bluuebunny/crossref_metadata_2025 huggingface dataset:
The pH Dependency of Aluminum Phytotoxicity Alleviation by Calcium Sulfate
Authors: Noble A. D. , Sumner M. E. , Alva A. K.
Published: July 2010

The alleviation of Al toxicity by CaSO4 is partly due to an increase in formation of less phytotoxic AlSO+4 species. Since ion‐pair formation is dependent on the solution pH, the magnitude of alleviation of Al toxicity by CaSO4 may be influenced by pH. In the present study, the alleviation of Al toxicity (80 µM) to soybean [Glycine max (L.) Me root growth by CaSO4 (625–10 000 µM) was investigated in dilute nutrient solutions at pH 4.2 or 4.8. The concentration of monomeric Al (by a modified aluminon technique) in these solutions ranged from 69.3 to 77.7 µM. An increase in CaSO4 in solution (625–10 000 µM) increased the root length by 3‐ and 2‐fold in solutions at pH 4.2 and 4.8, respectively. The predicted activity of Al3+ decreased while that of AlSO+4 increased with an increase in added CaSO4. The magnitude of alleviation of Al toxicity by CaSO4 was smaller at pH 4.8 than at pH 4.2. This pH dependency is due to lesser formation of AlSO+4 at pH 4.8 than at pH 4.2, together with an increase in formation of Al(OH)+2 at pH 4.8. Root length was poorly correlated with the predicted activity of Al3+ (R2 = 0.346) or sum of the activities of Al3+, hydroxy‐Al, and AlSO+4 species (R2 = 0.366). However, the relationship was improved when the sum of the activities of Al3+, Al(OH)2+ and Al(OH)+2 species was considered (R2 = 0.624) and further improved (R2 = 0.841) when the activities of these species were corrected for their respective valence. A good correlation was also found (R2 = 0.88) between root length and calcium aluminum balance; CAB = [2log(aCa2+)] − [3log(aAl3+) + 2log(aAl(OH)2+) + log (aAl(OH)+2)] index.
Distribution of Sulfur Fractions in Soil as Influenced by Management of Organic Residues
Authors: Castellano S. D. , Dick R. P.
Published: July 2010

There is increasing concern about the long‐term effects of crop management on soil properties that may be affecting soil productivity. Consequently, a study of the long‐term (55 yr) effect of organic residue and inorganic N applications on the distribution of S fractions (inorganic sulfate, C‐bonded, ester sulfate, residual, and sulfolipid S) in a Typic Haploxeroll under a wheat‐fallow (Triticum aestivum L.) rotation was undertaken. The biennial treatments were: (i) straw (control), (ii) straw plus fertilizer (+N) (34 kg N ha−1 from 1931–1966 and 90 kg N ha−1 from 1967–1986), (iii) straw plus 2.24 Mg ha−1 of pea vine residue (PV), and (iv) straw plus 22.4 Mg ha−1 of strawy manure (M). There was a significant treatment effect (P < 0.01) with the M treatment having 7 to 41% greater total S, and 9 to 22% greater ester sulfate hydriodic reducible S), and nearly two times more C‐bonded (Raney‐Ni reducible S) and sulfolipid S than the remaining treatments. The lowest level for total S occurred in the +N treatment (114 vs. 161 mg S kg−1 soil in the M treatment). A significantly lower level of residual S (nonreducible) for the +N treatment suggests that the addition of inorganic N causes a depletion of S from the residual pool. On a biennial basis, treatments receiving only straw (control and +N) had net inputs (amount of S added with residue minus S removed in grain) of −0.51 and −1.72 kg S ha−1, respectively, and PV and M treatments had net S inputs of 1.92 and 31.05 kg S ha−1, respectively. Calculation of the coefficient of simple determination (r2) among S fractions and other soil properties showed that whereas organic C and total N had a high r2 value (0.81), total S had a low r2 (0.29) with organic C and was more closely related to total N (r2 = 0.55). The r2 values among the organic S fractions were quite low (<0.23), except for sulfolipid S and C‐bonded (r2 = 0.45).
Phosphorus Sorption of Subtropical Acid Soils as Influenced by the Nature of the Cation Suite
Authors: Russell J. S. , Kamprath E. J. , Andrew C. S.
Published: July 2010

Previous field studies with pasture on subtropical acid soils in eastern Australia showed a long residual effect of relatively low rates of fertilizer P. Samples of six soils from eastern Australia were collected to determine their P sorption characteristics. Monocalcium phosphate solutions containing 0.005 M CaCl2 were equilibrated with samples which were untreated, limed or CaCl2‐leached. Measurements were made of the amount of P sorbed and P remaining in solution. The soil chemical properties affecting P sorption, P buffering and amount of P sorbed needed to provide 0.2 µg P mL−1 were determined by multiple regression analysis. Phosphorus sorption and buffer capacity increased with increasing CuCl2‐extractable Al and decreased with increasing exchangeable Na saturation or increased soil solution Na. Amounts of sorbed P needed for 0.2 µg P mL−1 in the soil solution were relatively small for the untreated and limed Natrustalfs and ranged from 13 to 37 mg P kg−1 soil. A given application of P fertilizer will provide a higher soil solution P in subtropical soils which contain appreciable Na, such as Natrustalfs, than those in which Ca is the dominant cation.
Drop Impact Energy‐Soil Exchangeable Sodium Percentage Interactions in Seal Formation
Authors: Shainberg I. , Singer M. J.
Published: July 2010

Constant intensity rain (40 mm h−1) with 3.2‐mm drops falling from 0.25‐, 0.90‐, and 2.63‐m heights and impact energies of 1.8, 7.6, and 18.6 kJ m−3, respectively, was used to produce seals on two soils in 55‐mm deep by 82‐mm diam acrylic cylinders. Soil exchangeable sodium percentage (ESP) was altered to ESP 0 (Casaturated soil), 5, and 10 before rain was applied. Infiltration rate (IR) and hydraulic conductivity (HC) of A horizon material from the Wyman (fine loamy, mixed, thermic Typic Haploxeralfs) and Wyo (fine loamy, mixed, thermic Mollic Haploxeralfs) soils decreased due to formation of soil seals as raindrop energy and ESP increased. The Wyo was more susceptible to sealing than Wyman despite its higher organic C content because of its higher (17 vs. 9%) clay content. Seal formation on Ca‐soils (ESP 0) increased gradually with increasing drop impact energy. Soils with ESP 5 and 10 were more susceptible to sealing at low energy rain than were ESP 0 soils. Relative HC and final IR (FIR) decreased with increasing ESP with all rainfall energies and with the no rain treatment on both soils. Aggregate dispersion by raindrop impact and chemical dispersion by sodicity are two complementary processes leading to seal formation. A 5‐Mg‐ha−1 phosphogypsum treatment applied to the Wyman surface reduced seal formation and maintained HC and FIR near the unrained‐on values for the 1.8 and 7.6 kJ m−3 treatments. The 18.6 kJ m−3 raindrop energy produced a seal on the gypsum treated soil with relative HC and FIR more than four times as high as the untreated Wyman.
Effect of Soil Depth and Erosion on Yield in the Mississippi Blacklands
Authors: Hairston J. E. , Sanford J. O. , Rhoton F. E. , Miller J. G.
Published: July 2010

Farmer fields were used 4 consecutive yr (1982–1985) to determine effects of soil depth and other parameters on soybean [Glycine max. (L.) Merr.] yield in the Mississippi Blackland Prairie. Soybean yields were sampled on 25 miniplots (1.8 m2) at each of two sites the first 2 yr and from six sites the third and fourth years. Soil depth ranged from 100 to 1500 mm across the miniplots at each site, and most plots had a silty clay texture. Soil samples were collected the second, third and fourth years from the 0‐ to 150‐mm depth and analyzed for pH, organic matter and extractable nutrients. Seasonal rainfall distribution was measured at each site the third and fourth years. Grain yields were variable from year to year for specific sites as well as from site to site within a given year. Regression analyses indicated that differences from site to site were due to variation in soil organic matter and rainfall distribution; whereas, differences within a site were influenced by organic matter, soil depth, and other parameters such as pH and available K which were related to depth. Grain yields ranged from near zero to over 2.5 Mg ha−1, depending on depth, organic matter content and seasonal rainfall distribution. Differences due to fertility were less pronounced. Soil depth was a much better predictor of yield at sites with low organic matter, especially when rainfall was also low. A regression model for depth vs. yield indicated that 10 mm of soil was worth an average of 0.006 Mg ha−1 of soybean grain within the 500‐ to 1500‐mm depth but worth 0.06 Mg ha−1 within the 50‐ to 150‐mm depth.
Variations in Surface‐Layer Color, Texture, pH, and Phosphorus Content Across Prairie Dog Mounds
Authors: Carlson D. C. , White E. M.
Published: July 2010

Spatial variations of soil surface color, texture, pH, and phosphorus content were studied so the effects of relict and modern prairie dog (Cynomys ludovicianus) pedoturbation on soil surface properties will be more predictable in southwestern South Dakota. When first formed, prairie dog mounds are made of surface soil. In time, lower‐layer materials are added to the surface. The overall textural variation usually increases with pedoturbation because the original surface layer has a different texture than the subsoil. The mound pH is usually greater than the adjacent soil because calcareous subsoil is deposited in the mound. With time, the mound pH decreases as carbonate leaches and the color becomes darker as organic matter accumulates. The color hue gradually changes to a 10YR if the subsoil was not originally a 10YR hue. Fecal and skeletal phosphorus are deposited in and on the mound to increase areal variation in phosphorus content as a mound continues to be used.
Temperature and Water Profiles During Diurnal Soil Freezing and Thawing: Field Measurements and Simulation
Authors: Pikul J. L. , Boersma L. , Rickman R. W.
Published: July 2010

Agricultural soils of the inland Pacific Northwest undergo frequent freezing and thawing during the winter and early spring. Repeated freezing and thawing of the soil surface may accelerate breakdown of soil aggregates, resulting in decreased water infiltration, and erosion resistance. The objective of this research was to simulate soil temperature and water distributions in a field soil during freezing and thawing. A finite difference numerical model was used to simulate soil temperature, depth of freezing, and water movement. Field measurements of soil temperature, ice and water content, and freezing depth in a bare surface treatment were used to validate the simulation model. The model couples heat and water flow equations by the change in soil ice content. An experimental relationship between unfrozen water content and degrees below freezing was used to estimate the change in soil ice content. Soil heat and water flux during 7 h of freezing followed by 12 h of thawing were simulated for two different days when the soil froze to a depth of 1.5 cm, Test 1, and 0.75 cm, Test 2. Simulated maximum frost depths were 1.4 and 0.8 cm for the respective tests. Simulated ice and water content of the 0‐ to 1‐cm soil layer, at the time of maximum forst penetration was 0.46 and 0.41 cm3/cm3, which compares to measured values of 0.49 and 0.49 cm3/cm3 for the respective tests. Correlation of measured soil temperature and simulated soil temperature at the 1‐cm depth was 0.99 for both tests. Standard deviation of the differences between measured and simulated temperature at the 1‐cm depth was 1.04 and 0.29 °C for the respective tests. These results support the validity of this modeling approach for diurnal simulations of heat and water flux, near the surface, in freezing and thawing soil.
Sunflower Growth and Nutrient Uptake: Response to Tillage System, Hybrid Maturity and Weed Control Method
Authors: Deibert Edward J. , Utter Rodney A.
Published: July 2010

Limited information is available on the influence of reduced tillage systems, weed control methods and hybrid maturity on growth and nutrient uptake of sunflower (Helianthus annus). A study was conducted during 1985 to 1986 on a Fargo clay (fine, frigid, montmorillonitic Vertic Haplaquoll) to evaluate plant growth, drymatter production, and N, P, and K content at vegetative stage (V‐16), reproductive stage (R‐5), and seed at harvest of early and late maturity hybrids as influenced by conventional tillage (fall plow) or reduced tillage (fall sweep, fall intertill, and no‐till) and weed control by herbicides or herbicides plus cultivation. Plant height and dry‐matter at V‐16 were higher with reduced tillage in 1985 with limited precipitation, but lower than conventional tillage in 1986 with above normal precipitation. Hybrids performed similarly at V‐16, but by R‐5, height and drymatter were greater for the late hybrid. No‐till and intertill systems produced more drymatter than plow at R‐5. Maximum seed drymatter was produced with intertill and no‐till in 1985, but in 1986 the plow system gave the highest seed production. Nutrient content in sunflower plants and seeds was similar between hybrids, weed control methods, and years. Nutrients in sunflower plants and seeds were similar among tillage systems even though lower nitrate‐N and stratification of P and K in the soil was measured with reduced tillage. Results indicate that reduced tillage sunflower production with adequate weed control is similar to conventional plow systems and that early maturing hybrids produced yields comparable to late hybrids under these tillage and climatic conditions.
Chemical Properties of Native Savanna and Forest Soils in Central Brazil
Authors: Cochrane Thomas T.
Published: July 2010

Recent research of the well‐drained cerrados (savanna) soils of Brazil suggests that poor root growth associated with inferior crop production is often caused by subsoil Ca deficiency rather than Al toxicity. The present study was conducted to re‐examine this hypothesis and to compare native soil vegetation patterns. Horizon samples from 48 representative soils of the Geo‐Economic region of Brasilia, an area covering 22‐million hectares of central Brazil, were analyzed for NH4NO3 exchangeable cations, and cation and anion exchange capacity. Thirty eight of these soils were found under cerrados and 10 under the minor inclusions of native forests scattered throughout the predominantly savanna landscape. Calcium deficient soil conditions were only found in cerrados, although cerrados also occurred on high Ca soils. The Ca/Mg ratios were significantly higher in the forest vs. cerrados soils. Low Ca/K ratios and high anion exchange capacity/cation exchange capacity AEC/CEC ratios were common in cerrados soils. The Mg/K ratios were satisfactory in most of the soils. It is concluded that the Ca/Mg ratios of the cerrados soils should be examined in an agricultural context.
Silicification of Holocene Soils in Northern Monitor Valley, Nevada
Authors: Chadwick O. A. , Hendricks D. M. , Nettleton W. D.
Published: July 2010

In Monitor Valley, Nevada, two Entisols and an Aridisol containing volcanic glass have silica cementation that is first manifest as microagglomerates and later as macroscopic (>2‐mm) durinodes and weakly cemented s‐matrix. The initial effect of silicification is cementation of silt and clay by opaline SiO2, producing silt‐ and sand‐size microagglomerates that are one source of large −1.5 MPa H2O/clay values for the <2‐mm soil fraction. In the illuvial zone, microagglomerates are nuclei for further silica cementation and eventual durinode formation. Volcanic glass is a major source of silica for cementation; the 0.05‐ to 0.10‐mm sand fraction is commonly composed of >40% volcanic glass, of which 40 to 80% is partly weathered; greatest proportions of weathered glass occur at about the same depths as maximum pH. Laboratory measurements of water‐soluble silica and 0.5 M NaOH extractable silica, as well as the −1.5 MPa H2O/clay ratio, provide indications of incipient silicification. These values are relatively large throughout the sola but reach maxima before decreasing with increasing depth. This pattern indicates that glass weathering and relatively short‐distance silica illuviation influence these recent soils.
The Effect of Two Polymers and Water Qualities on Dry Cohesive Strength of Three Soils
Authors: Aly Saleh M. , Letey J.
Published: July 2010

The effects of two polymers, cationic guar (CP‐14) and anionic polyacrylamide (PAM), and two water qualities on dry cohesive strength of three soils were studied. The soils were Fallbrook sandy loam (fine‐loamy, mixed, thermic, Typic Haploxeralf), Bosanko sandy clay loam (fine, montmorillonitic, thermic, Chromic Pelloxererts), and Hanford loamy sand (coarse‐loamy, mixed, nonacid, thermic, Typic Xerorthents). The two polymers were applied with synthesized Friant‐Kern Canal or well water typical of the San Joaquin Valley of California (EC 0.05 and 0.7 dS m−1, respectively). The soil was used either directly (nonpretreated) or pretreated by spraying the waters containing polymers to create concentrations of 0, 25, 50 and 100 mg polymer per kg soil and then air‐drying the soil. Soil briquets and soil cores of pretreated soil were saturated with untreated water and nonpretreated soil was saturated with waters containing polymer concentrations of 0, 5, 25, 50 and 100 mg L−1. The saturated soil was drained, dried at 60 °C for 48 h and then the dry cohesive strength was measured by modulus of rupture (MR) of soil briquets and tensile strength (S) of soil cores. The rupture stress (RS) required for crushing three group sizes (2–4, 4–5.66 and 5.66–8 mm) of artificially prepared soil aggregates using the various solutions was also measured. Both polymers were effective in ameliorating soil hardness, but PAM was more effective than CP‐14 in either water. The degree to which MR, S and R decreased with polymer applications was dependent upon the soil type, water quality, polymer concentration and method of polymer application. Pretreated Bosanko soil showed higher MR values in canal water than in well water for both polymers. Fallbrook soil showed the same trend as Bosanko soil with CP‐14 and opposite results with PAM. Higher values of MR were obtained in nonpretreated soil than in pretreated soil for Bosanko soil in both canal and well water. In general, differences in MR between pretreated and nonpretreated Fallbrook soil were not great. Reasonable agreement was found between measured MR and RS of the three soils and predicted results based on flocculation and polymer adsorption on montmorillonite.
Aluminum Leaching by Mineral Acids in Forest Soils: I. Nitric‐Sulfuric Acid Differences
Authors: James Bruce R. , Riha Susan J.
Published: July 2010

In laboratory studies simulating snowmelt leaching of forest soils, HNO3 leached more Al than did H2SO4 from soil columns containing a forest floor‐spodic horizon sequence (FF/Bs) representative of high elevation forest soils and watersheds thought to be sensitive to acidification by acid precipitation. Increasing the HNO3 concentration 100‐fold (pH 5 to 3) increased total Al concentration in leachates from 0.70 to 0.85 mM, while increasing H2SO4 concentration had no effect. Addition of pH 3 H2SO4 to the FF/Bs columns raised leachate pH relative to pH 3 HNO3 and control treatments, and resulted in the lowest Al concentrations of all treatments in the first three of four sequential leachings. In albic (E) and ochric (A) mineral soil horizons below a forest floor, there were no differences between the acids and no effects of changing acid concentration. Concentrations of Al leached by the acids did not differ from those in control treatments. The differences in effects of HNO3 and H2SO4 on soluble Al and pH in the Bs horizon and the lack of effect of either acid in the E and A horizons imply that the type of mineral horizon below the forest floor and the kind of acid leaching through these horizons are pertinent to predicting lake acidification in diverse forested watersheds. The results also have implications for pollution control strategies focusing solely on SO2 emissions and designed to mitigate lake acidification.
Aluminum Effects on Northern Red Oak Seedling Growth in Six Forest Soil Horizons
Authors: Joslin J. D. , Wolfe M. H.
Published: July 2010

The response of northern red oak (Quercus rubra L.) seedlings to varying levels of soil Al was examined in a 16‐wk greenhouse study. Forest soil samples representing three soil series were used as growth media: Captina (Fragiudult, Missouri), Lexington (Paleudalf, Mississippi) and Becket (Fragiorthod, New York). Soil from two horizons from each series was separately amended in four treatments to create a wide range of soil Al availability: (i) control, (ii) limed [Ca(OH)2], (iii) acidified (HCl), (iv) acidified with supplemental calcium added (+ HCl and CaSO4). Treatments significantly (p < 0.05) altered soil pH (range 3.65 to 5.48), base saturation, and 0.01 M SrCl2‐extractable Al (range 0.6–37.2 mg kg−1). Compared to controls, both acidification treatments resulted in significant reductions in fine root and foliar biomass production or in fine root branching, in all horizons except the highly organic Bhs of the Fragiorthod. In the remaining five horizons, fine root branching and biomass production were highly and negatively correlated (R2 = 0.70 and 0.50, respectively) with 0.01 M SrCl2‐extractable Al. Although fine root tissue concentrations of Al correlated highly with 0.01 M SrCl2‐extractable Al levels, root tissue Al predicted root branching and biomass only moderately well (R2 = 0.30 and 0.21, respectively). Fine root branching was more sensitive to treatment effects than either root biomass production or root elongation. Reductions in foliar biomass appeared to be secondary responses to direct effects on root systems. Present soil Al levels and acidic deposition rates appear to pose no threat to northern red oak in the southern portion of its range, whereas the possibility of Al toxicity in northeastern Spodosols deserves further study.
Sulfur Speciation in Some Chesapeake Bay Tidal Marsh Soils
Authors: Haering K. C. , Rabenhorst M. C. , Fanning D. S.
Published: July 2010

In order to study S compounds and processes in Chesapeake Bay marshes, Sulfihemist profiles were sampled along a transect from inland to streamside marsh areas of Cedar Creek Marsh and in seven marshes along the Nanticoke River in Dorchester County, MD. In both areas, higher concentrations of pyrite were found in areas that received Fe inputs from tidal overwash or from diffusion from mineral layers within the profile. Pyrite accumulation was favored in streamside profiles that were subjected to frequent tidal flushing. Pyrite was the major form of S in most of the organic horizons of the Cedar Creek streamside pedons and in several of the Nanticoke pedons. Organic S was the major form of S in the Cedar Creek inland pedons. In both study areas, organic C was correlated with total S, apparently because of the S associated with organic materials and the ability of organic matter to hold sulfate‐containing tidal water. High total S values were found to be indicators of areas of organic S accumulation. Pyrite content was not significantly correlated with total S or organic C. Identification of “sulfidic materials” for purposes of soil classification should be based on analysis of pyrite S, as total S may be a poor estimate of oxidizable sulfides.
Canopy Shading Effects on Soil Heat and Water Flow
Authors: Horton Robert
Published: July 2010

A method to model two‐dimensional heat and water flow in soil as influenced by shading from a row crop is developed. The numerical method predicts the surface energy partitioning, soil temperature, and the water content as influenced by soil surface evaporation in the absence of water uptake by roots. Standard weather information, canopy shape factors, and soil thermal and hydraulic properties are the inputs required to make predictions. Although the present model does not include water uptake by roots, this feature can be added. The methods of prediction are compared with analytical methods in verification and benchmarking test problems. Predictions of soil surface temperature and subsurface temperature in a verification test scenario closely agree with analytical solution values. Predicted soil water contents during an infiltration event agree closely with analytical values predicted by a quasi‐analytic simulator (used in a benchmarking test), and also with experimental data (used in a validation test). A 10‐d simulation is performed to show the ability of the method to describe surface energy partitioning and soil profile conditions. The method is shown to provide reasonable results. For the specific scenario of this simulation, the diurnal time variation of surface energy partitioning, soil water content, and soil temperature exhibited a radical change when the soil located between plant rows dried to residual water content. Large spatial variations in soil energy fluxes, temperature, and water content are predicted when soil located between plant rows becomes drier than soil below the canopy. The method can predict these fluxes, which are very difficult to obtain by direct measurement. Thus, this method should have a wide range of applications in soil and crop sciences.
Bivalent Ion Adsorption by an Oxisol
Authors: Charlet Laurent , Sposito Garrison
Published: July 2010

Surface excesses of the bivalent ions Ca2+, Mg2+, and SO2‐4 were measured on a Brazilian Oxisol suspended in Ca(ClO4)2), Mg(ClO4)2, or Li2SO4 solution. The surface excess of Ca2+ increased proportionally with pH in the range 2.5 to 6.0 and was independent of ionic strength in the range 26 to 67 mol m−3. The surface excess of Mg2+ as a function of pH, however, showed a significant dependence on ionic strength in the range from 34 to 176 mol m−3. The surface excess of SO2‐4 showed a dependence on ionic strength in the range 12 to 37 mol m−3 if pH was less than the point of zero net charge (PZNC = 4.2), but showed no dependence on ionic strength if pH was above the PZNC. All three bivalent ions showed significant adsorption above the PZNC of the soil. These trends were interpreted conceptually to suggest that, although the three bivalent ions may form both outer‐sphere and inner‐sphere surface complexes, the latter are more important for Ca2+ than for Mg2+ or SO2‐4.
Spatial Variability of Soil Chemical Properties in Grazed Pastures
Authors: West C. P. , Mallarino A. P. , Wedin W. F. , Marx D. B.
Published: July 2010

Excretal deposition concentrates nutrients in animal watering and resting areas of pastures, and including these areas in soil sampling may bias fertilizer recommendations. Our objective was to determine the magnitude and extent of nutrient enhancement near a water source in each of two experimental tall fescue (Festuca arundinacea Schreb.) pastures. The rectangular 0.44‐ha pastures were in southcentral Iowa and included three soils: a fine, montmorillonitic, mesic Typic Argiaquoll, a fine‐loamy, mixed, mesic Typic Argiudoll, and a fine, montmorillonitic, mesic Aquic Argiudoll; pH 6.8 to 7.0. Before grazing began in 1976, extractable P (Bray and Kurtz P‐1) and exchangeable K ranged from 3 to 9 and 87 to 156 mg kg−1, respectively, at 0 to 75 mm. After 5 yr of grazing by cattle, soil was sampled at 0 to 75 and 75 to 150 mm on a grid pattern starting at the water source and analyzed for extractable P and exchangeable K, total N, and organic C. Chemical values between the grid points were interpolated by kriging, and contour plots were constructed for each variable. Extractable P and exchangeable K exhibited large accumulations near the water source, with many P and K measurements exceeding 100 and 1000 mg kg−1, respectively. The zone of enhanced P and K levels extended to approximately 10 to 20 m from the water source. Total N declined from 4.2 to 2.1 g kg−1 with progressive distances from the water; however, the range of values was proportionately less than for P and K. Organic C concentrations showed less distinct trends in relation to distance from the water source. The results showed a distinct zone of nutrient enhancement within 20 m of the water source that should be either avoided or sampled separately when sampling pastures for fertilizer recommendations.
Calcium and Magnesium Availability and Uptake by Rice in Acid Sulfate Soils
Authors: Moore P. A. , Patrick W. H.
Published: July 2010

Deficiencies of Ca and Mg have been suggested to be constraints on rice (Oryza sativa L.) growth in acid sulfate soils. This study was conducted to determine the solubility of Ca and Mg under natural conditions in these soils, to determine what governs the solubilities of these metals, and to investigate uptake of these metals by rice. Metal availability and uptake by rice were evaluated in 134 flooded acid sulfate soils in the Central Plains region of Thailand and in a growth chamber study utilizing 50 of the same soils. Metal activities in soil solutions were determined using GEOCHEM. The results of this study indicate that the soils studied were generally undersaturated with respect to Ca and Mg minerals, suggesting that mineral equilibria probably does not govern the solubility of these metals in acid sulfate soils. Exchange isotherms indicated that Ca2+ and Mg2+ in soil solutions were in equilibrium with Ca and Mg on the cation exchange capacity. Therefore, cation exchange reactions probably govern the solubility of Ca2+ and Mg2+ in acid sulfate soils. The results also showed that although Ca and Mg uptake by rice is correlated with Ca2+ and Mg2+ activity, a more pronounced relationship exists between uptake and the divalent charge fraction in soil solution attributable to these cations. This was believed to be due to competitive inhibition for uptake sites. This study also demonstrated that Ca and Mg deficiencies in rice may be occurring on these soils.
Processes and Rates of Pedogenesis in Some Maryland Tidal Marsh Soils
Authors: Griffin T. M. , Rabenhorst M. C.
Published: July 2010

Tidal marsh profiles from various locations around the Chesapeake Bay were dated using 210Pb geochronology. These soils, which were classified as Typic and Terric Sulfihemists, Typic and Histic Sulfaquents, and Histic Hydraquents, were characterized with respect to bulk density, organic matter content, S and Fe speciation, and pyrite content. These characteristics were interpreted in the context of marsh accretionary activity and soil forming processes. Rates of vertical accretion ranged between 0.35 and 0.75 cm yr−1, indicating that the marshes examined are keeping pace with published rates of sea level rise. Generally, those marshes accreting most rapidly contained a higher mineral content and a higher reactive Fe (FeS2‐Fe plus “free” Fe) content. Pyrite S and organic S were the dominant S species forming from the microbial reduction of SO2‐4. Redox conditions, Fe reactivity, organic matter content, and SO2‐4 concentrations were the major factors controlling S and Fe transformations. Models developed to define different marsh environments with respect to pyrite formation and the degree of pyritization illustrate that in those marshes receiving low rates of mineral sediments (i.e., slowly accreting marshes), the amount of reactive Fe is limiting FeS2 formation, the FeS2 content is low, degree of pyritization (Py) is high, and the dominant S species is organic S. Where the reactive Fe content is high (i.e., rapidly accreting marshes) and SO2‐4 reduction is not retarded, the FeS2 content is high and Py is moderate to high. If reactive Fe is high and SO2‐4 reduction is impeded for some reason, then FeS2 formation becomes limited by the SO2‐4 reduction rate, and the FeS2 content and Py will be variable.
Erosion Effects on Productivity of Cecil Soils in the Virginia Piedmont
Authors: Thomas P. J. , Simpson T. W. , Baker J. C.
Published: July 2010

A study was initiated in two counties in the southern Virginia Piedmont to assess the effects of erosion on soil properties and crop productivity. Plots were established in farmer‐cooperator fields on slightly, moderately, and severely eroded Cecil soils (clayey, kaolinitic, thermic Typic Kanhapludults). The Ap horizon decreased as severity of erosion increased, although no differences were observed for Bt and solum thicknesses. Clay content of the Ap horizon increased as the severity of erosion increased. Increases in clay content were reflected by several soil properties. The volumetric water contents at −10 kPa and −1500 kPa increased with clay content of the Ap horizon, but the differences in plant available water remained at 0.09 m3 m−3. Thus, the effect of erosion on plant available water in both the Ap and Bt horizons was negligible. Cation exchange capacity was higher on the severely eroded sites. Exchangeable Al, expressed as either percent of the exchange complex or as concentration in the soil, was lower than expected and had no apparent adverse effect on yields. Available P decreased with severity of erosion and was significantly correlated with soybean [Glycine max (L.) Merr.] grain yield. Grain yields were greater on the slightly and moderately eroded sites compared to the severely eroded sites. This was attributed to levels of available P in the slightly and moderately eroded soils that were above the 18 mg kg−1 critical P level for optimal crop growth, while available P was below 18 mg kg−1 in the severely eroded soils. The magnitude of difference between noneroded and eroded soils may be difficult to assess because of the scarcity of uneroded upland Piedmont soils by which such comparisons are made. Thus, estimates of the impact of the severity of erosion in the Piedmont may be difficult to establish.
Kinetic Studies of the Reactions of Benzidine with Humic Acid
Authors: Ononye Aloysius I. , Graveel John G. , Wolt Jeffrey D.
Published: July 2010

The mechanism of the reaction of benzidine (4,4′‐diaminobiphenyl), a toxic biphenyl amine, with humic acid in aqueous solutions has been studied using both commercial and soil‐extracted samples of humic acid. The reaction trend is similar for all the samples and involves a byphasic decay in the concentration of benzidine. The phase I reaction is rapid and complete within 1 h and is approximated by second‐order kinetics, while the phase II reaction (a slow process which attains a steady state in benzidine concentration after about 14 d) follows a single exponential first‐order reaction with respect to benzidine. Sorption of benzidine by humic acid was higher for the commercial samples than for the soil‐extracted sample.
Influence of Oxidation Treatments on Surface Properties and Reactivities of Short‐Range Ordered Precipitation Products of Aluminum
Authors: Violante A. , Huang P. M.
Published: July 2010

Organic C contents, specific surface and P adsorption of pseu‐doboehmites or x‐ray noncrystalline precipitation products of Al formed in the presence of various organic ligands (citric, tartaric, tannic or aspartic acid) and Cl were studied before and after oxidation treatment of NaOCl or H2O2. Contents of residual C after NaOCl or H2O2 treatment ranged from 22 to 60% and from 55 to 90% of the original C, respectively. This evidence coupled with their IR spectra indicates that organic ligands are present on the surfaces and in the structural network of Al precipitation products. Specific surface values of samples formed in the presence of citrate or tannate were increased by NaOCl treatment, whereas those of samples formed in the presence of aspartate or Cl were relatively insensitive to oxidation. Before oxidation, samples formed in the presence of strong chelating ligands (citrate, tartrate, or tannate) adsorbed less P than those formed in the presence of aspartate or Cl. After oxidation, adsorption of P by samples formed in the presence of citrate and especially tannate was substantially increased. This is attributed to partial oxidation of organic ligands binding the precipitates and subsequent disintegration of aggregates. The data thus reveal that the influence of oxidation pretreatment on specific surface and P adsorption ability of Al precipitation products varied with the nature and amount of organic ligands coprecipitated.
Environmental Factors Affecting Microbial Production of Dimethylselenide in a Selenium‐Contaminated Sediment
Authors: Frankenberger W. T. , Karlson U.
Published: July 2010

Selenium poisoning from agricultural wastewater has been blamed for wildlife deaths and deformities at Kesterson Reservoir (Merced County, California). One approach in reducing the Se content in seleniferous sediments is based on microbial methylation of Se. This study was conducted to determine the optimum environmental conditions for volatilization of Se. A saline (> 20 dS m−1) seleniferous soil collected from Pond 4, Kesterson Reservoir was assayed for dimethylselenide (DMSe) production by incubating it for up to 120 h at 22 °C under various treatments. The DMSe was monitored by gas chromatography and identified by gas chromatography‐mass spectrometry. The conditions or additions optimum for DMSe production were: pH 8.0; moisture content, field capacity (−33 kPa); temperature, 35 °C; L‐methionine, 100 mg kg−1 soil; galacturonic acid, 3.6 g C kg−1 soil; and protein sources including casein (2.0 g C kg−1 soil) and albumin (0.05 to 2.0 g C kg−1 soil). Albumin applied to soil enhanced gaseous Se production 19.3‐fold over the unamended control. It should be possible to apply these findings in a management practice to detoxify seleniferous sediments.
Long‐Term Tillage and Crop Rotation Effects on Bulk Density and Soil Impedance in Northern Idaho
Authors: Hammel J. E.
Published: July 2010

Conservation tillage management for winter wheat (Triticum aestivum L.) production in northern Idaho may increase bulk density (ρb) and soil impedance (SI) of surface layers and limit crop growth, particularly when combined with spring cropping practices which require cultural or tillage operations during moist soil conditions. Bulk density and SI were measured in a long‐term tillage‐crop rotation experiment after 10 yr of continuous management to determine if differences resulting from tillage or cropping practices existed. Soils of the experimental site were two similar series, Palouse (fine‐silty, mixed, mesic Pachic Ultic Haploxeroll) and Naff (finesilty, mixed, mesic Ultic Argixeroll) silt loams. Tillage treatments included conventional (CON, moldboard plow), minimum (MIN, chisel), and no‐tillage (NOT). Crop rotations were a 2‐yr winter wheat‐spring pea (Pisum sativum L.)rotation and a 3 yr winter‐spring barley (Hordeum vulgare L.)‐spring pea rotation. Bulk density was determined on intact cores using gamma attenuation. Soil impedance was measured with a constant‐rate penetrometer. Tillage had a significant (P < 0.05) effect on ρb, but not SI. Crop rotation did not significantly influence either soil property. The main effect of depth and a tillage × depth interaction, however, produced significant (P < 0.01) differences on ρb and SI. Both MIN and NOT had SI values exceeding 1.5 MPa at a depth of 0.05 to 0.15 m, which were 0.5 to 1.0 MPa greater than CON. Higher SI values under reduced tillage while not preventing root growth may, when combined with cool, wet soil conditions during the spring, limit root function and decrease crop growth potential.
Physical Conditions of a Lake Plain Soil as Affected by Deep Tillage and Wheel Traffic
Authors: Johnson B. S. , Erickson A. E. , Voorhees W. B.
Published: July 2010

Normal fall and spring tillage practices create poor physical conditions for crop growth on lake plain soils in Michigan. Charity clay [fine, illitic (calcareous), mesic Aeric Haplaquept] (Mahjoory and Whiteside, 1976) is an example of such a soil. It has poor internal drainage due to its naturally dense subsoil and is susceptible to physical degradation because of its unstable surface. Tillage studies were conducted from 1983 to 1985 to evaluate the potential for reducing the physical limitations of Charity clay. Treatments consisted of four combinations of a primary and secondary tillage variable. The primary tillage variable involved the application or omission of deep tillage using a triple‐shanked subsoiler prior to moldboard plowing. The secondary tillage variable involved the presence or absence of tractor wheel traffic prior to planting. Subsoiling improved the physical conditions of Charity clay below the Ap horizon. Soil bulk density (ρb) was reduced by 0.05 Mg m−3, and pore size distribution (PSD) was altered such that the volume of pores with radii larger than 150 µm was doubled. Preplant wheel traffic caused subsoil compaction, increasing ρb by about 0.06 Mg m−3, and altered all indicators of soil compaction in the Ap horizon, especially PSD and saturated hydraulic conductivity. The need to minimize wheel traffic regardless of the primary tillage practices employed was evidenced by the results of this study.
Estimating Root Length Density by the Core‐Break Method
Authors: Bland William L.
Published: July 2010

Rapid and accurate methods of measuring root length density (RLD, cm root cm−3 soil) are needed for verifying growth predictions and assessing genotypic differences. The core‐break technique, in which the number of roots visible at a broken cross section of a soil core is used to estimate rooting, was evaluated as a means of measuring RLD. Root systems of wheat, Triticum aestivum L., cotton, Gossypium hirsutum L., and sorghum, Sorghum bicolor (L.) Moench, were sampled and core‐break root counts regressed on RLD measured in the same soil core. Linear relationships were obtained between counts and RLD for each crop on each day of sampling. Calibration equations were derived from regressions of all data for a species. Prediction intervals (90%) for an estimate of RLD from the mean of several core‐break counts were about ± 0.3 cm−2 for wheat, ±0.2 cm−2 for cotton, and ±0.8 cm−2 for sorghum. The core‐break method yields only a low‐precision estimate of RLD from the mean of several core counts, even if calibrated for the soil and crop combination of interest.
Modifications of the Minirhizotron Video Camera System for Measuring Spatial and Temporal Root Dynamics
Authors: Ferguson J.C. , Smucker A.J.M.
Published: July 2010

Current video cameras used to measure in situ root activities lack essential registration and identification components for repeated accurate measurements. This report describes a rapid, inexpensive and completely portable approach for controlling and identifying camera position when making repeated video recordings from minirhizotrons in large field experiments. These registration handle and microcomputer additions to an agricultural microvideo color camera provide new opportunities for measuring root and nodule development. Preliminary measurements indicated that corn roots appeared and disappeared to depths of 75 cm for different N treatments 86 to 99 d after planting. Additionally, root development, maturation, and death can be observed in situ throughout the root profile. These modifications offer a uniform method for comparing root turnover rates and other specific dynamics of the rhizosphere at 1.2‐cm intervals in contrasting soil and climatic conditions.
Optimal Design of Two‐Chamber, Gas Diffusion Cells
Authors: Glauz R. D. , Rolston D. E.
Published: July 2010

Two‐chamber diffusion cells have been used for measuring the gas diffusivity of packed or undisturbed soil cores. Gas diffusivity is calculated from gas concentrations measured initially and at later times in an inlet chamber. The published analytical solution to diffusion in such diffusion cells for the general case of unequal air chamber size was arranged to solve for the soil‐gas diffusivity explicitly and error analyses conducted in order to provide guidance in designing diffusion cells. An equation to calculate the first root of the resulting equation was derived. The optimum apparatus design was determined from error analysis to minimize experimental error in measuring the soil‐gas diffusivity. The error analysis showed that the inlet and outlet chambers should not necessarily be of equal size, but that the chamber not being sampled should be larger than the sampled chamber. Total measurement error is greatest for very small soil‐air contents and small times between initial and successive measurements of gas concentration. The optimum size of both the exit chamber and the soil core increases with measurement time. Thus, an optimum design of diffusion cells should be selected based upon range of soil‐air contents expected, desired measurement times, and soil core length. Diagrams of total relative error and optimum soil core and chamber lengths with time for several soil‐air contents and total relative error as a function of soil core and sampled chamber lengths provide guidance in designing diffusion cells with minimum experimental error. These estimates of optimum design can be easily changed for additional chamber characteristics or improved precision for measuring gas concentration.
Mechanism of Water Entry into Simulated Macropores
Authors: Phillips R. E. , Zeleznik J. M. , Dunn G. H. , Quisenberry V. L.
Published: July 2010

It is commonly believed that, when the soil is unsaturated, water cannot enter soil macropores that begin below the soil surface. The objective of this research was to show that water under negative pressure can enter simulated macropores, after first establishing a continuous water film on the full length of the macropore walls. The simulated macropores were hollow, cylindrical, straight‐walled glass tubes 4.88, 2.60, and 0.85 mm in diameter. Water flux through the simulated macropores was obtained down to a negative water pressure of −1.02 kPa. This was shown by placing simulated macropores against a porous fritted‐glass plate 60 mm in diameter with pore diameters between 40 and 60 µm after establishing a water film on the walls of the simulated macropores. The flux of water down the simulated macropores varied from 0 to 67 mm3 s−1 depending on the contact of the simulated macropore with the porous plate, which influenced the continuity of water in the porous plate with water films on the walls of the simulated macropores. A water manometer was connected to the bubbler of the burette in order to measure the total negative water pressure operating in the simulated macropores. The total negative water pressure operating in the simulated macropores was equal to the sum of (i) the negative water pressure due to the difference in elevation of water menisci of the water manometer and (ii) the matrix potential in the pores of the fritted‐glass plate.
Using Breakthrough Curves for Parameter Estimation in the Convection‐Dispersion Model of Solute Transport
Authors: Yamaguchi T. , Yokosi S. , Moldrup P.
Published: July 2010

We present two easily applicable models for simultaneous estimation of the convective velocity (u0) and the hydrodynamic dispersion coefficient (D0) from breakthrough curve (BTC) data. The two models can be used for both saturated and unsaturated flow. Both models are derived from an analytical solution to the convection‐dispersion equation (CDE). The first model, labeled the “slope method,” is exact. It uses the slope of the BTC to estimate u0 and D0. The second method is approximate because it is only based on the first term of the analytical solution to the CDE. This model is labeled the “first‐term method” and is not valid for very small values of Brenner number. A simple version of both models is developed. A discussion of numerical stability and choice of increments in the model calculations is given. The simple version of the slope method is found to be too numerically unstable when applied to actual BTC data. The remaining methods are tested against two sets of actual measured BTC data by applying each method several times for different parts of each BTC. The values of coefficient of variation between the results are low for all methods (0.1–1.3% for u0 and 2.7–32% for D0). The agreement between the mean values of the parameters u0 and D0 obtained by using the methods presented in this paper and the parameter values for the same BTC data sets reported by other authors is excellent.