bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Cropping Intensity and Nitrogen Fertilizer Rates on In Situ Nitrogen Mineralization
Authors: Kolberg R. L. , Westfall D. G. , Peterson G. A.
Published: July 2010

Cycling of N through an agroecosystem can be managed more effectively if effects of N management and cropping sequence on soil N microbial processes are understood. Effects of cropping intensity and N fertilizer rate on net soil N mineralization were studied as well as their correlation with precipitation, air temperature and soil water content. Net soil N mineralization was measured by incubating undisturbed soil cores (15‐cm depth) containing anion and cation exchange resins at their bottoms. Cores were incubated during each of five time periods (3–4 wk each) during the fallow phase (mid‐April to mid‐September) of two no‐till cropping systems, wheat (Triticum aestivum L.)‐fallow (WF) and wheat‐corn (Zea mays L.)‐fallow (WCF). Past N fertilizer applications were over four rates with total amounts applied during the previous 6 yr of 0, 95, 190, and 286 kg N ha‐1 in WF and 0, 134, 269, and 403 kg N ha‐1 in WCF. Soils were an Aridic Paleustoll at Sterling and an Aridic Argiustoll at Stratton in eastern Colorado. Total net N mineralization in WCF was half that in WF (22 vs. 43 kg N ha‐1; 2‐site average), probably due to greater immobilization as evidenced by nearly three times greater accumulation of crop residue on the soil surface after 6 yr of no‐till management. Greater conservation of applied N and soil N can be expected in the more intensive WCF system. Total mineralized N increased with N rate by = 0.2 kg ha‐1 for each kg ha‐1 of previously applied N. Precipitation in combination with air temperature and their interaction term gave the best prediction of average daily N mineralization at both sites.
Rapid Changes in Soils Following Eucalyptus Afforestation in Hawaii
Authors: Binkley Dan , Resh Sigrid C.
Published: July 2010

Intensively managed plantations of trees occupy vast areas of the tropics. The productivity of these forests depends strongly on nutrient supply, and nutrient supply may change rapidly under intensive management regimes. We documented changes in a Hawaiian soil after 32 mo of development of a plantation of eucalyptus [Eucalyptus saligna (Sm.)]. Soil C did not change significantly (average = ‐23 g C m‐2 yr‐1 to 30 cm; 95% confidence −139 to +93 g C m‐2 yr‐1). This lack of change in soil C resulted from a rapid loss of older soil C derived from sugarcane (−191 g C m‐2 yr‐1) and a rapid gain of new soil C from eucalyptus (160 g C m‐2 yr‐1). Soil N declined by 19 g N m‐2 yr‐1 (P = 0.08), despite fertilizer additions of 31 to 70 g m‐2. Large reductions in exchangeable Ca and Mg probably resulted from dissolution and leaching of residual lime from prior agricultural management. We conclude that intensive sampling regimes may detect relatively small changes in tropical forest soils, and that expectations of C accumulation in soils following afforestation may need to be reconsidered.
Use of Diffusion to Determine Inorganic Nitrogen in a Complex Organic Matrix
Authors: Mulvaney R. L. , Khan S. A.
Published: July 2010

Serious interference can arise in carrying out quantitative or isotopic analyses of inorganic N in samples having a high content of labile organic N. Studies to evaluate existing Mason jar diffusion methods for interference by a high concentration of various amino acids and amino sugars showed the need to minimize the diffusion period. This was accomplished by increasing the volume of H3BO3‐indicator solution (to 7 mL), and by carrying out diffusions from a fixed volume (10 mL) with a high salt concentration (4 M KCl). Quantitative recovery (≥98%) of 4 mg of NH4‐N was achieved in the presence of 10 mg of organic N, either in 18 h at 25°C, or in 1.5 h by heating on a hot plate at 45 to 50°C. Under the same conditions, complete recovery of NO3‐N and NO2‐N was achieved in the presence of 4 mg of organic N by increasing the amount of Devarda's alloy from 0.3 to 1.5 g. The modified diffusion methods were much more accurate and precise than conventional steam distillation techniques for inorganic N analysis of animal waste or other complex samples treated with labeled NH4‐N, NO3‐N, or NO2‐N. Recovery of the labeled N by diffusion ranged from 96 to 107%, and the coefficient of variation was usually <2%. The isotopic analyses from these diffusions were usually accurate to within 4%, as determined by isotope‐dilution calculations. The latter finding provides ample evidence that no interference arises from labile organic N.
Soil Water Content Determination Using Network Analyzer Reflectometry Methods
Authors: Starr G. C. , Lowery B. , Cooley E. T. , Hart G. L.
Published: July 2010

Time domain reflectometry (TDR) can be a good automated system for measuring soil water content (θv); however, TDR can yield noisy data and cannot measure frequency dependence of the dielectric constant (Ka). Using a network analyzer (NA) with a low‐noise synthesized TDR, parallel‐rod probes, and a resonant waveguide approach, θv was measured from 0.02 to 0.25 m3 m‐3 within the range of 50 to 900 MHz in sand. Below 100 MHz, Ka was higher than it was within the range of 100 to 900 MHz; however, in the 100 to 900 MHz range Ka did not change with frequency. The NA compared favorably with TDR.
Soil Carbon, Nitrogen, and Aggregation in Response to Type and Frequency of Tillage
Authors: Franzluebbers A. J. , Langdale G. W. , Schomberg H. H.
Published: July 2010

Little information exists on the biogeochemical effects of combining no‐tillage planting with paraplowing (to improve deep water penetration) or with secondary tillage (to control weeds). We determined surface residue and soil C and N pools (total, particulate, microbial biomass, and mineralizable) and water‐stable aggregation at depths of 0 to 25, 25 to 75, and 75 to 150 mm from a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults) in Georgia. Soil tillage treatments were a factorial arrangement of tillage type [(i) minimal disturbance with in‐row chisel at planting, (ii) no‐tillage planting with autumn paraplow, and (iii) no‐tillage planting with secondary tillage during the summer] and tillage frequency [(i) every year, (ii) every second year, and (iii) every fourth year]. No‐tillage planting without further disturbance occurred in remaining years. At a depth of 0 to 25 mm, basal soil respiration averaged 9 mg kg‐1 d‐1 with conventional tillage, 27 mg kg‐1 d‐1 with no‐tillage planting and soil disturbance every year, and 36 mg kg‐1 d‐1 with no‐tillage planting and soil disturbance every fourth year. At a depth of 0 to 150 mm, mean‐weight diameter averaged 1.03 mm with conventional tillage, 1.12 mm with paraplow, 1.17 mm with secondary tillage, and 1.23 mm with in‐row chisel. No‐tillage planting with alternative tillage types and frequencies not only improved surface soil properties compared with conventional tillage, but also improved seed cotton yield an average of 19%. Biophysical improvement of surface soil structure would presumably lead to greater water infiltration and improved water use efficiency in the long term.
Parent Material and Vegetation Affect Soil Erosion in Eastern Spain
Authors: Cerdà A.
Published: July 2010

Landscapes in eastern Spain are characterized by a wide range of erosion susceptibility. We hypothesized that parent material and vegetation affect infiltration, runoff, and erosion. Sixty field rainfall simulation trials (55 mm during 1 h on 0.22–0.27 m2 plots) were carried out on soils formed on marl, clay, limestone, and sandstone parent material under three vegetation cover rates: 0 to 20 (bare), 40 to 60 (intermediate), and 80 to 100% (vegetated) in eastern Spain to test this hypothesis. Surface runoff and erosion were related to parent material and vegetation cover. Vegetation enhanced infiltration and reduced surface runoff and erosion, and their variability decreased as vegetation cover increased. For bare soils, the steady‐state infiltration rates ranged from 3 to 55 mm h‐1, the runoff from 0 to 83%, and the erosion rates from 0 to 3720 g m‐2 h‐1. On the vegetated soil, the values were 53 to 55 mm h‐1, 0 to 9%, and 0 to 6 g m‐2 h‐1, respectively, for infiltration, runoff, and erosion rates. Runoff and erosion were greatest for marl soils (0–83% and 0–3720 g m‐2 h‐1, respectively) and intermediate for clay and limestone (0–46% and 0–131 g m‐2 h‐1). Sandstone generated negligible water and soil losses (0–7 % and 0–0.29 g m‐2 h‐1). The interaction of vegetation and parent material showed that, on marl soils, plant cover was the main factor preventing high runoff and erosion rates.
Seasonal Relationships Between Precipitation, Forest Floor, and Streamwater Nitrogen, Isle Royale, Michigan
Authors: Stottlemyer Robert , Toczydlowski David
Published: July 2010

The Upper Great Lakes receive large amounts of precipitation‐NH+4 and moderate NO‐3 inputs. Increased atmospheric inorganic N input has led to concern about ecosystem capacity to utilize excess N. This paper summarizes a 5‐yr study of seasonal N content and flux in precipitation, snowpack, forest floor, and streamwater in order to assess the source of inorganic N outputs in streamflow from a small boreal watershed. Average precipitation N input was 3 kg ha‐1 yr‐1. The peak snowpack N content averaged 0.55 kg ha‐1. The forest floor inorganic N pool was ≈ 2 kg ha‐1, eight times larger than monthly precipitation N input. The inorganic N pool size peaked in spring and early summer. Ninety percent of the forest floor inorganic N pool was made up of NH+4‐N. Forest floor inorganic N pools generally increased with temperature. Net N mineralization was 15 kg ha‐1 yr‐1, and monthly rates peaked in early summer. During winter, the mean monthly net N mineralization rate was twice the peak snowpack N content. Streamwater NO‐3 concentration peaked in winter, and inorganic N output peaked in late fall. Beneath the dominant boreal forest species, net N mineralization rates were positively correlated (P < 0.05) with streamwater NO‐3 concentrations. Forest floor NO‐3 pools beneath alder [Alnus rugosa (Du Roi) Spreng] were positively correlated (P < 0.01) to streamwater NO‐3 output. At the watershed mouth, streamwater NO‐3 concentrations were positively correlated (P < 0.05) with precipitation NO‐3 input and precipitation amount. The relatively small snowpack N content and seasonal precipitation N input compared to forest floor inorganic N pools and net N mineralization rates, the strong ecosystem retention of precipitation N inputs, and the seasonal streamwater NO‐3 concentration and output pattern all indicated that little streamwater NO‐3 came directly from precipitation or snowmelt.
Organic Matter Fractions Contributing to Soil Nitrogen Mineralization Potential
Authors: Curtin Denis , Wen Guang
Published: July 2010

Organic matter pools contributing to N mineralization potential have not been adequately defined. We analyzed 61 soil samples (0–15 cm depth) representing all agroecological regions of Saskatchewan, Canada to determine the relationships between mineralization parameters [i.e., potentially mineralizable N (N0) and the rate coefficient k, measured by aerobic incubation at 35°C for 24 wk] and N fractions defined by a series of chemical and physical extraction procedures. Light‐fraction (LF) organic matter, isolated by flotation on NaI solution at specific gravity 1.7, soluble organic matter measured in saturated paste extracts, and NH4‐N released by two chemical procedures [digestion in 2 M KCl (100°C for 4 h) and steam distillation inphosphate‐borate (PB) buffer at pH 11.2] were evaluated as indices of mineralizable N. Nitrogen released by hot KCl represented 2.5 to 16% of N0, which ranged from 71 to 631 mg kg‐1. Hot KCl N was poorly correlated with N0 (R2 = 0.13, P < 0.01), but it was reasonably well related to N mineralized in the first 2 wk of incubation (R2 = 0.65, P < 0.001), and to dissolved organic matter (R2 = 0.58, P < 0.001). The value of k, which ranged from 0.025 to 0.18 wk‐1, increased as hot KCl N increased as a proportion of N0 (KCl N/N0 accounted for 64% of the variability in k). These results suggest that hot KCl may be selective for the most labile (possibly water‐soluble) organic N. Phosphate‐borate extracted an average of 3.5 times as much N as hot KCl, but relationships with mineralization parameters were generally similar to those found for hot KCl. Light‐fraction N was the largest N pool measured (33–652 mg N kg‐1). It was well correlated with N0 (R2 = 0.83, P < 0.001), but not with N mineralized in the early part of the incubation or with k, indicating that LF N mineralizes slowly compared with chemically extracted N. When LF N was added to PB N, there was roughly enough N in the combined pool to account for N0.
Seasonal and Soil‐Drying Effects on Runoff Phosphorus Relationships to Soil Phosphorus
Authors: Pote D. H. , Daniel T. C. , Nichols D. J. , Moore P. A. , Miller D. M. , Edwards D. R.
Published: July 2010

Controlling phosphorus levels in runoff is often recommended as the best way to minimize eutrophication of streams and lakes. Previous research has shown that increased concentrations of dissolved reactive P (DRP) in runoff from grassland are highly correlated to increased soil test P (STP) levels. We conducted an experiment to investigate the hypothesis that seasonal changes in field conditions (especially soil moisture) along with the practice of air‐drying soil samples prior to analysis may affect such correlations. Grass plots with a wide range of STP were randomly divided into two groups. In May (wet season), soil samples were taken from each plot in the first group, simulated rain was applied (75 mm h−1) to produce 30 min of runoff, and filtered runoff samples were analyzed for DRP. Each soil sample was analyzed for H2O content, sieved (2 mm), and split into two subsamples. One subsample from each plot was kept field‐moist at 4°C, and the other was air dried. Phosphorus saturation was determined only on air‐dry soil, but all soil subsamples were analyzed by Mehlich III and distilled H2O methods. In August (dry season), the second group of plots received the same treatment. All correlations of STP to runoff DRP were significant (P < 0.01), regardless of season or STP method. Water‐extractable STP from air‐dry soil and Mehlich III STP were not affected by season, but DRP concentration in August runoff was almost double that in May , so the resulting correlations were affected. Water‐extractable STP from field‐moist soil was higher in August than in May , and P saturation levels showed a similar trend. Runoff volumes were smaller in August, so season had little effect on mean DRP–mass loss.
Phosphorus Transformations and Their Relationships with Calcareous Soil Properties of Southern Western Australia
Authors: Samadi Abbas , Gilkes R. J.
Published: July 2010

The agronomic effectiveness of phosphate fertilizers is strongly affected by reactions of P with soil constituents. The transformation of P added to soil and the effect of soil properties on these transformations was investigated for 14 alkaline and calcareous soils from southern Western Australia. The decline of NaHCO3‐extractable P (Olsen‐P) with time followed a second order kinetic equation. The kinetic rate constant (k) increased with increasing oxalate‐extractable Fe (Feo), citrate–dithionite–bicarbonate (CDB)‐extractable Al and Fe (Ald and Fed), CaCO3‐free clay content, cation‐exchange capacity (CEC), and ratio of CDB‐extractable Fe (Fed) to active CaCO3 equivalent (ACCE), and k decreased with increasing ACCE. A combination of these soil properties described 93% of the variation in rate constant, of which 78% of the variation was predicted by the Fed/ACCE ratio alone. A combination of clay related properties (Ald, clay, Feo, and CEC) described 62% of the variation in Ca2–P determined by specific extraction. Carbonate‐related properties (ACCE and CCE) together described 71% variation in Ca8–P. Clay‐related and carbonate‐related properties jointly described 97% and 81% of the variation in Fe–P and Olsen‐P respectively. Surface area (SA) and Ald together accounted for 43% of the variation in Al–P. Scanning electron microscopy analyses showed that added P was uniformly distributed in the soil matrix to the limit of the spatial resolution of the technique (≈2 μm).
Dissolution Kinetics of Hornblende in Organic Acid Solutions
Authors: Zhang Hailin , Bloom Paul R.
Published: July 2010

The dissolution rates of most primary and secondary minerals are promoted by the presence of proton‐ and complex‐forming ligands. Effects on the rates of dissolution of hornblende by naturally occurring organic acids at concentrations commonly encountered in soil solutions and surface waters was studied in a pH 4.0, 0.01 M HOAc–LiOAc buffer. Crushed hornblende samples were purified by magnetic and density separation, followed by an initial period of weathering in a buffered aqueous solution for 39 d. After the initial weathering the rate of dissolution was measured at different concentrations of citric, oxalic, polygalacturonic, tannic, and fulvic acids at pH 4.0 for another 32 d in a batch‐type reactor. Although nearly linear kinetics were observed for the release of Si, the release of Al, Fe, and Mg decreased with time. The dissolution was nonstoichiometric during the study period with preferential release of Al, Fe, and Mg relative to Si. All ligands studied were found to accelerate the dissolution process and the rates increased with solution concentrations of organic acids. The reaction orders with respect to dissolved organic C were generally low, ranging from near zero to 0.37 for different organic acids. At a concentration of 2.5 mM of dissolved C the relative effectiveness of these ligands on promoting dissolution was oxalic > citric > tannic > polygalacturonic > fulvic acid. The strengths of organic acids to promote dissolution is related to the quantity of phenolic and carboxylic functional groups present on the organic compounds, and it is related to the strength of the metal–ligand complex formed in solution or on the mineral surface.
Subsurface Migration of Copper and Zinc Mediated by Soil Colloids
Authors: Karathanasis A. D.
Published: July 2010

Colloid migration in subsurface environments has attracted special attention lately because of its suspected role in facilitating transport of contaminants to groundwater. This study investigated the potential role of water‐dispersible soil colloids (WDCs) with variable composition in transporting Cu and Zn through undisturbed soil columns. Copper or Zn solutions without colloids (controls) and combined with suspensions of montmorillonitic, mixed, illitic, and kaolinitic colloids with a range of surface properties were applied at a constant flux into undisturbed soil columns. The soil columns represented upper solum horizons of Maury (fine, mixed, mesic Typic Paleudalf) and Loradale (fine‐silty, mixed, mesic Typic Argiudoll) soils with contrasting porosities and organic C (OC) contents. Colloid and metal recoveries in the eluent varied with metal, colloid, and soil properties. The presence of colloids typically enhanced metal transport by 5‐ to 50‐fold over that of the control treatments, with Zn being consistently more mobile than Cu. The greatest metal transport potential was shown by colloids with high negative surface charge and OC content and the lowest by colloids with large particle size, low negative surface charge, and high Fe‐ and Al‐hydroxyoxide contents. Although the dominant transport mechanism was metal sorption by colloids and cotransport, the additional soluble Cu and Zn transported in the presence of colloids suggests involvement of physical exclusion, competitive sorption, or increased metal solubilization processes. Increased amounts of OC content in the soil column appeared to overshadow the effects of macroporosity on the transport of both metals, especially Cu. These findings have important ramifications on the use of contaminant transport prediction models and the application of efficient remediation technologies.
Modeling Aluminum and Organic Matter Solubility in the Forest Floor Using WHAM
Authors: de Wit Helene A. , Kotowski Marek , Mulder Jan
Published: July 2010

Several studies suggest that solution concentrations of Al in organic surface soils are controlled by complexation with organic matter. We applied the mechanistic Windermere humic aqueous model (WHAM) to describe the solubility of Al and organic matter as observed in a batch equilibrium study with a forest floor Oe horizon. WHAM is unique in that it considers interactions of soil organic matter with protons and metals. We also compared WHAM with a previously proposed linear regression model that describes Al solubility. A range of soil Al contents was established by adding different amounts of Al in batch prior to titration with acid or base. The soil Al content was described by the bound Al ratio (BAR), defined as the equivalent ratio of organically bound Al and carboxyl groups. The bound Al ratio and pH ranged from 0.1 to 3, and from 1.7 to 6.3, respectively. Solutions were undersaturated with respect to Al(OH)3, except at BAR ≥ 2 and pH ≥ 4.5. Aluminum solubility increased with increasing BAR. Organic matter solubility was greatest at low BAR and high pH. WHAM reproduced the observed pH and Al concentrations, using parameters derived from experimental data. At BAR < 0.7, pH–pAl relationships were approximately linear. At BAR ≥ 0.7, there was a nonlinear increase in ΔpAl/ΔpH with pH. WHAM simulated the changing slope of the pH–pAl curves satisfactorily and reproduced observed trends in dissolved organic C (DOC) concentrations. This supports the hypotheses and assumptions concerning mechanisms for binding Al to soil organic matter in a forest floor, as embodied in WHAM.
Magnesium‐ and Silicon‐Induced Phosphate Desorption in Smectite–, Palygorskite–, and Sepiolite–Calcite Systems
Authors: Shariatmadari H. , Mermut A. R.
Published: July 2010

Carbonates are one of the most important group of minerals that fix phosphates in soils. Magnesium and silicon are known to reduce the P fixation of calcite. The effect of Mg and Si addition on P sorption–desorption of a mixture of 90% clay and 10% calcite was studied. The mixtures were montmorillonite–calcite (Mont–CaCO3), palygorskite–calcite (Pal–CaCO3), and sepiolite–calcite (Sep–CaCO3). Concentrations of 0.0, 5.0, and 10.0 mg L−1 of dissolved Mg or Si were introduced into P sorbing systems. The chemical speciation of P sorption solutions was predicted using the SOILCHEM computer program. Desorption of sorbed P on different samples was studied in successive extractions with 0.01 M KCl. The P sorption of Mont–CaCO3, Pal–CaCO3, and CaCO3 were similar (≈10 cmol kg−1). Addition of 10.0 mg L−1 Mg or Si sharply reduced the P sorption of calcite to <1 cmol kg−1, while it induced only a 20% reduction in P sorption of the mixtures. Magnesium and silicon treatments increased the desorption of sorbed P. The Sep–CaCO3 mixture showed a P sorption 60% lower than that of pure CaCO3 The desorption of sorbed P by Sep–CaCO3 was far above that of other clay–CaCO3 combinations. Addition of Mg and Si inhibited the formation of Ca–phosphates, which would otherwise make major contributions to P retention in all samples used in this study. Phosphate sorbed by silicate clays was the second major fraction of retained P, limiting the effects of Mg and Si treatments. As a slow release source of Mg and Si, sepiolite increased the desorption of P sorbed by CaCO3 This has an important implication for P availability in arid soils containing sepiolite. This mineral may be mixed thoroughly with commercial P fertilizers before P application into soil.
Fractionation of Phosphorus in a Mollisol Amended with Biosolids
Authors: Sui Yaobing , Thompson Michael L. , Shang Chao
Published: July 2010

Information about soil P fractions is useful to predict the bioavailability of P in soil as well as to predict the likelihood of its transport. In this study, we used a sequential fractionation procedure to investigate the forms of P in a Mollisol amended at the soil surface with biosolids (i.e., anaerobically digested sewage sludge). Soil samples from three depths (0–5, 5–20, and 20–35 cm) were collected from a Cumulic Vertic Endoaquoll in a field experiment with three biosolid application rates, two vegetation treatments [hybrid poplar–cottonwood trees (Populus × euramericana — clone NC‐5326) and switchgrass (Panicum virgatum L.)], and four replications per treatment. The Hedley fractionation scheme (dividing soil P into six empirical fractions [water‐soluble, NaHCO3‐soluble inorganic and organic P; NaOH‐soluble inorganic and organic P; HCl‐soluble P, and residual P)] was employed. After 6 yr of continuous application of biosolids to poplar plots, the absolute concentrations of all P fractions at the 0‐ to 5‐cm depth increased significantly (P < 0.05). Some P fractions at the 5‐ to 20‐cm depth increased significantly, whereas at the 20‐ to 35‐cm depth, none of the fractions was affected by biosolids amendment. At the 0‐ to 5‐cm depth of both poplar tree and switchgrass plots, the relative concentrations of some of the P fractions (e.g., HCl–P, NaOH–OP, and residual P) decreased rather than increased. Because NaHCO3–IP and H2O–P increased in the biosolids‐amended soil at rates disproportionate to their concentrations in the biosolids, we conclude that HCl–P applied with biosolids was transformed to more labile forms.
Separating Soil Respiration into Plant and Soil Components Using Analyses of the Natural Abundance of Carbon‐13
Authors: Rochette P. , Flanagan L. B. , Gregorich E. G.
Published: July 2010

In presence of vegetation, the CO2–C produced by respiration activity in soils originates from plant C (rhizosphere respiration, Rrh) and from soil C (soil respiration, Rs). Quantitative estimates of the CO2 produced by each source are required in many studies of C dynamics in the soil–plant system. In this study, we (i) used measurements of the 13C value of soil CO2 to separate total soil respiration (Rt) into subcomponents Rrh and Rs in a maize (Zea mays L.) field under undisturbed conditions and (ii) compared these Rrh estimates with values obtained using the root‐exclusion approach. The maximum contribution of Rrh to total respiration was 45%, observed in August. Estimates of Rrh increased from zero 30 d after planting to 2 g CO2–C m−2 d−1 70 d after planting, remained relatively constant at that level in August, and then decreased until the end of the growing season. The total C losses as Rrh were 17% of the crop net assimilation. Estimates of Rs gradually declined from 3.3 g CO2–C m−2 d−1 in late June to 1.4 g CO2–C m−2 d−1 at the end of the season. Losses of soil C represented ≈6% of total soil C. Variable values of δ13C of the soil CO2 in the control plot after Day 250 made the technique less reliable late in the season. However, several observations indicated that the approach has potential to provide quantitative estimates of Rrh and Rs First, the seasonal pattern of the Rrh estimates coincided with that of the plant growth and physiological activity. Second, the cumulated Rrh across the growing season agreed well with published data obtained using 14C labeling techniques. Third, in the maize plot, variation in the estimated Rs was closely correlated with changes in soil temperature with a Q10 of 1.99 Finally, the estimates of Rrh obtained using the isotopic approach agreed well with those obtained using the root exclusion technique.
Aggregation and Organic Matter Decomposition in Soils Amended with De‐Inking Paper Sludge
Authors: Chantigny Martin H. , Angers Denis A. , Beauchamp Chantal J.
Published: July 2010

De‐inking paper sludge (DPS) has been traditionally disposed of by burning or landfilling, but could be used as an organic amendment in agricultural soils. Our objective was to assess the impact of DPS incorporation on organic matter and aggregation of a clay loam (Typic Dystrochrept) and a silty clay loam (Typic Humaquept). Whole soil C, particulate (>53 μm) and light fraction (density <1.8 Mg m−3) C, and water‐stable aggregation were measured periodically during a 3‐yr period after a single application of DPS at rates of 0 (control), 50, and 100 Mg ha−1 Microscopic observations of water‐stable aggregates were also performed. Adding DPS increased whole soil C content, which remained greater than in the control for the duration of the study. After 2 yr, about 40% of the initial material remained in the soil. The proportion of residual C attributed to DPS and present in the particulate fraction remained constant at 70 to 90% during the first 2 yr of the study, whereas the proportion of residual C present in the light fraction decreased from >95% for fresh DPS to <50% after 2 yr. One year after incorporation of DPS, the proportion of water‐stable aggregates >1 mm was 2 to 6 times larger in amended soils than in the control. This effect was still statistically significant after 3 yr. Microscopic observations revealed that DPS formed into clusters of wood fibers which became encrusted with mineral particles. We hypothesized that this encrustation provided physical protection to the decaying DPS which remained particulate (>53 μm) in size and progressively densified to >1.8 Mg m−3 As a result, water‐stable macroaggregates were formed with DPS as a central core.
Using an Ion Sink to Extract Microbial Phosphorus from Soil
Authors: Myers R. G. , Thien S. J. , Pierzynski G. M.
Published: July 2010

Two ion sinks (FeO‐coated paper and anion exchange resin membrane) were tested to improve accuracy and precision in analysis of microbial P (Pm) in soil biomass. We used a noncarcinogenic biocide, hexanol. Ion‐sink extracted FeO‐Pm [Pm(FeO)] and resin‐Pm [Pm(Res)] were compared with bicarbonate extracted Pm [Pm(Bic)]. Fractional recovery of Pm (Kp) was determined with 50 μg Pm from five different organisms, first, from preparations without soil, giving Kp of 0.49 for Pm(Bic), 0.63 for Pm(FeO), and 0.66 for Pm(Res), and second, from soil‐organism mixes, giving Kp of 0.36 for Pm(Bic), 0.49 for Pm(FeO), and 0.52 for Pm(Res) This indicated ion sinks can improve accuracy of Pm recovery. We tested 18 Kansas soils with three different levels of C + N substrates to provide varying levels of microbial activity. For unamended soils, Pm values (mg kg−1) were 5.9 for Pm(Bic), 8.2 for Pm(FeO), and 6.3 for Pm(Res) Corresponding values in soils with low levels of C + N amendments were 6.0 for Pm(Bic), 18.2 for Pm(FeO), and 18.7 for Pm(Res) In soils with high levels of C + N amendments plus alfalfa (Medicago sativa L.), corresponding values were 12.7 for Pm(Bic), 30.9 for Pm(FeO), and 37.3 for Pm(Res) Above 10.0 mg kg−1, Pm(FeO) and Pm(Res) were at least twice as much as Pm(Bic) In addition, Pm(FeO) and Pm(Res) both had lower CVs than Pm(Bic), indicating greater precision by the ion‐sink methods.
Subaqueous Soils Pedogenesis in a Submersed Environment
Authors: Demas George P. , Rabenhorst Martin C.
Published: July 2010

Proposals for the inclusion of permanently submersed materials in soil taxonomic systems have periodically been put forth since some time in the mid 1800s. The proposals were largely conceptual in nature, relying more on subjective reasoning rather than analytical and field data. Advances in computer and global positioning technology, and the continuing development of the discipline of pedology provided the opportunity to examine shallow water estuarine sediments within a pedological framework. Morphological and analytical data from 85 1.5‐ to 2.0‐m profiles from Sinepuxent Bay, Maryland, indicate that the four pedogenic processes of additions, losses, transformations, and transfers outlined in the generalized theory of soil genesis are active in a subaqueous environment. The evidence of pedogenic processes includes the addition of biogenic calcium carbonate (shells), organic fragments, and organic matter; the loss of organic matter and surficial material; the transfer of oxygen through diffusion and bioturbation processes; and the transformation of humic substances and sulfur (sulfidization). The change in the concept of estuarine substrates from sediment to soil has significant ramifications for pedologists, ecologists, estuarine researchers, and government agencies involved in soil resource inventory and estuarine restoration programs. Application of these concepts could help further our understanding of the relationships between subaqueous soil distribution and submersed aquatic vegetation (SAV); clam, scallop, and oyster habitat; and dredge sites with potential acid‐sulfate weathering. This work resulted in a change to the definition of soil in Soil Taxonomy to include subaqueous soils that are capable of or presently support rooted SAV.
Carbon and Nitrogen Conservation in Dryland Tillage and Cropping Systems
Authors: Schomberg Harry H. , Jones Ordie R.
Published: July 2010

Soil C and N greatly influence long‐term sustainability of agricultural systems. We hypothesized that cropping and tillage differentially influence dryland soil C and N characteristics in the Southern High Plains. A Pullman clay loam (fine, mixed, thermic Torrertic Paleustol) cropped to wheat (Triticum aestivum L.)–sorghum [Sorghum bicolor (L.) Moench]–fallow (WSF), continuous wheat (CW) and continuous sorghum (CS) under no‐tillage (NT), and stubble mulch (SM) was sampled at three depths to determine soil C and N characteristics. For CW, CS, and WSF phases (FWSF, SWSF, WWSF), soil organic C (SOC) averaged 10.6 to 13.1 kg m−3 and was greatest for CW. Carbon mineralization (CMIN) at 0 to 20 mm was 30 to 40% greater for CW and FWSF than for CS, SWSF, or WWSF Cropping system by depth influenced soil organic N (SON) with greatest SON at 0 to 20 mm in CW (1.5 kg m−3). At 0 to 20 mm for SM and NT, SOC was 9.9 and 12.5 kg m−3, soil microbial biomass C (SMBC) was 0.80 and 1.1 kg m−3, and soil microbial biomass N (SMBN) was 0.14 and 0.11 kg m−3 Also at 0 to 20 mm, NT had 60% greater CMIN, 11% more SMBC as a portion SOC, and 25% more SON compared to SM. Summed for 0 to 80 mm, NT had more SOC (0.98 vs 0.85 kg m−2) and SON (0.10 vs 0.9 kg m−2) than SM, and CW had greater or equal C and N activity as other systems. Negative correlations between yield and SOC, SMBC, CMIN, SON, and SMBN indicate N removal in grain negatively affects active and labile C and N pools. Under dryland conditions, C and N conservation is greater with NT and with winter wheat because of less soil disturbance and shorter fallow.
Characterization of Sugar Beet Seedbed Structure
Authors: Aubertot J.N. , Dürr C. , Kiêu K. , Richard G.
Published: July 2010

Little information is available on the distribution and shape of aggregates or their spatial arrangement within seedbeds, although it influences crop emergence. The aim of this study was to obtain quantitative information on seedbed structure by sampling soil layers, sieving, surface photographs, and stereological analysis of embedded sample sections. Seedbeds prepared with a combined implement (spring tine cultivator and rollers) in a silt loam soil (Typic Hapludalf) with two seeders (K and Pl) on plowed (P), not plowed (NP), and not plowed and compacted (NPC) plots, were analyzed. Aggregates were described by measurements of L, l, h, the longest, intermediate and shortest axes and visually classified according to their surface roughness (smooth, 0; to rough, 4). The D fitting parameter of the power‐law aggregate size distribution after seeding was significantly smaller (3.4) on NPC than on the other plots (3.8–4.0). The aggregate aspect ratios (l/L and h/L) did not vary with aggregate size or plot, their overall means were 0.77 and 0.55 respectively. Aggregates of roughness classes >2 were 28 to 32% on NPC and NP plots, compared with 74% on P plot. Seeders reduced the number of aggregates >10 mm by one‐third compared with the values before seeding. Seeder K placed over 60% of the aggregates > 20 mm on the soil surface. Aggregates were uniformly distributed across the row by K seeder and away from the center of the row by Pl seeder. The information obtained will be used in a computerized seedbed generator.
Morphological Characteristics of Macropores and the Distribution of Preferential Flow Pathways in a Forested Slope Segment
Authors: Noguchi Shoji , Tsuboyama Yoshio , Sidle Roy C. , Hosoda Ikuhiro
Published: July 2010

Water flow through soil macropores is important in determining hydrologic responses in forested watersheds. Morphological characteristics of macropores and distribution of preferential flow pathways were evaluated in a forest hillslope segment using a combination of staining agents. Almost 80% of described macropores were roughly elliptical with eccentricities ranging from 0.256 to 0.998 (mean of 0.652) and lengths ranging from 2.0 to 61.8 cm (mean of 11.6 cm). Tortuosity of macropores tended to increase with increasing length up to about 30 cm, with a mean value of 1.14. Macropores were aggregated in large clumps within the soil profile. Living and decayed roots and associated vertical zones of loose soil and humus contributed to preferential flow pathways in this soil. Subsurface flow patterns, detected by upslope injection of dilute white paint solution, showed a strong interaction between the soil matrix and macropores. Subsurface flow was lateral along the bedrock and between A and B horizons, with a perched water table occurring on sections of both. Dye tests also showed that flow occurred within surface bedrock fractures. This fracture flow was sometimes connected to macropores through zones of local wetness. Thus, we conclude bedrock topography and fracture characteristics may contribute significantly to preferential flow pathways at the hillslope scale. Even though individual macropores were rather short, the coupling of these flow paths with the soil matrix, bedrock fractures, living and decayed roots, and perched water tables produced complex networks of interconnected preferential flow pathways, all of which help explain the stormflow response observed in the catchment.
Three‐Dimensional Quantification of Macropore Networks in Undisturbed Soil Cores
Authors: Perret Johan , Prasher S. O. , Kantzas A. , Langford C.
Published: July 2010

The role of macropores in soil and water processes has motivated many researchers to describe their sizes and shapes. Several approaches have been developed to characterize macroporosity, such as the use of tension infiltrometers, breakthrough curve techniques, image‐analysis of sections of soils, and CAT scanning. Until now, efforts to describe macropores in quantitative terms have been concentrated on their two‐dimensional (2‐D) geometry. The objective of this study is to nondestructively quantify the three‐dimensional (3‐D) properties of soil macropores in four large undisturbed soil columns. The geometry and topology of macropore networks were determined using CAT scanning and 3‐D reconstruction techniques. Our results suggest that the numerical density of macropores varies between 13421 to 23562 networks/m3 of sandy loam soil. The majority of the macropore networks had a length of 40 mm, a volume of 60 mm3, and a wall area of 175 mm2 It was found that the greater the length of networks, the greater the hydraulic radius. The inclination of the networks ranged from vertical to an angle of ≈55° from vertical. Results for tortuosity indicated that most macropore networks had a 3‐D tortuous length 15% greater than the distance between their extremities. More than 60% of the networks were made up of four branches. For Column 1, it was found that 82% of the networks had zero connectivity. This implies that more than 4/5 of the macropore networks were composed of only one independent path between any two points within the pore space.
Dual Thermal Probes near Plane Interfaces
Authors: Kluitenberg G. J. , Philip J. R.
Published: July 2010

The dual probe estimates the thermal properties of soils. Because it is strongly dependent on water content, volumetric heat capacity is useful for moisture estimation. A previous study of probe errors due to soil heterogeneity is taken further with the aid of a new solution for instantaneous line sources near a plane interface between two regions. The solution allows for different conductivities and heat capacities in the regions, but requires uniform diffusivities. This condition holds reasonably well near wetting fronts in a range of soils. Previous error bounds are confirmed and sharpened. The conclusion in the previous study that errors are small when the heterogeneity is no closer to the probes than the probe separation (typically 0.006 m) is reinforced. The expectation that the dual probe gives good resolution of water content close to fronts and interfaces is strengthened.
Assessment of Isotopically Exchangeable Zinc in Polluted and Nonpolluted Soils
Authors: Sinaj S. , Ma¨chler F. , Frossard E.
Published: July 2010

In this study, an isotope exchange kinetics (IEK) approach was used to study soil Zn exchangeability in five polluted and six nonpolluted soils. Results were used in a compartmental analysis to quantify the amount of Zn isotopically exchangeable within 1 min, the amount of Zn exchangeable between 1 min and 15 d, and the amount of Zn that could not be exchanged within 15 d. Results derived from short‐term IEK experiments (100 min) allowed for a precise prediction of the increase of exchangeable Zn throughout 15 d in most of the soils studied. The compartmental analysis conducted on the 11 samples allowed clear separation of the polluted from the nonpolluted soils and showed that most of the soil Zn is either very slowly or not at all exchangeable. The proposed approach yielded simultaneously the intensity factor, the quantity factor, and a parameter related to soil properties governing Zn sorption onto soil [r(1)/R]. The amount of Zn exchangeable within 15 d was found to be very close to Zn extractable by 0.005Mdiethylene triamine pentaacetic acid (DTPA) + 0.01MCaCl2+ 0.1Mtriethanolamine (TEA) (ZnDTPA) in all soils, suggesting that both methods were characterizing the same pool of soil Zn.
Adsorption Effects on Kinetics of Aldicarb Degradation Equilibrium Model and Application to Incubation and Transport Experiments
Authors: Guo Lei , Wagenet Robert J. , Jury William A.
Published: July 2010

The assumption of equilibrium adsorption was applied to both batch incubation and soil column leaching experiments to estimate degradation rate constants of the pesticide aldicarb [2‐methyl‐2‐(methylthio) propionaldehyde o‐(methylcarbamoyl) oxim] in the liquid (μl) and sorbed (μs) phases. The estimation was based on the observed Kd–μ relationship yielded in a soil amended with various amounts of activated C (AC), where Kd is the adsorption coefficient, and μ is the composed degradation rate constant from both phases. The inverse dependence of aldicarb degradation on Kd reveals that μl is faster than μs For batch incubation experiments, the calculated μl and μs were 0.1228 and 0.0019 d−1, respectively, differing by a factor of 65. In continuous‐flow columns, μl and μs were both increased, with an estimated value of 0.2063 and 0.0055 d−1, respectively, resulting in an accelerated overall degradation rate of aldicarb by 181% compared with the batch reactors. The results of our study indicate that, although degradation of aldicarb occurred primarily in the soil solution, it did not cease completely on the sorbed chemicals. The relative contributions of the two phases to the total degradation were therefore dependent on both the adsorption coefficient and the relative degradation rate constants for the dissolved and sorbed chemicals.
Screening for Plant Growth–Promoting Rhizobacteria to Promote Early Soybean Growth
Authors: Cattelan A. J. , Hartel P. G. , Fuhrmann J. J.
Published: July 2010

Although many studies have been conducted to identify the specific traits by which plant growth–promoting rhizobacteria (PGPR) promote plant growth, usually they were limited to studying just one or two of these traits. We selected 116 isolates from bulk soil and the rhizosphere of soybean [Glycine max (L.) Merr.] and examined them for a wide array of traits that might increase early soybean growth in nonsterile soil (PGPR traits). A subsample of 23 isolates, all but one of which tested positive for one or more of these PGPR traits, was further screened for traits associated with biocontrol, (brady)rhizobial inhibition, and rhizosphere competence. Six of eight isolates positive for 1‐aminocyclopropane‐1‐carboxylate (ACC, a precursor of ethylene) deaminase production, four of seven isolates positive for siderophore production, three of four isolates positive for β‐1,3‐glucanase production, and two of five isolates positive for P solubilization increased at least one aspect of early soybean growth. One isolate, which did not share any of the PGPR traits tested in vitro except antagonism to Sclerotium rolfsii and Sclerotinia sclerotiorum, also promoted soybean growth. One of the 23 isolates changed bradyrhizobial nodule occupancy. Although the presence of a PGPR trait in vitro does not guarantee that a particular isolate is a PGPR, the results suggest that rhizobacteria able to produce ACC deaminase and, to a lesser extent, β‐1,3‐glucanase or siderophores or those able to solubilize P in vitro may increase early soybean growth in nonsterile soil.
Erosion Mechanics of Soils with an Impermeable Subsurface Layer
Authors: Froese Jane C. , Cruse Richard M. , Ghaffarzadeh Mohammadreza
Published: July 2010

More than 50% of annual soil loss in a number of temperate regions of the world occurs when frozen soils are thawing. Such losses occur as a consequence of relatively high surface soil water contents due to the presence of a subsurface impermeable layer. This laboratory study addressed the soil mechanical principles governing erosion of soils with an impermeable subsurface layer (frozen or compacted, etc.). We examined (i) the effect of a freeze–thaw cycle on soil cohesion and (ii) the effect of a subsurface impermeable layer on soil detachment during raindrop impact for two soils: a Galva loess (silty clay loam, mixed, mesic Typic Hapludoll) and a Nicollet glacial till (loam mixed, superactive mesic Aquic Hapludoll). A Mohr diagram was constructed, based on a series of triaxial tests at three matric potentials. Soil cohesion for each treatment was determined from the Mohr diagrams. Soil water content treatments of 0.15 and 0.25 g g−1 were imposed before freezing and thawing. The freeze treatment was 90 min at −12°C, followed by a 30‐min thaw period. Immediately thereafter, shear strength and detachment were measured. Soil cohesion values were <50 kg m−2 and were not affected by freezing or by water content‐at‐freezing. The single‐water‐drop detachment values for soils with an impermeable layer vs. without an impermeable layer increased from 0.016 ± 0.0065 g to 0.054 ± 0.0265 g for loess and 0.036 ± 0.0071 g to 0.145 ± 0.0635 g for till. With an impermeable subsurface layer, soil matric potential is driven towards 0 Pa, resulting in extremely weakened soils prone to high soil‐detachment values and quite likely high soil‐erosion losses.