bluuebunny/crossref_metadata_2025 huggingface dataset:
Model Calculations for the Extraction of Soil Water by Ceramic Cups and Plates
Authors: van der Ploeg R. R. , Beese F.
Published: July 2010

A numerical method is developed with which the flow of moisture towards suction units in soil can be evaluated. For a number of selected problems the unsaturated moisture flow equation is solved twice: (i) for radial flow towards a suction plate or suction cup; (ii) for vertical downwards flow under the same conditions, but without a suction unit in the soil. The calculations are performed for a flat soil without a plant cover. It is found that even for little vacuum, large differences may exist between the seepage rate as determined from a suction unit as compared to the seepage rate of the unextracted soil. It is also shown that the radius of influence of a suction unit, which extracts water continuously, can be several feet wide. It is concluded that in order to be reliable, data collected with suction units should be analyzed with care.
Experimental Studies of Wetting Front Instability Induced by Gradual Change of Pressure Gradient and by Heterogeneous Porous Media
Authors: White I. , Colombera P. M. , Philip J. R.
Published: July 2010

The stability of infiltration flows in Hele‐Shaw cells was examined. Flows were perturbed either by gradually increasing G, the pressure gradient behind the wetting front, or by heterogeneities in the cells. Two methods were used to increase G gradually through zero: (i) by allowing the air ahead of the front to be compressed by the flow, and (ii) by monotonically increasing the hydraulic conductivity of the cell with depth. In the other class of experiments, the flow was instantaneously perturbed by a step‐increase in conductivity at selected depths.

It was found that Philip's (1975a, 1975b) stability analysis adequately predicted both the onset of instability and the wavelength of the initial disturbances. For quadratic increase in conductivity with depth the observed growth rate of disturbances was faster than expected from the linear theory.

Examination of the data of Peck (1965) and Hill and Parlange (1972) showed that Philip's analysis is also adequate for coarse sands.
Effects of the Addition of Phosphorus and Inorganic Nitrogen on Carbon and Nitrogen Mineralization in Andepts From Colombia
Authors: Munevar F. , Wollum A. G.
Published: July 2010

This study tested the hypothesis that the level of available P in volcanic ash soils is a rate‐limiting factor for organic matter mineralization. Additions of calcium phosphate to give levels of P of 1,200 and 2,400 ppm significantly increased the amount of N mineralized and CO2 evolved as compared to soils not treated with P. Although the addition of glucose to these soils increased CO2 evolved, there was significantly more CO2 evolved in the presence of glucose and P than when glucose had been the only addition. Amendment of the soils with N did not have any significant affect on the rate of CO2 evolution. Both N and P additions stimulated N mineralization. The P×N interaction was also significant for C and N mineralization. It was concluded that available P is a rate‐limiting factor for organic matter mineralization in Andepts.
Influence of Soil Amendments on Potato Growth, Mineral Nutrition, and Tuber Yield and Quality on Very Strongly Acid Soils
Authors: Lee C. R. , MacDonald M. L.
Published: July 2010

Potatoes (Solanum tuberosum L.) were grown in greenhouse soil pot cultures to evaluate soil amendments that might modify the fertility of very strongly acid Ultisols and improve potato production. Raising soil pH from 4.6 to either 4.9 or 5.2 with dolomitic limestone increased tuber yield and improved tuber quality. Superphosphate applied alone or in combination with dolomitic limestone also increased tuber yield. Tuber specific gravities were not improved with superphosphate alone, but only with combinations of superphosphate and dolomitic limestone. Cow manure applications increased tuber yield, but did not improve tuber specific gravity or quality. Manganese toxicity symptoms and potato leaf Mn content increased with cow manure applications. Magnesium sulfate alone or in combination with superphosphate was beneficial to potato tuber yield. Tuber quality was also improved with the combination of magnesium sulfate and superphosphate. The application of either potassium bicarbonate or Fe chelate did not improve potato growth, tuber yield, or quality. It was concluded that potato production on very strongly acid Ultisols can be improved either by raising soil pH to 4.9 with dolomitic limestone or by the application of Ca phosphate and Mg fertilizers without raising soil pH. Cow manure also improved potato tuber yield but did not improve tuber quality.
Hydrologic Response and Nutrient Concentrations Following Spring Burns in an Oak‐hickory Forest
Authors: Knighton M. Dean
Published: July 2010

Annual spring burns were applied for 1 to 3 years on a 25 to 50% slope in an oak‐hickory forest (Quercus—Carya) in southwestern Wisconsin. Overland flow and sedimentation did not increase, although no severe storms occurred during the study.

Fires of light to moderate intensities, consumed most of the fresh litter and sometimes all of the fermentation layer. Mean weight of litter plus fermentation layers were significantly reduced (α = 0.05) from 15,800 kg/ha to 10,100 kg/ha by three annual burns. Bulk density, total pore volume, organic carbon content, and water permeability of the mineral soil were unaltered. Stems <5 cm in diameter at breast height were killed, but shrubs sprouted vigorously and herbaceous vegetation was not altered.

Mean concentrations of both anions [PO4‐P and (NO3 + NO2)‐N)] and cations (Ca, Mg, K) in the soil leachate collected at 15‐cm depth appeared to increase after burning although the differences were small and highly variable. Significant changes (α = 0.05) in the concentration of both anions were measured through the growing season. Concentrations of (NO3 + NO2)‐N peaked 6 weeks after the mid‐April fires, which reflects increased nitrification following burning. Sodium concentrations were not affected by burning. Although it was increased by burning nutrient loss to deep leaching appeared to be approximately equivalent to, or less than, estimated annual input from precipation.
An Ultrasonic Nebulization Technique for Adding Aqueous Solutions Uniformly to Dry Soils
Authors: Mubarak A. , Woodriff R. , Olsen R. A.
Published: July 2010

An ultrasonic nebulizer has been successfully utilized to provide a relatively convenient laboratory means for wetting dry soil with aqueous solutions to any selected moisture or electrolyte content. The technique is believed to cause a minimum of alteration of the chemical and physical properties of the sample and causes aqueous solutions to become very uniformly distributed throughout all accessible zones.
Basaluminite and Alunite: A Possible Cause of Sulfate Retention by Acid Soils
Authors: Adams Fred , Rawajfih Zahir
Published: July 2010

Pure‐solution and soil‐solution experiments were conducted in which the solubility products of synthetic basaluminite and alunite in pure solutions were compared with the ion‐activity products of Al4(OH)10SO4 and KAl3(OH)6(SO4)2 in soil solutions of sulfate‐treated soil. Solution experiments were conducted in which 0.05M Al2(SO4)3 was titrated with NaOH, KOH, or Ca(OH)2 to an OH/AI mole ratio of 2.0. The initial precipitate was amorphous, with the chemical composition of basaluminite, Al4(OH)10SO4·5H2O. Aging the amorphous precipitates under different conditions transformed them to compounds of different composition and crystallinity: amorphous precipitate remained unchanged when aged in their mother solutions at 25°C; crystalline basaluminite formed in Ca mother solutions when aged at 50°C; crystalline alunite formed in Na and K mother solutions when aged at 50°C; crystalline alunite formed in K mother solutions that had been seeded with alunite or bentonite when aged at 25°C. The solubilities of the amorphous and crystalline precipitates were determined in dilute NaClO4 solutions and gave the following average calculated pKsp values: 116.0 for amorphous basaluminite; 117.7 for crystalline basaluminite; 79.7 for Na‐alunite; and 85.4 for K‐alunite. Similar Ksp values for basaluminite were found for soil solutions from a sandy loam soil that had been treated with different rates of K2SO4. However, the soil solutions were supersaturated with respect to alunite. When the SO4‐treated soil was subsequently treated with a high rate of KH2PO4, the soil solution remained supersaturated with respect to alunite, but became undersaturated with respect to basaluminite. It is proposed that sulfate retention by acid soils is a consequence of the solubility of basaluminite and/or alunite.
On the Use of the Langmuir Equation in the Interpretation of “Adsorption” Phenomena
Authors: Veith J. A. , Sposito Garrison
Published: July 2010

A theoretical discussion in terms of molecular theory and the results of model experiments are employed to demonstrate that the conventional analysis of “anion fixation” data, through linear least squares regression of the points in a Langmuir plot, usually will not be sensitive enough to show the failure of the Langmuir equation whenever solubility product considerations are essential in the fixation reaction. The theoretical discussion points out that although the Langmuir equation is not restricted to two‐dimensional phenomena (i.e., adsorption), it cannot apply if the reacting anions must be present at some threshold concentration before fixation occurs. An analysis of model experiments on the reactions of OH‐ with Al‐ or Fe‐resin and of Cl‐ with Ag‐resin shows that secondary precipitation phenomena always result in a statistically significant, linear correlation of the variables in a Langmuir plot if the concentration of the reacting anions is much larger than the threshold value needed to initiate precipitation of the secondary solid phase. This condition generally can be expected to be met when anions such as o‐phosphate react with soils or soil constituents. Therefore, the Langmuir equation usually will appear to apply, on the basis of a statistical analysis, even when its applicability is impossible in principle. It follows that the Langmuir equation cannot be used statistically to determine whether adsorption or precipitation (formation of secondary minerals) is occurring during anion fixation reactions in soils and that the parameters in the Langmuir equation cannot be interpreted in terms of surface reactions without additional, independent evidence that only adsorption is involved in anion fixation.
Analysis of the Saturated‐unsaturated Hydraulic Conductivity in a Mixed Sodium‐Calcium Soil System
Authors: Russo David , Bresler Eshel
Published: July 2010

A model is developed to diagnose the effect of Na/(Ca)1/2 ratios and soil solution concentrations on the hydraulic conductivity for an unsaturated soil. The model takes into account the porous nature and the electrical properties of the soil. Interactions between ions in the exchange phase and in the liquid phase are expressed quantitatively by the diffuse double‐layer theory. Experimental data on the effect of soil solution and soil‐water pressure on clay‐platelet organization and structure were considered in the model. A test is made of the sensitivity of the model to variations in the various input parameters. The model is found to be sensitive to the relationship between the number of platelets per clay particle, and the ESP of the soil. The diagnostic model is compared with experimental data for three soils of different texture. The model approximates the hydraulic conductivity function for many practical combinations of Na/(Ca)1/2 ratios and soil solution concentrations for the ranges of soil water content in which most of the water flow occurs.
Effect of Redox Potential on the Stability of Zinc and Copper Chelates in Flooded Soils
Authors: Reddy C. N. , Patrick W. H.
Published: July 2010

Stability of Zn and Cu chelates of EDTA and DTPA was studied under controlled redox potential‐pH soil conditions. The metal chelates ZnEDTA, ZnDTPA, CuEDTA, and CuDTPA were reacted with soil suspensions incubated at six different redox potentials (−200, −100, 0, +100, +300, and +500 mV) and at pH 7 for reaction periods varying from 2 to 192 hours.

The redox potential has a very significant effect on the stability of all four metal chelates studied. The percentage of added Zn/Cu that remained in soil solution decreased with decreasing redox potential from +500 to −200 mV. Even though Zn and Cu chelates were stable at higher redox potentials, their stability decreased with time, apparently due to physical adsorption and microbial decomposition of metal‐chelate complex. At lower redox potentials, Zn and Cu chelates were found to be highly unstable. This instability was found to be mainly due to chemical fixation of added Zn and Cu, not due to physical/microbial decomposition of metal‐chelate complex. Iron, Mn, Ca, and Mg were found to be forming metal‐chelate complexes with EDTA and DTPA ligand molecules once Zn and Cu were removed from their metal‐chelate complexes.
Retention and Leaching of Nutrients in a Limed Ultisol Under Cropping
Authors: Juo A. S. R. , Ballaux J. C.
Published: July 2010

The response of maize (Zea mays L. Cv. TZB) to liming and the retention and leaching of Ca and other nutrient ions were studied in the greenhouse using an acid Ultisol from southern Nigeria. The soil was limed to various pH levels and maize was grown for 10 weeks. The largest growth response occurred when the soil pH was raised from 4.3 to 5.0 by liming (1.3 metric ton/ha). The highest yield was obtained when the soil pH was between 5.5 to 6.0.

Substantial downward movement of Ca from the limed surface layer (0–15 cm) was noted, but these Ca ions were mostly adsorbed in the unlimed subsurface layer. The vertical distribution of exchangeable Ca in the limed soils followed a similar trend with pH, but was inversely related to exchangeable Al.

Leaching losses of applied nutrient ions (Ca, Mg, K, NO3) during the 10‐week cropping period were relatively small. There was a significant increase in nitrate content in leachates when soil was limed above pH 7.0. Only 1% of the applied Ca was in the leachate while about 80% of the applied Ca was retained in exchangeable form when the soil was limed at a rate of 2 metric ton/ha.
Determination of Total Sulfur in Tidal Marsh Soils by X‐ray Spectroscopy
Authors: Darmody R. G. , Fanning D. S. , Drummond W. J. , Foss J. E.
Published: July 2010

Two X‐ray spectroscopy techniques, called additions and corrections, were developed for total S analysis of soils. The techniques are especially applicable to tidal marsh soils because of the wide range in organic matter contents of these soils and the importance of S in their genesis, classification, and management. Both methods involve basically the same equation: %S = (Sample counts/sec)/(counts/sec per %S), where c/sec is the sulfur Kα counts/sec (peak minus background). In the additions technique, the c/sec per %S is estimated by adding a known concentration of S as thiourea to a powdered soil sample and determining c/sec with and without addition. In the corrections technique, the c/sec per %S is based on the soil organic matter content, since c/sec per %S increases in a regular manner with increasing organic matter content. Results by the additions technique agreed well with values from Na2CO3 fusion analyses of tidal marsh soils and with Leco furnace analyses of powdered rock samples, and analyses by the corrections technique agreed well with those by the additions technique. When compared with National Bureau of Standards values for standard coals, however, total S contents were underestimated by the additions technique as employed, apparently at least partly related to a pyritic S form in the coals. Pyritic S gives less c/sec per %S than thiourea. An organoleptic “whiff” (aroma) method for field estimation of S in marsh soils is also described. “Whiff” values gave a highly significant correlation (r = 0.53) with surface soil S content as measured by the X‐ray additions technique. Maryland tidal marsh soils examined contained 0.10 to 96% organic matter and 0.02 to 5.44% total S.
Regional Distribution of Fluorine in Illinois Soils
Authors: Omueti J. A. I. , Jones Robert L.
Published: July 2010

Fluorine concentrations in 201 Illinois surface soils range from 70 to 618 mg/kg with an arithmetic average of 271 mg/kg or a geometric mean of 256 mg/kg. Interpretation of a cumulative frequency plot of the data on a probability‐log graph suggested that there were at least four populations of F in the state. Multiple regression analysis showed that clay content was the most highly associated variable (r = 0.924) with soil F. The only other significant variables, pH and clay by organic carbon interaction, accounted for 4 and 1%, respectively, of the variance. Variations in these three soil properties resulting from influences of topography, drainage, degree of weathering and soil development, vegetation, and parent materials were most closely associated with the observed distribution of F in Illinois soils.
Solution Activities of Aluminum and Silicon in Highly Weathered Soils that contain Gibbsite and Kaolinite
Authors: Weaver R. M. , Bloom P. R.
Published: July 2010

Solution activities of aluminum (Al3+) and monosilicic acid (Si(OH)4) in dilute acid suspensions of six Brazilian Oxisols were measured over a period of 145 days. The steady state activity function of pH‐⅓pAl ranged from 1.86 to 2.69, while that of pSi(OH)4 ranged from 3.69 to 4.22. Although all of the soils contained kaolinite and gibbsite, the observed solute activity functions of pH‐⅓pAl and pSi(OH)4 deviated considerably from those expected for a thermodynamic equilibrium between gibbsite and kaolinite. It was found that the solution activities of Al and Si(OH)4 in these soils appeared to result from the dissolution of a surface aluminosilicate component (R) of variable composition‐{[Al(OH)3](1‐x)[SiO2]x}R rather than gibbsite and kaolinite.
The Shear Resistance of Root‐Permeated Homogeneous and Stratified Soil
Authors: Waldron L. J.
Published: July 2010

Mechanical reinforcement which stabilizes soil on slopes has been attributed to plant roots. To measure such reinforcement, direct shear tests were made on 25‐cm diameter root‐permeated soil columns. Roots of alfalfa (Medicago sativa), barley (Hordeum vulgare), and yellow pine (Pinus ponderosa), each increased the shear resistance of homogeneous and compacted layers of silty clay loam at 30‐cm depth. One‐year‐old alfalfa had a much greater reinforcing effect than pine trees 16 months after transplanting or barley at its maximum growth. Barley had a greater effect in the clay loam than pine, but its effectiveness decreased as depth increased from 15 to 30 to 45 cm. Alfalfa roots were more effective than either pine or barley roots in increasing the resistance to shearing between a dense gravel‐sand layer (simulating weathered rock) and the overlying soil, increasing shearing resistance to as much as 5 times that of fallow soil. A model is presented of soil reinforced by nonrigid roots. Calculations are given of slope safety factor increases from root reinforcement.
Water Movement in Bare and Cropped Soil Under Isolated Trickle Emitters: II. Analysis of Cropped Soil Experiments
Authors: Earl K. D. , Jury W. A.
Published: July 2010

Soil moisture and plant root distributions were evaluated when plots of summer squash (Cucurbita pepo var. Zucchini) were trickle irrigated with two contrasting frequencies of water application. Replicated plots receiving the same total volumes of water were irrigated three times daily and once weekly, with irrigation volumes adjusted according to evapotranspiration and tensiometric data. In the presence of actively growing zucchini, weekly irrigations produced a greater movement of water both laterally and vertically downward than daily irrigations. Plant roots were distributed according to the wetted volume of soil, with roots of weekly irrigated plots being more evenly distributed than in daily irrigated plots where roots were concentrated beneath the emitter. The imposition of a water stress demonstrated a marked increase in root density beneath the emitters as a result of proliferation of fine root material.

Zucchini yields in the outer ring of weekly irrigated plants (100 cm from emitter radially) were 30% higher than the most productive daily irrigated plot. Furthermore, total green matter and dry matter yields were greater in weekly irrigated plots.
Reactions of Aluminosilicates, Aluminum Hydrous Oxides, and Aluminum Oxide with o‐Phosphate: The Formation of X‐ray Amorphous Analogs of Variscite and Montebrasite
Authors: Veith J. A. , Sposito Garrison
Published: July 2010

The formation of X‐ray amorphous analogs of variscite and Namontebrasite was demonstrated to occur when Al2O3 · nH2O, synthetic allophanes, and allophanic soils were reacted with sodium o‐phosphates, Na3‐AHAPO4, of varying acidity A. The formation of the two amorphous Al‐phosphates, Al(OH)2H2PO4 and AlOHNaPO4, respectively, was favored both by an increase in lability of Al (i.e., by large values of the hydration number n in Al2O3·nH2O or the presence of Si‐O‐Al bonds in the aluminosilicates) and by an increase in the acidity A of the added o‐phosphate solution.

Evidence for the formation of amorphous Al‐phosphates by secondary precipitation rather than the formation of a surface o‐phosphate phase by adsorption was indicated by the slowness of the reaction between o‐phosphate and Al‐containing material, by the immediate and significant increase of Si in solution when aluminosilicates were reacted, and by the large amounts of P reacted (e.g., 82% of the P added as equimolar H3PO4 reacted with synthetic allophane). The presence of amorphous Al(OH)2H2PO4 in the products was demonstrated by showing that a solid phase, Al‐P compound was formed in all of the reactions studied that had the same pH stability limites (2.5 ≤ pH ≤ 9) and solubility product pKso (28.1 ± 0.1) as were observed in a previous investigation for amorphous Al(OH)2H2PO4 formed directly from the reaction of Al‐hydroxy‐chlorides and o‐phosphate. The presence of amorphous AlOHNaPO4 in the products was inferred from an analysis of their formation curves (P in a solid phase vs. pH) and from measurements of the amount of Na bound with Al and P, corrected for adsorption of Na, as a function of pH. The formation of the amorphous, basic, Na‐containing AlOHNaPO4 begins at pH ≃ 6 and ends with the appearance of Al(OH)4‐ at pH ≃ 10.
Lead Adsorption by Montmorillonite Using A Competitive Langmuir Equation
Authors: Griffin R. A. , Au A. K.
Published: July 2010

The adsorption of Pb from pure Pb(NO3)2 solutions by Ca‐montmorillonite at pH 5.00 and 25°C was found to be sensitive to the weight of the clay sample. This apparent sensitivity of the adsorption of Pb to the weight of the sample was attributed to Ca competition for exchange sites as determined from Pb/Ca ratios found in the solutions. Adsorption of Pb from 0.1M Ca(ClO4)2 solutions was substantially lower and was insensitive to the weight of the clay sample. This further supported our conclusion that adsorption of Pb was dependent on the Pb/Ca ratio.

Application of the “simple” Langmuir equation to Pb adsorption by 0.05 and 0.10 g of clay resulted in a linear relation over the entire concentration range (0 to 1,200 ppm Pb). However, increasing non‐linearity was observed at the lower Pb concentrations when 0.50 and 1.00 g of clay were used, respectively. These Langmuir plots yielded lower adsorption maxima than maxima obtained from the two lower weights of clay and the shapes of the isotherms indicated two distinct regions of adsorption. The data were then plotted according to a “competitive” Langmuir equation, which successfully resolved the data for all four weights of clay into a single linear adsorption plot.
Gas Chromatographic Analysis of Soil Atmospheres
Authors: Blackmer A. M. , Bremner J. M.
Published: July 2010

A gas chromatographic procedure is described that permits rapid, specific, and precise determination of N2, O2, Ar, CO2, CH4, N2O, and other gases in soil atmospheres. It involves use of an ultrasonic detector and two columns of Porapak Q at different temperatures, and it does not require temperature programming, column conditioning, stream splitting, column switching, or switching of recorder polarity. Unlike thermal conductivity and helium ionization detectors previously used for gas chromatographic analysis of soil atmospheres, the ultrasonic detector is not adversely affected by gases found in soil atmospheres and permits determination of these gases at concentrations ranging from <10 ng/ml to 100%.
Decomposition of Carbon‐14 Labeled Plant Material Under Tropical Conditions
Authors: Jenkinson D. S. , Ayanaba A.
Published: July 2010

Ryegrass (Lolium multiflorum) and maize (Zea mays) tissue uniformly labeled with 14C were mixed with soil and allowed to decompose under field conditions in the open or under shade. The incubations were done in the forest zone of Nigeria, using a range of contrasting Nigerian soils. Of the ryegrass Coriginally added to the soil, 20% remained after 1 year, falling to 14% after 2 years. After 1 year the soil retained slightly less maize C than ryegrass C, but the difference was small and the overall pattern of decomposition similar. There was little difference between the rate of decomposition under shade or in the open, even though soil temperatures were considerably greater in the open. A soil containing 6% clay (Apomu series) retained slightly less maize C after 1 year than a soil with 16% clay (Egbeda series), but in general the decomposition rates in the different soils were similar.

For ryegrass, the decomposition pattern was very similar under Nigerian conditions to that previously observed for the same plant material in England, except that the whole decomposition process was four times faster in Nigeria.
The Function of Different Types of Macropores During Saturated Flow through Four Swelling Soil Horizons
Authors: Bouma J. , Jongerius A. , Boersma O. , Jager A. , Schoonderbeek D.
Published: July 2010

The hydraulic function of three types of macropores during saturated flow through four swelling fine clayey and very fine clayey soil horizons was characterized with methylene blue as a tracer, and was quantified in large thin sections with the Quantimet 720. All three types of macropores, described as channels, vughs, and planar voids, contributed to flow. Distinction between “smooth” and “rough” ped faces in field structure descriptions proved meaningful for three soils with high linear extensibility values, because vertical flow did not occur along interconnected planar voids adjacent to “smooth” peds, whereas it did occur along “rough” peds. However, flow did occur along “smooth” ped faces in the fourth soil, which had significantly lower extensibility values. Calculations of hydraulic conductivity Ksat, based on the observed dye patterns, are difficult because the dye solution flowed in interrupted patterns along the walls of the macropores without apparently filling them, due to the occurrence of smaller pore “necks” in overlying soil. But the number and percentages of colored pores for each of the three macropore‐types showed (with one exception for planar voids) consistant differences among the four soils, which corresponded with differences in measured Ksat values.
Spodic Horizon Brittleness in Leon (Aeric Haplaquod) Soils
Authors: Brandon C. E. , Buol S. W. , Gamble E. E. , Pope R. A.
Published: July 2010

Three delineations of Leon soils (Aeric Haplaquod; sandy, siliceous, thermic) on two geomorphic surfaces in the lower Coastal Plain of North Carolina were studied. Consistence of the upper part of the spodic horizon ranges from friable to brittle. Brittleness was associated with mineral material that was slightly finer in mean particle size, less well sorted, and slightly more fine skewed than spodic horizons that were not brittle. No chemical, mineralogical, or organic matter composition was related to brittleness. Brittle spodic layers are very different from nonbrittle layers in micromorphology, having their macropacking voids filled with organic matter and silt‐sized mineral material.
Effects of Fertilizer Nitrogen on Tree Growth, Foliar Nitrogen, and Herbage in Eastern Cottonwood Plantations
Authors: Blackmon B. G.
Published: July 2010

When five rates of nitrogen fertilizer (0 to 672 kg/ha) were tested in two eastern cottonwood (Populus deltoides Bartr.) plantations 7 and 10 years old in the Mississippi River floodplain, first season volume growth was more than doubled by fertilization. By the end of the third season, the direct effect of fertilization had apparently disappeared although a volume advantage caused by the large initial response was still evident. In one plantation, volume growth for the 3 years after fertilization was greatest at 336 kg N/ha, and in the other volume growth was greatest at 672 kg N/ha. However, lower rates gave more volume growth per unit of applied N. Fertilizer also increased the N content of herbaceous plants.
Anion‐Aluminum Hydroxide Gel Interactions
Authors: Serna Carlos J. , White J. L. , Hem Stanley L.
Published: July 2010

The interaction of the nitrate, sulfate, and carbonate anion with aluminum hydroxide gel was studied by infrared spectroscopy. A lowering in the anion symmetry due to the interaction with the aluminum hydroxide surface was observed. Evidence suggests that the nitrate anion interaction is outside of the coordination sphere of the aluminum cation and therefore is mainly electrostatic. However, the sulfate and carbonate anions both show evidence of coordination with the surface aluminum cations. The carbonate interaction appears to be the strongest and is believed to be responsible for the relatively high degree of stability of carbonate‐containing aluminum hydroxide gel.
Fluorine Content of Soil from Morrow Plots Over a Period of 67 Years
Authors: Omueti J. A. I. , Jones Robert L.
Published: July 2010

Between 1904 and 1971, F content in Morrow Plot soils varied from a mean of 275 to 381 mg/kg. The cause of variation in F content was shown to be related to phosphorus fertilization practices. Much of the F added to the soils in the form of rock phosphate between 1904 and 1924 was retained by 1955. Average loss of F from the soil per annum between 1924 and 1944 was calculated to be about 2.5‐mg F/kg. Recent samplings contain large, unaccounted‐for variability.
Evaluation of Antimetabolites for Retardation of Urea Hydrolysis in Soils
Authors: Mulvaney R. L. , Bremner J. M.
Published: July 2010

Studies to evaluate three antimetabolites patented as inhibitors of urea hydrolysis in soils (pyridine‐3‐sulfonic acid, desthiobiotin, and oxythiamine chloride) showed that they had no effect on production of urease by soil microorganisms and did not retard urea hydrolysis in soils or reduce gaseous loss of urea N as ammonia, even when applied at rates far exceeding those recommended for inhibition of urea hydrolysis.
Water Uptake by Plants: I. Divided Root Experiments
Authors: Herkelrath W. N. , Miller E. E. , Gardner W. R.
Published: July 2010

The influence of soil water content and soil water potential upon root water uptake was investigated in a controlled laboratory environment. Water extraction rates by roots of winter wheat were measured in situ in a soil column instrumented with a gamma‐ray attenuation water‐content meter, tensiometers, and psychrometers. In addition, the leaf water potential was measured with an in situ leaf hygrometer. In order to measure the vertical distribution of water uptake, the column was divided into five sections by wax layers which were penetrated by roots, but which prevented movement of water between sections in the soil. A measurement of the average root potential was obtained by allowing a thin “test section” of soil to dry toward equilibrium with the root water potential while the rest of the soil was kept wet. Although 86% of the root zone soil was at a water potential above about −0.1 bar, the roots dried the test section to a potential of −5 hars, indicating a root potential at least this low. Because the average leaf water potential was also −5 bars, the data imply that whereas there was little flow resistance between the roots and the leaves, the resistance to flow between the soil and the root xylem was large. Root extraction rates hegan to decrease rapldly when the soil water content fell below about 0.10 cm3 water/cm3, corresponding to a soil water potential of about −0.1 bar. This result agrees with data in the literature, but is at variance with the soil‐water diffusivity‐based root uptake model, which predicts little effect of soil dryness upon root uptake at high soil moisture potential.
Water Uptake By Plants: II. The Root Contact Model
Authors: Herkelrath W. N. , Miller E. E. , Gardner W. R.
Published: July 2010

In the standard analysis of root water uptake, it is assumed there is a constant root membrane resistance in series with a soil resistance which is dependent upon the soil moisture diffusivity. The relation of root extraction rate to soil water content and to soil water potential predicted by this standard model was compared to the results of divided root experiments. The extraction rates predicted by the theory were as much as eight times larger than the measured values. A reasonable fit between theory and experiment could only be obtained by assuming in the theoretical calculations that the rooting density was 100 times smaller than that measured in the experiments. An alternative model emphasizing the possibility of a root‐soil contact effect was developed. It was assumed that as the soil dried, the surface area of the roots in contact with the soil decreased, which caused an increase in the root membrane resistance. By assuming that the effective root membrane permeability was simply proportional to the relative saturation of the soil, a much better fit to the data was obtained than by using the conventional theory.
An Evaluation of Several Methods of Estimating Soil Volume Change
Authors: Parker J. C. , Amos D. F. , Kaster D. L.
Published: July 2010

The accuracy of several previously proposed methods of estimating potential soil volume change was evaluated using samples from the B2 horizons of three pedons of each of five soil series having various swelling characteristics. Models involving swell index, plasticity index, clay content, activity index, initial and final water contents, shrinkage limit, shrinkage ratio, liquid limit, linear shrinkage, and hygroscopic moisture content were evaluated by regression analysis with percent volume change of natural clods as the dependent variable. Most methods were found to be either too imprecise or too involved to be useful. The most practical correlations were with swell index (r2 = 0.92) and with plasticity index (r2 = 0.79). Estimates using these procedures should be used cautiously since their accuracy is only ± 12 to 18% volume change, respectively, at the 95% confidence level.
Applications and Misapplications of the Langmuir Equation to Soil Adsorption Phenomena
Authors: Harter Robert D. , Baker Dale E.
Published: July 2010

When the development of the Langmuir adsorption equation is critically examined, it is evident that the equation soil scientists have been using [C/x/m = C/k + I/kb, where C is concentration of adsorbate, x/m is the amount adsorbed per unit weight adsorbent, k is the adsorption maximum, and b is a constant] is in the wrong form. This error is of no great importance when the equation is merely used to obtain a calculated adsorption maximum for comparison to other adsorbent properties. However, it does become important when attempts are made to understand adsorption dynamics and bonding strengths. The commonly reported curvilinear nature of the C/x/m vs. C plots is simply the result of not considering the effect of desorbed ions in the equilibrium solution, rather than being due to multiple adsorption mechanisms. When the equation is corrected by considering desorbed ions, the isotherm becomes linear. In addition, the constant, b, of the Langmuir equation is not simply related to the bonding energy of the adsorbed ion, but to the ratio of adsorbed and desorbed ion bonding energies.
Proton Binding in Fulvic Acid Extracted From Sewage Sludge‐soil Mixtures
Authors: Sposito Garrison , Holtzclaw Kenneth M. , Keech D. A.
Published: July 2010

Aqueous solutions of two fulvic acids (FA) extracted from sludge‐soil mixtures and converted to K‐fulvates were titrated potentiometrically at 25°C with HCl in ionic media of 0.1M and 0.2M KCl. Data were obtained for a range of concentrations of FA, although during a titration experiment both FA concentration and ionic strength were rigorously held constant. A simple model was employed to interpret the formation functions calculated using the titration data. This model ascribes the acidic properties of a FA solution to an assembly of hypothetical macromolecules (“mean fulvic acid units”) that contain several distinct classes of functional group and are able to associate through hydrogen bonding. Conditional protonation constants were computed for each class of acidic functional group that protonates in the pH range 3–11. The common logarithms of the average protonation constants at 25°C were found to be 3.9, 6.5, and 9.4 for the three classes of weakly acidic functional groups studied. These values were independent (within experimental error) of FA composition and concentration, and of ionic strength in the range investigated.
Potassium Accumulation and Movement In an Irrigated Soil Treated With Animal Manures
Authors: Pratt P. F. , Laag A. E.
Published: July 2010

Data from a 4‐year experiment with animal manures are reported. Soluble and exchangeable K and K/Cl ratios indicated that K moved into the 90‐ to 120‐cm depth, but little if any moved below the 120‐cm depth. Potassium/Cl ratios indicated that K moved down in a relatively abrupt front, that the 0‐ to 30‐cm and 30‐ to 60‐cm depths had nearly equilibrated with the K input, but that deeper layers had not. Soluble K accumulated in the soil in proportion to the amount of manure added and reached a maximum of 36.5% of the total soluble cations in the saturation extract of the surface layer of the plots that received the highest rate of manure. The maximum exchangeable K was found in the 30‐ to 60‐cm depth of the same plots. The K fixed in the soil appeared to be greater than the reduction in CEC.
The Stratigraphy and Geomorphology of the Hofmann Forest Pocosin
Authors: Daniels R. B. , Gamble E. E. , Wheeler W. H. , Holzhey C. S.
Published: July 2010

Hofmann Forest is a 34,000 ha pocosin (swamp‐on‐a‐hill) that has about 25,000 ha of Histosols 0.4 to 2‐m thick. The pocosin is about 17 m above sea level, and large organic areas are uncommon at these altitudes in North Carolina. A stratigraphic and geomorphic study of Hofmann Forest was made to determine what factors were responsible for the accumulation of organic materials.

The organic materials of the pocosin mantle a gentle undulating marine plain that was exposed to subaerial weathering about 220,000 years ago. Few streams drain the area and the organic materials occupy the undissected interstream divides where the distance between streams is from approximately 0.5 km to 8 km. Flux rates indicate that the very low hydraulic conductivity of the pre‐Croatan formations and their closeness to the surface prevent significant removal of excess water through the permeable thin surficial beds to the adjacent streams. Rainfall exceeds evapotranspiration and the excess water must be removed primarily by overland flow to the streams.

The shallow depth to the pre‐Croatan aquicludes, the large distance between streams, and an excess of rainfall over evapotranspiration are the three major reasons why organic materials mantle a gently undulating plain about 17 m above sea level. The first two have remained nearly unchanged over the major part of the Hofmann Forest organic areas for the last 220,000 years. These conditions make the pocosin a potential area for organic accumulation. It is possible that organic deposits have been discontinuous during the last 220,000 years because of wide fluctuations in temperature and presumably in rainfall.
Comparison of Sulfur‐coated Urea and Ammonium Nitrate as Fertilizers for Pensacola Bahiagrass on a Spodosol
Authors: Blue W. G.
Published: July 2010

Two slowly available experimental sulfur‐coated urea (SCU) materials produced by the Tennessee Valley Authority were compared with ammonium nitrate as N sources for ‘Pensacola’ bahiagrass (Paspalum notatum Flugge) on Myakka fine sand (sandy, siliceous, hyperthermic Aeric Haplaquod). One of the SCU materials contained 35.4% N with a S coating of 23% while the other contained 40.2% N with a 12.6% coating which included S plus 2% diatomaceous earth and 0.25% coal tar. Four levels of N (0, 112, 224, and 336 kg/ha) were applied annually for 3 years to an established grass sod which had not been fertilized with N during the previous 2 years. Ammonium nitrate was applied in single and split applications, and the SCU materials were applied in single annual applications. Single applications were made in late March of each year. For the split applications of ammonium nitrate, one‐half was applied in late March and one‐half approximately 1 July. Forage growth increased with each level of N from all sources. Nitrogen utilization efficiency was higher (67%) from the 224‐ and 336‐kg/ha N rates than from the 112‐kg/ha rate (57%). Forage yield increase from the SCU (35.4% N) material was relatively poor the first year; pellets of this material were found consistently in the grass thatch at the soil surface 1 year after application. However, forage yields and N contents for each N rate over the 3‐year comparison period were not affected by N source or number of applications. The residual effect of SCU materials during the fourth year as measured by N content of forage ranged from 2 to 7% of the total N applied. These quantities of N were generally less than the decline in N content of the stolon‐root system. Forage production and N content distribution with time were not drastically altered by these slow release materials compared with ammonium nitrate.
Nature of the Organic Coating on Sand Grains of Nonwettable Golf Greens
Authors: Miller R. H. , Wilkinson J. F.
Published: July 2010

The organic coating of nonwettable sand grains from localized dry spots on sand golf greens was extracted with 5% NaOH. An infrared spectrum of resin purified, freeze‐dried extract was similar to spectra of soil fulvic acids. All other supporting data such as solubility, color, failure to precipitate upon acidification, noncrystalline nature, and a high extinction coefficient were consistent with the conclusion that the organic coating was fulvic acid. The relationship of the synthesis of fulvic acids to basidiomycete hyphae in the affected soil layer is discussed.
Post‐Mazama Natrargids in Dixie Valley, Nevada
Authors: Alexander E. B. , Nettleton W. D.
Published: July 2010

Some of the youngest Natrargids in central Nevada are in basin‐fill containing volcanic ash. South of the salt flat in Dixie Valley they are associated with Torrifluvents and Torriorthents in a continental climate with mean temperatures about 12 to 14°C and mean annual precipitation between 10 and 15 cm. Since there are lenses of Mazama ash below the natric horizons in some of these Natrargids, they are know to be < 6,600 radiocarbon years old.

A representative Typic Natargid in silty post‐Mazama basin‐fill sediments is described. Illuviation is confirmed by clay skins in the natric horizon. The present precipitation is adequate to account for its development.
Linear and Nonlinear Models of Infiltration From a Point Source
Authors: Ben‐Asher J. , Lomen D. O. , Warrick A. W.
Published: July 2010

Numerical and analytical solutions for water flow from a point source are compared. The numerical solution was for the nonlinear moisture flow equation and the analytical solution for the corresponding linearized form. For cyclic conditions, results were approximately the same with regard to range in values between the wettest and driest values. However, the numerical results show a faster response both for wetting and drying. Computational times required of the analytical solution were of the order of 1/20 to 1/200th of that required for the finite difference solutions.
Effects of Soil Moisture on the Diffusion Coefficients and Activation Energies of Tritiated Water, Chloride, and Metribuzin
Authors: Scott H. D. , Paetzold R. F.
Published: July 2010

Diffusion coefficients of tritiated water, chloride, and metribuzin were determined in Captina silt loam as functions of soil water content and soil temperature. Tritiated water and metribuzin were found to diffuse in both liquid and vapor phases, whereas chloride diffusion was restricted to the solution phase. For a given soil water content, values of the diffusion coefficients were larger in soil samples from the Ap horizon than in those from the B2t horizon for tritiated water and chloride. This was attributed to the greater tortuosity in the B2t horizon. Metribuzin had similar diffusion coefficients in both horizons, apparently reflecting offsetting effects due to the greater adsorption by the Ap and greater tortuosity in the B2t.

Thermodynamic studies indicated that the energy requirement for diffusion of these solutes was inversely related to soil moisture content for tritiated water and metribuzin. Activation energies for chloride diffusion were lower than for other solutes at equal soil water contents.
Effects of Clay Type and Content, Exchangeable Sodium Percentage, and Electrolyte Concentration on Clay Dispersion and Soil Hydraulic Conductivity
Authors: Frenkel H. , Goertzen J. O. , Rhoades J. D.
Published: July 2010

The hydraulic conductivities and gradients along soil columns packed with montmorillonitic, vermiculitic, and kaolinitic soils adjusted to different levels of exchangeable sodium were determined at different salt concentrations. The data show that plugging of pores by dispersed clay particles is a major cause of reduced soil hydraulic conductivity for surface soils irrigated with sodic waters.
Sulfate Adsorbed on Hydrous Alumina, Ligands Displaced, and Changes in Surface Charge
Authors: Rajan S. S. S.
Published: July 2010

To obtain a better understanding of the short term reactions between sulfate and hydrous alumina the relationships between the amount of sulfate retained by the alumina and reaction time, concentration, ligands displaced by sulfate, and changes in surface charge were studied. Experimental conditions were 3 hours reaction time, 0.01M NaCl medium, pH 5.0, 30°C, and nitrogen atmosphere.

Sulfate adsorption was very rapid and about 90% of the reaction was over in 10 min. There was little change in adsorption after 3 hours. The adsorption increased with increasing final solution concentration up to about 6 µeq/ml after which it decreased.

Sulfate adsorption resulted in the release of OH‐ from, and the neutralization of positive charge on the surface. From the quantitative relationships between sulfate adsorbed, the ligands displaced, and the changes in surface charge it is proposed that sulfate is adsorbed on hydrous alumina as SO42‐ bridging across two aluminum atoms, forming a six‐membered ring. At low concentrations sulfate preferentially displaces aquo groups (Al‐OH2) from the positive sites. With increasing concentration, increasing proportions of hydroxo groups (Al‐OH) from the neutral sites are displaced. The decrease in adsorption above 6 µeq/ml of sulfate concentration is inexplicable at this stage.
Adsorption of Mercury(II) by Iron Hydrous Oxide Gel
Authors: Kinniburgh D. G. , Jackson M. L.
Published: July 2010

Freshly prepared iron hydrous oxide gel suspensions, 0.093M and 0.001M with respect to Fe, strongly adsorb Hg(II) from solutions containing 2.5 × 10−5M Hg(II) and 1.0 × 10−6M Hg(II), respectively. The pH at which 50% of the total adsorption occurred in the latter system is 4.3. In the presence of chloride (Cl/Hg(II) mole ratio of 4/1), the adsorption of Hg(II) is considerably reduced, with no significant coadsorption of 36Cl, indicating that Hg(II)‐Cl complexes are not adsorbed by Fe gel.