Showing papers in "Soil Science in 2003"

Achieving soil carbon sequestration in the united states: a challenge to the policy makers

Abstract: Carbon (C) sequestration in soil implies enhancing the concentrations/pools of soil organic matter and secondary carbonates. It is achieved through adoption of recommended management practices (RMPs) on soils of agricultural, grazing, and forestry ecosystems, and conversion of degraded soils and dra

Transport and Fractionation of Dissolved Organic Matter in Soil Columns

Abstract: Dissolved organic matter (DOM) is a heterogeneous mixture of organic compounds that plays an important role in the movement of DOM-associated pollutants. In this study, transport and fractionation of DOM in soils was investigated in flow-through soil columns. Dissolved organic matter derived from spent mushroom substrate weathering was pumped through packed columns (2.5 cm × 10 cm) comprising a coarseloamy subsoil (mixed, semiactive, mesic Typic Hapludult), and effluents were monitored for changes in the composition of DOM. Effluent DOM was characterized for UV absorbance, molecular weight, acidity, and hydrophilicity. Transport through the columns resulted in preferential retention of specific DOM constituents as indicated by comparison with a Br - tracer. During the transport process, effluent DOM exhibited decreasing values of E 2 /E 3 (from 10.3 to 6.2), acidity (from 20.8 to 13.1 mmol c g -1 C), and hydrophilicity (39.0 to 28.4%), and increasing values of molar absorptivity (from 164 to 310 L mol -1 C cm -1 ) and number and weight-averaged molecular weight (from 1770 to 3150 and 2450 to 4180 Da, respectively). These results indicate that DOM fractions with higher molecular weight, higher molar absorptivity, lower E 2 /E 3 ratio, lower acidity, and lower hydrophilicity were adsorbed preferentially by soil minerals, whereas the inverse fractions were transported preferentially. The adsorbed DOM could not be completely desorbed by DOM-free background solution, indicating a strongly bound fraction. Sorptive fractionation of DOM during transport likely affects the transport behavior of DOM-complexed constituents.

Field evaluation and performance comparison of soil moisture sensors

Abstract: Agricultural producers who choose to supplement their crops’ water requirement are able to determine irrigation scheduling practices better when the soil water content of their fields is known. The objective of this study was to statistically evaluate numerous sensors for their ability to accurately estimate water content in a 90-cm soil profile, based on calibrated neutron probe measurements. The sensors tested were Irrometers, Watermarks, EnviroScan, Troxler Sentry, AquaTel, AquaFlex, Trime, AquaPro, and GroPoint. The sensors were field tested at different water content levels and a variety of irrigation frequencies over a 3-year period in a Warden silt loam soil (Coarse-silty, mixed, mesic, Xerollic Camborthids) planted to alfalfa. The default factor calibration was used to estimate the soil water content from all sensors except the neutron probe, which was calibrated for the soil using the gravimetric moisture content method. The Irrometer and Watermark sensors utilized a local soil water retention relationship in order to convert soil water potential into volumetric water content. The results suggest that most sensors were able to follow the general trends successfully as soil water content changed during the growing season, and there was significant correlation between the sensors and the neutron probe readings. Although sensor trends were similar, visual and statistical analyses indicated that the actual measured values varied significantly between the sensors and the calibrated neutron probe measurements. Therefore, a soil specific calibration of each sensor would have been necessary to obtain a high degree of absolute accuracy in soil water content measurements. The results suggest that irrigators can still use uncalibrated sensors to improve their watering schedules by setting irrigation trigger points that may relate only to a specific sensor in a specific soil. These trigger points cannot easily be related to different soils, different sensors, and other sources of information such as extension fact sheets and research publications, however, because the actual water content measurements may not be correct.

Quantification of myo-inositol hexakisphosphate in alkaline soil extracts by solution 31P NMR spectroscopy and spectral deconvolution

Abstract: Inositol phosphates are the dominant class of organic phosphorus (P) compounds in most soils, but they are poorly understood because they are not easily identified in soil extracts. This study reports a relatively simple technique using solution 31P NMR spectroscopy and spectral deconvolution for the quantification of myo-inositol hexakisphosphate (phytic acid), the most abundant soil inositol phosphate, in alkaline soil extracts. An authentic myo-inositol hexakisphosphate standard added to a re-dissolved soil extract gave signals at 5.85, 4.92, 4.55, and 4.43 ppm in the ratio 1:2:2:1. Spectral deconvolution quantified these signals accurately (102 ± 4%) in solutions containing a mixture of model P compounds by resolving the envelope of signals in the orthophosphate monoester region. In NaOH-EDTA extracts from a range of lowland permanent pasture soils in England and Wales, concentrations of myo-inositol hexakisphosphate determined by spectral deconvolution ranged between 26 and 189 mg P kg- 1 soil, equivalent to between 11 and 35% of the extracted organic P. Concentrations were positively correlated with oxalate-extractable aluminum and iron but were not correlated with total carbon, total nitrogen, clay, or the microbial biomass. This suggests that myo-inositol hexakisphosphate accumulates in soils by mechanisms at least partially independent of those controlling organic matter stabilization and dynamics. Furthermore, myo-inositol hexakisphosphate concentrations were positively correlated with plant-available inorganic P and negatively correlated with the carbon-to-organic P ratio, suggesting that biological P availability may, in part, regulate myo-inositol hexakisphosphate concentrations in soils, perhaps because organisms capable of degrading this compound are favored in more P-limited environments. Solution 31P NMR spectroscopy and spectral deconvolution offers a relatively simple method of quantifying myo-inositol hexakisphosphate in soil extracts.

Land use and management impacts on structure and infiltration characteristics of soils in the north appalachian region of ohio

Abstract: Effects of land use and management treatments on soil mechanical and hydrological properties were assessed by analysis of bulk and core soil samples and water infiltration measurements in the field, using double ring infiltrometers in five plots located at the experimental farm of the North Appalachian Experimental Watersheds (NAEW) near Coshocton, Ohio. The five treatments were no-till without manure (NTWM), no-till with manure (NTM), no-till corn (Zee mays)-soybean (Glycine max) rotation (NTCSR), conventional tillage (CT), and meadow (M). Treatments significantly influenced water infiltration characteristics, soil bulk density (p b ), aggregation, and mean weight diameter (MWD). The maximum cumulative infiltration after 3 h (I) of 109.3 ± 29.0 cm (average of 9 measurements at 3 landscape positions) was measured for the NTM treatment and the lowest of 27.7 ± 21.0 cm (average of 3 measurements at shoulder slope or S) for the CT treatment. The infiltration rate at 5 min (is), steady state infiltration rate after 3 h (i c ) and field capacity water content 24 h after the infiltration (FC) were higher in NTM (1.5 cm min -1 , 0.4 cm min -1 , and 0.35 gg -1 , respectively) than other treatments. The least values of i 5 , i c and FC (0.4 cm min -1 , 0.18 cm min -1 , and 0.22 gg -1 , respectively) were observed for the CT treatment. Saturated hydraulic conductivity (K s ) measured on soil cores was the highest for the NTM (0.29 cm min -1 ) for 0 to 10 cm and NTCSR (0.24 cm min -1 ) for 10 to 20 cm depth. The ρ b (1.52 g cm -3 for 0 to 10 cm and 1.62 g cm -3 for 10 to 20 cm depth) was the lowest and water stable aggregates (WSA) were the highest (WSA of 89% and 63%) for both depths for the NTM treatment. The ρ b was much higher for the CT (1.75 g cm -3 for 0 to 10 cm depth) and NTWM (1.77 g cm -3 for 10 to 20 cm depth) than NTM, NTCSR and M treatments for either depth. The landscape positions did not have a significant influence on soil physical and water transmission properties nor on total biomass. The manuring treatment improved soil aggregation and water transmission properties (NTM > NTWM > NTCSR).

Soil physical properties and crop productivity of an eroded soil amended with cattle manure

Abstract: Erosion changes soil properties, especially physical properties, mainly because it removes surface soil rich in organic materials and exposes lower soil layers. In 1988, a study was established to determine the effects of soil erosion and long-term manure applications on selected soil phys­ ical properties and corn (Zea mays L.) production. After 10 years of an­ nual manure applications, soil core samples were collected in 7.6-cm in­ crements at three depths, 0 to 7.6, 15 to 22.6, and 30 to 37.6 cm, to determine soil bulk density (� b ), hydraulic conductivity of saturated soil (K s ), and water retention. Bulk density and K s increased slightly with ero­ sion level. Water retention did not change in the surface 7.6 cm, but it did decrease with increasing erosion level at deeper depths. Long-term

Effects of interaction of organic and inorganic p with ferrihydrite and kaolinite-iron oxide systems on iron release

Abstract: The solubility of iron oxides in soils is governed by crystal size, crystal order, isomorphous substitutions, and associations with other minerals. Their dissolution occurs by protonation, reduction, or complexation with ligands such as phosphate and inositol phosphates. In this work, the interaction of inositol hexaphosphate (IHP) and phosphate (Pi) with ferrihydrite (Fh) or ferrihydrite-kaolinite systems (Fh-KGa2) was studied to assess the effects on iron oxide dissolution. Adsorption of IHP and Pi on a two-line Fh and Fh-KGa2 was performed in the range 0 to 0.004 mol P L -1 , and the release of P and Fe from samples of Fh or Fh-KGa2 saturated with IHP or Pi was evaluated at different pHs. The amount of P adsorbed on Fh increased, reaching a plateau at 2.12 μmol m -2 for IHP and 4.57 μmol m -2 for Pi. Sorption on KGa2 was lower. It increased to 2.24 μmol m -2 for IHP and to 2.96 μmol m -2 for Pi on Fh-KGa2. On the basis of the IHP/Pi ratios, it was hypothesised that IHP interacted with Fh through two of its six phosphate groups, whereas it interacted with Fh-KGa2 through one P group. Phosphate desorption from these complexes occurred only at pH ≥ 4.5 and was higher for Pi than for IHP and from the Fh-KGa2 system than from Fh. The desorption of IHP was followed by a consistent Fe release, higher at basic pHs. By contrast, Pi adsorption inhibited dissolution of both minerals, although the anion was desorbed in higher amounts compared with the P organic form.

An analytical solution to one-dimensional thermal conduction-convection in soil

Abstract: The equation of one-dimensional thermal conduction and convection in soil is solved analytically by applying the traditional harmonic method (HM) and the Laplace transform method (LTM). A simple method to determine accurate values of soil heat diffusivity and liquid water flux density is given. Usin

Sodicity And Water Quality Effects On Slaking Of Aggregates From Semi-arid Soils 1

Abstract: Aggregate slaking is one of the main mechanisms responsible for the breakdown of aggregates. Exchangeable sodium percentage (ESP) and electrolyte concentration (C) of the soil solution play a significant role in determining soil physical properties and the response of soil clays to dispersion and swelling. However, studies of sodicity and C effects on aggregate stability have yielded inconsistent results. Our objective was to evaluate the effects of sodicity and C on aggregate slaking in soils with different clay contents. Using the high-energy-moisture-characteristics (HEMC) method, we studied aggregate slaking in 56 samples of Israeli topsoils varying in clay content (80-675 g kg -1 ) and ESP levels (0-30). In this method, accurately controlled wetting of the aggregates (i.e., the driving force for slaking) was the only force exerted on the aggregates. Aggregates (0.5-1.0 mm) were placed in a funnel equipped with a fritted disk and, using a peristaltic pump, were wetted either fast (100 mm h -1 ) or slowly (2 mm h -1 ). Two salinity levels were studied: dionized water (DW, C = 0.04 mmol c L-1) and saline water (SW, C = 20 mmol c L -1 ). Thereafter, the aggregates were subjected to stepwise increases in matric potential up to 5.0 J kg -1 to obtain a moisture retention curve that served as the base for calculation of aggregate susceptibility to slaking. The latter was expressed in terms of stability ratio (SR). The SR of low ESP soils increased from 0.298 to 0.751 and from 0.508 to 0.799 for DW and SW, respectively, with the increase in soil clay content from 11.3 to 67.4%. Increase in ESP decreased SR (i.e., enhanced aggregate slaking), whereas use of SW increased SR compared with DW. A triple interaction among ESP, C, and clay content (P = 0.001) in their effect on aggregate slaking suggested that the combined effects of these variables on slaking were complex. Our results suggested that: (i) in soils having inherently low aggregate stability (clay 35%), aggregate slaking decreased upon use of SW only when ESP > 15.

Tillage Effects On Physical And Hydrological Properties Of A Typic Argiaquoll In Central Ohio

Abstract: No-till management is generally preferred over conventional tillage, especially in fine-textured soils where tillage can increase soil compaction, disrupt the natural structure formation process, and have long lasting effects on soil quality. The objective of this project was to quantify the interactive and residual effects of different tillage systems on the water transmission and structural properties of Kokomo silty clay loam (fine, mixed, superactive, mesic Typic Argiaquoll). Soil physical properties were assessed at the Don Scott experimental farm of the Ohio State University, Columbus, Ohio, 9 years after initiating the study and 20 months after the last tillage operation. Three tillage treatments were replicated four times: moldboard plow (MB), chisel plow (CP), and no-till (NT). Tillage operations took place during the fall of each year between 1993 and 2000, and soil samples for physical property assessment were obtained during summer 2002 for 0-10- and 10-20-cm depths. The water infiltration tests conducted on each of the 12 experimental plot showed that the highest cumulative infiltration (I, 90 cm) and steady state infiltration (i c , 27 cm h -1 ) were for the NT treatment and varied in the order NT > CP ∼ MB. Soil bulk density (ρ b ) varied in the order MB > NT ∼ CP, available water capacity (AWC) and air filled porosity (f a ) NT > MB ∼ CP. The water stable aggregation (WSA) (943 g kg -1 ) and the volume of transmission (TrP) (0.10 cm 3 cm -3 ) and storage pores (StP) (0.31 cm 3 cm -3 ) were the highest for the NT plots for 0-10-cm depth. For the 10-20-cm depth, the WSA and MWD were in the order NT > MB ∼ CP; AWC-NT (2.00 cm) ∼ CP (1.71 cm) > MB (1.36 cm). Tillage effects on soil properties between MB and CP seemed to diminish at the end of the growing season, and the infiltration rate after 5 min, i c , I, WSA, and soil ρ b values were similar. Canonical correlation analysis indicated strong association between volumes of StP and I, i c and soil ρ b , and SOC and soil ρ b .

Spatial prediction of soil particle-size fractions as compositional data

Abstract: Particle-size fractions (psf) of mineral soils and, hence, soil texture, are the most important attributes affecting physical and chemical processes in the soil. More often, psf data are available only at a few locations for a given area and, therefore, require some form of interpolation or spatial

Modeling diffusion and reaction in soils: X. A unifying model for solute and gas diffusivity in unsaturated soil

Abstract: Diffusion processes in the soil water and air phases often govern transport and fate of nutrients, pesticides, and toxic chemicals in the vadose zone. This final paper in a 10-part series on diffusion-reaction processes in soils concerns the development of a unifying model platform for predicting so

Trace metal accumulation by red clover grown on sewage sludge-amended soils and correlation to mehlich 3 and calcium chloride-extractable metals

Abstract: With the availability of sensitive multielement analytical capability, it is no longer essential to use chemically aggressive soil tests to extract measurable levels of most trace elements. However, the relative abilities of mild and aggressive extractants to assess metal bioavailability in soils have rarely been compared. A greenhouse experiment was carried out to compare a mild soil extractant (hot 0.01 M CaCl(2)) with an aggressive one (Mehlich 3) for predicting accumulation of trace metals by red clover (Trifolium pratense L.). Clover was grown on large columns of nonacid fine-textured and acid coarse-textured soils that had been amended several years earlier by a heavy application of sewage sludge products, and pH was subsequently adjusted using CaCO(3) or H(2)SO(4). The soil extractants (CaCl(2) and Mehlich 3) and clover tissue were analyzed for trace metals (As, Cd, Mo, Cu, Ni, Mn, Pb, and Zn) by axial-view ICP spectrophotometry. Linear regression analyses were performed to relate the concentration of each trace element in the red clover tissue to the concentration extracted from the soil. The results indicate that CaCl(2) extraction is more reliable than Mehlich 3 extraction when evaluating plant availability of trace elements in soils with a wide range of properties (especially pH). The strongly acidic nature of the Mehlich 3 extractant caused large quantities of metals such as Zn, Cd, Cu, and Ni to be extracted from metal-contaminated soils even when the plant availability of these metals was low because of near-neutral soil pH or high clay and organic matter content. Conversely, in coarse-textured and acid soils containing lower total concentrations of metals, plant-available metals were often relatively high, yet Mehlich 3 frequently extracted smaller quantities of metals from these soils than from the near-neutral soils. We conclude that dilute CaCl(2) is preferable to Mehlich 3 as a universal soil extractant for estimating short-term trace metal availability to crops.

Concentrations and properties of dissolved organic matter in forest soils as affected by the redox regime

Abstract: Changes in concentrations and properties of dissolved organic matter (DOM) caused by oxygen deficiency are poorly understood. We estimated the influence of redox conditions on DOM dynamics in the field, sampling soil solutions at different depths of three soils (Humic and Histic Gleysol, Chromic Cam

The effects of compost and crop rotations on carbon turnover and the particulate organic matter fraction

Abstract: Management practices that influence the quantity of C inputs returned to the soil from cropping systems and compost applications alter subsequent biotic activity broadly, contribute to seasonal fluctuations in nutrient dynamics, and may increase C sequestration. The effects of crop rotations and compost applications on soil-C sequestration and decompostion, and the turnover time of C 4 -derived corn C were assessed via changes in the C content and 13 C values of particulate organic matter (POM) and total soil organic C (SOC). The majority of organic inputs entered the POM fraction, defined as the sand-sized soil separates remaining on a 53-μm sieve after removal of residues (>2 mm), dispersion in 5% sodium polyphosphate, and 12 h of shaking. Before the application of compost to soil, 85% of the C in the compost material was classified as POM. Measurements of POM-C in the soil were 45% higher and SOC was 16% greater where compost was applied in place of N fertilizer. Addition of compost to POM-C diminished the value of POM as an indicator of short-term changes in nutrient dynamics. However, POM-C remaining from compost applications made during the period 1993 to 1997 may be an indicator of enhanced macroaggregate stability: improved soil tilth and the retention of soil C and N. The turnover time of C 4 -derived C in the POM fraction was 11 years compared with 22 years in SOC. The presence of compost C did not affect the turnover time of corn-derived C. High cropping intensity and chisel plow management increased C sequestration relative to the preceding alfalfa management.

Experimental evaluation of infiltration models for different land use and soil management systems

Abstract: Soil structural and water transmission properties, as influenced by land use and soil management, affect the coefficients of infiltration predictive models. Ten infiltration models were analyzed to assess these coefficients. The models tested include Green and Ampt (1911), Kostiakov (1932), Horton (1940), Mezencev (1948), Philip (1957), Holtan (1961)-two and three-parameters, Stroosnijder (1976), Swartzendruber (1987), and Kutilek and Krejca (1987). Parameters were evaluated for time-dependence and precision and with regard to the effects of land use/soil management and landscape positions. The field water infiltration data used in these models were based on double ring infiltrometer tests conducted for 3 h at six different land use/soil management treatments at the North Appalachian Experimental Watersheds (NAEW) near Coshocton, Ohio. The treatments were no-till without manure (NTWM), no-till with manure (NTM), no-till corn-soybean rotation (NTCSR), conventional tillage (CT), meadow (M) and forest. Measurements were made at three landscape positions (e.g., shoulder or upper slope (US); back or middle slope, (MS); and foot slope (FS)). The algebraic parameters of the infiltration models and nonlinear least squares regression were fitted using measured infiltration time [I (t)] data. Among process-based infiltration models, the Swartzendruber model performed best and matched the measured I (t) data with lower sum of squares (SS) and higher model efficiency (EF) and Wilmot's index of agreement (W). Overall the three-parameter Horton model gave the best representation of the I (t) relationship with the lowest SS and the highest EF and W for most of the land use treatments, including forest. The treatments had significant influence on the parameters related to initial infiltration rate or sorptivity and final steady state infiltration rate or hydraulic conductivity near saturation, whereas landscape positions had significant influence on the sorptivity parameter only. The fitted parameters (i.e., sorptivity and hydraulic conductivity near saturation) were time dependent and were higher for NTM than for other treatments.

Kinetics of Phosphorus Release from Manure-Amended Alkaline Soil

Abstract: The release and transport of phosphate from manure-amended soils is detrimental to surface water because it leads to eutrophication. However, reaction rates and mechanisms of P release from manure-amended alkaline soils have not been completely characterized. The objectives of the present study were to determine the rate of P release from a manure-amended soil and to apply solubility models to predict the mineralogical phases that control soil-solution P concentrations. Phosphate release kinetics were measured on a soil that had received solid-dairy manure applications for more than a decade. To measure total P that would be released under leaching conditions, we conducted experiments in which we replenished the solution continuously until the P concentration reached a steady state (sequential desorption experiment). Measured P release kinetics indicate that 80% of the soluble P was released within 24 h, followed by a slow release that continued for up to 504 h. We applied several models, including a reversible first-order model, the Elovich model, and a modified version of the Elovich model that was empirically correlated to soil organic matter and percent clay, to describe our experimental data. The data were best fit with the Elovich model. Total P released from the manure-amended soil in the sequential desorption experiments was 29% from the surface soil (0-10 cm) and 8% from the subsurface soil (45-65 cm). Results from this study suggest that P release from manure-amended soils is controlled by rate-limited dissolution of meta-stable Ca-P mineral phases.

Role of wetting rate and rain energy in seal formation and erosion 1

Abstract: Seal formation, runoff, and erosion are controlled by soil texture, rain kinetic energy (KE), and wetting rate (WR) of soils aggregates. The ob- jective of this study was to determine the relative importance of WR and rain KE in seal formation, runoff production, and erosion, in soils vary- ing in their clay and silt content, using a drip-type rain simulator. Four soils, ranging in clay content from 22.5 to 61.2%, were packed in 0.2� 0.4-m trays, pre-wetted at WRs of 2, 8, or 64 mm h � 1 , and exposed to 60 mm of simulated distilled water (DW) rainfall with two KEs (8 and 15.9 kJ m � 3 ). Runoff and erosion increased as rain KE and WR increased; however, the magnitude of change depended on clay content. In the loam (22.5% clay), the effect of rain KE on seal formation and runoff was significant, and the effect of WR was small. Conversely, in the clay soils (51.3 and 61.2% clay), the effect of WR on seal formation was significant and the effect of rain KE was negligible. In the sandy clay soil (38.1% clay), the effects of both WR and rain KE on seal formation and runoff were significant. The effect of rain energy on soil erosion was significant in all soils. Since water erosion is the product of sediment detachment and transport of the particles by overland flow, increase in the impact of rain drops increases both soil detachment and transport capacity and in- creases soil erosion in all soils. In clay soils, erosion also increased with the increase in WR. Disintegration of the aggregates by fast WR com- bined with detachment by rain impact increased erosion from clay soils. The conclusion reached is that for seal formation and runoff production, rain KE predominates in medium- and light-textured soils and WR pre- dominates in heavy-textured soils. Conversely, for soil erosion from lab- oratory trays, detachment by rain KE is essential in all soils. (Soil Science 2003;168:54-62)

Waste Composting for Urban and Peri-urban Agriculture: Closing the Rural-Urban Nutrient Cycle in Sub-Saharan Africa

Abstract: the story of phosphorus global food security and food for food production is fundamental to our existence yet we are using up the world s supply of phosphorus a critical ingredient in growing food today phosphorus is mostly obtained from mined rock phosphate and is often combined in mineral fertilizers with sulphuric acid nitrogen and potassium, free access to scientific journals open access journals open access initiative is committed to make genuine and reliable contributions to the scientific community without restricting the access of published content

Characterization of Ten Sequentially Extracted Humic Acids and a Humin from a Soil in Western Massachusetts

Abstract: Humic substances are mixtures of macromolecules with varied structures and chemical compositions that are affected by differences in parental biomaterials and environmental conditions. This study used elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and solid-state 13 C nuclear magnetic resonance spectroscopy (NMR) to identify the chemical and structural heterogeneity of 10 humic acids (HAs) and a humin. The HAs were obtained by progressively extracting solution from a soil in western Massachusetts, eight times with 0.1 M Na 4 P 2 O 7 and two times with 0.1 M NaOH. The humin was the residual fraction after 10 base extractions. As indicated by solid state NMR analysis, the aliphatic carbons (0 ∼ 108 ppm) of the HAs increased gradually from 50% in fraction 1 (F-1) to 62% in fraction 9 (F-9) and 70% for the humin, but the aromatic carbons (108 ∼ 162 ppm) were highest in F-1. The band assigned to aliphatic carbon (2930 cm -1 ) in the DRIFTS spectra gradually increased with further extractions, and the relative intensity of this peak was the highest in humin. The atomic C/H ratio declined from 1.1 for F-1 to 0.6 for F-10 and the humin, consistent with the spectroscopic analyses. In addition, both elemental and spectroscopic data reveal that the last extracted HA and humin contained relatively lower contents of polar functional groups such as carboxylic and phenolic groups. This study shows significant chemical, structural, and molecular differences among the 10 sequentially extracted HAs and humin, even from a single soil.

Phosphate Sorption By Pacific Northwest Calcareous Soils

Abstract: Understanding phosphorus (P) sorption of calcareous soils is important for the development of successful fertilizer and manure management practices. This study was conducted to identify soil chemical properties controlling P sorption in semiarid calcareous soils of the Pacific Northwest. Sorption isotherms of 18 primarily calcareous soils ranging widely in soil physical and chemical properties were constructed by equilibrating 4 g of soil with 40 mL of 0.01M CaC12 containing between 0 and 700 mg P 1.- 1 for 24 h. The P sorption isotherms at low to medium P concentrations fit the Freundlich isotherm (r2 ? 0.93). The slope of the isotherm generally increased abruptly at high P concentrations, suggesting Ca-P precipitation. The maximum P sorption prior to Ca-P precipitation was closely related to organically complexed Fe and Mn (R2 > 0.98), suggesting that such complexes may regulate P sorption in these soils. The equilibrium P concentration at the point where Ca-P precipitation begins to dominate was closely related to pH and organic carbon. A better understanding of the role of organically complexed metals in controlling P sorption in calcareous soils is needed to determine how P solubility is affected by organic matter additions and how this will ultimately impact the plant availability and potential off-site transport of P from these soils.

Prehistoric alteration of soil properties in a central german chernozemic soil: in search of pedologic indicators for prehistoric activity

Abstract: There is no consistent theory that explains the patchy distribution of chernozemic soils in Central Germany. Mounting evidence suggests that prehistoric human activities may have interfered with natural pedogenesis on a large scale. Therefore, we undertook to identify parameters that would enable researchers to infer a human interference with pedogenesis. We selected a soil with a known history of prehistoric influence (Seeben), later referred to as ancient soil, and a reference soil (Zoberitz) with properties representative of the chernozemic soils in the vicinity. We did a survey of parameters that are commonly used to characterize pedogenetic dynamics and combined this with an investigation of organic matter properties. We found that prehistoric land use has predominantly modified the properties of the subsoil, rendering it unlikely that such modifications are the result of either (i) contemporary agricultural management or (ii) natural input dynamics via root systems or bioturbation. Soil color was darker, bulk density higher, and C/N ratio wider in the ancient soil. The mineral matrix was uniform down to a depth of 95 cm in the ancient soil, whereas a B-horizon with a corresponding change in clay mineral assemblage was developed in the reference soil. Compared with the reference soil, the carbon stock was elevated by a factor of 2.5 in the ancient soil, with more carbon associated with the clay fraction. We identified large contributions of charred organic matter in the ancient soil by two independent methods (Benzene polycarboxylic acid BPCA; Transmission electron microscopy, TEM), and confirmed by means of solid-state cross-polarization/magic angle spinning/nuclear magnetic resonance ( 13 C-CP-MAS-NMR) spectroscopy that organic matter aromaticity was higher in the ancient soil. We suggest that any simultaneous occurrence of several of the observations listed above should be regarded as a strong indication for human interference with soil genesis.

Nitrogen, Phosphorus, and Carbon Mineralization in Response to Nutrient and Lime Additions in Peatlands

Abstract: This objective of this study was to determine if mineralization of C, N, and P was pH stressed and/or nutrient limited in a bog and fen in northeastern Minnesota. Although soil activity in northern peatlands can be limited by low pH, low temperatures, high C:N and C:P ratios of soil organic matter,

Long-term effects of cultivation on particle size and water-retention characteristics determined using wetting curves

Abstract: Short-term (i.e., seasonal) variations are expected with some soil physical properties, whereas other properties, such as particle size, are considered static. However, less is known about long-term (i.e., decadal) variations in properties, such as particle-size fractions and water-retention characteristics, caused by continuous annual cultivation. The objective of this study was to determine the effect of land use (i.e., undisturbed virgin prairie vs. cultivated agriculture) and years of continuous annual cultivation on soil particle-size fractions and water-retention characteristics determined using soil wetting curves. Particle-size fractions (i.e., 0.05-2 mm, 0.002-0.05 mm, and <0.002 mm representing sand-, silt-, and clay-sized fractions, respectively) were determined on soil samples collected in 1987 and 2001 from the 0- to 10-cm depth along a transect across four adjacent fields representing a range from 0 to 44 years under continuous annual cultivation. Soil wetting curve data, obtained from a dewpoint potentiameter by re-wetting air-dried, crushed, and sieved soil, were fit by nonlinear regression to determine modeled water-retention characteristics for the native prairie and cultivated agricultural soil from samples collected in 2001. Particle-size fractions and water-retention characteristics were significantly affected by land use and years under continuous cultivation. The sand-sized fraction decreased and the clay-sized fraction increased significantly for the agricultural soil that had been annually cultivated the longest. Results indicate that long-term changes in particle-size fractions can occur following decades of continuous annual cultivation and that the effects of tillage on soil-water-retention characteristics can be ascertained after removing the confounding effects of initial differences in soil and pore structure by using soil wetting curves.

Organic chlorine in deciduous and coniferous forest soils in southern sweden

Abstract: The concentration of organic chlorine (Clorg) was determined in soil samples collected in the O-horizon in forest soils in southern Sweden to describe differences among stand types and elucidate th ...

Phosphorus Relationships to Manganese and Iron in Rice Soils

Abstract: Rice plants (Oryza sativa L.) grown on soils containing low soil test-extractable P frequently do not respond to fertilizer P application under reduced conditions. The lack of rice response to fertilizer P in soils with low extractable P has been attributed to increased solubility of Fe-associated P upon flooding. The increased solubility of Mn oxides and release of Mn-associated P in flooded soils may also increase P availability to rice plants. The effect of Mn oxides on P availability has not been adequately described or quantified. In this experiment we used rice soils with low soil test P and high or low Mn or Fe oxides to measure the effects of Mn oxides on P availability under field, greenhouse, and laboratory conditions. Soils were incubated under oxidized or reduced conditions for 35 days. At the end of 0, 2, 5, 8, 11, 15, 20, 25, 30, and 35 days, soil solution pH and Eh and soluble and extractable P, Fe, and Mn were determined. Greenhouse and field experiments showed that rice plants did not respond to P application in three of four soils despite low extractable P. A large increase in P concentration following reduction was observed and was correlated positively with reactive Fe and Mn oxides in soils. During incubation water-soluble P in soils increased from 0.06 to 0.37 mg P kg -1 , Fe from 0.2 to 22.0 mg Fe kg -1 , and Mn from 0.08 to 6.43 mg Mn kg -1 . Linear stepwise regression analysis indicated that 65 to 91% of solution P variation was attributable to Fe oxides and about 14 to 28% was attributable to Mn oxides. The contribution of Fe reduction to increased P availability was highly significant and related to large amounts of poorly crystalline Fe oxides in soils extracted by oxalate. The manganese oxide contribution to P availability was important, especially in the early stages of soil reduction in soils with large amounts of reactive Mn. In soils dominated by Mn oxides, the reduction of Mn-associated P can be a significant source of P for plants.

Comparative Evaluation of Spatial Prediction Methods in a Field Experiment for Mapping Soil Potassium

Abstract: Accurate prediction and mapping of soil nutrient levels are essential for implementing variable rate technology. For the prediction of soil potassium (K), we evaluated the performance of the inverse distance weight of powers 1, 2, and 3, ordinary kriging, cokriging, multiple linear regression assuming independent error, and multiple linear regression with autocorrelated error structure. Two forms of ordinary kriging were evaluated: kriging the residuals from a trend surface regression (geographic locations only as predictors) and kriging the residuals from a regression of K on geographic location and other soil property predictors (soil pH and apparent electrical conductivity, ECa). The autocorrelated error model as implemented in the Statistical Analysis System (SAS) mixed linear model was employed to adjust for autocorrelated error structure in the regression models used for prediction. For cokriging, either soil ECa or soil pH was used as a secondary soil property to predict K. The root mean square error (RMSE) and mean error (ME) calculated from an independent validation data set (n = 68) were used as comparison criteria. The best result was obtained with the methods that incorporated geographic locations, other soil property predictors, and the correlated error structure. This investigation demonstrated the flexibility of the regression-based autocorrelated error model for spatial prediction compared with other methods. Further, the results of this study have important implications for screening economically acceptable soil and site characteristics that can be used to improve prediction of soil nutrients at unsampled locations within a field.