Soil Science Society of America Journal

Published by Soil Science Society of America
Online ISSN: 1435-0661
Publications
Equipment used to establish Hexadecane residual saturation and to freeze and contain samples during flight. Left: Liquid nitrogen vapor shipper used to quickly freeze samples during KC135 flight (about 15 s). Right: Suction system to establish residual saturation of Hexadecane in capsule. 
The trajectory of the KC135 aircraft showing a typical 0-g maneuver. Each parabola consists of a 0-g period of approximately 25 s and 1.8-g period of approximately 40 to 60 s.
Representative accelerometer profile of KC-135 flight. Unit for y axis is g(t )/g(1 ) where g(t ) is acceleration of gravity at time t and g(1 ) equals acceleration of gravity on Earth (1 g ).
Cumulative blob size distributions from Day 4 experiments of KC-135 flight. 
Volume increase of glass beads sample under microgravity aboard KC-135 flight. (a) Comparison of samples of Day-2 experiments; (b) Comparison of samples of Day-3 experiments under 1.8 and 0 g . 
Article
Designing a reliable plant growth system for crop production in space requires the understanding of pore fluid distribution in porous media under microgravity. The objective of this experimental investigation, which was conducted aboard NASA KC-135 reduced gravity flight, is to study possible particle separation and the distribution of discontinuous wetting fluid in porous media under microgravity. KC-135 aircraft provided gravity conditions of 1, 1.8, and 10(-2) g. Glass beads of a known size distribution were used as porous media; and Hexadecane, a petroleum compound immiscible with and lighter than water, was used as wetting fluid at residual saturation. Nitrogen freezer was used to solidify the discontinuous Hexadecane ganglia in glass beads to preserve the ganglia size changes during different gravity conditions, so that the blob-size distributions (BSDs) could be measured after flight. It was concluded from this study that microgravity has little effect on the size distribution of pore fluid blobs corresponding to residual saturation of wetting fluids in porous media. The blobs showed no noticeable breakup or coalescence during microgravity. However, based on the increase in bulk volume of samples due to particle separation under microgravity, groups of particles, within which pore fluid blobs were encapsulated, appeared to have rearranged themselves under microgravity.
 
Nutrient solution total organic C (TOC) levels over time. (a)  
Nutrient solution acid (HNO 3 ) requirement for pH control Fig. 2. Plant growth over time for no chelate (NC), HEDTA, MESover time, an indication of NO 3 uptake rates for no chelate (NC), buffer, and humic acid (HA) treatments. Absolute growth (g plant 1 ) HEDTA, MES-buffer and humic acid (HA) treatments. Least sigwas fitted to logistic growth curves. The coefficient of determinanificant difference (LSD 0.05 ) was used to compare cumulative acid tion, r 2 , for the fitted model was 0.98, indicating a very good fit of additions at a fixed date. the model to the data. The P value for the F-test comparing the four treatment groups was 0.0335. Post hoc pairwise comparisons of the treatment groups showed NC and HA were the most dissimieffect of stress on productivity, growth curves can  
Leaf tissue (a) Cu and (b) Zn concentrations over time for no  
Article
Humic acid (HA) is a relatively stable product of organic matter decomposition and thus accumulates in environmental systems. Humic acid might benefit plant growth by chelating unavailable nutrients and buffering pH. We examined the effect of HA on growth and micronutrient uptake in wheat (Triticum aestivum L.) grown hydroponically. Four root-zone treatments were compared: (i) 25 micromoles synthetic chelate N-(4-hydroxyethyl)ethylenediaminetriacetic acid (C10H18N2O7) (HEDTA at 0.25 mM C); (ii) 25 micromoles synthetic chelate with 4-morpholineethanesulfonic acid (C6H13N4S) (MES at 5 mM C) pH buffer; (iii) HA at 1 mM C without synthetic chelate or buffer; and (iv) no synthetic chelate or buffer. Ample inorganic Fe (35 micromoles Fe3+) was supplied in all treatments. There was no statistically significant difference in total biomass or seed yield among treatments, but HA was effective at ameliorating the leaf interveinal chlorosis that occurred during early growth of the nonchelated treatment. Leaf-tissue Cu and Zn concentrations were lower in the HEDTA treatment relative to no chelate (NC), indicating HEDTA strongly complexed these nutrients, thus reducing their free ion activities and hence, bioavailability. Humic acid did not complex Zn as strongly and chemical equilibrium modeling supported these results. Titration tests indicated that HA was not an effective pH buffer at 1 mM C, and higher levels resulted in HA-Ca and HA-Mg flocculation in the nutrient solution.
 
Article
Mixtures of zeolite and phosphate rock (PR) have the potential to provide slow-release fertilization of plants in synthetic soils by dissolution and ion-exchange reactions. This study was conducted to examine solubility and cation-exchange relationships in mixtures of PR and NH4- and K-saturated clinoptilolite (Cp). Batch-equilibration experiments were designed to investigate the effect of PR source, the proportion of exchangeable K and NH4, and the Cp to PR ratio on solution N, P, K, and Ca concentrations. The dissolution and cation-exchange reactions that occurred after mixing NH4- and K-saturated Cp with PR increased the solubility of the PR and simultaneously released NH4 and K into solution. The more reactive North Carolina (NC) PR rendered higher solution concentrations of NH4 and K when mixed with Cp than did Tennessee (TN) PR. Solution P concentrations for the Cp-NC PR mixture and the Cp-TN PR mixture were similar. Solution concentrations of N, P, K, and Ca and the ratios of these nutrients in solution varied predictably with the type of PR, the Cp/PR ratio, and the proportions of exchangeable K and NH4 on the Cp. Our research indicated that slow-release fertilization using Cp/PR media may provide adequate levels of N, P, and K to support plant growth. Solution Ca concentrations were lower than optimum for plant growth.
 
Article
Incorporation of Mg, S, and plant-essential micronutrients into the structure of synthetic hydroxyapatite (HA) may be advantageous for closed-loop systems, such as will be required on Lunar and Martian outposts, because these apatites can be used as slow-release fertilizers. Our objective was to synthesize HA with Ca, P, Mg, S, Fe, Cu, Mn, Zn, Mo, B, and Cl incorporated into the structure, i.e., nutrient-substituted apatites. Hydroxyapatite, carbonate hydroxyapatite (CHA), nutrient-substituted hydroxyapatite (NHA), and nutrient-substituted carbonate hydroxyapatite (NCHA) were synthesized by precipitating from solution. Chemical and mineralogical analysis of precipitated samples indicated a considerable fraction of the added cations were incorporated into HA, without mineral impurities. Particle size of the HA was in the 1 to 40 nm range, and decreased with increased substitution of nutrient elements. The particle shape of HA was elongated in the c-direction in unsubstituted HA and NHA but more spherical in CHA and NCHA. The substitution of cations and anions in the HA structure was confirmed by the decrease of the d[002] spacing of HA with substitution of ions with an ionic radius less than that of Ca or P. The DTPA-extractable Cu ranged from 8 to 8429 mg kg-1, Zn ranged from 57 to 1279 mg kg-1, Fe from 211 to 2573 mg kg-1, and Mn from 190 to 1719 mg kg-1, depending on the substitution level of each element in HA. Nutrient-substituted HA has the potential to be used as a slow-release fertilizer to supply micronutrients, S, and Mg in addition to Ca and P.
 
Article
The incorporation of micronutrients (e.g., Fe, Mn, Cu) into synthetic hydroxyapatite (SHA) is proposed for slow release of these nutrients to crops in NASA's Advanced Life Support (ALS) program for long-duration space missions. Separate Fe3+ (Fe-SHA), Mn2+ (Mn-SHA), and Cu2+ (Cu-SHA) containing SHA materials were synthesized by a precipitation method. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the location of Fe3+, Mn2+, and Cu2+ ions in the SHA structure and to identify other Fe(3+)-, Mn(2+)-, and Cu(2+)-containing phases that formed during precipitation. The EPR parameters for Fe3+ (g=4.20 and 8.93) and for Mn2+ (g=2.01, A=9.4 mT, D=39.0 mT and E=10.5 mT) indicated that Fe3+ and Mn2+ possessed rhombic ion crystal fields within the SHA structure. The Cu2+ EPR parameters (g(z)=2.488, A(z)=5.2 mT) indicated that Cu2+ was coordinated to more than six oxygens. The rhombic environments of Fe3+ and Mn2+ along with the unique Cu2+ environment suggested that these metals substituted for the 7 or 9 coordinate Ca2+ in SHA. The EPR analyses also detected poorly crystalline metal oxyhydroxides or metal-phosphates associated with SHA. The Fe-, Mn-, and Cu-SHA materials are potential slow release sources of Fe, Mn, and Cu for ALS and terrestrial cropping systems.
 
Article
The National Aeronautics and Space Administration's (NASA) Advanced Life Support (ALS) Program is evaluating the use of Fe-, Mn-, and Cu-containing synthetic hydroxyapatite (SHA) as a slow release fertilizer for crops that might be grown on the International Space Station or at Lunar and Martian outposts. Separate Fe-, Mn-, and Cu-containing SHA materials along with a transition-metal free SHA (pure-SHA) were synthesized using a precipitation method. Chemical and mineralogical analyses determined if and how Fe, Mn, and Cu were incorporated into the SHA structure. X-ray diffraction (XRD), Rietveld refinement, and transmission electron microscopy (TEM) confirmed that SHA materials with the apatite structure were produced. Chemical analyses indicated that the metal containing SHA materials were deficient in Ca relative to pure-SHA. The shift in the infrared PO4-mu 3 vibrations, smaller unit cell parameters, smaller particle size, and greater structural strain for Fe-, Mn-, and Cu-containing SHA compared with pure-SHA suggested that Fe, Mn, and Cu were incorporated into SHA structure. Rietveld analyses revealed that Fe, Mn, and Cu substituted into the Ca2 site of SHA. An Fe-rich phase was detected by TEM analyses and backscattered electron microscopy in the Fe-containing SHA material with the greatest Fe content. The substitution of metals into SHA suggests that metal-SHA materials are potential slow-release sources of micronutrients for plant uptake in addition to Ca and P.
 
Article
Nutrient release in clinoptilolite-phosphate rock (Cp-PR) systems occurs through dissolution and cation-exchange reactions. Investigating the kinetics of these reactions expands our understanding of nutrient release processes. Research was conducted to model transport kinetics of nutrient release in Cp-PR systems. The objectives were to identify empirical models that best describe NH4, K, and P release and define diffusion-controlling processes. Materials included a Texas clinoptilolite (Cp) and North Carolina phosphate rock (PR). A continuous-flow thin-disk technique was used. Models evaluated included zero order, first order, second order, parabolic diffusion, simplified Elovich, Elovich, and power function. The power-function, Elovich, and parabolic-diffusion models adequately described NH4, K, and P release. The power-function model was preferred because of its simplicity. Models indicated nutrient release was diffusion controlled. Primary transport processes controlling nutrient release for the time span observed were probably the result of a combination of several interacting transport mechanisms.
 
Article
Two equations are currently available for estimating soil volumetric heat capacity (pc) with the dual-probe heat-pulse (DPHP) method. One is simple but gives only approximate results because it assumes that the DPHP sensor releases an impulse of heat instantaneously. The other explicitly accounts for the finite duration of heating and gives exact results. Unfortunately, the equation that gives exact results involves the exponential integral function, which is not available in most computer spreadsheet software packages or data logger function libraries. In this note we introduce an approximation of the exact equation that contains only simple algebraic functions. The approximation consists of the first five terms of a Taylor series, which are written as a telescoped polynomial for computational purposes. For most applications of the DPHP method, the polynomial approximation gives estimates of pc that are at least an order of magnitude more accurate than estimates obtained from the simple equation based on instantaneous heating.
 
Article
The incorporation of micronutrients into synthetic hydroxyapatite (SHA) is proposed for slow release of these nutrients to crops in the National Aeronautics and Space Administration's (NASA's) Advanced Life Support (ALS) program for Lunar or Martian outposts. Solid state 31P nuclear magnetic resonance (NMR) was utilized to examine the paramagnetic effects of Fe3+, Mn2+, and Cu2+ to determine if they were incorporated into the SHA structure. Separate Fe3+, Mn2+, and Cu2+ containing SHA materials along with a transition metal free SHA (pure-SHA) were synthesized using a precipitation method. The proximity (<1 nm) of the transition metals to the 31P nuclei of SHA were apparent when comparing the integrated 31P signal intensities of the pure-SHA (87 arbitrary units g-1) with the Fe-, Mn-, and Cu-SHA materials (37-71 arbitrary units g-1). The lower integrated 31P signal intensities of the Fe-, Mn-, and Cu-SHA materials relative to the pure-SHA suggested that Fe3+, Mn2+, and Cu2+ were incorporated in the SHA structure. Further support for Fe3+, Mn2+, and Cu2+ incorporation was demonstrated by the reduced spin-lattice relaxation constants of the Fe-, Mn-, and Cu-SHA materials (T'=0.075-0.434s) relative to pure-SHA (T1=58.4s). Inversion recovery spectra indicated that Fe3+, Mn2+, and Cu2+ were not homogeneously distributed about the 31P nuclei in the SHA structure. Extraction with diethylene-triamine-penta-acetic acid (DTPA) suggested that between 50 and 80% of the total starting metal concentrations were incorporated in the SHA structure. Iron-, Mn-, and Cu-containing SHA are potential slow release sources of Fe, Mn, and Cu in the ALS cropping system.
 
Article
Micronutrient-substituted synthetic hydroxyapatite (SHA) is being evaluated by the National Aeronautics and Space Administration's (NASA) Advanced Life Support (ALS) Program for crop production on long-duration human missions to the International Space Station or for future Lunar or Martian outposts. The stirred-flow technique was utilized to characterize Ca, P, Fe, Mn, and Cu release characteristics from Fe-, Mn-, and Cu-containing SHA in deionized (DI) water, citric acid, and diethylene-triamine-pentaacetic acid (DTPA). Initially, Ca and P release rates decreased rapidly with time and were controlled by a non-SHA calcium phosphate phase(s) with low Ca/P solution molar ratios (0.91-1.51) relative to solid SHA ratios (1.56-1.64). At later times, Ca/P solution molar ratios (1.47-1.79) were near solid SHA ratios and release rates decreased slowly indicating that SHA controlled Ca and P release. Substituted SHA materials had faster dissolution rates relative to unsubstituted SHA. The initial metal release rate order was Mn > Cu > Fe which followed metal-oxide/phosphate solubility suggesting that poorly crystalline metal-oxides/phosphates were dominating metal release. Similar metal release rates for all substituted SHA (approximately 0.01 cmol kg-1 min-1) at the end of the DTPA experiment indicated that SHA dissolution was supplying the metals into solution and that poorly crystalline metal-oxide/phosphates were not controlling metal release. Results indicate that non-SHA Ca-phosphate phases and poorly crystalline metal-oxide/phosphates will contribute Ca, P, and metals. After these phases have dissolved, substituted SHA will be the source of Ca, P, and metals for plants.
 
Article
Understanding the effect of gravity on hydraulic properties of plant growth medium is essential for growing plants in space. The suitability of existing models to simulate hydraulic properties of porous medium is uncertain due to limited understanding of fundamental mechanisms controlling water and air transport in microgravity. The objective of this research was to characterize saturated and unsaturated hydraulic conductivity (K) of two particle-size distributions of baked ceramic aggregate using direct measurement techniques compatible with microgravity. Steady state (Method A) and instantaneous profile measurement (Method B) methods for K were used in a single experimental unit with horizontal flow through thin sections of porous medium providing an earth-based analog to microgravity. Comparison between methods was conducted using a crossover experimental design compatible with limited resources of space flight. Satiated (natural saturation) K ranged from 0.09 to 0.12 cm s-1 and 0.5 to >1 cm s-1 for 0.25- to 1- and 1- to 2-mm media, respectively. The K at the interaggregate/intraaggregate transition was approximately 10(-4) cm s-1 for both particle-size distributions. Significant differences in log(10)K due to method and porous medium were less than one order of magnitude and were attributed to variability in air entrapment. The van Genuchten/Mualem parametric models provided an adequate prediction of K of the interaggregate pore space, using residual water content for that pore space. The instantaneous profile method covers the range of water contents relevant to plant growth using fewer resources than Method A, all advantages for space flight where mass, volume, and astronaut time are limited.
 
Article
Exchangeable Al in subsoils of Ultisols in the southeastern USA can restrict rooting depth. Downward movement of basic cations (Ca, Mg, and K), applied as lime and fertilizer, may diminish that restriction over time. Materials from the argillic horizon were collected from three paired sites, having managed (long-term cropping) and nonmanaged topsoils (Typic Paleudults and Hapludults). One managed site was cropped continuously for 15 yr while the others were cultivated for more than 30 yr. Concentrations of extractable cations and other nutrients from the paired sites were compared to determine the magnitude of change due to management. The ability of the subsoils to support plant growth was evaluated in a missing-nutrient greenhouse experiment with sorghum [Sorghum bicolor (L.) Moench]. Subsoils of managed sites had greater effective cation-exchange capacity (CEC) and base saturation than those of non-managed sites. While availabilities of Ca, Mg, and K in subsoils of nonmanaged sites were inadequate to support maximal plant growth, they were adequate in subsoils of managed sites. Compared with nonmanaged sites, KCl-exchangeable Al in subsoils of managed sites was 23% lower at the 15-yr location and 65 and 100% lower at the two other locations. In the absence of lime, sorghum growth was almost totally inhibited on nonmanaged subsoils amended with optimum nutrients. On the managed subsoils, where 100, 65, and 23% of the nonmanaged exchangeable Al had been neutralized by topsoil fertilization and liming, growth reductions under the same conditions were 0, 50, and 100%, respectively. Thus, relatively long-term management had improved these Ultisol subsoils for root growth and development.
 
Article
The effects of sagebrush conversion on the soil properties of a high-elevation portion of the Western Intermountain Sagebrush Steppe (West, 1983) are described. Changes were found in only a few soil chemical properties after conversion to grassland. It was found that surface concentrations of N were lower under grass vegetation than under undisturbed vegetation. Undershrub net N mineralization rates were higher under shrubs in the sagebrush vegetation than under former shrubs in the grass vegetation.
 
Article
Surface soil samples from a wide range of naturally occurring soils were obtained for the purpose of studying the characteristic variations in soil reflectance as these variations relate to other soil properties and soil classification. A total 485 soil samples from the U.S. and Brazil representing 30 suborders of the 10 orders of 'Soil Taxonomy' was examined. The spectral bidirectional reflectance factor was measured on uniformly moist soils over the 0.52 to 2.32 micron wavelength range with a spectroradiometer adapted for indoor use. Five distinct soil spectral reflectance curve forms were identified according to curve shape, the presence or absence of absorption bands, and the predominance of soil organic matter and iron oxide composition. These curve forms were further characterized according to generically homogeneous soil properties in a manner similar to the subdivisions at the suborder level of 'Soil Taxonomy'. Results indicate that spectroradiometric measurements of soil spectral bidirectional reflectance factor can be used to characterize soil reflectance in terms that are meaningful to soil classification, genesis, and survey.
 
Fiel d Setup for Measurement of Spectral Response from Dry and Hoist Fincastle Silt Loam with and without Surface Corn Residue.
Characteristics of Two Humid Mesic Regio n Glaciated Soils.
Chalmers Silty Clay Loam (Aquoll) and Fincastle Silt Loam (Aqualf) Soil Spectra Compared under Similar Field Condi tions. '
Response Ratios Demonstrating the Magnitude of Difference in Spectral Response Between Spectral Curves for Identically Treated Fincastle/Chalmers Soils. FIELDDRY = bare dry soil; FLDMOIST = bare most soil; RESDRY = dry soil with corn residue; RESMOIST = moist soil with corn residue; LABMOIST = laboratory-measured moist soil.
Article
Spectral responses of two glaciated soils, Chalmers silty clay loam and Fincastle silt loam, formed under prairie grass and forest vegetation, respectively, were measured in the laboratory under controlled moisture equilibria using an Exotech Model 20C spectroradiometer to obtain spectral data in the laboratory under artificial illumination. The same spectroradiometer was used outdoors under solar illumination to obtain spectral response from dry and moistened field plots with and without corn residue cover, representing the two different soils. Results indicate that laboratory-measured spectra of moist soil are directly proportional to the spectral response of that same field-measured moist bare soil over the 0.52 micrometer to 1.75 micrometer wavelength range. The magnitudes of difference in spectral response between identically treated Chalmers and Fincastle soils are greatest in the 0.6 micrometers to 0.8 micrometer transition region between the visible and near infrared, regardless of field condition or laboratory preparation studied.
 
Organic carbon (OC), Fe and Mn oxide contents, particle-size distribution, and observed Munsell colors of the four soils used in this study. _ 
Article
Recent breakthroughs in remote-sensing technology have led to the development of high spectral resolution imaging sensors for observation of earth surface features. This research was conducted to evaluate the effects of organic matter content and composition on narrowband soil reflectance across the visible and reflective infrared spectral ranges. Organic matter from four Indiana agricultural soils, ranging in organic C content from 0.99 to 1.72 percent, was extracted, fractionated, and purified. Six components of each soil were isolated and prepared for spectral analysis. Reflectance was measured in 210 narrow bands in the 400- to 2500-nm wavelength range. Statistical analysis of reflectance values indicated the potential of high dimensional reflectance data in specific visible, near-infrared, and middle-infrared bands to provide information about soil organic C content, but not organic matter composition. These bands also responded significantly to Fe- and Mn-oxide content.
 
Article
Bulk density a fundamental soil property that is difficult to determine for gravelly to gravelly soils because results vary significantly with volume. For such coarse soils, the representative volume (for whole-soil density) should be large, but guidelines for selecting an appropriate sample volume do not exist. We evaluate the representative volume for a soil with abundant rock fragments, by comparing measured properties of ranging in volume from 0.03 to 410 liters, For whole-soil bulk density determination, the representative volume is 4 liters or larger for a soil horizon containing gravel (by volume) and is between 5 and 50 liters for a soil horizon containing gravel. of that size are prohibitively large, so an alternative approach that starts with measurement of fine-earth bulk density. For earth bulk density, the sample volume needed for representative results is between 0.2 liters and 1 liter for gravelly to extremely gravelly soils. The alternative approach reliably synthesizes...
 
Article
The mobility of As in soils depends on several factors including redox potential, soil mineralogy, pH, and the presence of other oxyanions that compete with As for soil retention sites. We investigated the effects of pH and competing anions on the adsorption of arsenate [As(V)] on a-FeOOH (goethite) and (gibbsite). Batch equilibrium As(V) adsorption experiments were conducted with P and MO as competing anions in order to produce single-anion [As(V), P, and MO] and binary-anion [As(V/P and As(V)/Mo] adsorption envelopes (adsorp- tion vs. solution pH). Arsenate and P single-anion adsorption envelopes were similar with substantial adsorption occurring across a wide pH range, including pH values above the points of zero charge of the oxides. Maximum MO adsorption occurred across a narrower pH range (pH 4-6). On both oxides, equimolar P concentrations decreased As(V) adsorption within the pH range 2 to 11, whereas MO decreased As(V) adsorption only below pH 6. The constant capacita...
 
Relation between the clay content of the soil samples and the liquid limit for the natural soil (Treatment A), soil saturated with Ca (Treatment B), and salt-wasbed soil (Treatment C).  
Relation between the plasticity index (liquid limit minus plastic limit) and the clay content of the soils for the natural soil (Treatment A), soil saturated with Ca (Treatment B), and salt-washed soil (Treatment C).  
Relation between the water content at 0.03 MPa and the liquid limit for the natural soil (Treatment A), soil saturated with Ca (Treatment B), and salt-washed soil Treatment C).  
Electric conductivity of saturated extract (ECSE)-sodium adsorption ratio (SAR) stability line for Ebro Basin soil (from Lebron, 1989) and Treatments B and C soil samples.  
Article
General guidelines to reclaim saline or sodic soils do not adequately consider variables such as pH and the presence of organic matter that are known to affect soil stability. Poor structural stability of sodic, saline-sodic, and high-pH soils adversely influences crop yields; promotes piping, tunneling, and slope erosion; and can accelerate the failure of water conveyance systems. We evaluated six soil teats, used to measure physico-cbemical properties, for their suitability to evaluate the structural stability of a calcareous, saline-sodic soil under reclama- tion. The stability tests were wilting point, plastic limit, coefficient of linear extensibility (COLE,& water content at 0.03 MPa, liquid limit, and dispersion index. The range of electrical conductivity (EC) studied was 0.5 to 20 dS sodium adsorption ratio (SAR) 0 to 400 (mmol and pH 8.4 to 10.5. The results obtained indicate that the amount of water necessary for a soil to Sow under standard conditions for the liquid ...
 
Quarter-section identification map.
Median water content for various quarter-sections.
Article
A geostatistical analysis of soil salinity in an agricultural area in the San Joaquin Valley included measurements of electrical conductivity of soil paste extract and water content of soil samples supplemented by surface measurements of apparent electrical conductivity Prediction of soil salinity at unsampled points by cokriging and is worthwhile because measurements are quicker than soil sampling. This work studies how patterns of predicted by cokriging with are influenced by variation in gravimetric water content (W). The data are mean = 1.00 0.13 dS for 2378 locations, mean = 1.40 0.29 dS and mean gravimetric W = 0.260 0.003, both averaged for four samples from 0.3-m intervals to 1.2-m depth for 315 locations. The coefficient of determination for vs. increased with depth from 0.05 to 0.54 whereas the for vs. W decreased from 0.48 to 0.28. A gray-scale map contained nine out of 56 quarter-section boundaries coinciding with step variations in The t-statistics for differences in m...
 
Comparison of the stream tube model with the macroscopic convection-dispersion equation (CDE), with effective parameters based on the breakthrough curves in terms of flux-averaged concentration, &, for predicting &-profiles at t = 2 and 5 d as a result of a l-d application of a nonreactive solute to an initially solute-free field (BVP = boundary value problem; x = depth).
Breakthrough curves for the geld-scale flux-averaged concentration (&) at x = 250 cm for a perfect negative correlation between the pore-water velocity and the nonequilibrium parameter (pV. =-I).
Article
Field-scale solute transport is typically difficult to model due to the complexity and heterogeneity of flow and transport in natural soils. The stream tube model attempts to stochastically describe transport across the field for relatively short travel distances by viewing the field as a series of independent vertical soil columns. This study investigates the stream tube model with the chemical equilibrium and nonequilibrium convection-dispersion equation (CDE) for local-scale transport. A bivariate (joint) lognormal probability density function was used for three pairs of random transport parameters: (i) the dispersion coefficient, D, and the pore-water velocity, v; (ii) the distribution coefficient for linear adsorption, and v; and (iii) the first- order rate coefficent for nonequilibrium adsorption, a, and v. Expressions for travel time moments as a rsult of a Dirac input were derived to characterize field-scale transport according to the stream tube model. The mean breakthrough ...
 
Article
An instrument for making rapid measurements of the soil moisture content in the top few meters of soil is an essential tool for many applications, including understanding of soil water dynamics, evaluation of agriculture water stress, validation of soil moisture modeling, and assimilation of remotely sensed near-surface soil moisture data. Studies have shown that electrical resistance measurements may be used to measure soil moisture content. In this paper, electrical resistivity (resistance multiplied by a geometric factor) measurements of the soil using the OhmMapper instrument of Geometrics Inc. are compared with time domain reflectometry point measurements of soil moisture to a depth of 70 cm. It was found that the OhmMapper could measure soil moisture content with a correlation coefficient of up to 0.6. It is likely that this correlation coefficient would be greater if much deeper measurements of soil moisture were compared with the OhmMapper measurements. 1 1. INTRODUCTION Kno...
 
Distribution of total C and 6I3C values with depth in the three Oxisols (at a 0.05 significance level, the Tukey test's LSD between any points of the same profile or of two different profiles are 1.7 Mg ha-' and 0.59YÓ0 for total C and 6I3C, respectively).
Article
Etude de la distribution du carbone et de 13C et de leur variation suite au développement des cultures dans trois oxisols de la région de Piracicaba (Sao Paulo, Brésil)
 
Diagram showing the impact of plant type (C 3 and C 4 plants) and 13 C fractionation (Rayleigh fractionation coeffi ceint ε = 0 and ε < 0) on the relative pool sizes of relic soil organic C (SOC) and unharvested biomass remaining in soil after mineralization. PCR = plant C retained.
Article
The 13C natural abundance approach for determining soil organic C (SOC) stability and turnover has been used to determine SOC mineralization kinetics. These calculations generally assume that 13C fractionation during relic SOC and unharvested biomass mineralization is insignificant. The objective of this study was to determine the impact of this assumption on calculated relic SOC half-lives. Study sites were located in Minnesota and South Dakota. At the Minnesota site, SOC contained in the surface 30 cm of soil in a fallowed area decreased from 90.8 to 73.2 Mg ha-1 during a 22-yr period. Associated with this decrease was a 0.72 ppt increase in the soil delta 13C values (from -18.97 to -18.25 ppt). Based on these values, the Rayleigh fractionation constant (epsilon) of relic SOC was -3.45 ppt. At the South Dakota site, SOC decreased 10% (2.8 ± 1.8 g kg-1) and delta 13C increased 3.2% (0.548 ± 0.332 ppt) during a 5-yr period. The Rayleigh fractionation constant for this experiment was -6.94 ppt (±4.74 ppt). In a separate experiment, the delta 13C value of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] residue remained unchanged after 4 mo. The impact of 13C enrichment during relic C mineralization on calculated C budgets depends on the type of residue returned to the soil. A simulation study showed that for systems where C4 residues are returned to soil derived from C3 and C4 plants, not considering 13C enrichment during relic SOC mineralization will result in underestimating relic SOC half-lives and overestimating the contribution of fresh C4 biomass in the SOC. The effect of 13C enrichment during relic SOC and unharvested biomass mineralization had cumulative impacts on C budgets and did not cancel each other out. The reverse was true for C3 biomass. To minimize these errors, SOC maintenance rate experiments should measure 13C enrichment during relic SOC and unharvested biomass mineralization.
 
Article
A major impediment to the establishment of outplanted conifer seedlings is competition for available soil N by early successional species. The objective of this field study was to determine the fate of controlled-release fertilizer (CRF) N in soils with outplanted white spruce (Picea glauca [Moench] Voss.) and jack pine (Pinus banksiana Lamb.) seedlings, and the effect of weed control or vegetation management (VM) on fertilizer N accumulation. Nitrogen-15 labeled CRF was placed next to the seedling root plug during planting at four boreal mixed wood sites. After one growing season in the control plots, fertilizer N recovery as a percentage of 15N added was 4% in seedlings, 3% in competing vegetation, <1% leached, and 85% residual CRF. After two growing seasons, fertilizer N recovery was 15% in seedlings, 20% in competing vegetation, <1% leached, and 58% residual CRF. Overall, VM increased seedling fertilizer N uptake by almost 300% compared with conifer seedlings in control plots. In VM plots, fertilizer bags contained more N than in control plots after two growing seasons. In both treatments, >50% of the fertilizer N remained in the fertilizer bag, presumably remaining available in subsequent seasons. Calamagrostis (Calamagrostis canadensis) was the primary competitor for fertilizer N in both growing seasons, with minor competition from fireweed (Epilobium angustifolium L.), and aspen (Populus tremuloides Michx.). The use of a point source CRF delivery method resulted in high fertilizer use efficiency (FUE), and minimized losses to competing vegetation and leaching.
 
Article
Changes in soil C and N concentrations and contents in four samplings during a 32-yr period on Walker Branch watershed in Tennessee were determined and compared with previously measured C and N fluxes and with changes in ecosystem C and N pools during this period. Soils showed significant increases in C and N concentrations in surface horizons from 1972 to 2004, and most of this increase occurred between 1972 and 1982. A previously observed decline in soil C and N contents between 1982 and 1993 was reversed in 2004 such that the latter increased to near 1982 values. The changes in soil C content could be approximately accounted for by previously measured litterfall and soil CO2-C fluxes. Changes in soil N could not be accounted for by leaching, increments in vegetation, or by laboratory bias, changes during sample storage, or reasonable estimates of field sampling errors. We conclude that, although vegetation C and N pools increased steadily during the sampling period in most cases, changes in soil C and N pools on Walker Branch watershed are highly variable in both space and time, and there has been no unidirectional trend during the time period of this study.
 
(a) Simazine sorption isotherms on unamended sandy soil (Soil P2) and amended sandy soil plus liquid organic amendment (P2 
(a) Simazine and (b) 2,4-D dissapation curves in unamended 
Relative and cumulative Hg pore volume for unamended sandy soil (Soil P2) and amended sandy soil plus liquid organic amendment (P2 LOA), sandy soil plus solid organic amendment (P2 SOA), and sandy soil plus solid urban waste (P2 SUW). 
(a) Simazine and (b) 2,4-D breakthrough curves in unamended sandy soil (Soil P2) and amended sandy soil plus liquid organic amendment (P2 LOA), sandy soil plus solid organic amendment (P2 SOA), and sandy soil plus solid urban waste (P2 SUW). 
Article
Organic amendment (OA) addition is an agricultural practice that can greatly affect pesticide behavior in soil. The influence of three OAs, consisting of a liquid amendment (LOA), solid (SOA) humic amendment, and a solid urban waste (SUW), on sorption, persistence, and leaching potential of simazine (2-chloro-4,6-bis (ethylamino)-s-triazine) and 2,4-D (2,4-dichlorophenoxyacetic acid) in a sandy soil (P2) has been investigated. The OAs were added to P2 at a rate of 5% (w/w). Sorption was studied using the batch equilibration technique, degradation by incubations at 20 degrees C and -0.33 kPa moisture content, and leaching using handpacked soil columns. Simazine sorption increased in the order of P2 less than or equal to P2 + LOA < P2 + SUW < P2 + SOA. The herbicide, 2,4-D, did not sorb on P2 soil, but in amended soils sorption increased in the same order as simazine. The lower sorption of both herbicides in P2 + LOA as compared with P2 + SOA and P2 + SUW is attributed to higher dissolved organic matter (DOM) content of LOA. Simazine's half-life was reduced upon amendment. Degradation of 2,4-D followed a sigmoidal rate in P2, P2 + SOA, and P2 + SUW, but not in P2 + LOA, in which 2,4-D persistence was much higher. The higher stability of 2,4-D in P2 + LOA has been attributed to 2,4-D-dissolved organic C interactions. Leaching studies indicate that degradation affects movement to a higher extent than sorption, specially in the case of 2,4-D in P2 + LOA soil, in which the amounts leached are much higher than those in unamended soil. In the case of simazine and P2 + SUW soil, greater reduction in large-size conducting pores upon amendment, as revealed in Hg porosimetry studies, resulted in a greater reduction of leaching than that suggested from the small differences in sorption and degradation between P2 and P2 + SUW soil.
 
Relationship between sediment yield and the error factor representing how much soluble P in runoff was overpredicted, as taken from the data of Daniel et al. (1993).
Article
Phosphorus lost from agricultural soils has been identified as a nonpoint source pollutant of surface waters in Delaware and throughout the Mid-Atlantic Coastal Plain. The Field Hydrologic and Nutrient Transport Model (FHANTM) 2.0 can help identify areas with a high potential for P loss, but the method used to estimate P concentrations in runoff waters needs reevaluation. The equation P(d) = KP(o)t(alpha)W(beta) has been proposed to predict P desorption from soil to runoff. To test this equation for use in Delaware and the Mid-Atlantic Coastal Plain, we conducted rainfall simulations for 14 Delaware and Maryland soils packed into 5 by 20 by 100 cm boxes at a rainfall intensity of 7.5 cm h(-1) and a slope of 5% for 30 min. We collected all runoff and measured an average soluble P concentration in runoff for the entire simulation. We predicted P concentrations using the above equation and compared them with measured values. Predicted values were well correlated to measured values (r2 = 0.78), but P concentrations were overpredicted by an average of 20 times. After we added a calibration factor to the equation based on the amount of sediment lost in runoff during the rainfall simulation, measured and predicted soluble P concentrations exhibited a nearly 1:1 relationship. Results suggest that eroded sediment in runoff may resorb P from the runoff solution, causing the desorption equation to overpredict soluble P concentrations in runoff.
 
Article
Current management and harvesting practices can compact forest soils and degrade soil health. However, effects of soil compaction on microbial processes and composition are poorly understood. We measured microbial community responses to compaction in a sandy loam and a clay loam soil under laboratory and field conditions. Treatments of no, moderate (approximately 20% increase in bulk density), and severe (approximately 40% increase) compaction were manually applied to intact soil cores. A 67-d laboratory experiment, punctuated by four sampling dates, was used to evaluate microbial indices (biomass, respiration, total and culturable bacteria and fungi, N mineralization, surface CO2 efflux, C use (Biolog), and phospholipid fatty acids PLFA) and their relationship to soil physical properties (bulk density, pore-size distribution, water-holding capacity WHC, gas diffusion). Macropores (>30 micrometer diam.) were reduced 50 to 90% in compacted samples. In contrast, habitable-sized pores for microorganisms (0.2-30 micrometer diam.) increased at least 40% in both soils with compaction. Despite these changes, microbial measures were either unaffected by compaction or showed inconsistent increases (e.g., fungal hyphae, C use, total PLFA) across sampling periods and soil types. Surface CO2 efflux was reduced 34 to 51% in severe compaction samples. Minimal changes in microbial respiration indicate that reduced efflux was due to restricted gas diffusion. Microbial indifference to compaction also was verified at two mixed-conifer plantations in northern California. Soil strength values, ranging from 75 to 3800 kPa (no to severe compaction), were unrelated to either microbial respiration or biomass. The results show broad tolerance of microbial communities from contrasting soil textures to compaction, and indicate a poor link between physical and biological indices of soil health.
 
Article
Ion-sink methods, such as resin membranes or FeO coated strips or filter papers, have been used as soil tests for plant available P. We have standardized a resin procedure and compared extractable soil P with the FeO method for 24 soils from the continental USA. Bray-1 extractable P ranged from 0.3 to 221 mg kg(-1) and Olsen's extractable P ranged from 1.4 to 131 mg kg(-1) across all soils. We used anion resin membrane strips (RS) and traditional loose resin (LR) to extract soil P. Total surface area of one RS was 17.3 cm2, compared with 47.5 cm2 for one FeO-coated filter paper. We used one, two, or three RS saturated with bicarbonate (RS(bic)) or chloride (RS(Cl)), along with 1.5 g of moist LR saturated with either bicarbonate (LR(Bic)) or chloride (LR(Cl)). Using LR(Bic), the mean P was 64.3 mg kg(-1) compared with 52.5 with one RS(Bic), 55.2 with two RS(Bic), and 63.9 with three RS(Bic). Using LR(Cl), the mean P was 63.2 mg P kg(-1) compared with 48.7 with one RS(Cl), 54.8 with two RS(Cl), and 57.3 with three RS(Cl). The mean FeO-P was 36.4 mg kg(-1). Resin (Cl) hardly influenced pH of the extracting solution, LR(Bic) and RS(Bic) influenced pH most, and FeO-strips had an intermediate effect on solution pH. This study shows that RS with a total surface area of 51.8 cm2 can be used to extract soil P in place of more time-consuming LR methods.
 
Article
A large proportion of the organic P in soils can occur as scyllo-inositol phosphates. These compounds are rarely detected elsewhere in nature and remain poorly understood, partly because conventional procedures for their determination are lengthy and erroneous. We report a straightforward procedure for the determination of scyllo-inositol phosphates in soil extracts using solution 31P nuclear magnetic resonance (NMR) spectroscopy. Solution 31P NMR chemical shifts of a range of synthetic scyllo-inositol phosphate esters were determined in alkaline solution. Of these, only the signal corresponding to scyllo-inositol hexakisphosphate at approximately 4.2 ppm was identified in soil NaOH-EDTA extracts, constituting between 6.5 and 9.8% of the NaOH-EDTA extracted P. This signal has been previously assigned to choline phosphate, but we confirmed it to be an inositol phosphate using hypobromite oxidation, a procedure that destroys all organic matter except inositol phosphates. Lower order scyllo-inositol phosphate esters were not identified in the extracts studied here, and literature reports suggest that they probably occur in insufficient concentrations to be detected by this procedure. The identification of scyllo-inositol hexakisphosphate in soils and other environmental samples will allow its quantification in a range of environments, and facilitate research into the origins and function of this enigmatic compound.
 
Article
A dryland tillage and cropping system study for Triticum aestivum was conducted on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) from 1941-1977. Oneway disk tillage resulted in significantly fewer small dry aggregates than sweep tillage in the wheat-fallow system, but had no significant effect in the continuous wheat system. Organic matter concentration was lower for oneway than for sweep tillage in both systems, while continuous wheat resulted in higher OM concentration than wheat-fallow for comparable tillage methods. The soil did not contain enough coarse aggregates to control wind erosion, indicating the need to maintain residues on the soil surface to aid wind erosion control.-from Author
 
Article
The EM-38 is a noninvasive instrument, commonly used for monitoring salinity, mapping bulk soil properties, and evaluating soil nutrient status. Users in the Southwest USA have observed as much as 20% "drift" in the measurement of bulk soil electrical conductivity (ECa) with this instrument. This drift has usually been ignored or compensated for by statistical procedures. We performed laboratory and field experiments to determine if the drift is due to calibration instability of the instrument or to heating of the instrument by the sun. In laboratory experiments, after a warm-up period, the instrument provided constant readings in the range 25 to 40°C; above 40°C the response of the instrument was unpredictable. In field experiments, where we placed the EM-38 in a fixed location we observed an unexpected response at air temperatures below 40°C. Temperature sensors in different locations on the instrument demonstrated that temperature differences between the instrument's transmitting and receiving coils and the control panel (CP) were as great as 20°C. As the instrument is temperature compensated from this CP, erroneous compensation occurred when the instrument was placed in direct sunlight. In this study, we demonstrate that differential heating of the EM-38 is one cause of drift and erroneous bulk electrical conductivity measurement; shading the instrument substantially reduced this problem, effectively extending the reliable working temperature range by minimizing drift.
 
Comparison of (a) particulate organic matter (POM), (b) Rapid, and (c) hydrometer methods with standard pipette method for determination of soil sand, silt, and clay fractions. Each point plotted represents the mean of all samples taken at each location. The linear plot of y x is shown to illustrate deviation of methods from pipette standard. 
Article
Soil textural analysis is a key component of any minimum data set used for assessing soil quality and sustainability of agricultural-management practices. However, conventional methods of soil textural analysis can be costly and time-consuming. The objective of this study was to develop a rapid and simple method for evaluating soil particle-size distribution, which could be employed as a tool for initial soil-quality assessment. The method uses a combination of sieving and sedimentation steps and is designed to be used in conjunction with analysis of particulate organic matter (POM), or as a stand-alone textural analysis. Soils of varied texture and organic-matter content were collected from six sites in the Great Plains. Their sand, silt, and clay contents were determined using the proposed methods and standard hydrometer and pipette techniques. Averaged across all soils, absolute differences between the proposed and standard pipette analyses were <2% for sand, silt, and clay. Relative differences were 6, -1, and -4% for sand, silt, and clay, respectively. Coefficients of variation within soil samples averaged <5% for sand, silt, and clay fractions. Regression analysis between proposed and standard pipette methods produced coefficient of determination (r2) values of 0.99, 0.98, and 0.93 for sand, silt, and clay, respectively, and 0.98 across all particle-size ranges. The method provides an inexpensive and reliable estimate of soil texture, useful in soil-quality assessment.
 
Map of the USDA-ARS North Appalachian Experimental Watershed (NAEW) near Coshocton, OH. Small and large watersheds as well as 8.1-m 2 lysimeter locations are shown.  
Small watershed management practices. 
Article
Hydrologic data from agricultural watersheds are necessary to identify long-term trends and to develop and validate hydrologic and water quality models. These types of data have been collected for 70 yr at the North Appalachian Experimental Watershed (NAEW) near Coshocton, OH. The NAEW has 19 small (0.5–3.0-ha), single-land-use watersheds for which surface runoff data have been collected year round on an event basis for various time periods since 1939. There are six large (17–123-ha), mixed-use watersheds with perennial streams where flow is measured continuously. Hydrologic data have been collected from 11, 2.4-m-deep, 8.1-m2 surface area monolith lysimeters. Meteorological, land management, and soil property data are available. Water quality data have been collected from watersheds and lysimeters since the early 1970s. Collaborative research efforts utilizing this resource are encouraged; the NAEW web site (www.ars.usda.gov/mwa/coshocton; verified 19 Dec. 2009) has detailed information on the types of available data. Data are available through the authors.
 
Article
A simple method was developed to speciate inorganic Se in the microgram L(-1) range using coupled ion chromatography-hydride generation atomic absorption spectrometry. Because of the differences in toxicity and adsorption behavior, determination of the redox states selenite, Se(IV), and selenate, Se(VI), is important. We used anion exchange chromatography to separate Se(IV) and Se(VI) based on differences in retention times. Samples were then mixed with concentrated HCl and passed through a 130 degrees C sand bath to reduce Se(VI) to Se(IV) for Se determination as the hydride. Detection limits were 0.68 microgram L(-1) for Se(IV) and 0.55 microgram L(-1) for Se(VI). Spiking of actual sample solutions with Se(IV) and Se(VI) showed the procedure to be accurate for solutions with Se(IV)/Se(VI) ratios ranging from 1:4 to 4:1. Average recovery was 93.1% for Se(IV) and 108% for Se(VI). The technique was used to determine Se(IV) and Se(VI) in deionized water and actual and synthetic irrigation waters.
 
Article
Thesis (Ph. D. in Agronomy)--North Carolina State College.
 
Article
Soil water potentials, leaf water potentials, and transpiration rates of sweet corn (Zea mays L.), growing in a greenhouse, and grain sorghum (Sorghum bicolor L.), growing in a field, were determined to evaluate the magnitude of the combined soil and plant resistances to water flow in the plant system. Using a theoretical analysis of water absorption by roots, soil resistance was estimated. Plant resistance was inferred by the difference between the measured combined resistances and the estimated soil resistance. A wide range of soil hydraulic conductivity values for the plant rooting media which included nutrient solutions, peat-vermiculite-sand mixture, and a sand and clay soil maintained at various water potentials provided variations in calculated soil resistances. Our results showed that when root density was not unusually low, plant resistance to water transport was much larger than soil resistance, until the threshold soil hydraulic conductivity reached about 10-6 to 10-7 cm/day. This conductivity usually occurred at about -1 and -8 bars for the sandy and clay soils, respectively. These findings emphasize the need to consider plant resistance in water-uptake calculations when using equations that evaluate water potential gradients along the water flow path.
 
Natural abundance of 15 N in the forest floor of the reference watershed (W6) at the Hubbard Brook Experimental Forest. Natu- Fig. 2. Nitrate bulk deposition inputs and streamwater outputs for ral abundance of 15 N for the Oa horizon is shown with filled trianthe reference watershed (W6) at the Hubbard Brook Experimental gles, for the Oe horizon with open circles, for the Oi horizon with Forest. Annual inputs of nitrate in bulk deposition (dotted line) open squares, and for the Oie horizon with filled circles. Calculated, and outputs of streamwater nitrate (solid line) for the reference mass-weighted mean values for the Oie horizon in 1969 and 1978 watershed at Hubbard Brook Experimental Forest are shown for are shown with filled squares (see Materials and Methods section water years (June to May) from 1964 to 1992, after Likens and for calculation methods). Means within a horizon (Oa or Oie) Bormann (1995). associated with the same letter are not significantly different. Bars represent standard error (n 20). Oa horizon for 1969 and 1978, we found no correlation between LOI and 15 N. This suggests that the increase  
Article
To test the hypothesis that delta15N in the forest floor remains constant over time, we measured delta15N in forest-floor samples from 1969, 1978, 1987, and 1992 at the reference watershed, W6, at the Hubbard Brook Experimental Forest (HBEF), New Hampshire. The delta15N of the Oa horizon increased significantly (P < 0.05) from 3.00 per thousand in 1969 to 4.89 per thousand in 1978, then decreased significantly to 3.81 per thousand in 1987 and remained near that level in 1992. In the Oie horizon, delta15N increased significantly from 0.17 per thousand in 1969 to 0.91 per thousand in 1978 and remained at the higher level for the later years. Thus delta15N was not at steady state in either the Oie or Oa horizon for the period 1969 to 1992 in the reference watershed. These data suggest that even relatively short-term disruptions of the N cycle (either by anthropogenic or natural disturbance) can alter the delta15N in the forest floor, and should be considered in evaluating natural abundance data.
 
Article
A study was initiated to test the validity of using electromagnetic induction (EMI) survey data, a prediction-based sampling strategy, and ordinary linear regression modeling to predict spatially variable feedlot surface manure accumulation. A 30- by 60-m feedlot pen with a central mound was selected for this study. A Dualem-1S EMI meter (Dualem Inc., Milton, ON, Canada) pulled on 2-m spacing was used to collect feedlot surface apparent electrical conductivity (EC(a)) data. Meter data were combined with global positioning system coordinates at a rate of five readings per second. Two 20-site sampling approaches were used to determine the validity of using EMI data for prediction-based sampling. Soil samples were analyzed for volatile solids (VS), total N (TN), total P (TP), and Cl–. A stratified random sampling (SRS) approach (n = 20) was used as an independent set to test models estimated from the prediction-based (n = 20) response surface sample design (RSSD). The RSSD sampling plan demonstrated better design optimality criteria than the SRS approach. Excellent correlations between the EMI data and the ln(Cl–), TN, TP, and VS soil properties suggest that it can be used to map spatially variable manure accumulations. Each model was capable of explaining >90% of the constituent sample variations. Fitted models were used to estimate average manure accumulation and predict spatial variations. The corresponding prediction maps show a pronounced pen design effect on manure accumulation. This technique enables researchers to develop precision practices to mitigate environmental contamination from beef feedlots.
 
Article
Tillage intensity affects soil structure and the loss of soil organic C and N. We hypothesized that no-tillage (NT) and conventional tillage (CT) differentially affect three physically defined particulate organic matter (POM) fractions. A grassland-derived Haplustoll was separated into aggregates by wet sieving. Free light fraction (LF) and intra-aggregate POM (iPOM) were isolated. Natural abundance 13C was measured for whole soil C, free LF C, and iPOM C. The mean residence time of soil C under CT (44 yr) was 1.7 times less than in NT (73 yr). The amount of free LF C was 174, 196, and 474 g C m-2 for CT, NT, and NS, respectively. Total iPOM C amounts in CT, NT, and NS were 193, 337, and 503 g C m-2, respectively. The level of fine iPOM C (53-250 micrometer) level in macroaggregates (250-2000 micrometers) obtained after slaking was five times greater in NT vs. CT and accounted for 47.3% of the difference in total POM C between NT and CT. The amount of coarse iPOM C (250-2000 micrometers) was only 2.4 times greater and accounted for only 21% of the difference in total POM C. Sequestration of iPOM was observed in NT vs. CT, but free LF was not influenced by differential tillage. We conclude that differences in aggregate turnover largely control the difference in fine iPOM in CT vs. NT and consequently SOM loss is affected by both the amount of aggregation and aggregate turnover.
 
Article
Nutrient analysis was undertaken for adjacent, 40-yr-old stands of pure quaking aspen Populus tremuloides, white spruce Picea glauca, red pine Pinus resinosa and jack pine Pinus banksiana on 2 soils in Minnesota. On both soils, aspen and spruce stands accumulated more of most nutrients than did pine stands; these species differences were reflected in the litterfall. The weight of the forest floor did not differ among species, but nutrient accumulation and pH were greatest under aspen and spruce. Calcium content was about twice as high under aspen and spruce as under pines. In the mineral soil, P and K did not differ among species; organic matter and N tended to be lowest under aspen, and Ca was much lower under aspen and spruce than under the pines. Soil pH and cation exchange capacity were highest under the pines; this was directly related to soil Ca contents. Mineral soil differences related to species were most pronounced in the top 10 cm; few differences occurred below 25 cm. The large species differences in the N, Ca and Mg contents of vegetation, forest floor, and mineral soil show a redistribution of these nutrients, but their amounts in the entire ecosystem do not differ by species. In contrast, P and K in the ecosystem decrease in the order aspen > spruce > pines; this is largely a reflection of their accumulation in the vegetation since their differences in the soil are minimal.-Author
 
Article
Small precipitation amounts generally have low effectiveness for crop production in semiarid regions. Our objective was to determine potential evaporation (PE; 3, 6, or 12 mm d-1) and straw-mulch (0, 2, or 4 Mg ha-1) rate effects on water accumulation in Pullman (Torrertic Paleustoll, 37% clay) and Randall (Ustic Epiaquerts, 57% clay) soils when small amounts of water (simulated precipitation; 5, 10, or 20 mm) were applied. Water accumulation was affected in order by water-application amount > PE > mulch > soil clay content. Mulching at 2.0 and 4.0 Mg ha-1 increased storage efficiency of 5-mm water applications by > 60 and 100%, respectively, in both soils when PE was 3 mm d-1. With 5-mm water applications and 6 mm d-1 PE, > 10% of applied water was stored in mulched soils, but not in bare soils. When PE was 12 mm d-1, little storage from 5-mm applications occurred in bare soils, but 3 to 6% storage occurred when the mulch rate was 4.0 Mg ha-1. To obtain > 10% water storage when the PE rate was 12 mm d-1, 10-mm water applications and a 2 Mg ha-1 mulch rate were necessary. Evaporation rates were slightly higher for mulched soil than for bare soil in the late stage. Soil clay contents were correlated positively with accumulative evaporation in the late stage. Soil wetting depth increased with increases in mulch rates. Based on this study, straw mulching has potential for increasing soil water storage from small amounts of precipitation.
 
Article
ney, 1982), have been proposed. Stanford and Smith (1972) developed a biologically based, long-term incu- The success of variable rate N fertilizer application rests on our bation method whereby potentially mineralizable N can ability to predict the contribution of soil N to growing crops. We assessed relationships between soil N availability indices (SNAIs), be estimated using one-pool (Stanford and Smith, 1972), yield, and total N accumulation of wheat (Triticum aestivum L.) two-pool (Molina et al., 1983), or incremental models grown in a typical glacial till landscape in Saskatchewan, Canada. (Ellert and Bettany, 1988). Incubation methods are Soil samples were collected at 3-m intervals along a 300-m transect time-consuming by nature, and thus more recent re- comprised of low (LCFS) and high catchment footslopes (HCFS), search has focused on the development of more rapid and low (LCSH) and high catchment shoulders (HCSH). Total soil chemical extraction methods, such as the use of hot KCl, N and C, organic C, mineral N, depth of A horizon, spring soil mois-
 
The Grand Prairie region of eastern Arkansas. 
Total aboveground crop biomass at three sampling times in the 2002 and 2004 seasons for two and three cropping treatments, respectively. Crop growth stages at sampling times were green ring (83 d after crop emergence [DAE]), 50% heading (103 DAE), and shortly before harvest (133 or 127 DAE). Standard error bars are shown for each crop treatment. Levels of signifi cance are shown for the comparison of continuous rice with rice-soybean (2002) or the comparison of continuous rice with the group mean of rice-soybean and rice-corn (2004) where the level of signifi cance was based on a linear single degree of freedom contrast. For each sampling time in 2004, cropping treatments shown with different letters are signifi cantly different (P < 0.05) as determined by Duncan's multiple-range test.
Leaf N concentration for the "y" leaf of rice plants in two cropping treatments during the 2002 season. Sampling dates are described by their number of days after crop emergence (DAE).
Article
Soil C stocks in the Grand Prairie region of eastern Arkansas have declined under the prevalent 2-yr rotation of rice (Orzya sativa L.)-soybean [Glycine max (L.) Merr.]. Continuous rice cropping could promote soil C sequestration, but in previous work continuous rice averaged 19% less grain yield than rice following soybean, apparently due to N deficiency. To further study N cycling, microplots were imbedded during the rice phase of a crop rotation field study in 2002 and 2004. Urea labeled with 15N was applied preflood, when all N fertilizer is conventionally applied. Crop biomass was often smaller with continuous rice than with rice following soybean (sampled both years) and rice following corn (Zea mays L.) (sampled only in 2004), although the difference varied by growth stage. Crop uptake of native 14N, presumably mineralized from soil organic matter, was inhibited with continuous rice in both years. This trend was clearest at harvest (P = 0.02), when continuous rice averaged 40 kg 14N ha-1 less uptake than rice in the two rotations. Fertilizer 15N averaged only 30% of total crop N and its uptake differed among cropping treatments only in 2002. At harvest, soil C with continuous rice cropping was enriched by 42% with syringyl phenols and by 83% with cinnamic phenols compared with the rotations. These enrichments appear unrelated to estimated input rates of lignin-derived phenols. Results support the hypothesis that continuous rice cropping promotes the binding of soil N by lignin-derived phenols, thereby inhibiting N mineralization and late-season crop growth. Similar observations were reported for tropical rice production, suggesting that the responsible soil processes might be common in continuous rice cropping.
 
Article
Soil phenols have been implicated as inhibitors of soil N cycling within many agroecosystems, including irrigated lowland rice (Oryza sativa L.). To quantify the effects of crop management on temporal patterns of phenol accumulation in lowland rice soils, we measured phenol concentrations in two humic fractions at two crop growth stages in each growing season during a 4-yr field study at the International Rice Research Institute (Philippines). Samples were collected from two double-crop rotations (continuous rice and rice-maize [Zea mays L.]) with two N fertilizer rates (0 and nonlimiting), and with either aerobic or anaerobic decomposition of incorporated crop residues. Phenols were determined by tetramethylammonium hydroxide thermochemolysis. Compared with the other field treatments, anaerobic decomposition of crop residues with continuous rice and nonlimiting rates of N fertilizer promoted a gradual increase in the relative enrichment of phenols in the mobile humic acid fraction during the 4 yr. The level of enrichment varied among phenol compounds, developing the fastest and becoming most pronounced with the smaller molecules of molecular weight 168 or less. Anaerobic decomposition had less effect on phenol enrichment for continuous rice cropping without N fertilizer. No phenol enrichment was found with anaerobic decomposition of rice residues in the rice-maize rotation. Our results are consistent with previous findings of inhibited mineralization of humic N with anaerobic decomposition, continuous rice, and nonlimiting rates of N fertilizer. Rotation of maize with rice or other techniques to ensure aerobic decomposition of crop residues may help mitigate or prevent phenol accumulation.
 
Estimated N 2 O fl ux (f est , left axis) and relative error (RE, right axis) calculated using Linear, HM, and Quad schemes versus deployment time with effective chamber heights (h) of 10 (circles) and 30 cm (triangles) and with predeployment fl uxes (f o ) of (a) 1000 and (b) 100 μg N m-2 h-1. Open symbols and error bars represent means and standard deviations (σ), respectively, measurement error can be represented by constant CV=1.5%. Solid symbols represent f est calculated from baseline chamber data assuming no measurement error (open and closed symbols are indistinguishable in some cases). Baseline chamber N 2 O concentrations were simulated using Eq. [4] with 3 sampling events. Dashed lines represent f o .
Article
Chamber-based estimates of soil-to-atmosphere nitrous oxide (N2O) gas flux tend to underestimate actual emission rates due to inherently nonlinear time series data. In theory, this limitation can be minimized by adjusting measurement conditions to reduce nonlinearity and/or by using flux-calculation (FC) schemes that account for the so-called "chamber effect." The current study utilizes gas transport theory and stochastic analysis to evaluate accuracy and precision of N2O flux determinations under specific soil and chamber conditions. The analysis demonstrates that measures taken to increase the absolute accuracy of flux estimates, including shorter deployment times, larger chamber heights, and nonlinear FC schemes, will also increase the variance in flux estimates to an extent that depends on errors associated with sampling techniques and analytical instrument performance. These effects, in the absence of any actual variation in fluxes, can generate coefficients of variation ranging from 3 to 70% depending on measurement conditions. It is also shown that nonlinear FC schemes are prone to generating positively skewed distributions. These effects decrease confidence in N2O flux estimates and inhibit the detection of differences arising from experimental factors. In general, a linear FC scheme will be more likely to detect relative differences in fluxes, although less accurate in absolute terms than nonlinear schemes. The techniques described here have been codified into an accessible spreadsheet-based tool for evaluating accuracy and precision trade-offs under specific measurement conditions.
 
Probability density functions for the elevation data: (a) a comparison of all three fi elds from real-time kinematic global positioning system (RTKGPS) data at 10-m sample spacing; (b) a comparison of all data sets for the North fi eld; (c) a comparison of all data sets for the South fi eld; and (d) a comparison of all data sets for the West fi eld.
Article
Terrain attributes are commonly used to explain the spatial variability of agronomic, pedologic, and hydrologic variables. The terrain attributes studied here (elevation, slope, aspect, and curvature) are estimated readily from digital elevation models (DEMs), but questions remain about how the accuracy and sample spacing of the elevation data affect the estimated attributes. The main objective of this study was to quantify differences in each terrain attribute due to factors affecting DEM accuracy and grid cell size. Three data sources were compared: (i) real-time kinematic global positioning system (RTKGPS); (ii) satellite-differentially corrected global positioning system (DGPS); and (iii) U.S. Geological Survey (USGS) 30-m DEMs. The GPS data from three undulating agricultural fields in northeastern Colorado were interpolated onto 5-, 10-, 20-, and 30-m grid DEMs. The DGPS and USGS DEMs produced similar elevation differences relative to RTKGPS DEMs, but elevation differences in USGS DEMs were more spatially correlated. Estimates of curvature were highly sensitive to DEM differences and the sensitivity of slope, aspect, and curvature estimates decreased as grid cell size increased. The impacts of DEM accuracy and grid cell size were investigated using correlations between wheat (Triticum aestivum L.) grain yields and estimated terrain attributes. The highest correlation coefficients were obtained using RTKGPS data, and decreasing the sample spacing or grid cell size below 30 m did not consistently improve the correlations. These analyses on agricultural lands indicate the importance of accurate elevation data for detailed terrain analyses on grid cell sizes of 30 m or less.
 
Article
Most field erosion studies in agricultural areas provide little information on the probable errors associated. The aim of this paper is to evaluate the accuracy of different methods (LiDAR, photo-reconstruction, total station, laser profilemeter and pole) estimating gully erosion at a reach scale and the expected errors when 2D methods are used at gully scale. Field measurements of a reach 7.1 m long and nine gullies (100s m) were carried out near Cordoba, Spain. At the reach scale, the cross sectional area EA and reach volume EV errors were calculated. Sinuosity and measurement distance (D)influence on gully length error (EL) was investigated. Multiple configurations of gully cross sectional area were simulated to assess volume error variability (σEv) as a function of measurement distance factor (MDF) and to obtain a EV confidence interval for a given probability. 3D photo-reconstruction and total station produced EA values lower than 4%, whereas the remainder of the 2D methods, greater than 10%. For volume estimation, 3D methods deliver similar values, but 2D methods generated large negative EV values (
 
Experiment layout of the field study.
Measured and RZWQM-predicted soil water content distribu
Measured and RZWQM-predicted soil temperature at 10-cm depth from 1997 to 1999.
Measured and RZWQM-predicted persistence of acetochlor
Measured and RZWQM-predicted acetochlor and terbuthy
Article
Data collected from a 3-yr controlled field study in Hamilton, New Zealand were used to examine whether the Root Zone Water Quality Model is capable of predicting water movement and pesticide fate in the field based on key lab-measured parameters and environmental variables. Acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl) acetamide; 2.5 and 5.0 kg a.i. ha-1] and terbuthylazine (C9H16ClN5; 1.5 and 3.0 kg a.i. ha-1) were applied onto nine field plots (3 by 9 m each). Soil core samples were taken to a depth of 1 m to determine soil water contents and pesticide concentrations. Dissipation of both pesticides in the field at both application rates followed first-order kinetics (adjusted r2 > 0.91). The mean dissipation half-life was 16 d for acetochlor and 25 d for terbuthylazine. Relatively small amounts of the pesticides leached below 5 cm and none leached below 10 cm. Predicted soil water contents in the soil profile were not significantly different from those measured in the field (p > 0.84). Predicted acetochlor and terbuthylazine masses in the soil profile based on a linear instantaneous-equilibrium (I-E) partitioning model matched those measured in the field (adjusted r2 > 0.93). However, predicted pesticide concentrations in the soil profile were less satisfactory, with 68 and 35% of the predicted concentrations being within a factor of 2 of the measured concentrations for 0- to 5- and 5- to 10-cm depths, respectively. Calibration of each pesticide sensitive parameter individually did not significantly improve the overall predictions of pesticide mass and concentrations in the soil profile when the I-E partitioning model was used. The predictions were improved when a two-site, equilibrium-kinetic (E-K) sorption model was used.
 
Top-cited authors
Martinus Th. Van Genuchten
  • Federal University of Rio de Janeiro
Keith Paustian
  • Colorado State University
Rattan Lal
  • The Ohio State University
J. Six
  • ETH Zurich
Dawit Solomon
  • Cornell University