bluuebunny/crossref_metadata_2025 huggingface dataset:
Water Content Effect on Denitrification and Ammonia Volatilization in Poultry Litter
Authors: Cabrera M. L. , Chiang S. C.
Published: July 2010

Poultry litter is a mixture of excreta, bedding material, waste feed, and some soil that is removed from poultry houses and applied to soil as fertilizer. Because litter is commonly stockpiled outdoors before land application, losses of inorganic N may occur through denitrification and NH3 volatilization. This work was conducted to evaluate the effect of litter water content on denitrification and NH3 volatilization during storage. Litter samples from two broiler houses in northern Georgia were incubated (25°C) at four water contents for 13 d. Water contents used were 230 g H2O kg−1 in Litter A, 160 g H2O kg−1 in Litter B, and 800, 1200, and 2400 g H2O kg−1 in both litters. These water contents were equivalent to 8, 26, 40, and 79% water‐holding capacity (WHC) in Litter A and to 7, 33, 49, and 99% WHC in Litter B, respectively. Denitrification was evaluated by measuring N2O emission from samples incubated with 10 kPa C2H2, with and without additional NO−3 (15 mg Ng−1). Ammonia volatilization was evaluated by measuring NH3 evolved from samples incubated without C2H2. Denitrification was significant at the highest water content and increased with the addition of NO−3. Measured denitrification losses varied between 41 and 79% of the initial NO−3, although final NO−3 levels suggested that denitrification losses were larger (92–100%) and that part of the N2O produced remained entrapped in the litter. Ammonia volatilization losses ranged from 32 to 139% of the initial NH+4 and were increased by increasing water content. These results suggest that poultry litter should be stored under dry conditions to reduce N losses.
Thiosulfate Production in Cysteine‐Amended Soil
Authors: Zhong T. , Morra M. J.
Published: July 2010

Thiol‐labile compounds are produced in cysteine‐amended soil, as evidenced by the production of H2S following addition of reagents containing free sulfhydryl groups (−SH). Thiosulfate (S2O2−3) is a likely reactant candidate because it is an intermediate in biogeochemical S cycling and is reduced to H2S by ‐SH, but its presence in cysteine‐amended soils has not been documented previously. Four soils were amended with l‐cysteine (15 mmol kg−1 soil) incubated at 0.033 MPa soil water suction or under saturated conditions, and then extracted with 0.1 M LiCl. Colorimetric analysis of the extracts using cyanolysis with and without addition of a Cu2+ catalyst indicated the presence of S22−3 and a polythionate such as S4O2−6; positive interferences from the cyanolysis of S2− were minimal. Ion chromatographic analysis of the extracts showed a well‐resolved peak with the same retention time as S2O2−3 and yielded concentration estimates similar to those obtained by colorimetry, providing positive identification of S2O2−3 in cysteine‐amended soils. Thiosulfate production occurred under both saturated and unsaturated conditions, varied among soils from 0 to 35.2 mg S2O2−3‐S kg−1, and was nearly eliminated by autoclaving the soil before incubation or by addition of NaN3. Although the exact pathway for S2O2−3 production is unknown, it is likely that H2S formation and subsequent oxidation are responsible.
Prediction of Phosphorus Uptake by Field‐Grown Maize with the Barber‐Cushman Model
Authors: Lu Shen , Miller M. H.
Published: July 2010

Data collected from a field experiment conducted to determine the optimum P placement for maize (Zea mays L.) were used to test the Barber‐Cushman nutrient absorption model. Phosphorus absorption by maize predicted by the model was compared with that measured in a field experiment in which various rates of P were mixed with different volumes of soil. Shoot P content and root growth both in and outside the fertilized volume were measured at three times during early growth. Soil supply parameters were determined in the laboratory while literature values were used for plant absorption parameters. The ratio of predicted to measured absorption increased markedly as the P concentration in solution in the fertilized soil (Cli) increased, ranging from about 0.2 with low values of Cli (<0.03 mM) to as much as 2.0 with higher values of Cli (>0.06 mM). The ratio was highly sensitive to values of the maximum influx rate (Imax) at values of Cli >0.06 mM. Reducing the value of Imax eliminated the dependence of the predicted/measured ratio on Cli. With the lower value of Imax, predicted absorption ranged from 20 to 60% of that measured. This variation seemed due in part to the influence of vesicular‐arbuscular mycorrhizae on absorption. The sensitivity of the absorption model to Imax values at higher values of Cli indicates the necessity of measuring this parameter under conditions similar to those for which absorption is to be predicted.
Lateral and Vertical Bromide Ion Transport in a Piedmont Landscape
Authors: Afyuni Majid M. , Cassel D. Keith , Robarge Wayne P.
Published: July 2010

Variation in soil physical properties and soil water transport can affect solute transport at different positions within a landscape. Our objective was to evaluate the magnitude of lateral and vertical transport of Br− under natural rainfall conditions as a function of landscape position. Potassium bromide was surface applied (300 kg Br−/ha) on three transects of Georgeville soil (clayey, kaolinitic, thermic Typic Hapludults) in the Piedmont of North Carolina. Each transect included a footslope, linear slope, and interfluve landscape position. The KBr was applied on alternate plots (5 by 2.7 m) on two transects and on contiguous plots on the third transect. Soil cores as deep as 3 m were collected after 140, 560, and 1460 mm of rainfall. Extent of lateral Br− transport was determined using cores from plots that did not receive surface application of KBr. After 140 mm of rainfall, the maximum Br− concentration remained in the upper 30 cm and some measurable lateral Br− transport occurred at all landscape positions. After 560 mm of rainfall, the maximum Br− concentration was above 60 cm, but some was detected at 150 cm on the footslope and interfluve positions. Lateral transport of Br− at the footslope and linear slope positions was 150 cm, but maximum concentrations occurred 10 to 45cm downslope. After 1460 mm of rainfall, most Br− disappeared from the footslope. Downslope lateral transport of Br− was 225 cm at all landscape positions. Both vertical and lateral Br− transport were greatest at the footslope. The variability in Br− transport is related to soil profile characteristics and hydrology at different landscape positions.
Plot‐Scale Solute Transport in a Semiarid Agricultural Soil
Authors: Yasuda Hiroshi , Berndtsson Ronny , Bahri Akissa , Jinno Kenji
Published: July 2010

In semiarid areas, agricultural production is determined by limited water and nutrient supply. To develop efficient management practices, it is of importance to predict solute transport. In line with this, we present observed and calculated plot‐scale solute transport in an agricultural experimental field in northern Tunisia. A pulse of Br−‐tagged water was applied on the surface of two small field plots and leached under steady‐state soil water conditions. Solute samples were withdrawn through ceramic samplers at five different depths within each plot. The experimental data indicated a high degree of by pass or preferential flow within the small plots and nonsigmoid breakthrough curves, suggesting tailing phenomena and immobile fractions of soil water. The data were evaluated using the classical two‐parameter convection‐dispersion equation (CDE) and the four‐parameter non‐equilibrium convection‐dispersion equation (NECDE). Pore water velocities, v, and dispersion coefficients, D, were calculated by fitting the analytical solution of these two models to the breakthrough curves based on individual sample locations as well as using all samples in the plot simultaneously. None of the models could be fitted when data from all solute sampling depths were used in the optimization simultaneously. When using data at individual sample locations, the fit was somewhat better for the NECDE than for the CDE. The estimated values of D and v could be described by a power law relationship.
Mineral Effects on the Pyrolysis‐Field Ionization Mass Spectrometry of Fulvic Acid
Authors: Schnitzer M. , Kodama H. , Schulten H.‐R.
Published: July 2010

Fulvic acid (FA), physical mixtures of FA with quartz, Namontmorillonite, and kaolinite, and FA‐Na‐montmorillonite and FA‐kaolinite complexes were analyzed by pyrolysis‐field ionization mass spectrometry (Py‐FIMS). Use of this method made it possible to detect the following six major groups of FA components: carbohydrates, phenols, lignins, lipids, alkylaromatics, and N compounds, and to determine how the thermal evolution of these components was affected by the presence of minerals during pyrolysis. The thermal evolution of the six major FA components was delayed by the FA‐mineral mixtures but substantial retention of specific groups of FA components was shown only in the FA‐clay complexes. Thus, FA components retained by the clays in FA‐clay complexes were more thermostable than those in physical mixtures with FA. Pyrolysis‐field ionization mass spectrometry was found to have considerable potential for enhancing our understanding of the effects of the presence of minerals on the thermal behavior of FA.
Poultry Litter and Manure Contributions to Nitrate Leaching through the Vadose Zone
Authors: Adams P. L. , Daniel T. C. , Nichols D. J. , Pote D. H. , Scott H. D. , Edwards D. R.
Published: July 2010

Pastures are commonly fertilized with poultry litter or manure in northwestern Arkansas. We hypothesized that this practice may enhance NO3‐N movement to groundwater and wanted to ascertain the likelihood of common application rates causing excessive NO3‐N leaching. Our objective was to determine the effect of application rate of poultry litter or manure on NO3‐N concentration in vadose water under fescue (Festuca arundinacea Schreb.) plots as a function of depth and time. In August 1991, poultry litter was applied at 0 (control), 10 (PL10), and 20 Mg ha−1 (PL20) and poultry manure at 17.7 Mg ha−1 (PM20). In June 1992, we applied an additional 4.5 Mg ha−1 litter (PL5) to the PL10 plots and 3.8 Mg ha−1 manure (PM5) to PM20 plots. Pan lysimeters at the 60‐cm depth and suction‐cup lysimeters at 60 and 120 cm sampled soil water. The PL10, PL20, and PM20 treatments produced NO3‐N concentrations as high as 13, 54, and 41 mg L−1 at 60 cm. At 120 cm, NO3‐N reached 8, 24, and 37 mg L−1 for the PL10, PL20, and PM20 treatments. In 1992, the PL5 and PM5 treatments produced NO3‐N concentrations <1 mg L−1 at the 60‐ and 120‐cm depths. The recommended litter application rate in Arkansas is not more than 11.2 Mg ha−1 yr−1, split in two 5.6 Mg ha−1 applications. The PL10 and PL5 rates (similar to a maximum full‐year application plus a single split application) did not result in NO3‐N concentrations above the drinking water standard (10 mg L−1) at the 120‐cm depth.
Nutrient Runoff from Pasture after Incorporation of Poultry Litter or Inorganic Fertilizer
Authors: Nichols D. J. , Daniel T. C. , Edwards D. R.
Published: July 2010

Land‐applied poultry litter can elevate N, P, and C concentrations in surface water runoff. This study tested the hypothesis that incorporation of surface‐applied poultry litter and inorganic fertilizer by rotary tillage would improve runoff quality from tall fescue (Festuca arundinacea Schreber) pasture. Captina silt loam (fine‐silty, siliceous, mesic Typic Fragiudult) plots with 5% slopes and fescue cover received 4.5 Mg litter ha−1 or fertilizer equivalent to 218 kg N ha−1 and 87 kg P ha−1. Litter and fertilizer were surface applied or incorporated 2 to 3 cm deep by rotary tillage. Simulated rainfall was applied 7 d later at 50 mm h−1 to produce continuous runoff for 0.5 h. Runoff concentrations and mass losses of measured constituents were not significantly different (α = 0.05) between surface‐applied and incorporated treatments. Runoff concentrations of total Kjeldahl N (TKN), NH3‐N, NO3‐N, total P (TP), PO4‐P, chemical oxygen demand (COD), and total suspended solids (TSS) averaged 32.5, 12.4, 1.1, 15.4, 10.4, 427.8, and 86.8 mg L−1 for litter treatments, and 37.5, 39.0, 2.6, 26.2, 26.1, 87.8, and 20.6 mg L−1 for fertilizer treatments. Mass losses of TKN, NH3‐N, NO3‐N, TP, PO4‐P, COD, and TSS averaged 2.8, 1.0, 0.1, 1.3, 0.9, 32.3, and 6.7 kg ha−1 for litter and 2.9, 3.4, 0.2, 2.0, 2.0, 12.7, and 2.1 kg ha−1 for fertilizer treatments. Runoff mass losses of TKN and TP were not significantly different between litter and fertilizer treatments. Averaged across all treatments and replications, mass losses of TKN and TP were 2.8 and 1.7 kg ha−1, representing 1.3% of applied N and 1.9% of applied P.
Transport of Zinc and Cadmium in Soils: Experimental Evidence and Modeling Approaches
Authors: Hinz C. , Selim H. M.
Published: July 2010

This study was conducted to assess the suitability of several isotherm equations in describing single solute and binary ion exchange of Zn and Cd in two soils (Windsor and Olivier). Isotherms were determined using batch methods for equilibration times of 1 and 14 d. Ion exchange batch experiments (based on NH4OAc extraction) were carried out at different heavy metal/Ca ratios. Several isotherm equations were capable of describing 1‐ and 14‐d sorption isotherms. However, the general Langmuir‐Freundlich was most suitable for describing single solute (Zn and Cd) isotherms, whereas the Rothmund‐Kornfeld ion exchange equation well described binary data sets (Zn‐Ca and Cd‐Ca). Miscible displacement experiments were carried out to study Zn and Cd transport in uniformly packed soil columns (10 cm in length) for different flow velocities. For Windsor soil, the general isotherm equation predicted Zn transport results adequately but not Cd results. Moreover, under conditions of variable ionic strength, the use of constant selectivity (equal affinity) for ion exchange provided consistently superior predictions of Zn and Cd transport than the Rothmund‐Kornfeld (variable affinity) approach. Attempts to predict Cd and Zn transport in Olivier soil, using several isotherms and ion exchange approaches, were not successful. Local equilibrium appeared dominant for Windsor soil, whereas nonequilibrium sorption behavior may be rate limiting for Zn and Cd transport in Olivier soil.
Network Modeling of Diffusion Coefficients for Porous Media: II. Simulations
Authors: Steele D. D. , Nieber J. L.
Published: July 2010

Gas diffusion often dominates constituent transport in porous media (PM) and is dependent on pore geometry, water content, and water distribution in PM. Network models of PM offer the ability to investigate the influence and interaction of pore‐scale PM properties and fluid properties on macroscopic properties of the system. This study was conducted to investigate the macroscopic relative gas diffusion coefficient vs. air‐filled porosity relationship or diffusion characteristic (DC) of PM using a network model. The network model was used to simulate DCs in wetting and drying PM containing air and water. A network size of nine by nine by nine spheres was used; increasing the network size to 19 by 19 by 19 produced essentially no change in the DC. The DC was independent of Henry's law gas‐liquid partition coefficient (H) for H values of 0.1, 1.0, and 5.0. The product HRw, where Rw is the ratio between the bulk gas‐ and liquid‐phase diffusion coefficients, strongly influences the DC when H values of 1000 to 10 000 are considered; this indicates that certain organic compounds have DCs independent of air‐filled porosity. Hysteresis in DCs was found in selected network cases, with the wetting DCs being greater than the drying DCs for most air‐filled porosities, in accord with some experimental results reported in the literature. Spatial correlation of network pore space was shown to bring the simulated DCs into better agreement with some experimental DCs.
Soil Amendments for Reducing Phosphorus Concentration of Drainage Water from Histosols
Authors: Coale F. J. , Porter P. S. , Davis W.
Published: July 2010

Recently, the Everglades Agricultural Area (EAA) has been scrutinized by groups concerned with the impact of P‐enriched drainage water from organic soils (Histosols) on the ecology of adjoining wetlands. The objective of our research was to evaluate the effectiveness of soil amendments in reducing the P concentration in drainage water from an organic soil. Plastic cylindrical columns were filled with soil collected from a Pahokee muck (euic, hyperthermic Lithic Medisaprist). Three soil amendments were added to the soil columns: (i) a municipal drinking water purification facility waste material (“residual”), which is composed of CaO, Al2(SO4)3, and a starch‐based polymer; (ii) commercial agricultural dolomite [CaMg(CO3)2]; and (iii) commercial agricultural gypsum (CaSO4·2H2O). The amended columns were saturated for 60 d with an aqueous solution containing 5 mg P L−1 and then drained. The columns were then subjected to four P desorption cycles by saturating with distilled water and draining. Leachates were collected and analysed for total dissolved P (TDP). Residual and dolomite amendments reduced soil affinity for P sorption and resulted in a decrease in the quantity of soil P retained after repeated leachings. The net result from gypsum amendment was a small increase in P sorption capacity combined with an increased soil affinity for P. The reduced leachate TDP concentrations resulting from gypsum amendment were long lasting and were dependent on gypsum amendment rate. The effectiveness of gypsum amendments in reducing drainage‐water TDP concentrations needs to be evaluated under commercial agricultural field conditions.
A Steady‐State Model of Nutrient Uptake Accounting for Newly Grown Roots
Authors: Yanai Ruth D.
Published: July 2010

A model of solute uptake that accepts root growth, water uptake, and soil solution concentration as time‐varying input is required to interactively link plant and soil processes. The advantage of the steady‐state approach to solute uptake over more exact numerical solutions lies in the independence of the mathematical solution to previous conditions. Uptake thus calculated can accommodate unpredictable changes in root growth and mortality, root density, water uptake rates, and sources and sinks of nutrients such as decomposition and leaching, as required in simulating plant growth for multiple seasons in a dynamic soil environment. Previous steady‐state models were improved by including nonlinear uptake kinetics and the contribution of new root growth to uptake. The correction for new root growth is most important for relatively fast‐growing plants and immobile nutrients. The importance of each model parameter, as indicated by sensitivity analysis, depends on the values of other parameters. For example, root surface area and uptake kinetics are important when solution concentrations at the root surface are high, while root length, water uptake rate, and diffusion become important when delivery of solute to the root surface is limiting. Because the limiting factors can vary with environmental and plant conditions, it is important to represent these aspects of nutrient uptake in modeling plant‐soil interactions. A consistent derivation of the improvements and the original model is appended.
Long‐Term Changes in Soil Carbon and Nitrogen Pools in Wheat Management Systems
Authors: Franzluebbers A. J. , Hons F. M. , Zuberer D. A.
Published: July 2010

Crop management strategies that alter the timing, placement, quantity, and quality of crop residue input can affect the size, turnover, and vertical distribution of the active and passive pools of soil organic matter (SOM). Our objectives were to quantify long‐term changes in soil organic, soil microbial biomass (SMB), and mineralizable C and N in continuous wheat (Triticum aestivum L.), continuous wheat/soybean [Glycine max (L.) Merr.], and wheat/soybean‐sorghum [Sorghum bicolor (L.) Moench.] sequences under conventional tillage (CT) and no tillage (NT) with and without N fertilizer. A Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas was collected from a 9‐yr field study. Soil microbial biomass C (SMBC) and N (SMBN) were determined with the chloroform fumigation‐incubation method and mineralizable C and N were determined from 10‐d aerobic incubations at 25°C. More crop residue C input was retained as soil organic C (SOC), SMBC, and mineralizable C under NT than under CT. Soil organic C, SMBC, and mineralizable C at a depth of 0 to 50 mm were 33 to 125% greater under NT than under CT. Increasing cropping intensity increased SOC up to 22%, SMBC up to 31%, and mineralizable C up to 27% under NT. Differences in crop management systems significantly altered SMB and the associated mineralizable N level, which supplies crops with mineral N. High clay content soils of central Texas can be effectively managed to increase the active and passive pools of SOM using minimal fallow with NT.
Estimating Gross Nitrogen Mineralization and Immobilization Rates in Anaerobic and Aerobic Soil Suspensions
Authors: Smith C. J. , Chalk P. M. , Crawford D. M. , Wood J. T.
Published: July 2010

Zero‐order models for estimating gross rates of N mineralization (m) and immobilization (i) of NH+4 in soils were characterized by expressing the analytical solutions in a standard format. Three models of m were identified out of seven evaluated. One model was based on the solution of differential equations, and two on arithmetic mean data of ratios of labeled and total NH+4 pools. Data from well‐mixed anaerobic and aerobic soil suspensions amended with rice straw and labeled with (15NH4)2SO4 were used to compare the three models of m and four models of i for 56 d, with measurements every 7 d. Estimated rates of m declined during incubation, particularly during the first 21 d. Correction of m for remineralization of immobilized 15N in the anaerobic system using the total organic N pool (OT) had little effect, but the correction was more pronounced when the estimated active organic N pool (OT*) was used. Remineralization did not account for the observed decline in m during anaerobic incubation. Numerical modeling and nonlinear parameter estimation were also used to estimate m and i, with values being similar to analytical estimates for Days 0 to 7 (m) and Days 7 to 14 (i). The OT* comprised 10 to 11% of OT in both suspensions. Estimates of OT* were derived from the numerical analysis (anaerobic), or by assuming approximate isotopic equilibrium between the NH+4 (anaerobic) or NO−3 (aerobic) pools and the organic N pool following remineralization of immobilized isotope.
Genesis and Native Phosphorus Distribution in some Palexeralfs of Southern Spain
Authors: Smeck N. E. , Torrent J. , Barrón V.
Published: July 2010

Although deeply weathered soils are common on stable landscapes in Mediterranean regions, little information exists regarding the quantities and depth‐distributions of native P forms in such soils. The objective of this investigation was to gather such information to determine the P status of Palexeralfs representative of southern Spain and to evaluate the applicability of current models and paradigms for describing pedogenic P transformations in such soils. Base saturation, clay distribution, absence of primary carbonates, distribution of secondary carbonates, extent of rubification, and properties of Fe (hydr) oxides all indicate that the Palexeralfs are polygenetic. Yellowishred lower sola are considered relicts attributable to deep leaching and weathering during Pleistocene pluvial periods, whereas pedogenesis is active in upper yellowish‐brown B horizons. Low total and labile P contents and the dominance of reductant‐soluble and organic P fractions throughout entire >3‐m sola indicate that soil P distribution attained a terminal steady state during the paleo‐climatic regime and has been little affected during the current semiarid climate. Although organic P (Po) is a major component of total P, stabilization of Po by Fe (hydr) oxides restricts Po mineralization and fosters the labile P deficient state of these soils.
Interactions and Weathering Losses of Iron and Phosphorus in Palexeralfs of Southern Spain
Authors: Smeck N. E. , Torrent J. , Barrón V.
Published: July 2010

In Palexeralfs of southern Spain, Fe (hydr)oxides are the dominant reservoir of P. Thus, knowledge of P and Fe (hydr)oxide interactions is vital to understanding P dynamics in these soils. This investigation focused on the effect of mineralogy and properties of Fe (hydr)oxides on P distribution and transformations by calculating Fe and P gains and/or losses during formation of Typic, Aquic, and Calcic Palexeralfs. Although differential x‐ray diffraction could not positively identify hematite, differential x‐ray diffraction data, redness ratings, and estimates of Al substitution indicated differences in Fe (hydr)oxide properties between upper yellowish‐brown horizons and lower yellowish‐red horizons in Typic and Aquic Palexeralfs. The properties are consistent with goethite in the upper yellowish‐brown horizons and goethite with a small amount of hematite in the lower yellowish‐red horizons. The yellowish‐brown horizons not only show net Pd (reductant‐soluble P) losses but also greater gains of Fed (citrate‐bicarbonate‐dithionite‐extractable Fe) than the yellowish‐red horizons resulting in lower Pd/Fed molar ratios. Due to the minimal mineralogical differences, we conclude the lower quantity of P occluded in the Fe (hydr)oxides in the yellowish‐brown horizons is not a function of Fe (hydr)oxide mineralogy and properties but availability of labile P.
Periodic Plowing Effects on Soil Properties in a No‐Till Farming System
Authors: Pierce F. J. , Fortin M.‐C. , Staton M. J.
Published: July 2010

Soils in no‐tillage management are often plowed for crop rotation or to correct a pest or soil management problem. This study determined whether soil properties created by no‐tillage were retained or reestablished after plowing and return to no‐tillage. The study was conducted on a Capac loam (fine‐loamy, mixed, mesic Aeric Ochraqualf) in East Lansing, MI. In 1986 and 1987, one each of three treatments in no‐tillage since 1980 was plowed and subsequently returned to notillage (NTP86 and NTP87) and compared with conventional tillage (CT) and long‐term no‐tillage (NT). In all treatments, plowing, compared with NT, decreased bulk density by 0.17 to 0.28 Mg m−3, increased total porosity from 0.03 to 0.10 m3 m−3, increased macroporosity by 0.05 to 0.13 m3 m−3, and decreased microporosity by 0.03 to 0.05 m3 m−3. Wheel traffic increased bulk density 0.14 to 0.18 Mg m−3 in the plowed soils but only 0.04 Mg m−3 in the NT soil. Soil surface P, K, and organic C (OC) were redistributed in the surface 200 mm by plowing, but plowing did not eliminate stratification of chemical properties in the surface 50 mm. The NTP87 treatment enhanced mineralization of N over both CT and NT by 9.8 to 18.4 g N m−3 in the surface 50 mm in 1987. Residual effects were evident 1 yr after plowing. However, 4 to 5 yr after plowing, most soil properties had returned to levels of NT, although reestablishment of C and N in the surface remained lower than NT.
Relations between Soil Color and Landsat Reflectance on Semiarid Rangelands
Authors: Post Donald F. , Horvath E. H. , Lucas W. M. , White S. A. , Ehasz M. J. , Batchily A. K.
Published: July 2010

The reflectance of radiant energy from the earth's surface in sparsely vegetated arid rangelands is determined by the characteristics of the soil and geologic material on the land's surface. This study measured the color characteristics of earth surface materials collected from a semiarid rangeland in southeastern Arizona and compared these colors to digital numbers recorded by Landsat. Other parameters including particle size, slope, and vegetation were also evaluated, but the color characteristics of the fine earth soil and rock fragments measured with a colorimeter were most strongly correlated to Landsat digital numbers. The numerical values of the color components (hue, value, and chroma) for three different soil and rock fragment size fractions were related in a multiple linear regression equation to Landsat digital reflectance numbers. The R2 for Band 4 (0.5–0.6 µm), Band 5 (0.6–0.7 µm), Band 6 (0.7–0.8 µm), Band 7 (0.8–1.1 µm), and the sum of the four bands were 0.85, 0.69, 0.71, 0.68, and 0.75, respectively. The color of earth surface features in sparsely vegetated land areas should be precisely and accurately determined because of its very strong correlation with remotely sensed spectral data. The use of colorimeters to quantify the color of earth surface features will significantly help in evaluating remotely sensed data, particularly for land‐scapes in arid regions.
E. W. Hilgard and John Wesley Powell: Efforts for a Joint Agricultural and Geological Survey
Authors: Amundson Ronald , Yaalon Dan H.
Published: July 2010

Eugene W. Hilgard, professor of agriculture at the University of California, was a pioneer in agricultural, or soil, survey. In the mid to late 1880s, he vigorously sought to incorporate agricultural survey within the U.S. Geological Survey (USGS), then under the direction of Major John Wesley Powell. Hilgard recognized that agricultural survey fell within the USGSs original charge of land classification. Powell considered soil survey to be part of a much larger plan that was needed to develop the water and land resources of the arid American West. Through his early efforts, Hilgard was offered a position in the USGS (1886), which he declined, and he helped to make soil investigations part of the USGSs activities by the end of the 1880s. A bill to appropriate funds for the USGS to conduct an agricultural survey, supported by both Powell and Hilgard, was defeated by Congress in 1888. In 1889, Powell helped lead an effort to appoint Hilgard the Assistant Secretary of Agriculture (which Hilgard also declined), a position that would have given Hilgard power to help develop a national agricultural or soil survey. In the late 1880s and early 1890s, Hilgard was a strong supporter of Powell's attempts to transfer the USGS from the Department of Interior to the newly organized Department of Agriculture (USDA). Ultimately, Powell was attacked by western politicians, who rejected his plans for intensive mapping and land planning and for his attempts to join the USDA, effectively ending Hilgard's dream of a federal program of joint agricultural and geological surveys.
Compressive Strength for an Aggregated and Partially Saturated Soil
Authors: Nearing Mark A.
Published: July 2010

Soil strength increases with the application of soil water suctions, which impart an increasing level of effective confining stress on the soil mass. The relationship between effective confining stress and suction is influenced by soil water content. For sands, effective confining stress is approximated by the multiple of soil water suction and total saturation of the soil pores. For aggregated soils this is not true. This study was undertaken to test the hypothesis that the saturation of interaggregate pores in aggregated soils controls the level of effective stress and, subsequently, soil strength relationships. The soil used is a highly aggregated, mixed mineralogy, Paulding clay (very‐fine, illitic, nonacid, mesic Typic Haplaquept) from northwestern Ohio. Unconfined compressive strength was measured for five different aggregate size groups across a range of soil water suction levels. Triaxial compression strength was measured on saturated soil samples for which effective confining stress was well defined within the triaxial test cell. Results indicated that axial stress at failure for the soil was linearly related to the product of soil water suction and the saturation level of the interaggregate soil pores. Also, the slope of the regression line was statistically equivalent to the slope of the line relating axial failure stress and effective confining stresses in the saturated triaxial tests. The experimental results support the hypothesis that interaggregate pore water controls the effective confining stress level, and hence compressive strength, for aggregated soil.
Effect of Flow Rate and Path Length on p‐Nitrophenol Biodegradation during Transport in Soil
Authors: Kelsey Jason W. , Alexander Martin
Published: July 2010

The effect of flow rate and path length on the biodegradation of p‐nitrophenol (PNP) during its transport through soil was measured in columns of unsaturated soil receiving a continuous application of the compound. The PNP concentration in the effluents increased to a maximum and then decreased. Within 3 to 4 d after the initial addition of PNP, the number of microorganisms capable of degrading PNP reached a density that was sufficient to degrade all of the applied compound. The percentage of PNP entering the effluents from the soil decreased as the flow rate was reduced or the path length was increased, presumably because of the longer period of contact between the micro‐organisms and the test compound. When PNP was still leaching into the effluent from a 10‐cm column of soil, the microorganisms able to degrade PNP grew extensively at the 2.5‐ but not the 7.0‐cm depth. At the time that all of the PNP flowing through the soil was degraded, microorganisms capable of transforming PNP were concentrated in the top one‐fourth of the soil column. The reasons for the lack of extensive growth of the PNP‐degrading population at lower depths in soil containing PNP are unknown.
Denitrification, Immobilization, and Mineralization in Nitrate Limited and Nonlimited Residue‐Amended Soil
Authors: McKenney D. J. , Wang S.‐W. , Drury C. F. , Findlay W. I.
Published: July 2010

Although the use of cover crops and intercrops has been increasing, little information exists on effects these plant residues may have on soil microbial processes. Our objectives were to determine effects of several crop residues representing a range of C/N ratios (11.3–65.5) on mineralization, immobilization, denitrification, and dissimilatory NO3− reduction in Brookston clay loam with limiting and nonlimiting NO3− concentrations. Residues were obtained from two legumes, hairy vetch (HV; Vicia villosa L.) and red clover (RC; Trifolium pratense L.); two grasses, annual ryegrass (ARG; Lolium temulentum L.,) and reed canarygrass (RCG; Phalaris arundinacea L.); and corn (Zea mays L.). Nitrate consumption and NH4+, NO2−, NO, and N2O production were measured in soil with 10 g residue kg−1 in a gas flow system. In soil without added NO3−, during a 5‐d aerobic incubation, 86% of the existing NO3− was immobilized with RC, 66% with corn, 44% with HV and ARG, and 41% with RCG. Intense immobilization in the RC and corn treatments limited the amount of NO3− available for denitrification, whereas during the subsequent anaerobic phase, only HV, ARG, and RCG stimulated denitrification. The enhanced net immobilization with RC was surprising because the C/N ratio for this residue was relatively low (15:1). Ammonium production was greatest with the HV residue. Nitrate addition to HV‐amended soil further increased NH4+ production with 91 mg N kg−1 being produced during a 5‐d aerobic, 6‐d anaerobic incubation. The nature of the residue‐derived organic material is more important than simply the C/N ratio in regulating these microbial processes in these short‐term incubations.
Precipitation Use Efficiency of Soybean and Grain Sorghum in Monoculture and Rotation
Authors: Varvel Gary E.
Published: July 2010

Rainfed cropping systems are highly dependent on water use efficiency of crops in the rotation, especially in subhumid and semiarid areas. Precipitation use efficiency (PUE), an alternative to water use efficiency, is equally effective for water use evaluation in long‐term rainfed studies. We hypothesized that crop rotation and N fertilizer rates altered PUE of soybean [Glycine max (L.) Merr.] and grain sorghum [Sorghum bicolor (L.) Moench]. To test this, soybean (five cropping systems) and grain sorghum (four cropping systems) were grown under rainfed conditions at Mead, NE, on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll), each at three N fertilizer rates. Precipitation use efficiency values for the 1984 through 1991 cropping seasons varied from 15.5 to 59.9 and 21.6 to 159 kg ha−1 cm−1 for soybean and grain sorghum, respectively. Soybean PUE values averaged 30 kg ha−1 cm−1 and varied from 25 to 33 kg ha−1 cm−1 for the 8 yr. Grain sorghum PUE values averaged 89 kg ha−1 cm−1 and with sufficient N fertilization varied from only 94 to 99 kg ha−1 cm−1 for the 8 yr. Similar PUE values for soybean and grain sorghum (with adequate N fertilizer) within a given year and similar PUE values during the study among cropping systems for each crop indicated that both of these crops would be excellent options for rotations in areas with similar precipitation patterns.
Inorganic Nitrogen Determined by Laboratory and Field Extractions of Two Forest Soils
Authors: Van Miegroet Helga
Published: July 2010

To assess the effect of a delay in soil processing on inorganic N levels in N‐rich soils, field and laboratory extractions were compared at two forested sites with high N mineralization and nitrification potential. At eight sampling dates in 1989 and 1990, five mineral soil cores per site were taken between 0‐ and 10‐cm depth and transported on ice to the laboratory for KCl extraction and NH4‐N and NO3‐N analysis. At three sampling dates in 1990, soil extractions were performed in the field immediately following sampling, and inorganic N concentrations were compared between extractions. Nitrate‐N increased four‐ to sevenfold (net release of 2–7 mg NO3‐N/kg dry soil) due to the transport and relatively short delay (<24 h) in the processing of the soil samples, either coinciding with increased net N mineralization or due to transformation of NH4‐N into NO3‐N. This study indicates that if possible, soil samples should be extracted in the field, especially at N‐rich sites. The concerns raised by this study may not necessarily apply to N‐poor soils characterized by slow N transformation rates.
Simulating the Effects of Erosion on Corn Productivity
Authors: Shaffer M. J. , Schumacher T. E. , Ego C. L.
Published: July 2010

Soil erosion effects on corn (Zea mays L.) production are sparsely documented for the Corn Belt. Simulation of these effects would help identify important information gaps for the region and elsewhere and help in the understanding of basic soil‐plant processes and interactions that occur. The N Tillage Residue Management model was tested on nine field sites across the north‐central USA. The 119 site‐years of data simulated 78% (R2 of 0.78) of observed corn yield variability for a wide range of eroded soils. Slightly better predictions were made (R2 values of 0.82 and 0.80) for loess‐derived soils and soils in the eastern (wetter) study areas, respectively. Till‐derived soils and soils in the western (drier) areas had R2 values of 0.75 and 0.77, respectively. Crop yield predictions were most responsive to soil physical properties.
Surface Charge Characteristics of Podzolized Soil
Authors: Polubesova Tamara A. , Chorover Jon , Sposito Garrison
Published: July 2010

Recently developed methods for the accurate measurement of surface charge components and the points of zero charge in soils containing both permanent‐ and variable‐charge constituents were applied to a Haplorthod that is typical of podzolized soils in North America, Scandinavia, and Russia. Independently measured values of the density of structural surface charge, net proton charge, and net adsorbed ion charge were obtained for soil samples from the E2 and Bhs horizons suspended in LiCl or Li2SO4 solutions of ionic strength 1 or 10 mmol kg−1. Data taken across the pH range 2 to 6 tested successfully for conformity to the law of surface charge balance. Relationships between the point of zero net proton charge and the point of zero net charge were consistent with the fact that, at any pH, increasing ionic strength favored an increase in the net adsorbed ion charge, whereas changing from Cl− to SO2−4 favored a decrease in the net adsorbed ion charge. The methodology and charge balance analysis are applicable to any podzolized soil.
Solution/Soil Ratio and Release of Cations and Acidity from Spodosol Horizons
Authors: Skyllberg Ulf
Published: July 2010

The pH value, exchangeable acidity, and effective cation‐exchange capacity (CECe) are often used to characterize soils. In addition to properties of the soil itself, these parameters are highly attributed to electrolytes and ionic strength in extraction solutions, as well as to the solution/soil ratio (s/s ratio, liters per kilogram). The influence of the s/s ratio on pH, exchangeable acidity, and cations were studied in soil suspensions of Spodosol O, E, and Bs horizon soil samples in distilled water, 0.01 M CaCl2, 1.0 M KCl, and 0.5 M CuCl2. An enhanced s/s ratio resulted in a release of H ions from O and E horizon soil samples in agreement with a weak acid equilibrium, whereas the Bs horizon samples showed a higher buffer intensity of pH. A simultaneous release of organic acids and Al and the fact that samples from the spodic horizons were close to the point of zero charge indicate a more complicated pH buffering mechanism in these horizons. The amount of Al ions released from O and E horizon samples in 1.0 M KCl (Ale) were simply diluted when the s/s ratio was increased. Therefore, Ale is suggested to be a quite finite subpool of totally bound Al (Alt; extracted in 0.5 M CuCl2). A solution of 0.5 M CuCl2 extracted all exchangeable K+, Na+, Mg2+, Mn2+, Fe3+, and Al3+ in O horizon samples, independent of s/s ratio, whereas the release of Ca2+ was slightly enhanced with increased s/s ratio. Hydrogen ions exchangeable in 1.0 M KCl (He, centimoles of charge per kilogram) increased by 17 to 22% in O and E horizons and by 32 to 33% in Bs horizons when the s/s ratio increased from 100 to 150. Consequently, estimated He and CECe pertaining to different samples can only be accurately compared if they are obtained at the same s/s ratio or corrected for differences in the s/s ratio by specific functions for different soil horizons.
Herbicide Leaching under Tilled and No‐Tillage Fields
Authors: Gish Timothy J. , Shirmohammadi Adel , Vyravipillai Raviraj , Wienhold Brian J.
Published: July 2010

The effect of no‐tillage practices on water quality exiting the root zone of deep, well‐drained fields is largely unknown. This project was initiated to determine herbicide leaching characteristics as influenced by tillage practice and herbicide formulation. The research site consisted of four adjacent (0.25‐ha) fields, two fields each dedicated to either tilled or no‐tillage management. One field in each tillage regime received a controlled‐release formulation of atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] and alachlor [2‐chloro‐N‐(2,6‐diethylphenyl)‐N‐(methoxymethyl)‐acetamide, starch encapsulated], while the others received standard herbicide formulations of atrazine and alachlor. Both herbicide formulations were annually applied at the same rate: 1.7 kg ha−1 for atrazine and 2.8 kg ha−1 for alachlor. Atrazine, deethylatrazine [DEAT; 6‐chloro‐N‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine], alachlor, and Br− concentrations were monitored with 12 suction lysimeters (six each at 1.5‐ and 1.8‐m depths) in each field. Alachlor was detected in <3% of all samples collected, regardless of tillage practice or berbicide formulation, while atrazine was detected in >41% of the samples. Under no‐tillage, atrazine was detected in <28% of the samples with <13% exceeding the U.S. Environmental Protection Agency Health Advisory level of 3 µg L−1 atrazine. Under tilled conditions, 53% of the samples contained atrazine, with 35% exceeding 3 µg L−1 atrazine. Averaged atrazine metabolite concentration of DEAT under no‐tillage was 0.52 µg L−1 vs. 0.39 µg L−1 for tilled fields. Similar Br− transport between tillage practices and reduced atrazine levels under no‐tillage fields suggest that no‐tillage management, on deep well‐drained soils, can have a positive impact on groundwater quality.
Combined Microdiffusion‐Hypobromite Oxidation Method for Determining Nitrogen‐15 Isotope in Ammonium
Authors: Risgaard‐Petersen Nils , Revsbech Niels Peter , Rysgaard Søren
Published: July 2010

A limiting factor for work with biological N transformations has been unsatisfactory procedures for analysis of 15N isotope labeling in small amounts of NH+4. Using the procedure described here, it is now possible to perform accurate determinations in NH+4 pools as small as 2 nmol. By diffusion of NH3 through a gas phase, N in NH+4 is transferred from the sample and into a hypobromite solution, where an oxidation to N2 occurs. The N2 originating from the oxidation is mixed with N2 initially dissolved in the sample, which functions as a carrier during subsequent mass spectrometry. Random isotopic pairing of the N atoms originating from NH3 oxidation makes it possible to calculate the original 15N abundance in the NH+4 pool from the relative amounts of 14N15N and 15N15N in the reaction container. The combined microdiffusion‐hypobromite oxidation method for 15NH+4 analysis proved to be very precise (standard error <0.15 atom %, n = 5) when applied on samples with an 15N enrichment >1 atom %, and interference was found only for volatile methyl amines.
Organic Matter and Water‐Stable Aggregate Distribution in Ridge‐Tilled Surface Soil
Authors: Unger Paul W.
Published: July 2010

Soil surface conditions improve with increased organic matter (OM) and water‐stable aggregation (WSA), but surface variability may influence values obtained when soils are sampled to evaluate these factors. My hypothesis was that cultural operations for sorghum [Sorghum bicolor (L.) Moench] grown on ridges produce zones of differing soil OM and WSA. Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) was sampled at the 0‐ to 4‐cm depth in furrows, on ridge tops, and on ridge sides before and after planting, after reforming ridges, and after harvest in 1992. Tillage (conventional [CT] and ridge [early (RT‐E) or late (RT‐L) stalk shredding]), position, and crop cycle (sampling) stage affected OM and WSA. Compared with ridges, OM in furrows was greater due to residue accumulations. Mean WSA was greater on ridges with CT than with RT‐E or RT‐L because disk‐bedding to build the CT ridges moved more stable aggregates to ridges than the other treatments. More thorough mixing of residues by CT may have been involved also. Ridge and furrow positions and possibly ridge sides require separate sampling for obtaining representative OM and WSA data from ridge‐tilled soil, especially where ridge tops are cleared at planting. Ridge clearing at planting should be limited to avoid residue reduction and lowered WSA that could lead to soil crusting and impaired seedling emergence.