bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer‐Assisted Farmland Appraisal Systems
Authors: Doucette W. H. , Whiteside E. P.
Published: July 2010

A computer‐assisted, farmland appraisal system (the Agvalue System) based on agricultural productive capacity was developed and analyzed. The heart of the Agvalue System is a computer‐generated land value map (LVM). The appraiser interprets the LVM, using a transparent overlay that portrays pertinent information not contained in the LVM, e.g., property boundaries and roads.

Seven Agvalue System procedures were tested in a pilot study appraisal of 45 farmland parcels ranging in size from 4.32 to 40.0 ha (10.8 to 100.0 acres) in Alpine Township of Kent County, Mich. The Agvalue appraisal procedures tested consisted of seven different combinations of: (i) soil information sources (Series 1926, updated 1926, and 1973 soil maps), (ii) computed storage cell sizes (1 and 4 ha or 2.5 and 10.0 acres), and (iii) LVM interpretation methods (broken or full cell).

The pilot study showed that all seven Agvalue System procedure values were highly correlated to the state of the art manual appraisal values using 1973 soil maps. The Agvalue System procedure employing 1973 soils information, 1 ha (2.5 acres) cells, and broken cell LVM interpretations most closely duplicated the manual appraisal values, r = 0.994. Even the 1926 soils information and 4 ha (10 acres) cell size were also found to be highly correlated to the manual procedure, r = 0.960, but with greater variance than the most accurate procedures.

The Agvalue System essentially allows for the use of the Michigan State Tax Manual procedure en masse on all farms in a township at a cost of between $250 and $380 per year (1977 dollars) above 1977 expenditures. However, savings in appraiser's time more than offset these costs. Supplied with net income data, an Agvalue System can be used for an income approach to farmland appraisals.
Changes in Properties of a Newly Cleared Tropical Alfisol as Affected by Mulching
Authors: Lal R. , De Vleeschauwer D. , Nganje R. Malafa
Published: July 2010

Rapid deterioration in soil physical properties following deforestation for arable land use adversely affects crop production from soils in the humid and subhumid tropics. This investigation was conducted to determine whether the rate of deterioration can be minimized by the use of crop residue mulches. Changes in soil properties of a newly cleared tropical Alfisol resulting from mulch rates of 0, 2, 4, 6, and 12 tons ha−1 season−1 of rice (Oryza sativa) straw were investigated from 1976 to 1977. Total porosity, 18 months after initiating the experiment, was 48, 50, 55, 55, and 59%, respectively, for increasing mulch rate. Similarly affected were relative proportions of macropores, saturated hydraulic conductivities, field infiltration rates, and moisture retention at 0.1 and 0.3 bar suctions. Decrease in the maximum temperature was 3.3, 4.1, 4.5, and 5.4°C for 2, 4, 6, and 12 ton/ha mulch rates respectively, compared with the unmulched control. The water runoff was 18, 10, 4, 1, and 0% of the rainfall received for increasing mulch rates, respectively. The chemical fertility of the soil decreased with time after forest removal. However, the rate of degradation was less with increasing mulch rate. The rate of decline of organic matter content over the 18‐month period was 0.103, 0.100, 0.092, 0.083, and 0.078% per month for 0, 2, 4, 6 and 12 tons/ha of mulch, respectively.
Response of Semimature Slash and Loblolly Pine Plantations to Fertilization with Nitrogen and Phosphorus
Authors: Fisher R. F. , Garbett W. S.
Published: July 2010

Field trials to measure the response of semimature slash pine (Pinus elliottii var. elliottii Engelm.) and loblolly pine (Pinus taeda L.) in the southeastern U. S. lower coastal plain were established between 1968 and 1970 at 32 locations. Treatments consisted of N at 0, 55, 110, and 220 kg/ha, and P at 0 and 55 kg/ha in a complete factorial arrangement. Grouping sites on the basis of soil drainage class and depth to and nature of the B horizon served as an efficient way to interpret response to fertilization. After 8 years stands on most soils exhibited moderate to large volume gains when fertilized with N and P. Stands on wet soils with clay near the surface responded favorably to the addition of P alone.
Sodium Hypochlorite Treatment for Organic Matter Destruction in Tropical Soils of Nigeria
Authors: Omueti J. A. I.
Published: July 2010

Supporting evidence for the universal usefulness of NaOCl in removing organic matter from soils is needed. Apart from its higher efficiency in organic matter destruction, NaOCl adjusted to pH 9.5 was found to be an effective dispersing reagent for savannah soils (which make up over 60% of the land area of Nigeria) during particle size analysis. The additional discovery of the use of NaOCl was considered to be very significant over the conventional H2O2 method where extra treatment with (NaPO3)6 was needed to obtain dispersion. However, in the case of fine textured forest soils it was found that for them to be in the dispersed state, additional washing with 2% aqueous Na2CO3‐HaHCO3 must be performed after the NaOCl pretreatment.
Application of Sewage Effluent to Columns of a Mountain Meadow Soil: I. Errors in Calculating the Transport of Ionic Salts
Authors: Barbarick K. A. , Klute A. , Sabey B. R.
Published: July 2010

A series of soil columns was prepared using a device to ensure uniform packing. These columns were filled with the top 70 cm of the profile of a mountain meadow soil. All columns were leached with 0.01N CaSO4 and then irrigated for 12 weeks with sewage effluent from Hayden, Colorado. Two columns were destructively sampled each week to determine bulk density and the gravimetric moisture content. Porous cup extracts of the solution phase were obtained from seven depths in five columns, which were destructively sampled after 12 weeks of irrigation with the sewage effluent. The transport of ionic salts was calculated for the 9 weeks of steady‐state flow using the principle of mass conservation.

An error analysis showed that the error terms were additive with depth and were the same order of magnitude as the calculated fluxes. The measurement of the electrical conductivity of the porous cup extracts provided the largest component of the error term. If an error of 0.05 mg/cm−2 day−1 is desired for a calculated salt flux of 0.5 mg/cm−2 day−1 for the bottom 10‐cm increment of a 70‐cm column, the electrical conductivities would have to be measured to the nearest 0.003 mmho/cm.
Increases in the Cation Exchange Capacity of Variable Charge Soils Following Superphosphate Applications
Authors: Gillman G. P. , Fox R. L.
Published: July 2010

The cation exchange capacity (CEC) of soils from field plots which were fertilized with concentrated superphosphate for 8 years has been measured. The superphosphate was added in amounts equivalent to those needed to raise solution P to 0.001 to 1.6 µg/ml in the adsorption isotherm. Three variable charge soils from Hawaii, a Hydrandept, a Gibbsihumox, and a Eutrostox were examined, using a new method for estimating the CEC of variable charge soils. This method takes account of pH and ionic strength conditions in the field. Agronomically significant increases in CEC of the surface horizons with increasing superphosphate application were obtained. As a result, the leaching of applied nutrients, Ca, Mg, and K, was retarded, and greater quantities of these cations were present in the 0–50 cm profile than in the plots receiving no P, despite the fact that more cations were removed from the P treated plots by crops grown in succession.
Sorption of Copper, Zinc, and Cadmium by Some Acid Soils
Authors: Kuo S. , Baker A. S.
Published: July 2010

The sorption of Cu, Zn, and Cd as a function of pH was examined for three acid soils. Sorption occurred at pH levels markedly below the zero point of charge (ZPC). Copper sorption increased with increasing pH, and Cu was preferentially sorbed over Zn and Cd. The presence of Cu interfered with the sorption of Zn and Cd. The sorption at higher pH levels varied with the source of hydroxide used. Sodium hydroxide had a greater ability than calcium hydroxide to disperse organic matter and to reduce the ability of the soils to retain metals. Reduction of heavy metal sorption at high pH levels was attributed to the formation of metal‐organic complexes. The metal sorptive capability of Chehalis (Cumulic Ultic Haploxerolls) soil was greater than that of Puyallup (Fluventic Haploxerolls) and Sultan (Aquic Xerofluvents) soils, perhaps due to its higher organic matter and Fe contents and its higher cation exchange capacity (CEC). Further investigation revealed that the CEC played a more important role than soil organic matter content in the sorption of the metals. The solubility of Al and Mn in the soil solution may also help to regulate sorption of heavy metals by acid soils.
Effects of pH and Neutral Electrolyte Concentration on Free Radicals in Humic Substances
Authors: Ghosh Kunal , Schnitzer M.
Published: July 2010

Electron spin resonance (ESR) investigations on humic substances were carried out at different pH's and at different neutral salt concentrations, two of the main factors controlling chemical and biological reactions in soils. With increase in neutral electrolyte concentration, free radical concentrations of humic materials decreased. With both fulvic acid (FA) and humic acid (HA), spin contents increased after raising the pH from the near neutral to the alkaline range, because of the stabilization of semiquinone radicals. With FA, a minimum spin concentration region was observed from pH 5.0 to 6.5. Potentiometric titrations revealed that activities of both electron donor and electron acceptor groups in humic molecules were at a minimum around that pH range. Between pH 5.0 and 6.5, a range into which many agricultural soils fall, humic materials appear to be chemically least reactive, which may explain, at least in part, their stability in soils.
Carbon and Nitrogen Movement from Surface‐Applied Wheat (Triticum aestivum) Straw
Authors: Cochran V. L. , Elliott L. F. , Papendick R. I.
Published: July 2010

The N immobilization potential of surface‐applied wheat (Triticum aestivum L.) straw as compared with incorporated straw was evaluated in the laboratory with soil columns. The columns were leached weekly and C and N content of the leachate determined. Leachate C/N ratios for straw alone exceeded 20:1 on several occasions and reached a maximum of 56, indicating a potential for N immobilization. Less than 5% of the total C in the straw was recovered in the leachates, providing an immobilization potential of <5 kg N ha−1. Leachate C/N ratios from 1‐, 2‐, and 4‐cm deep soil columns with surface‐applied wheat straw and no fertilizer N ranged up to 55:1, 30:1, and 22:1, respectively, while the highest leachate C/N ratio from the 4‐cm mixed straw treatment was 30:1. A significant percentage of mineralized N was immobilized in the top 1 and 2 cm of soil by surface residues. Much less N was immobilized in the 4‐cm soil columns. Thus, placement of fertilizer N several centimeters below the soil surface would alleviate possible N immobilization from organic C leached from surface crop residues.

The amount of applied N recovered in the leachate during 9 weeks of incubation ranged from 60 to 70% for all soil column treatments with or without surface straw. There was no significant differences between treatments. In contrast, the recovery of applied N from the mixed straw treatment was only 36%, indicating a much greater potential for N immobilization with mixed than with surface straw. The quantity of the fertilizer N added probably masked the immobilization potential of the surface residues. Fertilizer N stimulated early release of C from the straw alone treatment, but after 9 weeks of incubation the overall C loss from both fertilized and unfertilized straw was about 30%.
Comparison of Nitrogen and Sulfur Mineralization in Soils
Authors: Tabatabai M. A. , Al‐Khafaji A. A.
Published: July 2010

The relationship between N and S mineralization has not been well understood. In this study, field‐moist soil‐grass beads mixtures were packed in glass columns and leached with 100 ml of 0.01M KCl and incubated at 20 or 35°C. The leaching procedure was repeated every 2 weeks for a total of 26 weeks. The leachates were analyzed for mineral N and S. Expressed as percentages of soil organic N, the total amounts of N mineralized at 20°C ranged from 1.8 to 6.7 (avg = 3.8%) and, at 35°C, ranged from 8.3 to 26.8 (avg = 16.6%). Expressed as percentages of soil organic S, the total amounts of S mineralized at 20 and 35°C ranged from 3.5 to 13.3 (avg = 7.8%) and from 8.9 to 34.9 (avg = 22.8%), respectively. Results indicate that organic S is depleted faster than organic N.

The cumulative amounts of N and S mineralized in each of the 12 soils studied were linear with time of incubation. The rates (µg/g soil/week) of N and S mineralized at 20°C ranged from 1.7 to 4.2 (avg = 2.9) and from 0.5 to 1.2 (avg = 0.8), respectively. At 35°C, the rates of N and S mineralized ranged from 7.7 to 17.0 (avg = 12.5) and from 1.6 to 3.5 (avg = 2.5). The ratios of N/S mineralized during 26 weeks of incubation at 20 and 35°C ranged from 2.4 to 4.4 (avg = 3.5) and from 3.4 to 6.1 (avg = 5.0). At 35°C, the ratios of N/S mineralized were significantly correlated with soil pH. Rates of S mineralization, however, were significantly, but negatively, correlated with soil pH.

The average Q10 of N mineralization of the soils was 3.0, and that of S mineralization was 1.9. The amounts of N and S mineralized during 26 weeks of inclubation were significantly correlated at 20°C (r = 0.95***) and at 35°C (r = 0.79**).
Effects of Temperature and Iron(III) Concentration on the Hydrolytic Formation of Iron(III) Oxyhydroxides and Oxides
Authors: Wang Ming K. , Hsu Pa Ho
Published: July 2010

Fe(ClO4)3 solutions, of concentration ranging from 0.01M to 0.1M, were hydrolyzed at different temperatures and periodically analyzed up to 14 months. The reaction products were very different in their appearance and stability. For a given iron(III) concentration, the sample appearance changed as the temperature of preparation changed. Beginning as true solutions at lower temperatures, the samples progressively appear as coarse precipitates, turbid suspensions and clear sols as the temperature of preparation increases. For a given temperature of preparation, the products showed the same sequence of changes with decreasing Fe(III) concentration. The products are largely goethite, with an occasional presence of lepidocrocite when prepared at 37°C or below, but are hematite and/or goethite when prepared at 55°C or above. The results suggest that the differences in appearance and stability merely reflect the distribution of particle size but not the mineralogical composition. The degree of supersaturation is suggested as the key factor governing the initial number of nuclei relative to the concentration of monomeric Fe(III) ions, which, in turn, governs the appearance and stability of hydrolyzed Fe(III) solutions. A change in temperature results in changes in the reaction rate as well as the equilibrium constant and, thus, the degree of supersaturation.
Mineralogical Characteristics and Transformations of a Vertical Rock‐Saprolite‐Soil Sequence in the North Carolina Piedmont: I. Profile Morphology, Chemical Composition, and Mineralogy
Authors: Calvert C. S. , Buol S. W. , Weed S. B.
Published: July 2010

A lithologically continuous vertical rock‐saprolite‐soil sequence was studied in order to determine its mineralogical characteristics and transformations. The soil was a Typic Hapludult from the North Carolina Piedmont formed on granitic gneiss. The profile was sampled in 19 horizons, from the surface to slightly altered rock, on the basis of morphology and depth. Though weathering intensity was generally antipathetic with depth, this was not always the case, especially in the deep saprolite where two horizontal weathering fronts moved in opposite directions from a single fracture plane. The soil material differed morphologically from the saprolite by having soil structure and clay skins.

Elemental analysis of the samples revealed a release of Ca and Na from the altering rock, and a subsequent decrease in abrasion pH, presumably due to rapid plagioclase alteration. Aluminum seemed to precipitate initially as an Al‐rich clay mineral in the altering rock. However, this clay was rapidly resilicated coincident with a decrease in abrasion pH. The most rapid changes occurred in the deepest saprolite horizons.
Solute Transport in Aggregated Porous Media: Theoretical and Experimental Evaluation
Authors: Rao P. S. C. , Rolston D. E. , Jessup R. E. , Davidson J. M.
Published: July 2010

Breakthrough curves (BTC's) for 36Cl‐ and 3H2O displacement through water‐saturated columns of aggregated and nonaggregated porous media were measured at pore‐water velocities varying over an order of magnitude (2 to 96 cm/hour). These BTC's were used to verify two conceptual solute transport models in which the pore‐water was partitioned into inter‐ and intra‐aggregate regions. In both models, convective‐dispersive solute transport was assumed to be limited to the inter‐aggregate pore‐water region, while the intra‐aggregate pore‐water was assumed to behave as a diffusion sink/source for solute. The rate of solute transfer between the two pore‐water regions was described either by Fick's second law of diffusion written in spherical coordinates (Model I) or was assumed proportional to the concentraion difference between the two regions (Model II). Values of all input parameters in each model were measured in independent experiments rather than by curvefitting to the measured BTC's. Agreement between calculated and measured BTC's at all velocities was good for both models. The value of the mass transfer rate coefficient in Model II was found to vary with aggregate radius, time, and pore‐water velocity. This result was predicted based on theory and experimental results presented in an earlier paper. Conditions under which solute diffusion in aggregates leads to tailing or asymmetry in measured BTC's (during saturated water flow) were identified from a sensitivity analysis using Model I. For certain aggregate radii and pore‐water velocities, the diffusion sink/source effects of the aggregates could be incorporated into the dispersion coefficient, and this lumped‐parameter approach was used to successfully describe the measured BTC's.
A Combined Salt Transport‐Chemical Equilibrium Model for Calcareous and Gypsiferous Soils
Authors: Robbins C. W. , Wagenet R. J. , Jurinak J. J.
Published: July 2010

Chemical precipitation‐dissolution and cation exchange subroutines were interfaced with an existing water movement‐salt transport model. Three model options available for testing the prediction of salt transport and storage were (i) individual ion transport without soil interaction, (ii) precipitation and dissolution of lime and gypsum during transport, and (iii) cation exchange in addition to the precipitation‐dissolution reactions. The transport model also predicts relative crop growth and water uptake as affected by soil moisture and salinity. The chemical subroutine used by the second and third options calculated ionic activities, corrected for ionic strength and ion pair formation, and was used to calculate lime and gypsum precipitation and dissolution. Cation activities were also used to calculate Ca, Mg, Na, and K exchange equilibria by a method that allows for addition of any number of exchangeable cations. Values predicted by the three options for EC, SAR and Ca, Mg, Na, K, Cl, SO4, and HCO3 concentrations were compared to experimental data obtained from a lysimeter study and were only satisfactorily predicted when both chemical precipitations and cation exchange were considered for a gypsiferous and a nongypsiferous soil irrigated with a high, medium, and low CaSO4 water at two leaching fractions.
Nitrogen Mineralization as Affected by Soil Moisture, Temperature, and Depth
Authors: Cassman K. G. , Munns D. N.
Published: July 2010

Variation in the rate of N mineralization in a Yolo soil profile was studied using in vitro incubation methods. Negligible amounts of NH4‐N were recovered from leachates, indicating that the rate of N mineralization was the primary factor controlling N availability. During a 13‐week incubation at 25°C, 42% of the total estimated N mineralized was derived from the surface soil (0 – 18 cm), whereas 58% was contributed from the 18‐ to 108‐cm depths. Cumulative N mineralization in the 0‐ to 18‐cm and 18‐ to 36‐cm depth samples followed first‐order kinetics and was linear with respect to the square root of the incubation time. The mineralization rate constant differed more than twofold between the 0‐ to 18‐ and the 18‐ to 36‐cm depth samples. At lower depths (36 – 72 and 72 – 108 cm) the relationship between cumulative N mineralization and the square root of time was curvilinear.

Interactive effects of soil temperature and moisture were also examined in an experiment with four incubation temperatures (15, 20, 25, and 30°C) in factorial combination with six soil moisture levels (0.1, 0.3, 0.7, 2, 4, and 10 bars). There was a significant moisture × temperature interaction; N mineralization increased above that expected from additive effects at 30°. Multiple regression was used to generate an equation that predicted net N mineralization as a function of soil temperature and moisture.

The apparent effect of soil water content on N mineralization depended on experimental procdure. When soil water content was varied by adding water to air‐dry soil without complete equilibration, N mineralization declined linearly with water content. In contrast, there was a sharp decline between 0.3‐ and 2‐bar treatments and a more gradual decline at higher matric suctions when soil was equilibrated by pressure‐membrane desorption before incubation. These results indicate that both quantity and distribution of soil water affect in vitro estimates of N mineralization.
Biodegradation and Stabilization after 2 Years of Specific Crop, Lignin, and Polysaccharide Carbons in Soils
Authors: Martin J. P. , Haider K. , Kassim G.
Published: July 2010

The purpose of this study was to follow the biodegradation and stabilization in two soils of specific carbons of model and cornstalk lignins, lignin monomer alcohols, wheat straw, and the polysaccharide fraction of wheat straw over a 2‐year incubation period using 14C‐labeled substrates. Incubations were carried out in a closed, constantly aerated system and the 14CO2 released determined at specific intervals. After incubation the amounts of residual 14C in various soil humus fractions, in the biomass, and that solubilized by acid hydrolysis were determined. During the 2‐year period, about 40% of the ring and two‐side chain carbons of coniferyl and coumaryl alcohol units in model and cornstalk lignins had evolved as CO2. Losses of CH2OH and three‐side chain and of OCH3 carbons varied from 52 to 69%. The degradation rate was most rapid during the first 3 to 6 months of incubation. total C losses from whole wheat straw and cornstalks for comparison at 2 years were about 72% and for the polysaccharide portion of the wheat straw, 83%. During the first 6 months about 47% of the two‐side chain and ring carbons and 61 to 66% of the other carbons of free coniferyl alcohols had evolved as CO2. During the next 18 months these values had increased only about 11%. A major portion of the residual lignin carbons was recovered in the HA fractions, relatively small quantities were lost upon 6M HCl hydrolysis, and < 1% was estimated to be in the biomass. Most of the residual wheat straw C and especially the polysaccharide carbon was solubilized upon 6M HCl hydrolysis, 3 to 8% was still present in biomass, and 50% remained in the NaOH extracted soil. The results indicate that the major portions of the lignin carbons are incorporated into the more resistant or aromatic portions of the soil humus. The polysaccharide carbons, on the other hand, are metabolized and utilized for energy and synthesis of cell polymers, primarily proteins and polysaccharides, some of which are stabilized in the humus but are still susceptible to acid hydrolysis. Loss as CO2 and distribution of the residual carbons of free lignin alcohols in HA and losses upon 6M HCl hydrolysis were intermediate between the lignin and polysaccharide carbons.
Reflectance Technique for Predicting Soil Organic Matter
Authors: Krishnan P. , Alexander John D. , Butler B. J. , Hummel John W.
Published: July 2010

The objective of this research was to study the spectral reflectance of the selected soils in the infrared and visible wavelength regions and to identify optimal wavelengths for predicting the soil's organic matter content. Samples representative of soils of different texture and predicted organic matter content were collected from different areas in Illinois. Measurements of the spectral reflectance of soil samples in the infrared and visible wavelengths regions were recorded with a multipurpose computerized spectrophotometer with a Cary Model 14 monochromator attachment operated in a single beam mode. A stepwise multiple linear regression program was used to analyze the reflectance data and to determine the optimum wavelengths for predicting the organic matter content of the soil. An iterative procedure was used to identify the wavelengths that correlated best with organic matter content. No absorption peak due to soil organic matter was found in the infrared and visible regions of the spectrum scanned. The optimal wavelengths for predicting percent organic matter content are 0.6236 and 0.5644 µm and the model is of the form:

Organic matter content = K × d log(r‐10.6236)/dλ0.6234 / d log(r‐10.5844)/dλ0.5844
Soil Shrinkage Relationships of Texas Vertisols: II. Large Cores
Authors: Yule D. F. , Ritchie J. T.
Published: July 2010

Although soil shrinkage in the field has been related to water content changes, this relationship has not been correlated with small core measurements or defined in terms of structural and shrinkage water loss phases. Since field measurements are limited by the accuracy of the water content determination, undisturbed cores (73 cm diam and 140 cm long) from the eight Vertisols studied previously were studied to accurately measure water loss (by weighing). Sorghum plants were established, and a single drying cycle was studied. Vertical shrinkage was measured at the surface and at the 15‐, 35‐, 55‐, 95‐, and 115‐cm depths, and the water content profile was measured with neutron moisture and gamma density probes. These data were interpreted in terms of the shrinkage pattern found in the cores and with the use of small core data obtained by Yule and Ritchie. (1980).

Although the water loss data were confounded by large soil evaporation from shrinkage cracks at the side of the cores, the evidence suggested that the shrinkage response was a combination of structural and shrinkage water loss phases. Consequently, the shrinkage curve for the soil surface asymptotically approached the theoretical equidimensional, normal curve. Shrinkage curves with profile depth tended to parallel the soil surface curve. The water content profiles obtained were not precise, but shrinkage parameters calculated for various depth increments resembled the small core data obtained previously. The results showed that small core data could be used to predict field shrinkage responses if field soil water content profiles are known.
Recovery of Nitrogen by Rice from Blue‐Green Algae Added in a Flooded Soil
Authors: Wilson J. T. , Eskew D. L. , Habte M.
Published: July 2010

Uptake of N from a blue‐green alga (Aulosira 68) by rice (Oryza sativa L.) was studied in a greenhouse pot experiment. When a suspension of the alga was buried 5–7 cm deep, 52% of the N added was recovered in the grain and straw of the first rice crop, and an additional 5% was recovered by a ratoon crop and by a subsequent transplanted crop. Additions of NH4Cl equivalent to 100 kg N/ha did not affect the recovery of algal N. Surface placement of the alga reduced recovery by the first crop to 37% of the added N.
Nitrogen Transformations in Sewage Sludge—Amended Soils as Affected by Soil Environmental Factors
Authors: Terry R. E. , Nelson D. W. , Sommers L. E.
Published: July 2010

The objectives of this study were to determine the effects of soil pH, soil moisture tension, sludge application rate, incubation temperature, and nitrification inhibitor on N transformations in soils amended with an 15N‐labeled sewage sludge. Less than 0.1% of added sludge‐N was lost from any of the samples due to NH3 volatilization. Nitrification rates were faster in sludge‐amended soils as compared to nonamended acidic soils treated with NH4+‐N. Adding calcareous sewage sludge to acid soils produced a more favorable pH for nitrification. Nitrification was faster in sludge‐amended soil having an initial pH of 7.5 than in samples at pH 6.0 or 5.3. Nitrite‐N accumulated to levels of 100 µg/g in sludge‐treated soils with high pH values (∼ 7.5). Nitrification proceeded at a faster rate in sludge‐amended soils adjusted to −0.25 and −0.5 bar moisture tension than in soils at −1 bar. Nitrification rates were not greatly affected by sludge application rate, although more time was required for complete nitrification of greater quantities of NH4+‐N. Nitrapyrin inhibited nitrification for 112 days, after which nitrifying ability recovered. Temperature was the only factor evaluated which markedly affected mineralization of sludge‐organic N and immobilization of added inorganic‐N. The rates of both mineralization and immobilization increased as temperatures increased. At the end of 168 days of incubation at 21°C, 40% of added sludge‐organic N was mineralized in silt loam soils, but up to 26% of added NH4+‐N was immobilized. There were only small net changes in inorganic‐N concentrations in sludge‐amended soils after 168 days of incubation.
A Descriptive Model of Soil Test Nutrient Levels Following Fertilization
Authors: Cox F. R. , Kamprath E. J. , McCollum R. E.
Published: July 2010

For efficient utilization of fertilizer, a practical means of expressing the residual effect of certain plant nutrients is needed. A descriptive model was developed to show the change in extractable nutrient levels with time assuming a rapid increase after fertilization followed by a slower exponential decrease. The information needed or parameters for the model include (i) the equilibrium soil test level, (ii) the magnitude of the initial sorption reaction, and (iii) a loss constant. These were determined for seven long‐term fertilizer studies with phosphorus (P). There was a large difference in P‐sorption capacity of the soils; all parameters reflected this difference. The initial sorption reaction was linearly related to rate of fertilization in some soils and quadratically in others. The model was applied to conditions in which fertilizer was applied at various time intervals. Good agreement between observed and predicted values was obtained. The main value of this model is to be able to calculate the amount of fertilizer needed to establish and maintain a given soil test level.
Increasing Sensitivity of Organic Matter and Nitrogen Analysis Using Soil Separates
Authors: Tan K. H. , Troth P. S.
Published: July 2010

Little is known about the use of soil separates in the determination of soil organic matter and total‐N content. To achieve uniformity and complete oxidation, soil samples for use in these analyses are commonly finely ground. The present investigation was initiated to study organic matter and total‐N contents in sand (2.0‐0.050 mm), silt (0.050‐0.002 mm), and clay (< 0.002 mm) fractions of selected Alfisols, Aridisols, Entisols, Mollisols, Spodosols, Ultisols, and Vertisols. A further aspect of this study was to establish the correlation with the respective contents obtained by analysis of whole soil (< 2 mm) samples. Soil organic carbon was determined by the Walkley‐Black wet oxidation method, while total‐N was analyzed by the semi‐micro Kjeldahl method. All analyses were done in four replications. The results indicated that particle size separation had concentrated most of the organic matter in the soil fraction < 2 µm. Generally lower amounts of organic C and N were detected in the silt and sand fractions. In most cases, summation of organic C and total‐N percentages derived from soil separates yielded values higher than those obtained from analyses of whole soils, indicating that, by the use of whole soils, a considerable part of C and N was not analyzed. The higher‐organic C contents in clay fractions, exceeding in a number of cases those measured by the use of whole soils, and the detection of appreciable amounts of organic C and N in silt and sand, pointed to a more complete oxidation and better sample uniformity. The higher recovery of organic C by the use of soil separates also implied an increase in sensitivity of the analysis, improving reliability of results, which was of special importance with B horizon samples, where low levels of organic C were involved. The usual positive correlation between organic C and total‐N content was also obtained by using soil separates. The high correlation (r = 0.929, df = 23), together with increased sensitivity and complete oxidation resulting in higher values and improved reliability, makes the use of soil separates desirable in organic C and total‐N analyses.
Distinguishing the Forest Floors of Three Ecosystems
Authors: Quesnel H. J. , Lavkulich L. M.
Published: July 2010

Forest floor classifications have been based on morphological properties which were perceived to reflect genesis. These classification systems have not been compatible with soil or ecological classifications, which may have limited their application to forest management. Three biogeocoenoses or ecosystem types near Port Hardy, British Columbia were selected for studying forest floor properties. The sites chosen represent xeric, mesic, and hygric positions along a hygrotopic gradient. The forest floor of each site was stratified into LF(01) and H(02) horizons. A stratified random sampling procedure was used to collect 15 samples within the horizon units of each site. Forty variables were measured or calculated for each sample.

A two‐way analysis of variance in conjunction with the Student‐Newman‐Keuls Range Test was used to determine which variables, on an individual basis, would distinguish the forest floors of each site, the LF and H horizons overall, and the individual forest floor horizons of each site. The forest floors of the three sites could be differentiated on the basis of total K, exchangeable Na displaced by 1N NH4OAc, and the ratio of loss on ignition to total C (LOI/C). The LF and H horizons overall could be separated by total K, total Zn, exchangeable Ca and K displaced by 1N NH4OAc, exchangeable K displaced by 1N NaCl, base saturation at pH 7.0, pH measured in water and 0.01M CaCl2, LOI, the ratio of total Ca to total Mg, and the ratio of total Ca to total K. The forest floor horizons of all three sites could not be distinguished by use of single variables. Three stepwise discriminant analyses using nine, five, and two variables yielded classification accuracies of 94.4, 81.1, and 71.1%, respectively, for differentiating the forest floor horizons of all three sites. The multivariate analysis showed that the best combination of measurements for distinguishing the forest floor horizons of the individual sites are total N, total K, total P, LOI/C, and cation exchange capacity (CEC) estimated with 1N NaCl.
Oxidation and Ejection of Nickel and Zinc from Natural and Synthetic Magnetites
Authors: Sidhu P. S. , Gilkes R. J. , Posner A. M.
Published: July 2010

An acid dissolution technique was used to determine the distribution of nickel and zinc in large magnetite crystals and in hematite produced by oxidation of these crystals at high temperatures. About 10% Ni and 17% Zn content of crystals were ejected to the surface by this heating. These are smaller proportions than were observed for microcrystalline synthetic magnetites. The surfaces of partly dissolved crystals contained triangular patterns of etchpits and raised Ni‐rich regions, indicating that dissolution did not occur uniformly.

Finely ground natural magnetite altered directly to hematite, whereas synthetic magnetite altered to maghemite at low (ca.200°) temperatures. This difference may be associated with the presence of structural water in synthetic magnetites.
Transformation of Chlorite to Smectite Through Regularly Interstratified Intermediates
Authors: Senkayi A. L. , Dixon J. B. , Hossner L. R.
Published: July 2010

Trioctahedral, iron‐rich chlorite separated from east Texas lignite overburden shales by high gradient magnetic separation was characterized by XRD and by IR spectroscopy. The chlorite was then subjected to chemical oxidation by digestion (ca. 100°C) in a saturated bromine solution to simulate weathering. X‐ray diffraction indicated that the chlorite was transformed to smectite through regularly interstratified chloritevermiculite and chlorite‐smectite intermediates. The smectite ultimately dissolved. All of the chlorite reacted in 2 weeks. Electron micrographs of partially weathered particles of chlorite showed thin plates folded at the edges and unreacted cores in the center. Iron released during the reaction tended to precipitate along particle edges. It is postulated that the thin, folded edges and the cores were smectite and chlorite, respectively. Formation of the iron‐rich chlorite in the lignite overburden shales probably resulted from interactions between aluminous smectite and solutions rich in ferrous Fe. Exposure of the overburden shales to oxidizing conditions may result in the transformation of chlorite to smectite with precipitation of released Fe.
A Portable Device for Installing Lightweight Borders for Runoff and Erosion Plots
Authors: Warn W. R. , Allmaras R. R. , Muilenburg G. A. , Zuzel J. F.
Published: July 2010

Runoff and soil erosion studies in farm fields in the Pacific Northwest require that borders for runoff and erosion plots be placed after all farm operations are finished just before the winter rainy season. Such an experimental procedure requires a portable, lightweight device to install borders, which are also portable and reusable. A border installation device was developed for easy portage into fields, and use without any vehicular traffic in the field. The device was drawn toward the field boundary using a pickup‐mounted winch. This border system performed as well as galvanized borders. Yet operational costs were less, portability was achieved, and field disturbance was minimal.
Soil Hydraulic Properties as Stochastic Processes: I. An Analysis of Field Spatial Variability
Authors: Russo David , Bresler Eshel
Published: July 2010

Determinations of the sorptivity (S) and five parameters describing the hydraulic conductivity [K(h)] and soil water retentivity [θ(h)] functions have been used to analyze the spatial distribution of the hydraulic properties in an experimental field. The parameters are: saturated hydraulic conductivity (Ks); water entry value (hw); saturated (θs) and residual (θr) water contents; and a constant β characterizing the pore size distribution of the soil. For a given depth, each of these parameters is described as a realization of a stationary two‐dimensional isotropic and random process. These stochastic processes are characterized by truncated normal or log‐normal probability density functions independent of the spatial position, and by autocorrelation functions between any two spatial points in the field which depend solely on the size of the vector separating the two points. The spatial variability of each of the six parameters has a structure that is characterized by a characteristic length—the integral scale, J, representing the largest distance for which the parameter is correlated with itself. Values of J, which are calculated from the autocorrelation functions for each parameter generally decrease with depth. On the average over depth the calculated values of J are 21, 44, 55, 25, 35, and 15 meters for the parameters Ks, hw, θs, θr, S, and β, respectively. The spatial variability of the hydraulic functions are described by the probability density functions and the autocorrelation functions. Since the integral scales of K(h) and θ(h) vary with both h and depth, the characteristic length of the field has been chosen as the integral scale of the weighted mean diffusivity which is 18 m.
Spatial Dependence of Physical Properties of a Typic Torrifluvent Soil
Authors: Gajem Y. M. , Warrick A. W. , Myers D. E.
Published: July 2010

The spatial structure of soil properties has been examined on a Typic Torrifluvent soil at The University of Arizona Experiment Station at Marana. Nine hundred samples from nine transects were collected in straight lines (100 locations for each transect), at 20‐, 200‐, and 2,000‐cm intervals. All samples were at a 50‐cm depth. Variables include 0.1 and 15 bar water content, available water, surface area, particle size distribution, pH, EC, bulk density, and moisture content in the field seven days after irrigation. Autocorrelation functions were evaluated for each parameter and found to be correlated over space with patterns of three basic types: typical, random, or with a large zone of influence. Generalizations were difficult, but the calculated zone of influence was strongly dependent on distance between samples, with larger intervals tending to give greater values. In a few cases, this could partially be explained on the basis of larger standard deviations measured on longer transects. Results indicate future difficulty in assigning scale lengths by parameter or soil.
Effect of Four Continuous Tillage Systems on Mechanical Impedance of a Clay Loam Soil
Authors: Bauder J. W. , Randall G. W. , Swann J. B.
Published: July 2010

Soil strength may influence root growth as much as soil bulk density and matric potential. Aerial plant growth and harvestable crop yield have been positively correlated with root growth under some circumstances. Farm machine traffic and tillage practices affect soil strength and mechanical impedance. Most field studies of soil strength, mechanical impedance, root growth, and tillage have been performed on relatively coarsetextured, loamy sand soils. This study was conducted to evaluate the effect of four continuous tillage systems on strength, mechanical impedance, and soil physical properties of a Nicollet clay loam soil, a fine‐loamy, mixed, mesic Aquic Hapludoll.

Following 10 years of continuous tillage in a monoculture grain‐corn (Zea mays L.) production system, soil bulk density (ρ), porosity (ε), water content (θ), and mechanical resistance (cone index, CI) were measured on four tillage systems. Replicated measurements of ρ, ε, θ, and CI were made as a function of both depth and position relative to the crop row. No attempt was made to distinguish trafficked and nontrafficked interrow areas because of lack of complete traffic control. Tillage systems included (i) fall moldboard plow, (ii) fall chisel plow, (iii) spring disk, and (iv) no tillage‐slot plant.

Tillage treatment, soil depth, and depth by position interaction were sources of significant variation in CI. Differences in CI due to position relative to crop row were not significant. Significant differences in ρ, ε, and θ were attributed to depth and depth x tillage interaction.

Tillage and traffic pans were observed under all tillage systems except chisel plowing. Annual moldboard plowing and chisel plowing in the fall resulted in the least amounts of mechanical resistance. Maximum CI resulted from spring disking practices. Mechanical impedance following continuous no tillage was similar in distributional pattern to the spring disking system, although CI following no tillage was not as great. Continuous no tillage and spring disking resulted in pronounced increases in CI close to the soil surface (0–7.5 cm). These increases in CI were attributed to tillage, traffic pans, or to both. These zones of increased mechanical resistance may potentially be root‐restricting layers.

Increased emphasis on reduced and no tillage systems of seedbed preparation and monoculture production systems may lead to an increase in root‐restricting tillage pans in clay loam soils. If increased root growth is necessary to insure an adequate supply of water and nutrients, then periodic, relatively deep chisel or moldboard plowing may be necessary to eliminate or modify shallow tillage‐ and traffic‐induced pans that could potentially restrict root growth.
Saturated Flow Above a Terraced Barrier
Authors: Prunty Lyle
Published: July 2010

Steady‐state saturated flow through a permeable surface layer of uniform depth (verticle thickness) overlying a terraced barrier has been analyzed by the Gram‐Schmidt method. The geometry and boundry condition concepts of the problem originated in the reclamation of a surface mine where, after reclamation, a soil layer of relatively high permeability overlies impermeable spoil. The soil surface and the soil‐spoil interface both have a terraced contour, and the soil is of uniform thickness. The terraces consist of a series of level benches, each approximately 4 m higher in elevation than the next lower terrace. The terraces are joined by 10 m of 40% slope. The soil is 3 m in depth and it is assumed to be saturated.

A new iterative technique involving separating the flow region of concern into two overlapping regions is used to solve the problem. The results show a significant water flow in the soil layer only in the sloped region and in the immediately adjacent region. There is negligible flow in regions where the horizontal distance form the sloped portion of the soil exceeds the soil depth.
Solute Movement in Structured Soils: Two‐Region Model with Small Interaction
Authors: Skopp J. , Gardner W.R. , Tyler E.J.
Published: July 2010

A theory of solute movement is presented for those soils where the liquid‐filled pores can be partitioned into two distinct pore size classes. One region represents macro‐ or interaggregate porosity, and the other represents matrix or intraaggregate porosity. The regions may differ in dispersion coefficient, porosity, and flow velocity. In addition, an interaction coefficient characterizes the linear transfer between regions. A regular perturbation method is used to solve the model equations for small interaction coefficients. It is shown that if the interaction coefficient is large, the model approaches the classical dispersion equation. Esitmates of the interaction and its dependence on flow rate are presented along with the influence of interaction on the shape of the breakthrough curves.