bluuebunny/crossref_metadata_2025 huggingface dataset:
Corn Yield and Phosphorous Uptake with Banded Urea and Phosphate Mixtures
Authors: Fan M. X. , MacKenzie A. F.
Published: July 2010

Low fertilizer P use efficiency is a problem in crop production on acid soils, but efficiency can be affected by methods of fertilizer application. A field experiment was conducted on two eastern Canadian soils (fine‐silty to fine, mixed, frigid Typic Humaquepts) with different pH (5.0 and 6.0 initially) to evaluate the effect of banding different rates of urea with acidic P fertilizers on corn (Zea mays L.) yield and fertilizer use efficiency. Three rates of urea (0, 30, and 60 kg N ha−1) banded with two sources of P (triple superphosphate [TSP] and monoammonium phosphate [MAP] at 38.7 kg P ha−1) or alone without P fertilizer, as control, were studied in 1990. In 1991, three rates of TSP (0, 19.4, and 38.7 kg P ha−1) were used in combination with the same three rates of urea to determine the effect of banding ratio of urea‐N/TSP‐P. The residual fertilizer effects of the 1990 treatment were investigated in 1991. Banding urea with TSP or MAP increased soil extractable P (Mehlich III). At the six‐leaf stage, plant P concentrations and dry matter yield increased linearly with both banded N and P in the Ste. Rosalie soil, and quadratically in the Ormstown soil. Total N and P uptake by corn increased in both years by banding urea with TSP or MAP, and fertilizer P use efficiency increased by 40 to 80%. Urea banded with P increased grain yield in both soils. No interactions were found between banded N rates and P sources in 1990, and between banded N rates and P rates in 1991. Greater residual effects of P fertilizer were found on grain yields and P uptake where P was banded with urea compared with no urea.
Soil Water Content and Potential Measured by Hollow Time Domain Reflectometry Probe
Authors: Baumgartner Norbert , Parkin Gary W. , Elrick David E.
Published: July 2010

A new soil probe used in conjunction with time domain reflectometry (TDR), tensiometry, and solution extraction devices and designed to allow simultaneous in situ measurement of soil‐water content, matric potential, and solute concentration is proposed. Hollow stainless steel electrodes with a porous stainless steel tip serve as TDR wave guides in a standard two‐parallel‐probe configuration. The porous tip allows water inside the hollow rods to equilibrate with the soil water in an unsaturated or saturated system. A pressure transducer system is used to measure the soil matric potential around the porous tip. A vacuum pump can be used to withdraw soil solution through the permeable porous tip. A preliminary comparison between measurements of soilwater content obtained by a two‐solid‐wires TDR probe and the new probe gave encouraging results. Favorable agreement was obtained between measurements of the soil matric potential and depth to an artificial water table.
Nitrogen Mineralization and Ammonia Volatilization from Fractionated Poultry Litter
Authors: Cabrera M. L. , Tyson S. C. , Kelley T. R. , Pancorbo O. C. , Merka W. C. , Thompson S. A.
Published: July 2010

Passing poultry litter through a 0.83‐mm sieve generates a fine fraction higher in N concentration and cheaper to transport per unit of N than the whole litter. One objective of this work was to determine if the organic N in the fine fraction undergoes faster mineralization than that in the whole litter. Whole litter or fine fraction from three poultry houses was either mixed with samples of Dothan loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudult) or applied on the soil surface at a rate of 100 kg N ha−1. The treatments were incubated at water field capacity and 27°C, with samples extracted at 3, 7, and 14 d. Differences in N mineralization were relatively small between materials; by Day 14, the organic N had undergone a slightly higher mineralization in the fine fraction (51.5%) than in the whole litter (44.5%). A second objective was to compare the potentials for net N mineralization, NH3 volatilization, and respiration of whole poultry litter and fine fraction stored for 7 d at 25 °C and at two water contents (unamended [0.12–0.26 kg H2O kg−1] and 0.5 kg H2O kg−1). On an equal‐mass basis, net N mineralization and NH3 volatilization were larger in the fine fraction than in the whole litter, whereas respiration was similar in both materials. All processes increased with an increase in water content. These results suggest that the fine fraction should be managed similarly to the whole litter when applied to soil and that it may lose more NH3 than does the whole litter during storage, particularly at relatively high water contents.
Decomposition and Nitrogen Dynamics of Crop Residues: Residue Quality and Water Effects
Authors: Schomberg H. H. , Steiner J. L. , Unger P. W.
Published: July 2010

Understanding environmental and residue influences on decomposition and nutrient dynamics under diverse conditions is critical for efficient resource management. Our objective was to evaluate the influence of water on decomposition and N dynamics for surface and buried residues. Decomposition of alfalfa (Medicago sativa L.), grain sorghum (Sorghum bicolor [L.] Moench), and winter wheat (Triticum aestivum L. emend. Thell.) residues in fiberglass bags on the surface or buried at 120 mm in Pullman soil (fine, mixed, thermic Torrertic Paleustoll) at Bushland, TX, was measured from May 1990 to May 1991. A line‐source sprinkler provided five water regimes (336, 287, 166, 60, and 5 mm) while precipitation provided 305 mm water. Decomposition coefficients (k) were greater for alfalfa than for wheat or grain sorghum and were greater for buried than for surface residues. Rate coefficients increased linearly with water applied. The increase was greater for alfalfa than for sorghum and wheat. Net N mineralization occurred from alfalfa residues throughout the study. Net N immobilization was longer than 1 yr for surface wheat and sorghum and about 0.33 yr for buried residues. Both Nmax (grams N immobilized per kilogram of original biomass) and Neqv (grams N immobilized per kilogram of biomass loss) were influenced by crop and placement but not water regime. The Nmax value was similar for surface wheat and sorghum residues but was 50% lower for buried wheat than for sorghum. The Neqv indicated the N requirement of microorganisms was less for buried than for surface residues. Water and residue quality interactions affecting decomposition and N dynamics should be considered in residue management strategies for soil protection and nutrient cycling.
Strongly Contrasting Redoximorphic Patterns in Virginia Valley and Ridge Paleosols
Authors: Stolt M. H. , Ogg C. M. , Baker J. C.
Published: July 2010

Soils with bisequel morphology and classified as Typic or Plinthic Paleudults are common in the Virginia Valley and Ridge Province. Horizons in the older materials have redoximorphic features that are strongly contrasting with respect to color and distinctness of boundary. Research documenting these horizons is nonexistent. We examined the physical and chemical properties of these horizons to describe the strongly contrasting redoximorphic patterns (SCRP) and investigate their genesis. Two types of SCRP occur. In both types, redox concentrations have Munsell colors of 2.5 YR 3/6, 4/6, or 3/2. In one case, depletion features (10YR 5/6 or 6/2) are randomly distributed throughout the horizon. These horizons are dense (bulk density of 1.75 g cm−3), which restricts water movement and promotes Fe segregation. In the other type of SCRP, most Fe concentrations, depletions, and planar voids are oriented parallel to the soil surface. These soils have a fluctuating water table. Dithionite‐extractable Fe ranges from 70 g kg−1 in redox concentrations to 4 g kg−1 in adjacent depletion features. Goethite occurs in both redox concentration and depletion clay fractions. Hematite only occurs in the redox concentration clay fractions. Depletion features have lower coarse/fine ratios (separated at 20 µm), more oriented clay, and 10 to 20% more clay than associated redox concentrations. Horizons with SCRP are dominated by nodules and masses in ped interiors, and Fe depletion features along voids. Thus, Fe is primarily reduced along voids and moves into the matrix. Horizons with a fluctuating water table also contain Fe‐rich pore linings. Iron is concentrated on these surfaces because these pores are the first to drain as the water table recedes.
Morphology, Chemistry, and Mineralogy of Isotropic Aluminosilicate Coatings in a Guadeloupe Andisol
Authors: Jongmans A. G. , van Oort F. , Buurman P. , Jaunet A. M. , van Doesburg J. D. J.
Published: July 2010

Few micromorphological and in situ submicroscopical studies exist of neoformed amorphous and crystalline clay coatings, and little is known about the genesis and distribution patterns of these coatings and their dependence on site conditions. Our study describes the distribution and composition of isotropic coatings, infillings, and pseudomorphs after roots in a Hapludand on Holocene andesitic pyroclastics in humid tropical Guadeloupe. Field observations show the occurrence of fine‐textured, very pale brown to yellow (10YR 8/3‐8/6) coatings, infillings, and pseudomorphs after roots in large pores in the Bw2 and 2C horizons of the soil. Thin‐section analyses demonstrated that these features are isotropic, translucent, nonlaminated, and appear pale yellow in plane polarized light, indicating that they consist of amorphous material. In situ submicroscopical analyses revealed that the coatings in the Bw2 horizon consist of allophane and imogolite with an Al/Si ratio of 2, whereas those in the 2C horizon consist exclusively of allophane with an Al/Si ratio of 1.4. The fine groundmass adjacent to the coatings in the Bw2 horizon has an Al/Si ratio of 1.4. The coatings resulted from precipitation of weathering products of mainly volcanic glass and plagioclase. The observed differences in composition of the coatings in the Bw2 and 2C horizons are thought to be the result of different leaching conditions.
Long‐Term Effects of Crop Management in Wheat‐Fallow: II. CENTURY Model Simulations
Authors: Parton William J. , Rasmussen P. E.
Published: July 2010

There is increasing need to develop models to assess the long‐term effects of management practices on soil and environmental quality, and to test these models across a wide range of environments. The CENTURY model was used to simulated long‐term management practices for wheat (Triticum aestivum L.)‐fallow agriculture. The objectives were to compare the accuracy of predicted vs. observed data and use the model to help interpret observed data and to determine the long‐term impact of crop management on C and N stabilization in soil. The model simulated grain and straw yield and grain N uptake within ±10% of the observed data, and 0‐ to 30‐cm soil C and N within ±5%. Improvement in performance requires addition of a dynamic plant growth submodel to represent the effect of soil N on C and N allocation to roots, straw, and grain. Soil C changes were a linear function of aboveground C inputs; an input of 200 g C m−2 yr−1 (4650 kg straw ha−1) was required to stabilize soil C at its present level. Estimates of soil C stabilization efficiency ranged from 12 to 27% and was highest for the high N fertilizer treatment. Soil N stabilization efficiency was higher for organic N additions (37–46%) than for inorganic additions (18–26%). Inorganic N treatments had similar N removal in grain, higher other nonidentifiable N losses, but lower N stabilization in soil than organic N treatments. Soil N data suggest that mineralization of N from the 30‐ to 60‐cm layer needs to be considered in the N budget, as nearly 39 g m2 were mineralized between 1931 and 1986.
Spatial Distribution of Soil Nutrients in a Northern Everglades Marsh: Water Conservation Area 2A
Authors: DeBusk W. F. , Reddy K. R. , Koch M. S. , Wang Y.
Published: July 2010

Increased nutrient loading to the northern Everglades from the nearby Everglades Agricultural Area (EAA) has raised concerns of eutrophication of this oligotrophic wetland. A field study was conducted to determine the influence of nutrient loading on spatial distribution of P, N, C, and related physico‐chemical parameters in the peat soils (Histosols) of Water Conservation Area 2A (WCA‐2A) in the northern Everglades. Field sampling of the top 30 cm of soil was performed at 74 sites across WCA‐2A. Isarithmic plots of N and P forms based on geostatistical analyses revealed widespread enrichment of P, especially in areas proximal to surface inflows importing nutrient‐laden water from the EAA. Enrichment of less magnitude was shown for soil N, while spatial variability of C, bulk density, ash content, and pH were minimal. Concentration of soil porewater NH+4‐N was typically in the 1.5 to 2.5 mg L−1 range in the interior (less impacted) region of WCA‐2A, compared with 4 to 8 mg N L−1 near surface inflows at the northern end of WCA‐2A. In contrast, soluble reactive P in the porewater varied from ≈ 100 µg L−1 or less in the interior marsh to >1000 µg L−1 near inflow structures. Mean soil total P at a depth of 0 to 10 cm was 473 mg kg−1 in the interior marsh, compared with 1338 mg kg−1 in the areas adjacent to inflows. Results of this study show that WCA‐2A soil has served as a net storage for the increased load of P in nutrient‐laden surface inflows. Much of the additional soil P is available for plant uptake, based on the magnitude of P enrichment across a large area. Nutrient enrichment in the soil corresponded with the occurrence of cattails (Typha domingensis Pers. and T. Latifolia L.) in areas previously dominated by sawgrass (Cladium jamaicense Crantz).
Unsaturated Hydraulic Conductivity from Transient Multistep Outflow and Soil Water Pressure Data
Authors: Eching S. O. , Hopmans J. W. , Wendroth O.
Published: July 2010

Soil water retention and unsaturated hydraulic conductivity functions [K(θ)] estimated by the inverse solution technique through minimization of differences between measured and simulated transient outflow may be nonunique and differ from independently measured soil hydraulic data. Numerical and experimental studies have shown the benefit of using simultaneously measured soil water pressure head in the estimation of the soil water retention curve by the inverse technique. In this experimental study, soil water pressure head and transient cumulative outflow measured simultaneously are used to estimate K(θ). An alternative method for the direct measurement of K(θ) from transient multistep outflow experiments was adopted. Desorption experiments were carried out for disturbed Yolo silt loam (fine‐silty, mixed, nonacid, thermic Typic Xerorthent), Panoche loam (fine‐loamy, mixed [calcareous], thermic Typic Torriorthent), Hanford sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Xerorthent), and Oso Flaco fine sand columns. The optimized K(θ) values agreed well with the directly measured data for all soils, except the sand. Additionally, soil hydraulic functions so obtained for the Panoche loam agreed well with those determined using the evaporation method. Measured infiltration in a column of the Panoche loam matched numerical results using optimized parameters as determined from a sorption multistep experiment. The addition of soil water pressure head values in the optimization procedure provides unique parameters for the unsaturated hydraulic conductivity functions under our experimental conditions.
Infiltration and Redistribution of Organic Liquids in Layered Porous Media
Authors: Cary J. W. , Simmons C. S. , McBride J. F.
Published: July 2010

The remediation of many toxic waste sites throughout the world requires a better understanding of the flow of organic liquids in the vadose zone. The infiltration and redistribution of three water‐immiscible oils into columns filled with porous material containing different textural layers are reported. In some experiments, oil followed water into the columns and in others, water followed oil. An explicit, one‐dimensional, multiphase flow code was used to model the results. The numerical model contains elements of code that: (i) mimic the Haines jump phenomenon in dry sand, (ii) account for oil entrapment when water infiltrates, (iii) include forces on the oil phase caused by surface‐spreading pressures at the oil front in water‐wetted pores, (iv) include forces on the oil phase caused by water intrusion into hydrophilic oil‐saturated pores, and (v) generate a factor that matches the water potentials of textural layers for the initial boundary conditions. In general, the model did a reasonable job of predicting the distribution of both water and oil 8 h after infiltration was started, though some unresolved problems persist. The liquid potential matching factor and the hydrophobicity of the mineral particles induced by a transmission oil have practical applications. The matching factor may be easily adapted to all codes that model flow through layers. The in situ creation of hydrophobic mineral particles may prove useful for containing immiscible organic liquids that leak into the vadose zone.
Pore‐Scale Network Modeling of Compaction and Filtration during Surface Sealing
Authors: Ewing Robert P. , Gupta S. C.
Published: July 2010

Surface sealing increases the probability of runoff and soil erosion, and occurs on a variety of soils worldwide. Filtration (“washing‐in”) and compaction have been reported as mechanisms of surface sealing, but the relative importance of each has not been established. We developed a pore‐scale network model to simulate these mechanisms, with the objective of determining their relative importance. Filtration was more effective than compaction in reducing soil hydraulic conductivity during seal formation, even though compaction reduced seal porosity more than filtration. Most of the particles available for filtration were deposited on the network surface rather than being washed into the network. This suggests that surface deposition may be more important than compaction or filtration in determining the seal hydraulic conductivity. The network model can predict seal hydraulic conductivity from pore‐ and particle‐size distributions and the initial hydraulic conductivity, and is potentially a useful research tool in understanding pore‐scale mechanisms in soil structure research.
Interlayer Adsorption of Polymeric Hydroxy‐Aluminosilicate Ions by Montmorillonite
Authors: Lou G. Q. J. , Huang P. M.
Published: July 2010

Adsorption of polymeric hydroxy‐aluminosilicate (HAS) ions by montmorillonite and the formation of siliceous Al interlayers were studied. The interaction of HAS ions with Ca‐montmorillonite exhibited a linear C‐type adsorption isotherm within the range of solution Al and Si levels commonly found in acidic soils (10−5 to 10−4 M), suggesting a high capacity of Ca‐montmorillonite to adsorb HAS ions from solution. A soluble Si concentration of >6.6 × 10−5 M was required for the formation of HAS species and their adsorption by montmorillonite. The interlayer spacing (12.2–16.8 Å at 25°C and air dried) and the intensity of the major infrared bands of the adsorbed HAS ions (940 and 3500 cm−1) in the HAS‐montmorillonite complexes were found to increase with the increasing amount of HAS ions adsorbed, which further substantiated the interlayer adsorption mechanism for HAS‐smectite interactions. The partial interlayering of HAS ions in Ca‐montmorillonite resulted in the formation of HAS‐clay complexes with basal spacings of ≈12Å (at 25°C, air dried). The data suggest that the partial hydroxy‐interlayers of natural clays in acidic environments in temperate and subtropical regions may be siliceous in nature, depending on the Si level in soil solutions and other natural waters.
Aggregate‐Protected and Unprotected Organic Matter Pools in Conventional‐ and No‐Tillage Soils
Authors: Beare M. H. , Hendrix P. F. , Cabrera M. L. , Coleman D. C.
Published: July 2010

No‐tillage (NT) practices can result in greater soil aggregation and higher soil organic matter (SOM) levels than conventional‐tillage (CT) practices, but the mechanisms for these effects are poorly known. Our objectives were to describe the size and quality of biologically active pools of aggregate‐associated SOM in long‐term CT and NT soils of the southeastern USA. Samples were collected from replicated CT and NT plots on a Hiwassee sandy clay loam (clayey, kaolinitic, thermic Rhodic Kanhapludult) and separated into four aggregate size classes (>2000, 250–2000, 106–250, 53–106 µm) by wet sieving. Potentially mineralizable C and N and N2O emissions were measured from 20‐d laboratory incuhations of intact and crushed macroaggregates (>250 µm) and intact microaggregates (<250 µm). Three primary pools of aggregate‐associated SOM were quantified: unprotected, protected, and resistant C and N. Aggregate‐unprotected pools of SOM were 21 to 65% higher in surface soils of NT than of CT, with greater differences in the macroaggregate size classes. Disruption of macroaggregates increased the mineralization of SOM in NT but had little effect in CT. Rates of mineralization from protected and unprotected pools of C were higher in surface soils of CT than of NT. Macroaggregate‐protected SOM accounted for 18.8 and 19.1% of the total mineralizable C and N (0–15 cm), respectively, in NT but only 10.2 and 5.4% of the total mineralizable C and N in CT. Our results indicate that macroaggregates in NT soils provide an important mechanism for the protection of SOM that may otherwise be mineralized under CT practices.
Pelletizing and Soil Water Effects on Gaseous Emissions from Surface‐Applied Poultry Litter
Authors: Cabrera M. L. , Chiang S. C. , Merka W. C. , Pancorbo O. C. , Thompson S. A.
Published: July 2010

Several studies have shown that the application of animal manures to soil can increase N2O and CO2 emissions. Little information is available, however, on the effect that physical characteristics of the manure can have on these emissions. The objective of this work was to evaluate the effects of physical characteristics of poultry litter (fine particles or pellets) and soil water‐filled porosity (WFP, 58 or 90%) on rates and total amounts of N2O and CO2 emissions from surface applications of poultry litter to soil. Poultry litter at 30.7 g N m−2 was surface applied to samples of Cecil loamy sand (clayey, kaolinitic, thermic, Typic Kanhapludult) that were packed in acrylic plastic cylinders. Each cylinder was placed inside a jar that was closed with a screw‐cap lid fitted with a rubber septum, and all jars were placed in an incubator at 25°C for 28d. Periodic air samplings were conducted for N2O and CO2 analyses. Maximum rates of N2O and CO2 emission occurred within the first 4 d and were highest for fine‐particle litter at 90% WFP. Cumulative CO2 emission did not differ between treatments, but cumulative N2O emission was significantly lower for fine‐particle litter at 58% WFP than for the other treatments. Expressed as a percentage of the applied N, the N2O lost represented 0.2% for fine‐particle litter at 58% WFP, and an average of 2.8% for the other treatments. These results suggest that for surface applications under the conditions of this study, pelletized litter may produce similar CO2 emission as fine‐particle litter, and may cause equal or larger emissions of N2O than fine‐particle litter.
Soluble Carbon and Nitrogen Pools of Prairie and Cultivated Soils: Seasonal Variation
Authors: DeLuca T. H. , Keeney D. R.
Published: July 2010

Recent evidence indicates that long‐term cultivation of prairie soils reduces the ambient concentrations of soluble amino N and soluble sugars. It is not known whether cultivation has affected how these constituents fluctuate with season. This study was performed to determine if cultivation has affected how soluble sugars, soluble C, and soluble amino N fluctuate with season and whether this fluctuation corresponds with seasonal changes in microbial biomass and extractable N. Soils were sampled bimonthly and analyzed for 0.5 M K2SO4 soluble sugars (anthrone‐reactive carbon [ARC]), soluble organic C, microbial biomass, and 2 M KCl extractable amino N, NH4, and NO3. Cultivation has clearly reduced the levels of microbial biomass C, soluble ARC, and soluble amino N in these soils. Microbial biomass C was greatest in late February after thaw. Soluble ARC generally was greater in prairie soils than in cultivated soils but did not increase in concert with microbial biomass. Soluble amino N declined when microbial biomass and N mineralization increased in February. The ratio of soluble ARC to NO3‐N indicates that there is generally insufficient C available, as soluble sugars, to allow for immobilization of ambient NO3 in cultivated soils throughout the course of a year. The high ratio of soluble C to biomass C in cultivated soils may also be evidence of a reduction in organic matter quality as higher levels of soluble C appear to support lower levels of microbial biomass. Cultivation has reduced concentrations of soluble sugars and amino N and has affected how these constituents change with season. However, the relation of soluble sugars and amino N to microbial biomass is not clear.
Maintenance of Yields and Soil Fertility in Nonmechanized Cropping Systems, Bolivia
Authors: Barber R. G. , Díaz O.
Published: July 2010

Slash and burn farmers in the tropical rain forests of eastern Bolivia are abandoning land after one rice (Oryza sativa L.) crop because of declining yields. A trial was conducted on a Typic Paleudult for 41 mo to investigate whether alternative low‐input nonmechanized cropping systems could prolong soil fertility and yield maintenance, and whether soil fertility or weeds were responsible for declining yields. Twelve cropping systems were investigated in a factorial design, with three summer‐winter crop sequences: rice‐peanut (Arachis hypogaea L.), corn (Zea mays L.)‐bean (Phaseolus vulgaris L.) later substituted by cowpea [Vigna unguiculata (L.) Walp.], and rice‐fallow (control); two weed control treatments: minimal and optimal; and two fertilizer treatments: with and without 60 kg N ha−1 and 17.5 or 35 kg P ha−1. Crop sequences significantly increased exchangeable acidity; the rice sequences significantly reduced exchangeable Ca, and corn‐bean/cowpea and rice‐peanut significantly reduced exchangeable Mg. Fertilization significantly increased soil P but decreased Ca. Foliar analysis revealed N, Mg, and Zn deficiencies in all cropping systems. Rice yields, unlike corn, were significantly increased by optimal weeding. Corn yields were dominated by fertilization, whereas rice yields were mainly influenced by fertilization in the first and fourth years, and by weeds in the intervening years. Without fertilizers, rice‐fallow was not sustainable, and only corn‐bean/cowpea was sustainable for 3 yr. With fertilization, rice‐fallow plus optimal weed control and corn‐bean/cowpea with minimal or optimal weeding were sustainable for 3 yr. Additional fertilization and future liming would be necessary for more prolonged sustainability.
Chronosequence in Almar River Fluvial‐Terrace Soil
Authors: Dorronsoro C. , Alonso P.
Published: July 2010

The aim of this work was to analyze how soils formed fundamentally from the erosion of granites evolve under a subhumid Mediterranean climate as a function of age. Their evolution was evaluated by means of the changes in components and properties, as well as the use of developmental indices. The soils are Xerorthents (Holocene), Haploxeralfs (Upper Pleistocene), and Palexeralfs (Middle Pleistocene). The properties have been subject to several trends: (i) some properties increase with regularity throughout the chronosequence (available water and coefficient of linear extensibility [COLE] of the Bt horizons) (ii) other properties increase strongly only during the first phases, while some continue to increase with age but only moderately (Ap horizon water retention and cation‐exchange capacity, Bt horizon dithionite‐citrate‐extractable Fe, solum thickness, clay accumulation, quartz content, and quartz/feldspar ratio), whereas other Middle Pleistocene age soil properties cease to increase (the Ap horizon silt and available water, and Bt horizon water retention and cation‐exchange capacity; (iii) others decrease with age, with pronounced decreases during the first phases (Ap and Bt horizon feldspar content and sand content and Bt horizon bulk density); and (iv) some properties are not age related (the Ap horizon base saturation and N content and the Bt horizon silt content). The horizon development indices and the soil development indices indicate good relationships with age. In most cases the rate of increase declines strongly for the oldest soils. In the great majority of cases, the properties and development indices continue to evolve through the chronosequence without reaching a steady state.
Persistence of Loosened Horizons and Soybean Yield Increases in Bolivia
Authors: Barber R. G.
Published: July 2010

Soil compaction is a major factor limiting soybean [Glycine max (L.) Merr.] production in tropical eastern Bolivia. An experiment was conducted from 1985 through 1989 on a fine‐loamy, siliceous, isohyperthermic Aquic Ustropept with a compacted horizon (0.12–0.33 m) to determine the persistence of subsoil loosening by deep tillage and its effect on soybean yield responses. Four tillage treatments were investigated: conventional tillage consisting of disk harrowing to 0.12‐m depth (CN), subsoiling in 1985 only to 0.40‐m depth (SS/85), disk plowing in 1985 only to 0.30‐m depth (DP/85), and annual subsoiling (SS/YR). All three deep tillage treatments completely loosened the compacted horizon, reducing penetrometer resistance (PR) from a maximum of 3.05 to 2.01 MPa. From December 1987 onward, which coincided with an exceptionally wet period, subsoil reconsolidation occurred, and by June 1989 the PR of CN, DP/85, and SS/85 exceeded 3 MPa. Reconsolidation was attributed to a close‐packing rearrangement of soil particles under wet conditions. Coupled with increasing subsoil strength, a relatively greater reconsolidation occurred in SS/85 and DP/85, resulting in reduced “loosened” zones of 0.07‐m and 0.04‐m thickness, respectively. The pattern of relative reconsolidation suggests it occurred from above downward and from below upward, the latter perhaps being related to a high water table. In contrast SS/YR maintained a much thicker “loosened” horizon. overall subsoil reconsolidation, soybean yield responses continued for 3 yr with SS/85, and for 4 yr with DP/85 and SS/YR. Although substantial differences in relative reconsolidation existed between DP/85, SS/85, and SS/YR, few significant differences in yield were found when soil water was limiting.
New Mexican Locust and Parent Material: Influence on Forest Floor and Soil Macronutrients
Authors: Klemmedson James O.
Published: July 2010

The effect of the New Mexican locust (Robinia neomexicana Gray) on N, P, S, and Ca, Mg, K and organic C in the soil‐litter system of a ponderosa pine (Pinus ponderosa Douglas, ex P. Lawson & Lawson) forest in central Arizona was studied on sites with either basalt or limestone parent material. Samples of the Oi and Oe + Oa horizons (forest floor) and 0‐ to 5‐ and 5‐ to 15‐cm soil layers from 10 pairs (with and without locust) of randomly located pine stands were sampled and analyzed for total N, P, and S, total (forest floor) and exchangeable (mineral soil) Ca, Mg, and K, and organic C (Corg). The 10 stand pairs represented five sites with basalt and five with limestone parent material. There were no significant parent material × locust interactions for the nutrients considered. Locust presence increased nutrient concentrations of N and Ca most strongly (in both Oe + Oa and soil layers) and Corg, P, S, and K concentrations to a lesser extent. Concentrations of N, P, and K were significantly higher in mineral soils derived from basalt. Increased amounts of N in forest floor and mineral soil, and increased amount of P, Ca, Mg, and K in the forest floor were associated with locust presence. Amounts of Corg, N, P, and exchangeable K were greater in soil components of stands with basalt parent material. Forest floor mass was greatest for basalt sites with locust; this and nutrient composition differences between locust leaves and pine needles suggest greater nutrient differences between parent materials may accrue with age of locust stands.
Simplified Model of Integrated Water and Solute Uptake by Salts‐ and Selenium‐Accumulating Plants
Authors: Ben‐Asher J.
Published: July 2010

The rate of soil salinization and the accumulation of toxic ions in soils are affected by evapotranspiration and the uptake of ions by plant roots. These are two counteracting processes and the interrelationship between them can be quantified by a mathematical model. The objectives of this study were to: (i) formulate an analytical model describing soil salinization and accumulation of toxic ions and (ii) suggest a criterion for irrigation water quality (C*0) and demonstrate its behavior under varying transpiration rates. The processes by which the soil becomes saline were simulated with an analytical solution to the convection‐diffusion equation. The model was based on ion and water uptake by plant roots. The calculations indicated that crops classified as salinity tolerant remove more salt from the soil than salinity‐sensitive crops. The rates of ion removal are 5, 15, and 40 × 10−3 dS m−1 d−1 for salinity‐sensitive, semisensitive, and tolerant crops, respectively. Therefore the ratio between the uptake rates of ions and water per unit soil volume is presented here as a criterion for the upper limit of allowable salinity in irrigation water. This ratio is inversely related to transpiration rate (evaporation neglected). Theoretically, the maximum allowable salinity of salt‐tolerant crops, C*0, decreases from 20 to 4 dS m−1 when the transpiration rate increases from 2 to 10 × 10−3 m d−1. For the same transpiration rate increase, C*0 of sensitive crops decreases from 3 to 0.5 dS m−1; thus, a lower quality of water can be permitted for irrigation in a moderate or cool climate than in an arid climate. The model applies also for Se‐accumulating crops. Theoretically, at a transpiration rate of 5 × 10−3 m d−1, Se can be removed from a soil solution containing a high concentration (C*0 = 1 mg kg−1) when the uptake rate of the growing crop is 25.8 × 10−3 mg kg−1 d−1.
Simulation of Cation Exchange Involving Hydrogen Ion in Soil
Authors: Houng Kun‐Huang
Published: July 2010

A computer program for simulating cation‐exchange reactions in soil was developed and used for simulating the determination of exchangeable acidity with 1 M KCl and of hydrolytic acidity with 1 M NaOAc. The acidification process resulting from extraction of an initially base‐saturated soil with a dilute solution of an acid having various dissociation constant may also be simulated. From the calculated pH‐base saturation relationships for assumed K‐H exchange coefficent (KK‐H) varying from 1 × 101 to 1 × 10−6, it is noted that for KK‐H values of 1 × 10−n, the inflection point of the pH‐base saturation curve is at the pH value of n. Thus, the permanent charge sites of mineral soils appeared to have a KK‐H value of 1 × 10−1 and greater, while for the pH‐dependent charge sites the KK‐H values are smaller than 1 × 10−2. The acidity extracted by 1 M KCl solution corresponded to the H+ on the permanent charge sites, with KK‐H values of 1 × 10−2 and greater, but it may also include some portions of H+ bound on exchange sites with KK‐H values smaller than 1 × 10−2. Exchangeable H+ from sites with KK‐H smaller than 1 × 10−5 were practically not displaced by 1 M KCl solution. The use of 1 M NaOAc instead of Kcl could quantitatively displace the H+ held on the sites with KNa‐H values >1 × 10−3 by a single extraction, while those of 1 × 10−6 and greater may be displaced by repeated extractions. Calculations with KNa‐H values of 1 × 10−7 did not converge, but available soil data indicate that the pH‐dependent sites of soils have KNa‐H values in the order of 1 × 10−7. Use of a dilute acid solution in place of KCl or NaOAc solution simulates the acidification process of acid precipitations.
Purge‐and‐Trap Extraction of Geosmin and 2‐Methylisoborneol from Soil
Authors: Stahl Peter D. , Parkin Timothy B.
Published: July 2010

Although a number of techniques are available for estimating the biomass of filamentous microorganisms in soil, determination of their activity is much more difficult. We report on preliminary studies evaluating the potential use of the volatile microbial secondary metabolites geosmin and methylisoborneol as indicators of activity of filamentous microorganisms. The purge‐and‐trap technique for analysis of low concentrations of volatile organic compounds in air and water was tested for extracting the earthy‐musty odor compounds geosmin and 2‐methylisoborneol from soil. Two variations of this method were tried, one in which soil samples were placed in water for purging and another in which samples were purged with no added water. Volatile organic compounds purged from soil were collected on a porous polymer sorbent, Tenax TA. Naturally occurring geosmin and 2‐methylisoborneol and added standards were successfully extracted from soil by both methods. Recovery efficiencies, however, were low. Results indicated that wet purging was the most efficacious extraction method yielding maximum recovery rates of added geosmin and 2‐methylisoborneol standards of 15 and 24%, respectively.
Phosphorus Relationships in Flooded Rice Soils with Low Extractable Phosphorus
Authors: Shahandeh H. , Hossner L. R. , Turner F. T.
Published: July 2010

Rice (Oryza sativa L.) grain yields on some flooded soils are not increased by P fertilizer despite their low soil test P status determined on air‐dry soils by soil test methods such as Bray, Olsen, or Texas A&M. Conventional soil test methods apparently do not accurately assess the capacity of these soils to supply P to rice grown under flooded conditions. To test the possibility of an Fe‐P association, oxalate extractant (which would extract noncrystalline Fe and its associated P) was used to provide a more accurate measure of available P in flooded soil. Phosphorus response experiments were conducted on 10 rice soils under greenhouse and field conditions and related to the oxalate‐extractable Fe and P, P uptake, P adsorption, and P desorption under aerobic and anaerobic conditions. Oxalate‐extractable Fe significantly increased under anaerobic conditions in all soils including the soils that were nonresponsive to P and had low levels of extractable P using conventional extractants. Phosphorus adsorption and desorption data confirmed the importance of oxalate extractant in predicting P availability following anaerobiosis. The inability of Bray 1, Olsen, and Texas A&M soil test methods to accurately predict P availability in flooded rice soil appears to be due to their failure to extract the active reductant‐soluble P fraction. The measurement of P associated with poorly crystalline Fe by oxalate extractant is a useful soil test method for predicting the availability of P in flooded rice soils.
Sodium‐Affected Soil Identification in South‐Central Illinois by Electromagnetic Induction
Authors: Nettleton W. D. , Bushue L. , Doolittle J. A. , Endres T. J. , Indorante S. J.
Published: July 2010

The irregular shape, small size, and spotty occurrence of sodium‐affected soils (NaAS) in moderately thick to thin loess over Illinoian till have continued to slow mapping in south‐central Illinois. Use of a Geonics EM‐38 ground conductivity meter to recognize soils with natric horizons in Tennessee suggested that this device would be useful in Illinois. We selected eight areas of NaAS in five counties of south‐central Illinois to find if the EM‐38 would be useful for predicting exchangeable sodium percentage (ESP). Approximately 225 observation points, spaced at 10‐m intervals, were established in each area and 107 sample cores were collected for laboratory analyses. Weighted averages of the ESP, electrical conductivity of the saturation extract from a saturated soil paste (ECe), and field pH data for 0 to 75‐ and 75 to 150‐cm depths were compared with the horizontal (EMh) and vertical (EMv) responses and the mean ESP data increases with depth, i.e., 7.0 at 35 cm, 9.7 at 75 cm, and 12.5 at 135 cm. The EMh readings correlate almost as well with ESP (r = 0.73) as with ECe (r = 0.76) for the 0‐ to 75‐cm depths. The EMv readings correlate slightly better with ESP (r = 0.76) than with ECe (r = 0.68) for the 75‐ to 150‐cm depth. These results show that EM readings may by used to predict ESP. The correlations of the depth‐weighted average ESP at the maximum depth for meeting natric horizon criteria in these soils (75 cm), and the EMv readings show that the EM‐38 provides a rapid and accurate method to describe the composition of the map units of NaAS on moderately thick to thin loess over Illinoian till in south‐central Illinois.
Soil Structural Form and Stability, and Organic Matter under Cool‐Season Perennial Grasses
Authors: Carter M. R. , Kunelius H. T. , Angers D. A.
Published: July 2010

Temperate grasses conserve soil by providing vegetative cover and by favoring soil aggregation. A field study was conducted on a Charlottetown fine sandy loam (a coarse‐loamy, mixed, frigid Typic Haplorthod) to determine the effect of cultivars of orchardgrass (Dactylis glomerata L.) and tall fescue (Festuca arundinacea Schreb.), in comparison to timothy (Phleum pratense L.), on soil structure and organic matter fractions after 4 yr of growth. Timothy is one of the main grasses grown in the cool humid climate of eastern Canada. Bulk density (1.27–1.32 Mg m−3), pore‐size distribution, and shear strength (12.5–15.6 kPa), as a measure of soil structural form, were within the optimum range for this soil type under each grass species. Dry‐aggregate mean weight diameter (MWD) was similar (3.66–4.30 mm) among grass species. Wet‐aggregate MWD was greater under tall fescue cultivars and ‘Farol’ timothy (2.81–3.22 mm) compared with the orchardgrass and ‘Champ’ timothy (2.08–2.36 mm). These differences were also reflected by the difference or ratio of MWD between dry and wet sieving. Aggregate‐size distribution indicated that wet‐aggregate MWD differences were associated with greater levels of macroaggregates (>2 mm). Differences in water‐stable aggregate stability were not related to differences in plant parameters, organic matter, or organic matter fractions (i.e., microbial biomass C, carbohydrates, and particulate organic matter). These data suggest that organic matter parameters, commonly used to characterize soil stability in cropping systems, are less useful for soils under perennial grass with stable microaggregate structures.
Measuring and Predicting Ridge‐Orientation Effect on Soil Surface Roughness
Authors: Saleh Ali
Published: July 2010

Surface roughness significantly reduces soil erosion by wind. Methods commonly used to measure soil roughness function only in parallel and perpendicular directions to the oriented (ridge) roughness. This study was conducted to develop a simple procedure to estimate soil roughness at any given angle with respect to ridge orientation, for aggregated or nonaggregated ridged surfaces. Surface roughness was determined by the chain method. Surface roughness measured at different angles on simulated and field plots matched very closely (R2 ≥ 0.985, P ≤ 0.001) with those predicted from equations developed in this study. This simple method enables one to estimate a surface roughness parameter for any wind direction with respect to ridge orientation. This should result in a better evaluation of roughness influence on wind erosion.
Methane Production and Emissions from Four Reclaimed and Pristine Wetlands of Southeastern United States
Authors: Schipper Louis A. , Reddy K. R.
Published: July 2010

Wetlands are significant contributors to global CH4 emission. We measured CH4 emissions at two pristine wetlands [Okefenokee swamp and the Everglades (Water Conservation Area 2A)] and two reclaimed wetlands (Sunny Hill Farm and Apopka Marsh) in Southeastern USA, and we attempted to relate emissions to CH4 production rates of the soil and the soil's biological and chemical properties. Methane emissions through cattail [Typha sp.] and waterlily [Nymphaea ordorata (L.)] ranged from 0.09 to 1.7 g CH4 m−2 d−1 and exhibited high spatial and temporal variability. Diffusive flux of CH4 was calculated using dissolved CH4 profiles in the soil pore water and accounted for <5% of the plant‐mediated emissions. Potential CH4 production rates were measured as a function of depth using soil samples obtained at 2‐cm increments. Methane production rates were the same order of magnitude at all sites (<1–70 ng CH4‐C g−1 soil C d−1) and were highest in the surface soils (0–6 cm) at three of the wetland sites, indicating that the predominant source of C available to methanogens was in the surface soils. Methane production rates in the top 24 cm ranged from 0.3 to 1.1 g CH4 m−2 d−1 and annual C losses due to anaerobic decomposition accounted for between 0.68 and 3.7% of the total C in the surface 24‐cm soil depth. Methane production was observed at sites with porewater SO4 concentrations of up to 20 mg SO4‐S L−1, suggesting that methanogenesis occurred in the same soil layer as SO4 reduction, possibly in microsites where SO4 concentration was depleted.
Measurement of Soil Thermal Properties with a Dual‐Probe Heat‐Pulse Technique
Authors: Bristow Keith L. , Kluitenberg Gerard J. , Horton Robert
Published: July 2010

Although soil thermal properties are required in many areas of engineering, micrometeorology, agronomy, and soil science, they are seldom measured on a routine basis. Reasons for this are unclear, but may be related to a lack of suitable instrumentation and appropriate theory. We developed a theory for the radial conduction of a short‐duration heat pulse away from an infinite line source, and compared it with the theory for an instantaneously heated line source. By measuring the temperature response at a short distance from the line source, and applying short‐duration heat‐pulse theory, we can extract all the soil thermal properties, the thermal diffusivity, heat capacity, and conductivity, from a single heat‐pulse measurement. Results of initial experiments carried out on air‐dry sand and clay materials indicate that this heat‐pulse method yields soil thermal properties that compare well with thermal properties measured by independent methods.
Network Modeling of Diffusion Coefficients for Porous Media: I. Theory and Model Development
Authors: Steele D. D. , Nieber J. L.
Published: July 2010

Gas diffusion often dominates constituent transport in porous media and is dependent on pore geometry, water content, and water distribution in a porous medium. Network models of porous media offer the ability to investigate the influence and interaction of pore‐scale porous media properties and fluid properties on macroscopic properties of the medium. This study was conducted to investigate the macroscopic relative gas diffusion coefficient vs. air‐filled porosity relationship (diffusion characteristic) of porous media using a network modeling approach. A cubic sphere‐and‐tube network model of porous media was adapted from petroleum engineering using Fick's law and the principle of conservation of mass to simulate one‐dimensional, steady‐state, isothermal, isobaric, molecular diffusion of a dilute binary gas in a nonadsorbing porous medium containing a single nonwetting fluid (air) and a single wetting fluid (water). The network model simulates hysteresis in air and water distributions in porous media for boundary drying and wetting curves of the soil water characteristic and demonstrates the effect of air‐filled porosity, Henry's law liquid‐gas partitioning coefficient, the ratio between gas‐ and liquid‐phase diffusion rates, and pore geometry on the diffusion characteristic.