needed if prediction of potential mineralization is to be incorporated into fertilizer recommendation models. The objective of this study was to characterize spatial variability of N mineralization in a Kansas agricultural field. Intact undisturbed soil cores were collected at 108 locations within a 1.7‐ha field following wheat (Triticum aestivum L.) harvest. The undisturbed cores were incubated aerobically, and NO−3 was leached periodically as a measure of mineralization. Variability was characterized by examining the spatially distributed values of mineralization potential, N0, and mineralization rate constant, k, parameters of the classical first‐order mineralization rate model. Values of N0 were distributed normally with low variability (coefficient of variation [CV] = 15%) and weak autocorrelation. Values of k also followed a normal distribution with low variability (CV = 14%) but were spatially independent. Both N0 and k determined the spatial pattern of Nm, the quantity of N mineralized at a particular time. Variability in k controlled the spatial pattern of Nm earlier in the incubation period, and variability in N0 controlled the spatial pattern late in the incubation period. The incubation approach used in this study allowed characterization of the spatial patterns in N0, but the spatial variability of k observed in this study may not adequately represent field conditions because conditions of constant temperature and water content were used.
Preferential Transport of Solute through Soil Columns Containing Constructed Macropores
Authors: Li Yimin , Ghodrati Masoud 
Published: July 2010

AbstractImplication of macropore flow in enhancing solute transport has prompted much research. The objective of this study was to characterize solute transport in constructed macropores in three soils of different water conductivities. The macropores were constructed by inserting metal rods into uniformly packed soil columns of 0.2‐m i.d. and 0.3 m long. A set of nine soil columns was prepared and a total of 52 displacement experiments was conducted using NO3 as a tracer. Significant preferential flow occurred in the silt loam containing seven continuous macropores of 3‐mm diam. even at fluxes <0.5K, where K is saturated hydraulic conductivity of a column matrix. At fluxes far smaller than those causing saturation, no preferential flow took place and the breakthrough curves (BTCs) displayed single peaks, indicating that only the matrix contributed to solute transport. As fluxes increased, BTCs exhibited double peaks, and the relative magnitudes and positions of the two peaks were flux dependent. These two‐curve or double‐peak BTCs may represent solute transport through the macropores and the matrix, respectively. Due to the difficulty in keeping macropores open in silica sand, especially at fluxes ≥K, little evidence of preferential flow was observed in this system. This was also ascribed to the porous and conductive nature of the medium. Preferential flow also occurred in the loamy sand, but a greater flux was needed to get the same degree of preferential flow as in the silt loam. In general, in the coarser soil, less preferential flow occurred even at similar normalized flow rates. Macropore continuity has been shown to be increasingly important in macropore flow when flux increases.
A Generalized Solution to Infiltration from Single‐Ring Infiltrometers by Scaling
Authors: Wu L. , Pan L. 
Published: July 2010

AbstractWater infiltration into soil from a ring infiltrometer is an important issue for many scientific and engineering problems. Due to the complexity of the three‐dimensional water flow, no generalized solutions are available to describe the infiltration process from a finite ponding source. This study applied a scaling technique to three‐dimensional axisymmetric infiltration from a single‐ring infiltrometer to obtain a generalized infiltration solution and evaluated the effects of soil conditions and ring geometry on the scaled infiltration curves. A numerical model based on Richards' equation in the cylindrical coordinates was developed to simulate infiltration processes for three representative soils. By properly choosing length‐ and time‐scale factors, the infiltration curves of the three test soils representing different hydraulic properties were successfully scaled to essentially a single dimensionless infiltration curve. Tests showed that the dimensionless infiltration curve was not very sensitive to applied ponding head, ring diameter, ring insertion depth, and initial soil conditions. Finally a dimensionless infiltration equation in the form of i* = a + blt*0.5 was developed. The example showed that the generalized infiltration equation can predict the infiltration curve simulated by Richards' equation very well.