bluuebunny/crossref_metadata_2025 huggingface dataset:
Translocation of Iron In Acid Sulfate Soils: I. Soil Morphology, and the Chemistry and Mineralogy of Iron in a Chronosequence of Acid Sulfate Soils
Authors: van Breemen N. , Harmsen K.
Published: July 2010

In periodically flooded acid sulfate soils from Thailand various iron compounds are confined to distinct soil horizons. The unmottled substratum, which starts at several decimeters below the surface in the (youngest) mangrove and stage and at 2 m in well‐developed soils, invariably contains between 2 and 5% pyrite. Drainage of the mangrove mud is followed by pyrite oxidation which results in acidification of the soil and accumulation of iron as ferric oxide or jarosite at some distance above the pyritic substratum. Very little iron is precipitated just above the unmottled C horizon. As the soils become older and better drained, the upper boundary of the pyritic substratum and the B horizon with ferric oxide and jarosite, occur at progressively greater depths. Hydrolysis of pale yellow jarosite to ferric oxide at relatively shallow depth accounts for a separation of the B horizon in a brown mottled upper part and a predominantly yellow mottled lower part. The X‐ray amorphous ferric oxide is transformed to goethite, or, in the better drained soils, to hematite. In the older soils especially, periodic reduction of immobile ferric iron to mobile ferrous iron in the surface soil and at the top of the pyritic substratum, combined with perennially oxidized conditions in the B horizon, may contribute to the strong iron accumulation in the B horizon. Differences, in organic matter content and stability of ferric oxide, and the presence or absence of pyrite, probably account for the dissimilar behavior of the various horizons upon flooding. Besides conventional soil analyses, results of water analyses, EH‐pH determinations, and various laboratory experiments involving field samples are helpful in explaining details of the soil‐forming process involved.
Water Retention by Core and Sieved Soil Samples
Authors: Unger Paul W.
Published: July 2010

Mechanical analyses and water retention by core and sieved soil at ‐⅓ and −15 bar matric potentials were determined for samples from 26 sites ranging in texture from sand to clay.

Objectives were to obtain a basis for identifying which soils may be influenced by deep tillage and profile modification with respect to water storage capacity and to determine the magnitude of errors possible when using sieved soils to establish field soil water contents.

At ‐⅓ bar potential, cores retained more water than sieved soil when the water content was below 11%. The opposite occurred at higher water contents. At −15 bars potential, cores contained about 1 percentage point more water than sieved soils throughout the water content range encountered. These results show that treatments which thoroughly disrupt the natural soil structure may decrease and increase the storage capacity of coarse‐ and fine‐textured soils, respectively.

When expressed as a percent of the core water content, differences between core and sieved soil contents at ‐⅓ bar potential ranged from −40 to +25% at 5 and 40% core water contents, respectively. At −15 bars potential, the range was from −52 to −4% at 5 and 25% core water contents, respectively. These differences indicate caution should be used when using sieved soils to infer water retention by field soils, regardless of texture.

This study suggests deep tillage and profile modification may decrease and increase water storage in coarse‐ and fine‐textured soils, respectively. However, because of structural development, organic matter content, and possibly clay size and type, results for individual soils may differ from those indicated by the relationships established. To more accurately evaluate the possible effects of deep tillage and profile modification on water retention, the soil in question must be analyzed.
Soil Moisture Flux and Evapotranspiration Determined from Soil Hydraulic Properties in a Chaparral Stand
Authors: Scholl David G.
Published: July 2010

Measurements of rainfall, overland flow, soil moisture, and hydraulic properties were obtained from a sloping plot in a chaparral stand. The moisture characteristic and dynamic conductivity were determined from core samples of several soil layers to a depth of 420 cm. A water balance model requiring the above parameters and a Darcian moisture flux analysis was used to predict drainage below the root zone and loss by evapotranspiration. Daily results of the water balance were summarized during 2 water years. Predicted values agreed well with values measured on a nearby watershed during both years—the first an unusually dry year, the second unusually wet.
Infrared and X‐ray Study of Parathion‐Montmorillonite Sorption Complexes
Authors: Saltzman Sarina , Yariv S.
Published: July 2010

Infrared spectra indicate that parathion sorbed by montmorillonite coordinates through water molecules to the metallic cations in the interlayer space of the clay. By dehydrating the clay‐parathion complexes, parathion becomes directly coordinated with the monovalent cations. The main interaction is through the oxygen atoms of the nitrogroup, although interactions through the P=S group were also observed, especially for complexes saturated with polyvalent cations.
Octan‐I‐ol Extraction of Molybdophosphoric Acid in the Colorimetric Determination of Orthophosphate
Authors: Helyar K. R. , Brown A. L.
Published: July 2010

A method for the analysis of orthophosphate in aqueous solutions is described. The detection limit of the method is <0.1 µg orthophosphate P, and the molybdophosphoric acid can be concentrated at least 300 times by extraction into octan‐I‐ol. The complex is reduced to the colored form after extraction into octan‐I‐ol and Beer's Law is obeyed at least to an absorbance value of 1.5. A study of the effects of temperature, shaking time and rate, and the organic to aqueous ratio on the extraction of molybdophosphoric acid was carried out. The extinction coefficient for the method was 22,000 liters mole‐1 cm‐1. Possible interference by various cations and anions in the determination was investigated and the technique was used successfully to analyze for phosphate in calcium chloride extracts from soil.
Nitrite Decomposition in Flooded Soil Under Different pH and Redox Potential Conditions
Authors: Van Cleemput O. , Patrick W. H. , McIlhenny R. C.
Published: July 2010

Nitrite decomposition products were studied in a flooded soil suspension maintained under different pH and redox potential conditions. The effect of a sterilant, HgCl2, on nitrite breakdown was also investigated. Soil suspensions were incubated for several days with the pH maintained at 4.5, 6, and 8 and the redox potential maintained at 0 and + 200 mV. Nitrite was then added to the suspensions and the decomposition products were determined by mass spectrometry.

Under acid conditions significant amounts of N2 and nitrogen oxide gases (N2O, NO) were formed in both the moderately reduced (+200 mV) and reduced (0 mV) suspensions. At higher pH's the nitrite reduction rate was slightly less and the amounts of nitrogen oxide gases formed were considerably less with N2 being the major product. The chemical sterilant decreased the conversion of nitrite to N2 and markedly increased the formation of NO. The significant production of NO under acid conditions both with and without the sterilant, suggests the likelihood of self‐decomposition of nitrous acid as a major mechanism of nitrite loss.
Nitrogen Accretion in Developing Ceanothus Velutinus Stands
Authors: Youngberg C. T. , Wollum A. G.
Published: July 2010

Nodulation, N accretion, and above‐ground biomass production were investigated in Ceanothus velutinus (snowbrush) stands developing following wildfire and salvage logging in second growth ponderosa pine (Pinus ponderosa Laws) and logging and slash burning in old growth Douglas‐fir stands [Pseudotsuga menziesii (Mirb.) Franco]. In the pine site 82% of the Ceanothus plants were nodulated the first year, whereas in the fir site only 42% were nodulated. Above‐ground snow‐brush biomass production at the end of 10 years was 48,000 and 54,000 kg/ha, respectively, for the pine and fir sites. Nitrogen accretion in biomass, litter, and soil for the 10‐year period was 715 and 1,080 kg/ha, respectively, for the pine and fir sites. The higher accretion in the fir site despite slower nodulation is due to more favorable temperature and moisture conditions at the fir site than at the pine site.
Sulfur‐coated Fertilizers for Sugarcane: I. Plant Response to Sulfur‐coated Urea
Authors: Gascho G. J. , Snyder G. H.
Published: July 2010

Crop growth and yield on sand soils is often limited by low N availability due to leaching losses from the soil. This study was initiated to determine if sulfur‐coated urea (SCU) could supply adequate N nutrition and eliminate the need for repeated N applications for sugarcane (Saccharum spp.) grown on previously uncropped Immokalee fine sand in southern Florida. Single applications of two SCU's were compared with split applications of (NH4)2SO4 (AS), each at three N rates, 56, 112, and 168 kg/ha. Application of SCU at planting in November resulted in excellent growth and high leaf N concentrations in the spring but did not provide optimum N throughout the growing season. Leaf N concentrations in late summer and tonnages of sugarcane and sugar for SCU plots approached, but did not equal, those attained with four applications of AS. Higher tonnages were recorded for the slower releasing SCU than for the faster releasing source but both SCU sources released large amounts of N before the warm summer months when N is required in the highest quantities. The data indicate that SCU's which release N more slowly and/or a later application date should provide better N nutrition and eliminate the need for several split applications of soluble sources.
Analytical Properties of the Soluble, Metal‐Complexing Fractions in Sludge‐Soil Mixtures: I. Extraction and Purification of Fulvic Acid
Authors: Holtzclaw Kenneth M. , Sposito Garrison , Bradford Gordon R.
Published: July 2010

A laboratory method is described for extracting and purifying the fulvic acid fraction of sludge‐soil mixtures. The method, which does not include dialysis or the use of destructive chemical reagents, consists of: (i) extraction with 0.5N NaOH and acidification to pH 1.0 with HCl, (ii) repeated high‐speed centrifugation to remove Al‐Fe‐hydroxy phosphates, and (iii) use of both chelating and H‐form cation exchange resins to remove complexed metal impurities. The existing procedures for preparing fulvic acid, based upon research on natural soil organic matter, were concluded to be not fully adequate for studies on sludge‐soil mixtures. Primarily, this inadequacy is the result of the loss, through dialysis, of important reactive fractions during purification and the lack of specific steps that treat the greater variety of trace elements to be found in sludge materials. In addition, the presence of significant amounts of P in these mixtures complicates the removal of colloidal and complexed metal impurities. The application of the present method to representative sludge‐soil mixtures showed that ash contents are reduced to I‐2%. The procedure should be generally applicable in soil or sediment organic matter studies as well as to studies on the chemistry of sludge‐amended soil.
Relative Importance of Soil Resistance and Plant Resistance in Root Water Absorption
Authors: Reicosky D. C. , Ritchie J. T.
Published: July 2010

Soil water potentials, leaf water potentials, and transpiration rates of sweet corn (Zea mays L.), growing in a greenhouse, and grain sorghum (Sorghum bicolor L.), growing in a field, were determined to evaluate the magnitude of the combined soil and plant resistances to water flow in the plant system. Using a theoretical analysis of water absorption by roots, soil resistance was estimated. Plant resistance was inferred by the difference between the measured combined resistances and the estimated soil resistance. A wide range of soil hydraulic conductivity values for the plant rooting media which included nutrient solutions, peat‐vermiculite‐sand mixture, and a sand and clay soil maintained at various water potentials provided variations in calculated soil resistances. Our results showed that when root density was not unusually low, plant resistance to water transport was much larger than soil resistance, until the threshold soil hydraulic conductivity reached about 10‐6 to 10‐7 cm/day. This conductivity usually occurred at about −1 and −8 bars for the sandy and clay soils, respectively. These findings emphasize the need to consider plant resistance in water‐uptake calculations when using equations that evaluate water potential gradients along the water flow path.
Rhodanese Activity of Soils
Authors: Tabatabai M. A. , Singh B. B.
Published: July 2010

The detection of rhodanese (enzyme catalyzes the formation of SCN‐ from S2O32‐ and CN‐) in soils is reported, and a simple method of assaying rhodanese activity in soils is described. This method involves colorimetric determination of the SCN‐ produced by rhodanese activity when soil is incubated with buffered (0.05M THAM, pH 6.0) S2O32‐ and CN‐ solutions and toluene at 37°C for 1 hour. The method developed is rapid, sensitive, and precise. The procedure used to extract SCN‐ stops rhodanese activity in soils and gives quantitative recovery of the SCN‐ formed. Results showed that steam sterilization and formaldehyde inhibit, sulfate and chloride activate, and toluene has no effect on rhodanese activity in soils. The initial rates of SCN‐ formation obeyed zero‐order kinetics; in one soil, the rate slowed with time of incubation. The temperature dependence of the rate constant conformed to the Arrhenius equation up to the point of enzyme inactivation (65°C). The activation energy of rhodanese activity of the eight soils studied ranged from 5,160 to 8,110 (avg. 6,690) calories/mole. Studies of other properties of rhodanese activity in soils are reported.
Line Source Sprinkler for Continuous Variable Irrigation‐crop Production Studies
Authors: Hanks R. J. , Keller J. , Rasmussen V. P. , Wilson G. D.
Published: July 2010

The design details and a sample set of field test results for a line source sprinkler plot irrigation system are presented. The system produces a water application pattern which is uniform along the length of the plot and continuously, but uniformly variable across the plot.

By applying a fertility variable along a plot (at right angles to the water variable) planted in some test crop, the system offers a convenient means for developing crop production function data. The system test area and water supply are both small. However, the application of the system may be limited by wind and all water application levels within a plot must be supplied at the same irrigation frequency.
Estimation of Components of Soil Cation Exchange Capacity from Measurements of Specific Surface and Organic Matter
Authors: Curtin D. , Smillie G. W.
Published: July 2010

Cation exchange capacities of Irish soils developed from a wide range of parent materials were found to be highly correlated with organic matter content and specific surface but not with clay content. Multiple regression analysis showed that organic matter in combination with specific surface accounted for 97% of the variation in CEC whereas organic matter and clay content only accounted for 58% of the variation. The better correlation between CEC and specific surface than between CEC and clay content, is attributed to the ability of surface area measurements to reflect the presence of phyllosilicates in silt and sand fractions of soils and to the fact that these minerals have less variable surface charge densities than cation exchange capacities. It is proposed that specific surface provides a better estimate than clay content, of the mineral component of CEC for soils of varying mineralogy.
Estimate of Organic Carbon in World Soils
Authors: Bohn Hinrich L.
Published: July 2010

The current estimate of organic carbon in world soils, 7.1 × 1014 kg, is based on such meager data that it must be viewed skeptically. The FAO‐UNESCO soil map and other recent soil data indicate that the amount of organic soil carbon is about 30 × 1014 kg. This new estimate should allow more accurate portrayal of the role of soil carbon in the carbon cycle.
Heat and Water Movement Under Surface Rocks in a Field Soil: II. Moisture Effects
Authors: Jury W. A. , Bellantuoni B.
Published: July 2010

Results are presented from a field experiment conducted to determine the effect of surface rocks on soil water content changes under bare soil. First, stones were placed at intervals over an initially‐dry field (gravimetric water content = 0.021 g/g) and left for 6 weeks. Subsequent sampling showed a small but detectable excess of water stored under the rock compared to adjacent bare soil. Following an irrigation, buried thermal conductivity probes were used to monitor water content changes under and adjacent to surface rocks. After 24 days, the soil under the rock contained significantly more water than did the soil region adjacent to the rock, a finding confirmed by gravimetric sampling. Following this, the stones and probes were relocated for a further 24 days of observation, with similar results obtained.

In a separate laboratory experiment using a large sealed soil column with a rock covering part of the surface it was demonstrated that a significant amount of water moved to the cylinder of soil under the rock from the soil region under the bare surface due to horizontal temperature gradients induced by the rock covering part of the surface.

A two‐dimensional computer program calculating water vapor movement under thermal gradients was used with measured field temperature boundary conditions to estimate the amount of water vapor movement expected to occur due to a rock cover on the soil surface. Results qualitatively confirmed the observations of the sealed laboratory column experiment.
Soluble Cations Beneath a Feedlot and an Adjacent Cropped Field
Authors: Elliott L. F. , Travis T. A. , McCalla T. M.
Published: July 2010

Concentrations of Na, K, Ca, Mg, Zn, Cu, Fe, and Mn in the soil solution were measured beneath a feedlot and an adjacent cropped field for a 12‐month period. Only Ca, Mg, and Mn were higher in the feedlot soil solution than in the cropped field at the lower depths tested. At the lower depths, Ca and Mg appeared to be two to four times higher in soil solution from the feedlot than from the cropped field. Manganese was consistently higher beneath the feedlot than the field; however, Mn levels were low, and, with the limited water movement through feedlot soil, it is unlikely feedlots contribute significant Mn to groundwater.
Field Mapping Soil Conductivity to Delineate Dryland Saline Seeps with Four‐electrode Technique
Authors: Halvorson A. D. , Rhoades J. D.
Published: July 2010

Continuing incidence of saline‐seep areas in the northern Great Plains dryland soils has created a need for detecting and delineating encroaching saline seeps before plant growth is affected. We evaluated the four‐electrode conductivity technique for field mapping surface and subsurface soil salinity under dryland conditions.

Results indicated that the four‐electrode conductivity technique can be used successfully to quickly field map surface and subsurface soil salinity boundaries of existing and potential saline‐seep areas. This technique also depicted underground flow patterns of a shallow, saline ground water table.

Maps of apparent bulk soil conductivity values (ECa) were used to locate the position of the recharge area in relation to the discharge (seep) area. While maps of discrete depth interval conductivity values (ECx) provided more precise information, the time required may not warrant the additional required calculations unless a portable programable calculator is available. Mapping soil salinity with the four‐electrode conductivity technique is easy, rapid, and relatively inexpensive. This technique provides information useful in making management decisions to prevent or alleviate a saline seep or other soil salinity problems.
Chemical Distribution and Gaseous Evolution of Arsenic‐74 Added to Soils as DSMA‐74As
Authors: Akins Michael B. , Lewis Russell J.
Published: July 2010

Gaseous evolution of 74 As from a soil treated with arsenic‐74 labeled disodium methanearsonate (DSMA‐74 As) at 100 µg/g was a function of organic matter addition and moisture conditions. Loss of 74As was greatest from soils that received an exogenous carbon source and were maintained under wet conditions.

Arsenic‐74 sorbed by soils of pH 4, 6, and 8 was fractionated by a differential dissolution procedure commonly used for phosphorus. Iron arsenate (soluble in 0.1N NaOH) was the most abundant form followed by aluminum arsenate (soluble in 0.5N NH4F). The soils generally contained more aluminum arsenate at pH 4 than at pH 6 or 8. Calcium arsenate fractions (soluble in 0.5N H2SO4) were usually higher at pH 6 and 8 than at pH 4. Water‐soluble forms and nonextractable forms were inversely proportional to each other.
Microbial Formation of Volatile Selenium Compounds in Soil
Authors: Doran J. W. , Alexander M.
Published: July 2010

Selenium was volatilized from soils amended with elemental Se, selenite, selenate, trimethylselenonium chloride, selenomethionine, and selenocystine and incubated in air or anaerobically. The processes were wholly or largely the result of microbial action. The conversion of selenite and selenate to volatile products was enhanced if soil was amended with organic materials. Indigenous soil Se was also volatilized in the presence of supplemental organic matter. The products were identified by combined gas chromatography‐mass spectrometry. Dimethyl selenide was generated from all Se compounds tested when amended soils were incubated in the presence of air. Under anaerobic conditions, dimethyl selenide was produced from the three organic Se compounds and selenate, and a product tentatively identified as hydrogen selenide (H2Se) was evolved from soil receiving elemental Se, selenite, selenate, or selenocystine. Dimethyl diselenide was also formed from selenomethionine in soil incubated in air or anaerobically.
Effects of Boron and Nitrogen on Grain Yield and Boron and Nitrogen Concentrations of Barley and Wheat
Authors: Gupta Umesh C. , MacLeod J. A. , Sterling J. D. E.
Published: July 2010

In field experiments, 4.48 kg B/ha added to the soil decreased the grain yield of barley (Hordeum distichon L.) and wheat (Triticum aestivum L.). Under greenhouse conditions, 0.5 ppm, added B reduced wheat yields while 1.0 ppm added B reduced barley yields. The B toxicity in wheat in 1974 and barley and wheat in 1975 at 2.24 kg B/ha as associated with reduced yield was alleviated somewhat by the additions of N to the soil in field experiments, but the effect was not significant. Under greenhouse conditions, addition of 50 ppm N or more reduced B uptake and alleviated B toxicity. In general, the B toxicity symptoms on the foliage under field conditions were associated with >11 ppm B in wheat boot stage tissue (BST) and >14 ppm B in BST of barley. Added B increased the N concentration of grain where yields were decreased due to B toxicity. Wheat yields increased with increased rates of N application in all field experiments, while barley yields increased with increased rates of N in 2 of the 3 years. In field experiments the highest B value was 34 ppm. Concentrations as high as 312 ppm B were found in greenhouse experiments. In the presence of added B under greenhouse conditions, the barley tissue B concentration was much lower when the moisture level near the fertilizer band was low than when it was high.
Arsenic Stability in Contaminated Soils
Authors: Hess R. E. , Blanchar R. W.
Published: July 2010

Various Al, Ca, Fe, Mn, and Pb arsenate compounds were formed and their solubility products determined. The amount of arsenate in solution for each of the compounds could be predicted as follows: AlAsO4 · 2H2O(pAsO4 = 24.51‐3pH), FeAsO4 · 2H2O or Fe(OH)3 · FeAsO4(pAsO4 = 26.07‐3pH), Ca3(AsO4)2 · 14H2O(pAsO4 = 9.29‐1.5pCa), Pb3(AsO4)2 · 4H2O(pAsO4 = 19.75‐1.5pPb), and Mn3(AsO4)2 (pAsO4 = 35.6‐12.8Eh‐2.3pH), or (pAsO4 = 47.3‐25.3Eh‐3pH), with either Mn2O3 or MnO2.

Samples from Sharpsburg and Menfro soils were equilibrated for 7 days at 25°C with dilute HCl and NaOH. Aluminum, Fe, Ca, Mn, Pb, and As contents and pH and E (platinum) were determined on the solution portions. The values of pAl + 3pOH, pAl + pAsO4, pFe + 3pOH, pFe + pAsO4, 3pCa + 2pAsO4, 3pMn + 2pAsO4, and 3pPb + 2pAsO4 were computed for each soil. The values of the ion products indicated that equilibrium solutions from both soils were undersaturated with respect to Al, Fe, and Ca and that Pb and Mn arsenate were stable in the Menfro and Sharpsburg soils.
Correction of “Tube Contribution” Interference in the Determination of Heavy Metals by X‐ray Spectroscopy using the “Additions Technique”
Authors: Keramidas V. Z. , Fanning D. S.
Published: July 2010

Cr and W X‐ray tubes emitted not only the target characteristic lines but the lines of Fe, Zn, Cu, and Ni as well. Such extraneous radiation, which probably originates primarily from contamination of the tube target by the metals and is referred to as “tube contribution,” may lead to erroneous qualitative interpretation of X‐ray spectra because peaks of the elements may appear in the spectra when the element is not present in the sample. The additions (or spiking) technique allows matrix problems to be overcome in the quantitative measurement of Zn, Cu, and Ni in soils and other materials, but an accurate estimation of the background under the peak is essential. Because of the “tube contribution” to the line of the element concerned, the background under the peak is increased and results in a positive error with the additions technique if no correction is made. The ratio of the peak to background beside the peak for the “tube contribution,” for each element, was found to be nearly constant in different materials free of Zn, Cu, and Ni. Thus, a background that includes the “tube contribution” may be calculated, for unknown samples containing the element concerned, by multiplying the background beside the peak by the ratio factor. Using the additions technique including measurement of the background as described, accurate measurements were made of Zn, Cu, and Ni in soils, sewage sludges, and plant and animal tissues.
Microbial Inorganic Polyphosphates: Factors Influencing Their Accumulation in Soil
Authors: Pepper I. L. , Miller R. H. , Ghonsikar C. P.
Published: July 2010

Infrared spectra of microbially synthesized, acid labile, inorganic P compounds extracted from soils provided additional evidence that they are inorganic polyphosphates (poly P). Incubation studies with glucose amended soils demonstrated the transient nature of naturally occurring poly P. Experiments are reported on the conditions which optimize poly P synthesis in soil. A 2‐week incubation period (preincubation) with a source of carbon (2% glucose or 4% straw) and a further 2‐day incubation period (postincubation) after adding a source of ortho P resulted in the maximum accumulation of poly P. The quantity of poly P also increased with increasing rates of orthophosphate from none to 1,000 µg soil/g. Longer periods of postincubation reduced poly P accumulation. Poly P synthesis was greater when relatively insoluble sources of P were added to soils and accumulation followed the order; FePO4 · 2H2O > rock phosphate > Ca(H2PO4)2 · H2O > KH2PO4. These results suggest that poly P synthesis may accompany P solubilization in soils and be an integral part of the soil P cycle.
The Red Latosols of Sri Lanka: II. Mineralogy and Weathering
Authors: de Alwis K. A. , Pluth D. J.
Published: July 2010

Soil samples from the principal soil series of the Red Latosols of Sri Lanka were subjected to (i) mineralogical analysis of the fine sand fractions by density, magnetic and optical methods, and (ii) mineralogical analysis of the clay and silt fractions by X‐ray diffraction, DTA, chemical, and electron optical methods in order to characterize these soils and elucidate their genesis.

Mineralogical analysis of the fine sand fractions confirmed that the parent materials were uniform with depth and within series, but differed among series. The near‐complete absence of easily weatherable minerals indicates intense weathering either before deposition or during soil formation.

The fine (< 0.2 µm) clays of all three Red Latosol soil series consist almost exclusively of well‐crystallized kaolinite. The remainder is made up of free iron oxides and a small amount of amorphous components. Similarly the coarse (2–0.2 µm) clays are dominated by kaolinite, but they also contain minor amounts of other minerals, chiefly mica and mixed layer minerals with anatase and possibly some interstratified materials being present as traces. Coarse clays from the Wilpattu series contain, in addition, a clay mineral that is probably a vermiculite‐smectite intergrade. The mica in the surface horizons appears to be stabilized against weathering, possibly by phytocyling of K. Free iron oxides are present mainly as discrete particles of hematite. Small amounts of amorphous materials also occur.
Sand and Coarse Silt Mineralogy of Selected Soils on the Lower Coastal Plain of North Carolina
Authors: Smith B. R. , Granger M. A. , Buol S. W.
Published: July 2010

Mineralogical characterization studies were made of sandy, loamy, and silty soils on the Pamlico, Talbot, and Wicomico terraces of the Lower Coastal Plain of North Carolina. Soils on the Pamlico terrace contain substantial amounts of weatherable minerals (as much as 35%), primarily feldspars. Soils on the higher Talbot and Wicomico terraces contain a stable mineral assemblage (mostly quartz) and only very minor amounts of weatherable minerals (<5%). Drainage class did not influence the sand mineralogy. The relationship between mineralogical composition of these soils and their occurrence on particular terraces is useful from the standpoint of soil classification because it affords a means of delimiting soils which belong to mixed or siliceous mineralogy families on the Lower Coastal Plain.
Persistence of Subsoil Compaction in a Mollisol
Authors: Blake G. R. , Nelson W. W. , Allmaras R. R.
Published: July 2010

Persistence of subsoil compaction was tested in Nicollet clay loam (a Mollisol) in southwestern Minnesota. Plots were either not packed or packed in 1960 in the bottom of each plow furrow using about 7.5 bars pressure, and were cropped to corn (Zea mays L.) and alfalfa (Medicago sativa L.) 9 years. Halves of plots were irrigated each year just prior to soil freezing. All plots were tilled with normal farm equipment after initial packing.

Soil bulk density below the plow layer did not change over the 9‐year period, but there were small trends for increased bulk density on the not‐packed treatment. Neither crop nor overwinter soil water content affected the packed subsoil. The packed layer was easily identified by penetrometer measurements.

Alfalfa root samples taken at the close of the experiment showed that packing reduced mean root weights by as much as 36% in the 40‐ to 90‐cm layer compared to 11% or less in the surface 40 cm. Packing affected the distribution of taproots and fibrous roots in the profile.

Soil hydraulic conductivity (K), either saturated or unsaturated, was reduced by packing. Decreases in saturated K averaged 65% in 10‐cm soil depths between 21 and 48 cm and 56% between 61 and 88 cm. Unsaturated K measured in situ also showed persistence of the packing treatment in the 18 to 55‐cm soil layer.
Soil Compaction After Tree‐Length Skidding in Northern Mississippi
Authors: Dickerson B. P.
Published: July 2010

After skidding with a rubber‐tired skidder, bulk densities of wheel‐rutted soils increased an average of 20% to 1.55 g/cm3; the increase was 10% for the soils between the ruts which were compacted by the movement of logs. Macropores were reduced 68% for wheel‐rutted soils and 38% for log‐disturbed soils; micropore space of both increased about 7%. Percolation rates decreased initially but recovered gradually. Wheel‐rutted soils require about 12 years to recover and log‐disturbed soils about 8 years.
Splash Erosion of Primary Particles and Aggregates
Authors: Kinnell P. I. A.
Published: July 2010

The previously supposed similarity between primary particles and aggregates in resisting splash erosion was shown to be partially incorrect. Mathematical treatment of splash‐cup data on which the earlier conclusion was based showed that for surfaces containing aggregates, the quantity of material lost per unit quantity of artificial rainfall varied with rainfall intensity; a result which contrasts to observations for primary particles.
Solute Movement in a Field Soil
Authors: Van De Pol R. M. , Wierenga P. J. , Nielsen D. R.
Published: July 2010

Solute and water movement was studied under steady‐state flow conditions in a field soil consisting of 70 cm of clay to silty clay over a medium sand. A steady‐state water flow condition was maintained by applying irrigation water at a constant flux of 2 cm per day. During the steady‐state condition some of the water leached into the plot was labelled with chloride and tritium. The positions of the chloride and tritium as functions of soil depth and time were measured by extracting samples of the soil solution with soil suction probes. Extremes in solute displacement occurred at equal and different depths within the plot. An analysis of these measurements indicated that observations of the pore‐water velocity and the apparent diffusion coefficient were log normally distributed. Twenty‐four soil suction probes, used to identify the rate at which a solute was displaced in the soil, will yield an estimate of the mean pore‐water velocity of this soil within a range of approximately ±25% of its true value providing the effects of potential solute‐soil interactions are taken into account.
Thermodynamic Stability and Solubility of Molybdenum Minerals in Soils
Authors: Vlek P. L. G. , Lindsay W. L.
Published: July 2010

The chemical reactions of molybdenum in soils were studied in the laboratory. Solubility diagrams were constructed from thermodynamic data obtained from the literature and from measurements made on pure minerals. Included in these diagrams were solubility relationships for MoS2 (molybdenite), Mo3O8 (ilsemannite), Fe2(MoO4)3 (ferrimolybdite), CaMoO4 (powellite), and PbMoO4 (wulfenite). From these diagrams it appears that wulfenite is one of the most stable Mo minerals likely to form in soils. Lack of thermodynamic data on other Mo minerals prevents their evaluation as possible reaction products.

The solubility of Mo in selected Colorado soils in the pH range of 5.5 to 7.7 was plotted on the wulfenite solubility diagram. Of the 13 soils used in this study, only one showed equilibrium with respect to wulfenite. When wulfenite was added to several other soils, the molybdenum solubility increased 10‐ to 100‐fold, confirming that wulfenite was not initially present. These wulfenite‐amended soils showed a close correspondence between soluble Mo and the wulfenite solubility isotherm.

In the absence of solid phase Mo compounds, the solubility of Mo in soils is controlled by specific adsorption.
Hydrologic Differences between Selected Forested and Agricultural Soils in Hawaii
Authors: Wood Hulton B.
Published: July 2010

Comparisons of hydrologic characteristics of soil under different land uses were made at 15 sites on the islands of Hawaii, Maui, and Kauai. A site consisted of at least two adjacent but different land uses on the same soil series. One land use at a site was always an ungrazed forest; the others were planted either to sugarcane (Saccharum officinarum) or pineapple (Ananas comosus), or used as pasture. Infiltration rates on 14 of the 15 sites were found to be higher under forest cover than agriculture uses. Mean weight diameters of the surface soil aggregates were larger for forested soils than for soils planted to sugarcane or pineapple. Aggregate size also varied with soil order and soil moisture content at time of testing. Lower bulk densities and greater porosities were found in forest‐covered soils than in the nonforested soils.
History of Chemical Fertilizer Development
Authors: Russel Darrell A. , Williams Gerald G.
Published: July 2010

Neolithic man probably used fertilizers, but the first fertilizer produced by chemical processes was ordinary superphosphate, made early in the 19th century by treating bones with sulfuric acid. Coprolites and phosphate rock soon replaced bones as the P source. The K fertilizer industry started in Germany in 1861. In North America the K industry started during World War I and expanded with development of the New Mexico deposits in 1931 and the Saskatchewan deposits in 1958. Modern K fertilizers are more the product of physical than of chemical processes. The first synthetic N fertilizer was calcium nitrate, made in 1903 from nitric acid produced by the electric arc process. The availability of synthetic ammonia after 1913 led to many new N fertilizers, but physical quality was poor. In 1933 TVA was formed with a national responsibility to increase the efficiency of fertilizer manufacture and use. More than 75% of the fertilizer produced in the United States is made with processes developed by TVA.

Major fertilizers and fertilizer intermediates introduced by TVA include ammonium nitrate, high‐analysis phosphates, diammonium phosphate, nitric phosphates, ammonium polyphosphate, urea ammonium phosphates, 11‐16‐0 and other liquid base solutions, superphosphoric acid, wet‐process superphosphoric acid, suspensions, granular urea, and S‐coated urea. These have had major impact upon the production of mixed fertilizers, bulk blending, and the fluid fertilizer industry. Future fertilizers not only must be technologically feasible, economical, and agronomically suitable—as have been past fertilizers—but also must meet various air and water pollution standards during production and have reduced total energy requirements.
Ion Activity Products of Calcium Carbonate in Waters Below the Root Zone
Authors: Suarez Donald L.
Published: July 2010

The pH, Ca2+, and HCO3‐ relations were investigated in 28 well waters obtained from beneath irrigated fields in Arizona. The mean [Ca] [CO3] ion activity product (IAP) was 11.3 × 10−9 (pIAP = 7.95) with a standard error of 0.7 × 10−9 based on field measurements of pH. As indicated by ionic strength the residence time of the waters in the soil vary widely. The lack of a trend in pIAP vs. ionic strength indicates the kinetics of calcite equilibration (from supersaturation) is quite slow in soil‐water systems. This conclusion was supported by an average pIAP of 7.97 calculated from 35 water analyses obtained from wells in the Grand Valley of Colorado and by a pIAP value of 7.96 obtained from a soil water sample in a lysimeter study. Since these pIAP values are quite consistent and were obtained under a wide variety of conditions, a pIAP value of 7.95 is recommended for use in predictive models when CaCO3 precipitation occurs.
Exchange Capacity of Calcium and Sodium Soils as Determined by Different Replacing Cations
Authors: Ravina Israela , Gurovich Eliezer
Published: July 2010

Experimentally determined CEC values are dependent on the nature of the initially adsorbed cation and the replacing one. Cation exchange capacities of Na‐saturated and Ca‐saturated soils were determined using monovalent and divalent cations. In the exchange of initially adsorbed Na or Ca by monovalent cations, the magnitude of CEC increases with increasing ionic radius or polarizability of the replacing cation. The Na soil shows a greater CEC than the Ca soils.

The Na soil and Ca soil behave differently with respect to the exchange by divalent cations. While the CEC of a soil initially saturated with Ca increases as the ionic radius of the replacing cation is larger, the magnitude of CEC of a Na soil decreases.
Titration Studies on the Polynuclear, Polyacidic Nature of Fulvic Acid Extracted from Sewage Sludge‐soil Mixtures
Authors: Sposito Garrison , Holtzclaw Kenneth M.
Published: July 2010

Aqueous solutions of two fulvic acids extracted from sludge‐soil mixtures were studied by potentiometric titration with either KOH or HCl in an ionic medium of 0.1 mol/kg KCl. Data were obtained for a range of concentrations of FA at 25°C and for a single concentration at 35°C that duplicated one of those employed at the lower temperature. Formation functions giving the amount of H+ neutralized as a function of the free OH‐ concentration or of the pH were computed for each set of titration data. Analysis of these functions led to the conclusions that: (i) sludge‐derived FA contains functional groups ranging in acidity from very strong (ionized at pH < 2) to very weak (ionized at pH > 10); (ii) the strongly acidic groups are probably sulfonic acid groups and are relatively numerous; (iii) the more weakly acidic groups are probably carboxyls, N‐containing groups, phenolic OH, and SH groups; (iv) the strongly acidic groups can bind H+ from solution (counter‐ion condensation) when they get close to complete neutralization; (v) the H+ binding effect is enhanced by lowering the concentration of FA or by raising the temperature; and (vi) the reversibility of the titration curves is influenced greatly by the presence of the strongly‐acidic functional groups. These conclusions support the conceptualization of sludge‐derived FA as a heterogeneous polynuclear polyacid whose intrinsic acidity will show a pronounced dependence on its concentration and on the temperature. Thus the behavior of this material in soil solutions may be expected to be quite complex.
Relationships Between Soil Urease Activity and Other Soil Properties
Authors: Zantua M. I. , Dumenil L. C. , Bremner J. M.
Published: July 2010

Surface samples of 21 diverse Iowa soils representing a wide range in pH, texture, and organic matter content were studied to determine the relationships between soil urease activity and other soil properties.

Simple correlation analyses showed that urease activity was correlated very highly significantly with organic C (r = 0.72***), total N (r = 0.71***), and cation‐exchange capacity (r = 0.67***). Urease activity also was significantly correlated with clay (0.53*), sand (−0.47*), and surface area (0.45*), but was not significantly correlated with pH, silt, or CaCO3 equivalent. Multiple regression analyses showed that organic matter content accounted for most of the variation in urease activity.
Fragipan Horizons in Soils of the Memphis‐Loring‐Grenada Sequence in West Tennessee
Authors: Buntley G. J. , Daniels R. B. , Gamble E. E. , Brown W. T.
Published: July 2010

The distribution of soils on the loess‐mantled landscapes of west Tennessee does not fit the traditional concept that the older, more strongly developed soils occur on the more stable positions in the landscape. The objective of this study was to attempt to ascertain whether the development and distribution of these soils were related to weathering associated with the modern landscape or whether they were in part relict from the earlier period of weathering. Power augers were used along west to east transects to determine the characteristics and thickness of the three identifiable loess sheets involved and to explore their relationship to the distribution of soils within landscapes at different points along the loess thickness sequence. The top of the Roxana loess was everywhere marked by a distinctly brittle zone 1 to 2 m thick. Evidence that the brittle zone in the top of the Roxana is a product of pre‐Peorian weathering is the fact that it occurs under calcareous loess near the bluff and can be traced eastward under the thinning Peoria loess until it grades into the fragipan horizons within the sola of the Loring and Grenada soils. The stratigraphic, geomorphic, and morphologic evidence leads to the conclusion that the fragipan horizon of the Loring and Grenada soils is a relic of pre‐Peorian weathering that has undergone subsequent modification by processes related to the modern surface.
Water Movement Through Pedal Soils: I. Saturated Flow
Authors: Anderson J. L. , Bouma J.
Published: July 2010

Apparent dispersion coefficients were determined with a chloride tracer in 55‐cm long undisturbed columns from four pedal soil horizons of three pedons. Five medium subangular blocky structures were compared with five coarse prismatic structures, all with a silty clay loam texture. Dispersion coefficients (D), which could not always be calculated due to “nonideal” behavior of the flow system, were significantly different for the two types of structures. Application of an unlimited quantity of traced water to drained columns resulted in very high dispersion particularly for the subangular blocky structures. Some practical implications of the occurrence of hydrodynamic dispersion are discussed.
Water Movement Through Pedal Soils II. Unsaturated Flow
Authors: Anderson J. L. , Bouma J.
Published: July 2010

Very high hydrodynamic dispersion, occurring during application of an unlimited dose of chloride‐traced water to 10 drained 55‐cm long columns with undisturbed pedal soils, was strongly reduced by a daily application of 1 cm of water. Dispersion in five columns with subangular blocky structures remained significantly higher than that measured in five columns with prismatic structures. Differences are explained by a hypothetical analysis of flow patterns in both types of structure. Application of a surface crust strongly reduced dispersion in the subangular blocky structures, even though the flow rate remained approximately 1 cm/day. This was attributed to lack of flow into the larger vertical pores extending through the columns. Pronounced differences in terms of hydrodynamic dispersion were found among two types of structures from three soil series, all with a silty clay loam texture. This demonstrates the potential usefulness of routine soil structure descriptions as a correlative tool for predicting certain aspects of physical behavior.
A Comparison of In Situ Extractors for Sampling Soil Water
Authors: Levin M. J. , Jackson D. R.
Published: July 2010

Comparisons were made of two in situ extractors for collection of soil water samples: Amicon hollow fibers and porous ceramic cup lysimeters. Intact soil cores removed from a fescue pasture were fitted with lysimeters and fibers at 10 and 20 cm depth. Cores were leached by adding increments of water in excess of field capacity weekly. After drainage, soil solutions were extracted using lysimeters and fibers. Concentrations of Ca and Mg in soil solutions were greater at 10‐cm than at 20‐cm soil depths. Neither extractor altered the concentrations of Ca, Mg, or PO4‐P during collection.

These studies suggest that lysimeters and hollow fibers are viable devices for extracting of soil water samples. Porous ceramic cup lysimeters are preferable for field plots, while hollow fibers are advantageous for intact soil cores. A major advantage of the hollow fiber technique is the small soil displacement required for installation.