bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Estimation of Cation‐Exchange Capacities of Soils and Clays with Methylene Blue Exchange
Authors: Wang M. K. , Wang S. L. , Wang W. M.
Published: July 2010

Four methods to determine the cation‐exchange capacities (CEC) of soils and clays were evaluated: (i) conventional NH4‐Na exchange, (ii) methylene blue (MB) capacity with MB acid, (iii) CEC of tetrasodium pyrophosphate (TSPP), and (iv) MB‐water filter paper spot test titration methods. Eighteen surface soils (0–15 cm) from farm fields in Taiwan and four reference clays obtained from the Source Clay Repository (Clay Minerals Society, Columbia, MO) were used in this work. Under appropriate conditions of concentration, equilibration period, and flocculation of MB solutions, MB absorption can be used to determine the CEC of soils and clays. Regression analyses gave R2 values 0.91, 0.99, and 0.74 for MB‐acid, MB‐TSPP, and MB‐water titration methods, respectively, vs. NH4‐Na exchange. The CEC values of MB‐TSPP titration showed a good linear correlation with values from the NH4‐Na exchange method. Thus, the method of MB‐TSPP filer paper spot‐test titration is recommended for rapid CEC determination in field test of soils.
Legume Productivity and Soil Nitrogen Dynamics in Lowland Rice‐Based Cropping Systems
Authors: Ladha J. K. , Kundu D. K. , Angelo‐Van Coppenolle M. G. , Carangal V. R. , Peoples M. B. , Dart P. J.
Published: July 2010

Rice (Oryza sativa L.) in wet season (WS) preceded by a dry season (DS) fallow, commonly practiced in rainfed lowlands, causes large losses of N through NO3 leaching and denitrification. The green‐manure legumes as NO3 catch crops is economically unattractive to farmers. In a 2‐yr study, we (i) assessed productivity of one grain and four forage legumes (pigeonpea [Cajanus cajan (L.) Millsp.], crotalaria (Crotalaria juncea L.), clitoria (Clitoria ternatea L.), desmanthus [Desmanthus virgatus (L.) Willd.], and siratro [Macroptilium atropurpureum (Mocino & Sessé ex DC.) Urban]) grown in the DS, (ii) examined NO3‐N and NH4‐N dynamics in soil (a Typic Tropaquept), and (iii) evaluated legume residues as a N source for succeeding rice. Nitrate‐N was dominant in the 30‐cm topsoil and was higher under legumes compared with weedy fallow. The legumes produced 4.9 to 9.1 t aboveground biomass ha‐1, accumulated 132 to 306 kg N ha‐1 of which 67 to 81% was derived from N2 fixation. After harvests, 2.9 to 5.2 t ha‐1 of residues containing 81 to 162 kg N ha‐1 were returned to soil. By 3 to 4 wk after flooding, legume‐treated plots had as much as 33 to 40 kg mineral N ha‐1 in topsoil compared with 10 to 13 kg N ha‐1 in weedy fallowed plots. Residues significantly increased rice yield and N uptake. Rice recovered 15 to 31% of the residue N. Failow plots required 25 to 50 kg fertilizer N ha‐1 to produce comparable plant growth responses to that obtained after the legumes. Belowground residues of the legumes apparently contributed 13 to 37 kg N ha‐1 to rice. Such DS legumes that improve farm productivity as well as increase soil fertility might ensure sustainability of production in rainfed lowlands.
Chemical Conditions Conducive to the Release of Mobile Colloids from Ultisol Profiles
Authors: Kaplan Daniel I. , Sumner Malcolm E. , Bertsch Paul M. , Adriano Domy C.
Published: July 2010

Dispersed colloidal clay particles may enhance the transport of environmental contaminants adsorbed to the colloid surfaces. The objective of this study was to determine how soil pH (4.3–6.9), low total electrolyte concentration (TEC, 0.4–2.8 molc m‐3), and low Na adsorption ratios (SAR, 0.3–1.8 [molc m‐3]0.5) affected the concentration of mobile colloids released from 13.5‐m3 reconstructed Ultisol profiles. Critical flocculation concentration (CFC, the minimum TEC to induce flocculation of a clay suspension) tests were conducted using the water‐dispersible clay fraction of the Ap horizon of these profiles, which is the primary source for the mobile colloids. Surface soil pH, TEC, and SAR levels of the profiles that released high concentrations of colloids fell within the dispersion domain identified by the laboratory CFC tests. The effect of SAR on dispersion appears to be a continuum that approaches zero, and this effect is significantly (P ≤ 0.01) dependent on TEC. The dispersible nature of these soils is in part attributed to their very low TEC, generally <2 molc m‐3, which results from low concentrations of weatherable minerals. The TEC of 10 of the 13 profiles were <2 molc m‐3, the CFC for SAR = 1 (molc m‐3)0.5, indicating that if the pH is not limiting (pH greater than ≈6.0), colloidal dispersion will occur. Thus, these weathered soils can be highly dispersive within limited chemical conditions, and only small increases in SAR or pH may induce dispersion. By identifying these limits, the risk of enhancing subsurface contaminant transport by soil‐derived mobile colloids can be reduced.
Assessing Forest Soil Disturbance through Biogenic Gas Fluxes
Authors: Dulohery C. J. , Morris Lawrence A. , Lowrance Richard
Published: July 2010

Soil damage from wet‐weather timber harvests may persist after some physical and chemical properties have been restored through tillage and fertilization. This study's objective was to determine if the gaseous products of aerobic and anaerobic soil biological activity could reveal harvest‐damage effects, even after applying costly mitigation treatments. Fluxes of CO2, CH4, and N2O across the soil surface were measured in Ultisols of a Coastal Plain pine flat damaged during timber harvest, then mitigated by bedding and fertilization (100 kg ha‐1 N, P, and K). Gas fluxes were measured with large static chambers (0.5 by 1.0 m sampling area) to compensate for high microsite variability and the presence of coarse debris on the forest floor. Carbon dioxide evolution was a robust and consistent indicator of residual damage, declining an average of 34% in planting beds on damaged vs. undamaged soils. For example, in a late summer reading, efflux of CO2‐C from beds installed over former skid trails was 143 mg m‐2 h‐1 vs. 258 mg m‐2 h‐1 from undamaged beds and 231 mg m‐2 h‐1 from undisturbed forest floor. Methane and N2O fluxes were ephemeral and, thus, generally unreliable as indicators of harvest damage — though bedding produced scattered high peaks in both. Carbon dioxide was also the only gas flux that responded significantly to fertilization, with an average 26% increase up to 4 mo after fertilization. These results suggest that suppression of gross soil biological activity by harvest damage was not restored by intensive mitigation in the next rotation's establishment phase.
Forest Fire Effects on Soil Phyllosilicates in California
Authors: Ulery A. L. , Graham R. C. , Bowen L. H.
Published: July 2010

Thousands of hectares of forests are burned annually in wildfires and prescribed burns nationwide. Our objective was to determine the effects of such fires on soil phyllosilicates. At five sites throughout California representing Inceptisols, Andisols, and Mollisols, surface soil samples from similar depths were collected in burned and nearby unburned areas. Fires produced no visible soil alterations except in 1 to 2% of the land area where concentrated fuel such as logs or stumps burned slowly and at higher temperatures, effectively baking the underlying soil. Within the upper 1 to 8 cm at these severely burned areas, kaolin was completely destroyed or substantially depleted and d001 spacings of clay‐sized vermiculite, chlorite, chlorite‐vermiculite, and hydroxy‐interlayered vermiculite collapsed toward 1.0 nm or were decomposed as shown by x‐ray diffraction. Dehydroxylation of severely burned Fe‐bearing phyllosilicates was indicated by Mössbauer spectroscopy. The decomposition of virtually all phyllosilicates in the upper 2 cm of the soil was observed at one site after burning. The effects of severe burning on the soil phyllosilicates remained clearly expressed at least 3 yr after a fire.
Evaluation of a Line Heat Dissipation Sensor for Measuring Soil Matric Potential
Authors: Reece Clive F.
Published: July 2010

The accuracy and operational limits of a new heat dissipation sensor for measuring soil matric potential are evaluated. The measurement is based on the rate of temperature rise from a line heat source embedded in a cylindrical porous ceramic that is in equilibrium with soil water. Different heating currents or times can be accounted for by basing calibration on sensor thermal conductivity rather than temperature rise. Six sensors were calibrated against pressure plate and psychrometer measurements of matric potential. Inverse of sensor thermal conductivity was linearly related to the logarithm of matric potential between −10 and −1200 J kg−1. This range of measurable matric potentials is much larger than previous heat dissipation sensor designs. The heat dissipation sensor was accurate to within 20% of the independently measured matric potential. Normalizing sensor readings by sensor thermal conductivity after oven drying results in a calibration that accounts for between‐sensor variability. In a growth chamber experiment with fluctuating soil temperatures, heat dissipation sensor estimates of soil matric potential compared favorably with tensiometer and psychrometer measurements. Heat dissipation sensors based on this design appear useful when a wide range of matric potentials needs to be studied.
A High‐Temperature Catalytic Oxidation Technique for Determining Total Dissolved Nitrogen
Authors: Merriam J. , McDowell W. H. , Currie W. S.
Published: July 2010

A high‐temperature catalytic oxidation method for determination of total dissolved N has been developed and tested on soil solution and throughfall. Unlike methods generally used for total dissolved N, this method is rapid, quantitative, and does not require use of strong acids or bases. The technique couples a commercially available chemiluminescent N detector with the combustion furnace of a commercially available C analyzer. An aqueous sample is combusted in an ultra pure oxygen environment at 680°C, converting all forms of N to nitric oxide, which then reacts with ozone. The product, metastable NO2, is measured chemiluminescently by the N detector. The method is appropriate for samples collected in studies of forest soil solution and throughfall, having a method detection limit of 0.03 mg L−1 total N, and a range from 0.03 to 10.0 mg L−1. Tests of several organic and inorganic N‐containing compounds showed recoveries >90% for concentrations up to 5.0 mg N L−1. Urea was the only compound tested with recoveries <90%. Numerous field samples were analyzed and compared with results obtained using persulfate oxidation and high‐temperature oxidation (uncatalyzed oxidation at 1100°C). Results from this high‐temperature catalytic oxidation method compare well with persulfate oxidation and high‐temperature oxidation.
Proton Binding and Cadmium Complexation Constants for a Soil Humic Acid Using a Quasi‐particle Model
Authors: Bolton K. A. , Sjöberg S. , Evans L. J.
Published: July 2010

In order to better understand the fate of Cd in soils it is important to ascertain the influence of soil humic substances on the retention of Cd in soils. In this study the acid‐base and Cd complexation properties of a humic acid fraction extracted from a soil were investigated using potentiometric titrations. A number of electrostatic and nonelectrostatic equilibrium models were considered in order to obtain the simplest model that would best describe the titration data. All proton binding and Cd complexation constants were determined using the optimization procedure in the computer program FITEQL. The model that best fit the experimental data was a nonelectrostatic model, which included two diprotic acids, H2 A and H2B. The dissociation constants for H2A were calculated to be log β‐1,0,1,0 = −4.00 ± 0.02 and log β‐2,0,1,0 = −9.32 ± 0.03 and for H2B were calculated to be log β‐1,0,0,1 = −7.43 ± 0.24 and log β‐2,0,0,1 = −16.66 ± 0.31. The model indicated the presence of four Cd complexes, CdHA+, CdA0, CdH‐1A− and CdHB+, with complexation constants calculated to be log β‐1,1,1,0 = −1.29 ± 0.09, log β‐2,1,1,0 = −5.92 ± 0.07, log β‐3,1,1,0 = −14.39 ± 0.09, and log β‐1,1,0,1 = −3.72 ± 0.18.
Nitrous Oxide Emission Controls and Inorganic Nitrogen Dynamics in Fertilized Tropical Agricultural Soils
Authors: Davidson E. A. , Matson P. A. , Brooks P. D.
Published: July 2010

Use of N fertilizers in tropical regions has recently surpassed use intemperate regions, but understanding of N2O emissions from fertilized soils is based largely on experience from temperate regions. We studied N2O emissions from a sugar cane (Saccharum officinarum L.) plantation on the Hawaiian island of Maui. Young cane fields that were routinely fertilized had >15 mg NH4+‐N and NO3−‐N kg−1 soil, whereas mature cane fields not being fertilized had <2 mg NH4+‐N and NO3−‐N kg−1 soil. Emissions of N2O were also ≈10 times higher in the young cane fields than in the mature cane. The highest nitrification potentials and N2O emissions occurred near buried irrigation lines and lowest values between plant rows. Added 15NH4+ was nitrified within 48 h in both young and mature cane fields. Hence, microbial populations exist in both young and mature cane fields that can rapidly produce NO3−, and production of N2O is controlled primarily by when and where fertilizer N is applied. In contrast to many temperate agricultural soils where mineralization‐immobilization‐turnover processes contribute significantly to the supply of crop N, rates of gross N mineralization were low, indicating that the cane crop N came primarily from applied fertilizer. In the mature cane, soil inorganic‐N remains low because of high plant and microbial demand, but in the young cane, fertilizer applications exceed the plant and microbial sinks, and N2O emissions are large. Better fertilizer management in this early stage of the cane crop cycle might significantly reduce N2O emissions.
Tillage Depth Influence on Soil Nitrogen Distribution and Availability in a Rice Lowland
Authors: Kundu D. K. , Ladha J. K. , Lapitan‐de Guzman E.
Published: July 2010

Previous studies using artificial barriers at selected depths have shown the importance of N supply from soil below 15 cm to rice (Oryza sativa L.). Subsoil N availability and its use by wetland rice, however, have not been evaluated under normal field conditions. We examined distribution and availability of 2 M KCl‐extractable N in 0‐ to 15‐, 15‐ to 30‐, and 30‐ to 45‐cm layers of a submerged Alfisol during three successive crop seasons, as influenced by the depth of tillage imposed at the outset of the experiment. Mineral N availability in the 0‐ to 45‐cm profile and rice N uptake in the first season were significantly higher (20–25 kg ha−1 higher mineral N and 16–18 kg ha−1 higher crop N uptake) with tillage to a depth of 40 cm than to 15 or 25 cm, the increased N supply originating largely from the 15‐ to 30‐cm layer. In two following seasons, tillage to 40 cm gave the highest mineral N in the subsoil layers, and increased rice N uptake by 12 to 14 kg ha−1, compared with tillage to 15 cm. The beneficial effects of deep tillage were attributed to the elimination of mechanical impedence to root proliferation, and lower susceptibility of subsoil N to various loss mechanisms. Initial and final analyses of Kjeldahl N in the soil profile indicated no adverse effect of practicing 40‐cm‐deep tillage once in three seasons on soil N fertility. Further study is needed to determine optimum depth and frequency of primary tillage for different soil types to enhance N use efficiency.
Magnesium and Potassium Release by Weathering in Spodosols: Grain Surface Coating Effects
Authors: Courchesne François , Turmel Marie‐Claude , Beauchemin Paul
Published: July 2010

The effect of coatings on the rate of Mg and K release by weathering were determined on four soil horizons (Croche, Sutton, and LaTuque B and Croche C), collected from three Spodosols in southern Quebec, Canada. Rates of Mg, K, Fe, and Al release from the <2‐mm fraction of intact and treated (coatings removed with dithionite‐citrate‐bicarbonate [DCB] and H2O2) samples were measured in the laboratory using a continuous flow technique. The materials were leached with a 0.0005 M H2SO4 solution adjusted to pH 3.0 at a flow rate of 0.05 mL min−1 for 1080 h. Surface coatings were composed of Al, Fe, Si, and organic C with traces of Ca. Coating removal had no effect on cation release rates (α < 0.01) from the Croche C horizon, indicating that mineral surfaces were not altered by treatments with DCB and H2O2. Intact B horizons released Fe (3.04–4.87 µmol g−1 h−1/2) and Al (10.07–36.33 µmol g−1 h−1/2) at a faster rate than treated (Fe: 0.28–1.68 µmol g−1 h−1/2; Al: 1.21–27.34 µmol g−1 h−1/2) samples although effluent pH (pHf) was more acidic in the latter. Magnesium and K release rates were higher in treated (Mg: 0.35–2.03 µmol g−1 h−1/2; K: 0.052–0.073 µmol g−1 h−1/2) than in intact (Mg: 0.19–0.61 µmol g−1 h−1/2; K: 0.032–0.039 µmol g−1 h−1/2) samples for two of the three Spodic B horizons. In the Croche B horizon, the absence of rate differences (α < 0.01) was attributed to the incomplete removal of Al coatings from treated materials. Because differences in pHf levels could not be invoked to explain all of the observed rate variability, we suggest that the accumulation of coatings was an effective process isolating primary mineral surfaces, therefore reducing the extent of reactive surfaces available for Mg and K release.
Determining Soil Loss Using the Inventory Ratio of Excess Lead‐210 to Cesium‐137
Authors: Wallbrink P. J. , Murray A. S.
Published: July 2010

The anthropogenic nuclide 137Cs is widely used to measure soil movement. However, changes in 137Cs areal concentrations may not result from soil redistribution alone. There can be considerable variability in 137Cs fallout due to rain shadowing and small‐scale runon‐runoff processes at the time of deposition. Fallout 210Pb is also affected by these processes and thus areal concentrations of the two should be correlated. The ratio of fallout 210Pb to 137Cs reduces variability by up to a factor of two in undisturbed control forest sites at St. Helens, Tasmania. In addition, these two nuclides penetrate to different depths, thereby producing a varying activity ratio with depth, and this gives rise to a new method for determining soil loss. The average inventory ratios of fallout 210Pb to 137Cs from plots adjacent to the controls were measured; these had undergone “normal” and “minimal impact” logging procedures. The average core inventory ratio at the control locations was 2.24 ± 0.14 (n = 18), compared with means of 0.74 ± 0.09 (n = 10) and 1.73 ± 0.29 (n = 10) from the normal and minimal impact sites. The average depth of soil removed from the logged sites was then calculated by comparing these ratios with the inventory activity ratio curve from their respective control sites (40 ± 6 mm, normal site; 17 ± 5 mm, minimal site). We concluded that, compared with areal concentrations alone, ratios of fallout nuclides are likely to provide a less randomly variable (and thus more sensitive) method for investigating surface erosion in landscapes where vertical soil mixing is not sufficiently recent to be of concern.
Comparison of Kriging and Inverse‐Distance Methods for Mapping Soil Parameters
Authors: Gotway Carol A. , Ferguson Richard B. , Hergert Gary W. , Peterson Todd A.
Published: July 2010

Variable‐rate technology may provide a means of increasing fertilizer use efficiency by matching applications to specific conditions at a given field location. Effective implementation of this technology depends on accurately characterizing the spatial variability of soil parameters used to define the application rate. Kriging and inverse‐distance‐squared are two commonly used techniques for characterizing this spatial variability and interpolating between sampled points. To assess the accuracy of these techniques, data sets obtained from grid sampling two field research sites were used in a prediction‐validation comparison of ordinary kriging and inverse‐distance methods using powers p = 1, 2, and 4. The accuracy of the inverse‐distance methods tended to increase with the power of distance for data sets with a coefficient of variation less than about 25% (typical of soil organic matter). However, for data sets with greater variation (such as soil NO3−), inverse‐distance prediction methods using high distance powers (2 or 4) can give very inaccurate predictions. The accuracy of predictions from kriging was generally unaffected by the coefficient of variation, and was relatively high for all of the sampling configurations considered in this study. These tendencies were also observed using 48‐ and 72‐m subsamples, although the use of wider sampling spacings greatly reduced the information in the maps constructed by each method. Careful thought should be given to the choice of sample spacing and interpolation method to be used before data are collected. Summary statistics, and the coefficient of variation in particular, are simple measures that can give an indication of the relative accuracy of the inverse‐distance and kriging mapping approaches.
Iron and Manganese Distribution in Nodules from a Young Texas Vertisol
Authors: White G. Norman , Dixon J. B.
Published: July 2010

Iron and Mn distributions in the black nodules from the BCk3 horizon of the microlow position of a Burleson soil, a fine, montmorillonitic, thermic, Udic Haplustert, from a terrace of the Brazos River were mapped with scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) x‐ray analysis. Spherical nodules were concentrically banded, and the irregularly shaped nodules lacked well‐developed banding of Fe and Mn. More and better expressed banding was found by decreasing pixel size used for mapping and by increasing the count time per pixel for banded nodules. Bands of higher or lower Fe and Mn concentration were not coincident. The Mn/Fe weight ratios of individual nodules analyzed by EDS were between 0.71 to 2.85. Banded nodules had a narrower range of Mn and Fe concentrations and a narrower range in Mn to Fe ratios than unbanded nodules. Barium concentration in the nodules was unusually high, averaging 30 g kg−1, and correlated strongly with Mn concentration. Some interelement correlations (e.g., Fe vs. Mn, r = −0.56; Fe vs. Al, r = −0.58) reflected partitioning into the oxide or silicate minerals of the soil. Fractured nodules revealed the interior to have only a few very small pores. The 30 nodules examined are well developed solid bodies that are expected to persist in the soil environment. They appear to contain unique and important information about the weathering history of the Burleson soil and the landscape in which it occurs. The order and expression of the banding is a relict of the redox history of the nodules, which can be used to induce the redox history of the soil.
The Microbial Activity Season in Southeastern Hydric Soils
Authors: Megonigal J. P. , Faulkner S. P. , Patrick W. H.
Published: July 2010

The growing season requirement is an often overlooked part of the definition for hydric soils. The current technical definition for a hydric soil states that flooding or soil saturation must occur during the portion of the year when soil temperature at 50 cm is >5°C. In this study, we defined the portion of year when soils were >5°C at 50 cm as the microbial activity season and reserved the term growing season for plant activity. In the technical criteria for hydric soils, specific microbial activity season months have been assigned to each of the soil temperature regimes. Our objectives were to determine the portion of the year when southeastern U.S. hydric soils are <5°C at 50 cm and to estimate rates of microbial activity during winter flooding. We found that 34 bottomland hardwood forest soils in South Carolina, Louisiana, and Mississippi were never <5°C at 50 cm during a period of 2 to 3 yr. Also, winter rates of soil respiration and O2 consumption (1.6 mL O2 L−1 air d−1) are apparently sufficient to cause anoxia in saturated soils. Based on the available data, we recommend a 12‐mo microbial activity season for southeastern bottomland hardwood forests. Additional data will be necessary to determine the relationships between temperature, soil saturation, and development of redoximorphic features in southeastern soils.
Hydroperiod Influences on Nutrient Dynamics in Decomposing Litter of a Floodplain Forest
Authors: Lockaby B. G. , Murphy A. L. , Somers G. L.
Published: July 2010

Lack of clarity regarding the relationship between hydroperiod and decomposition dynamics has long been a barrier to the development of a clear understanding of floodplain biogeochemistry. Relationships between hydroperiod and decomposition processes were investigated using a controlled, field approach on the Ogeechee River floodplain in south Georgia. The study intent was to develop cause‐effect relationships between specific flooding regimes and decomposition parameters. Microcosms designed to manipulate flooding regimes were installed and used in combination with litterbags containing abscised foliage. Treatments were designed to mimic realistic hydroperiod‐nutrient inflow scenarios and included: a nonflooded control, flooded for 6 mo, flooded for 3 mo, flooded intermittently for 4 mo, flooded for 3 mo with elevated P inflow, and flooded for 3 mo with elevated N inflow. Mass, C, N, and P dynamics were studied for a 106‐wk period. Flooding stimulated mass, C, N, and P loss. The data suggest that single, brief flooding regimes may stimulate mass and C loss to the greatest extent. The proportion of N and P remaining after 106 wk was only marginally different among flooding regimes. However, temporal patterns of immobilization‐mineralization were strongly influenced by the nature of the flooding regime.
Soil Organic Matter Mineralization after Compost Amendment
Authors: Sikora L. J. , Yakovchenko V.
Published: July 2010

The addition of composts and manures to soils has often resulted in increased plant yields that are not obviously related to the nutrients in the added organic material. A study was conducted to determine if compost additions to soil resulted in increased mineralization of soil organic matter (SOM). The organic matter of a Sassafras sandy loam soil (fine‐loamy, siliceous, mesic Typic Hapludult) was labeled with 14C by incubating uniformly labeled wheat (Triticum aestivum L.) straw with the soil through a minimum of 60 wetting‐drying cycles during 2 yr. A municipal solid waste‐biosolids compost (MSWC) or a biosolids compost (BC) was added to the labeled soil or to acid‐washed sand and incubated for 1440 h. Decomposition of MSWC was low with 95% of the compost‐C remaining in sand or soil after 1440 h. Ninety‐two percent of BC‐C remained in sand and 86% remained in soil after 1440 h. Total and 14CO2 data indicated that neither compost stimulated SOM decomposition. Municipal solid waste‐biosolids compost reduced slightly SOM decomposition at 545 and 715 h. The soil, however, stimulated BC decomposition. Nitrogen mineralization of the BC + soil mixture was greater than soil alone, and the N apparently came from the compost. The benefits from addition of BC to Sassafras soil was not attributed to increased mineralization of SOM.
Soil Organic Matter Pools during Early Adoption of Conservation Tillage in Northwestern Canada
Authors: Franzluebbers A. J. , Arshad M. A.
Published: July 2010

Changes in soil organic matter (SOM) pools during adoption of reduced (RT) or zero tillage (ZT) can influence soil physical properties, nutrient cycling, and CO2 flux between soil and atmosphere. We determined soil organic C (SOC), soil microbial biomass C (SMBC), basal soil respiration (BSR), and mineralizable N to a depth of 200 mm at the end of 3, 5, and 6 yr after implementation of tillage management on a Falher clay (fine, montmorillonitic, frigid Typic Natriboralf) near Rycroft, Alberta, in a canola (Brassica campestris L.)‐wheat (Triticum Aestivum L.)‐barley (Hordeum vulgare L.)‐fallow cropping system. At the end of 6 yr, SOC was not different among tillage regimes and averaged 8.6 kg m−2. At the end of 3 and 5 yr, SMBC was not significantly different among tillage regimes, but at the end of 6 yr SMBC was 7% greater in RT and 9% greater in ZT than in conventional tillage (CT). Basal soil respiration and mineralizable N at the end of 6 yr were not different among tillage regimes following barley and averaged 2.7 g CO2‐C m−2 d−1 and 5.0 g inorganic N m−2 24 d−1, respectively. However, BSR following fallow was 2.2, 2.5, and 2.6 g CO2‐C m−2 d−1 in CT, RT, and ZT, respectively. Mineralizable N following fallow was 5.8 g inorganic N m−2 (24 d)−1 in RT and ZT and 7.3 g inorganic N m−2 (24 d)−1 in CT. At 0 to 50 mm, there was no significant increase in SOC at the end of 6 yr, a 17 to 36% increase in SMBC, and a 12 to 69% increase in BSR with ZT compared with CT, depending on rotation phase. Relatively small changes in SOM pools with adoption of conservation tillage may be attributable to the large amount of SOM initially present and the cold, semiarid climate that limits SOM turnover.
Leaching of Nitrogen from Slow‐Release Urea Sources in Sandy Soils
Authors: Wang F. L. , Alva A. K.
Published: July 2010

Application of readily soluble forms of N fertilizers to sandy soils may cause leaching of NO3‐N resulting in contamination of groundwater. The leaching loss of N may be reduced to some extent by using slow‐release forms of N. An intermittent leaching and incubation technique, to mimic natural occurrence of rainfall and dry conditions, was used to examine the leaching of N from readily soluble (NH4NO3) and slow‐release fertilizers [isobutylidene diurea (IBDU) and a polyolefin resin‐coated urea, Meister] in Wabasso (sandy, siliceous, hyperthermic Alfic Haplaquod) and Candler (hyperthermic, uncoated Typic Quartzipsamment) soils. After 29 d, the cumulative recovery of the applied fertilizer N in the leachate for the treatments decreased in the following order: NH4NO3 (88‐100%) > IBDU (27–32%) > Meister (11.5–11.7%). A significant portion (19.5–35.5%) of the total N leached from IBDU and Meister was in the urea form in the initial leaching; however, after 9 d, NO3 and NH4 forms represented the major portion of leachate total N. Although N from NH4NO3 was leached completely from the Candler sand, 12% of the applied N (as NH4NO3) was not recovered in the leachate from the Wabasso sand. Cumulative NH4‐N leached from the Wabasso sand was only 58% of that from the Candler sand. The results demonstrate that the amounts and forms of fertilizer N leached from the sandy soils depend on the solubility of the fertilizer, the soil type, and the duration of intermittent leaching.
Indigenous Knowledge and Classification of Soils in the Andes of Southern Peru
Authors: Sandor J. A. , Furbee L.
Published: July 2010

Indigenous cultures throughout the world have substantial, systematic knowledge of soils gained during many generations of land use; however, little of this knowledge has been scientifically documented. Recent literature indicates that knowledge among traditional cultures could add to scientific understanding of soils and be useful in international agricultural development. This study investigated indigenous soil knowledge in the Colca Valley, Peru, where terrace agriculture has been practiced for at least 15 centuries. Previous research suggested enhanced tilth and fertility of ancient agricultural soils, measured by criteria such as thickened A horizons, lower bulk density, and greater levels of organic C, N, and P relative to nearby uncultivated Mollisols. Long‐term soil conservation is partly attributed to traditional management practices such as terracing, a form of conservation tillage, fertilization, and irrigation. To test the hypothesis that a body of knowledge underlies traditional soil management practices, interdisciplinary studies were conducted, involving linguistic evaluation of soil terms, anthropological field interviews, soil and geomorphic mapping, and basic morphological and laboratory characterization of soils identified by farmers. Anthropological research revealed a hierarchical soil classification system, with up to four categorical levels and about 50 soil and earth material names, that emphasizes soil texture and other properties important in agricultural management. Soil analyses indicated a fairly close correspondence between indigenous texture classes and those used in U.S. soil classification. Local farmers recognize several soil features and horizons such as duripans, soil variation with depth, distribution of soils on the landscape, and changes in soil behavior under different conditions.
Biodynamic vs. Conventional Farming Effects on Soil Structure Expressed by Simulated Potential Productivity
Authors: Droogers P. , Bouma J.
Published: July 2010

Effects of alternative farming systems on soil structure need to be quantified to judge the sustainability of the systems. This study was conducted to compare two farming systems by converting “static” basic soil properties into a “dynamic” assessment using simulation modeling. Increasingly popular biodynamic farming systems use no commercial fertilizers and pesticides but apply organic manure and compost. Soil conditions on four fields on two farms where biodynamic and conventional soil management had been practiced for about 70 yr were investigated with morphological and physical methods. Soils (Loamy, mixed, mesic Typic Fluvaquents) were pedologically identical. Four procedures were used to express differences in soil structure as a function of different management: (i) morphological description; (ii) measurement of basic and static soil parameters such as bulk density, organic matter, and porosity; (iii) measurement of soil hydraulic characteristics; and (iv) determination of simulated water‐limited yields. The latter procedure provides a criterion that is quantitative, is directly related to a practical aspect of soil behavior, and reflects the highly nonlinear soil‐water processes. The WAVE simulation model was used to predict water‐limited potato (Solanum tuberosum L.) yields with climatic data of 30 yr. Basic static soil parameters were not significantly different but simulated yields were significantly different and were 10 200 and 10 300 vs. 9400 and 9700 kg dry matter tuber yield ha−1 yr−1 for the biodynamic and the conventional fields, respectively. Simulation modeling of crop yields thus provides a relevant expression for the production potential of the two different farming systems.
Reaction in Soil of Phosphorus Released from Poultry Litter
Authors: Robinson J. Stephen , Sharpley Andrew N.
Published: July 2010

Poultry production generates large amounts of litter or manure, which can be a valuable source of P for crops. However, litter application rates are usually based on data for mineral P fertilizer recommendations. In order to determine if this is agronomically and environmentally sound, the availability, fractions, and sorptivity of P from poultry litter or KH2PO4 were determined in six Oklahoma soils following incubation for up to 28 d. An average 50% more P from KH2PO4‐treated (78 mg kg−1) than from leachate‐treated soils (52 mg kg−1) was bioavailable, as determined by extraction with Fe‐oxide‐impregnated paper strips, after 28‐d incubations. Conversely, more NaHCO3‐extractable P was found in leachate‐treated (66 mg kg−1) than KH2PO4‐treated soils (42 mg kg−1). Calculated from Langmuir isotherms, P sorption maxima averaged 548 mg kg−1 for leachate‐treated and 304 mg kg−1 for KH2PO4‐treated soils, while binding energies averaged 0.527 and 0.456 L mg−1, respectively. The higher P sorption maxima and binding energies of leachate‐treated soils may result from the formation of Ca‐P complexes, given the increased Ca content of these soils. The different reaction in soil of P added as poultry litter leachate to that added as KH2PO4, indicates manure application rates should be based on soil tests that are sensitive to P source‐dependent sorption characteristics and/or manure trials, and not just on mineral fertilizer trials.
Smectite Mineralogy and Charge Characteristics along an Arid Geomorphic Transect
Authors: Reid D. A. , Graham R. C. , Amrhein C. , Douglas L. A.
Published: July 2010

Smectites are a major mineral group often found in the clay fraction of soils. Our objective was to evaluate the effect of pedologic environments on smectites in the arid Carrizo Plain, California. Six pedons (one Argixeroll, three Haploxeralfs, one Natrargid, and one Salorthid) were described and sampled along a geomorphic and salinity gradient transect. The transect soils have formed in alluvial parent materials derived from Miocene marine sandstones, siltstones, and shales. The fine clay fractions of transect soils were studied using x‐ray diffraction, interlayer swelling with alkylammonium cations, and chemical analyses. Both beidellitic and montmorillonitic smectites occurred in the transect soils, suggesting multiple origins for these minerals. The chemical composition of the beidellites are similar to those of a tetrahedrally charged, dioctahedral mica. Since mica was identified in shale parent materials and in the fine silt and clay fractions of the soils, the beidellites are apparently a weathering product of mica. Minor variations in the chemical composition of mica precursors may account for observed differences in beidellite charge characteristics. The chemical composition of montmorillonites was variable, making a common origin for these minerals unlikely. Montmorillonites from saline pedons contained more Fe and Mg and less Al in the octahedral sheet than montmorillonites from nonsaline pedons. Montmorillonites in the nonsaline pedons are probably inherited from montmorillonites identified in parent materials, whereas montmorillonites in saline soils may be neoformed. Groundwater within the Salorthid was supersaturated with respect to both montmorillonite and beidellite.
Changes in Ponderosa Pine Site Productivity following Removal of Understory Vegetation
Authors: Busse M. D. , Cochran P. H. , Barrett J. W.
Published: July 2010

Competition from understory vegetation for water and nutrients can limit productivity of young forest stands. Less is known of the effect of understory vegetation on long‐term stand growth or soil organic properties. The effect of understory vegetation on periodic annual increments (PAIs) of basal area, height, and volume for ponderosa pine (Pinus ponderosa Dougl.) in central Oregon at 4‐ or 5‐yr intervals was examined for a 35‐yr period. Soil C, N, and microbial biomass C (MBC) were also quantified after 32 and 35 yr with and without understory vegetation on a sandy loam pumice soil (Xeric Vitricryand). Five tree spacings, ranging from 2.0 to 8.0 m (154–2469 trees ha−1), in combination with two understory treatments (understory vegetation present or continuously absent) were installed in 1959. Total understory vegetation cover averaged 35% between 1959 and 1994 for treatments with understory vegetation present, and was dominated by three shrub species: antelope bitterbrush [Purshia tridentata (Pursh) DC.], greenleaf manzanita (Arctostaphylos patula Green), and snowbrush (Ceanothus velutinus Dougl. ex Hook.). Covariance analyses of PAIs for each successive interval were performed using appropriate stand parameters at the start of each interval as covariates. Tree growth was reduced by competing understory vegetation during the first 12 to 20 yr only; understory vegetation did not reduce the adjusted PAIs during the last 15 yr. Soil C and N were measured incrementally to a depth of 24 cm. Presence of understory vegetation resulted in greater C and N in the O horizon and upper 4 to 12 cm of mineral soil. Seasonal MBC, measured at 14‐d intervals from May to November, was greater when understory vegetation was present. The results suggest that understory vegetation plays an important role in maintaining soil quality.
Hydraulic Conductivity in a Clay Soil: Two Measurement Techniques and Spatial Characterization
Authors: Reynolds W. D. , Zebchuk W. D.
Published: July 2010

Infiltration, drainage, and chemical leaching are strongly influenced by the magnitude and spatial distribution of the field‐saturated soil hydraulic conductivity (Kfs). The Guelph permeameter (GP) method shows promise as an effective means for field measurement of Kfs and its spatial distribution, but its accuracy in medium‐ and fine‐textured soils is not well established. To further assess its accuracy and effectiveness, the GP method was compared with the auger hole (AH) method at the 0.5‐m depth at 68 grid locations in a texturally uniform silty clay soil that had stable but spatially variable structure. The two methods yielded similar geometric mean Kfs values (P < 0.001), as well as similar semivariograms. The two methods were also positively correlated (r = + 0.6565, P < 0.0001). We therefore concluded that the two methods gave equivalent estimates of Kfs at this field site, and that the GP method is capable of providing valid estimates of Kfs in at least some fine‐textured soils. The Kfs values were not correlated with soil texture, organic C content, or soil surface topography, but were negatively correlated (r = −0.7240 for GP method, r = −0.6070 for AH method, P < 0.0001) with antecedent volumetric water content (θa) measured in situ prior to the GP measurements using a down‐hole time domain reflectometry probe. The semivariogram for θa was similar to those for Kfs. These results suggest that the magnitude, range, and pattern of variability of the Kfs measurements were controlled primarily by the well‐developed and stable soil structure at the field site, rather than by texture, organic C content, or surface topography.
Characterization of Water Extracts of Two Manures and Their Adsorption on Soils
Authors: Liang B. C. , Gregorich E. G. , Schnitzer M. , Schulten H.‐R.
Published: July 2010

To uncover possible chemical differences between stockpiled and composted dairy manures, water extracts of these manures were analyzed by 13C nuclear magnetic resonance (NMR) and by pyrolysis‐field ionization mass spectrometry (Py‐FIMS). Judging from the 13C NMR, which took into consideration all of the organic C present, aliphatic and aromatic C in the composted and stockpiled manure extracts were similar but the composted manure extract appeared to be richer in protein C, phenolic C, and carboxylic C and poorer in carbohydrate C than the stockpiled manure extract. Major components of the extract of the stockpiled manure extract determined by Py‐FIMS, which measured only volatile organics, were N compounds > phenols + monolignins > carbohydrates > alkylaromatics > peptides = lipids > lignin dimers > sterols > fatty acids > suberins. On the other hand, the quantitative order of organic components of the composted manure extract was phenols + monolignins > N compounds > carbohydrates > peptides > alkylaromatics > lipids > fatty acids > sterols = lignin dimers > suberins. The relatively low total ion intensity of the water extract of the composted manure and its greater aromaticity suggested that composting increased polymerization and cross‐linking and so led to the formation of larger molecules. Water‐soluble organic C (DOC) extracted from the manures was used to study adsorption isotherms on soils varying in clay content from 3 to 54%. The adsorption of the DOC by the soils increased as the clay and organic matter contents and the surface areas of the soils increased. Increased adsorption of the DOC extracted from the composted manure appeared to be due to increased molecular weights of the major DOC components.
Using Field Data and Simulation Modeling to Determine Nitrogen Cycle Parameters
Authors: Larocque M. , Banton O.
Published: July 2010

The identification of representative parameter values is an important aspect of N modeling because many parameters are unavailable or difficult to evaluate. Reversed modeling was performed using a conceptual simulation model, AgriFlux, and NO3− concentrations from a field near Quebec City, Canada, to identify N cycle parameters. A sensitivity analysis of the model with regard to the unavailable N cycle parameters identified three parameters related to the organic N transformations that largely control soil N dynamics (efficiency of the internal synthesis of the microbial biomass, litter humification fraction, and humus mineralization rate). The available parameters and those of lesser influence were kept constant while various combinations of the three influential parameters were used for the simulations. An optimal parameter set was identified using the root mean square error procedure, and its uniqueness was confirmed by the isocontouring technique. For the site studied, low values of humus mineralization combined with low values for the efficiency of the microbial biomass and small transfers from the litter pool to the humus pool generated the NO3− concentrations that compared the most favorably with the measured values. However, a fitting difference was observed between simulated and measured concentrations that can be imputed to nonoptimized parameters or processes not differentiated in the model.
Diffusion Technique for Preparing Salt Solutions, Kjeldahl Digests, and Persulfate Digests for Nitrogen‐15 Analysis
Authors: Stark John M. , Hart Stephen C.
Published: July 2010

When diffusion techniques are used to prepare samples for 15N analyses, low or variable N recovery is sometimes observed. The effect of low recovery on estimates of 15N enrichment is unknown. Also, the suitability of diffusion techniques for use with a variety of salt solutions and digests containing very low N concentrations (<0.8 mg L−1) has not been determined. We evaluated a diffusion technique where NH3‐N is trapped on acidified filter paper disks that are sealed between two strips of Teflon [polytetrafluoroethylene (PTFE)] tape. Because the PTFE protects the acid trap from neutralization, large volumes of solution can be diffused in plastic specimen containers and the sample can be vigorously mixed during the diffusion period. Six days of diffusion at 22°C resulted in >92% recovery of 50 µg NH+4‐N from 75 mL of 2 M NaCl, total Kjeldahl digests, or 2 M KCl preserved with acid. Leaving sample containers open for 5 d after diffusion for NH+4 completely eliminated contamination of NO−3‐N by residual NH+4; however, recovery of NO−3 was inversely related to the length of the open period. Recovery of NO3−‐N from 0.5 M K2SO4 and alkaline persulfate digests after a 3‐d open period was 90 and 77%, respectively. Complete recovery of NH+4 or NO−3 was not required to obtain accurate estimates of 15N enrichment; however, when recovery was <100%, the method of blank correction was critical. When the mass of N contamination measured in diffusion blanks was used to blank‐correct 15N enrichments, diffused standards often had 15N enrichments that were significantly different from nondiffused standards; however, when the mass of N in blanks was estimated using an isotope dilution equation, there was excellent agreement between diffused and nondiffused standards, regardless of the degree of recovery.