bluuebunny/crossref_metadata_2025_split huggingface dataset:
Water Table Dynamics in Tile‐Drained Fields
Authors: Skaggs T. H. , Mohanty B. P. 
Published: July 2010

AbstractWe present a method for simulating water table dynamics in tile‐drained fields that are subject to intermittent precipitation or irrigation. A stochastic state equation for the water table height midway between drain laterals is obtained by adding a random noise term to van Schilfgaarde's deterministic drainage model. The random term accounts for dynamics not modeled by van Schilfgaarde's equation, which is based on numerous simplifying assumptions. The continuous‐discrete Kalman filter is used to obtain an estimate of the time variation of the water table height, as well as the variance of the estimate. The method is demonstrated using experimental data from the literature and is shown to have advantages over alternative approaches. Additional testing is necessary to fully assess the validity of the stochastic state equation and the utility of the filtering procedure.
Organic Matter Stabilization in Two Semiarid Tropical Soils: Size, Density, and Magnetic Separations
Authors: Shang C. , Tiessen H. 
Published: July 2010

AbstractSoil organic matter (SOM) in many tropical soils is less stable than that of temperate soils, in part due to faster decomposition processes in the tropics, but possibly also due to different mechanisms of organomineral stabilization. We studied the mineral associations of SOM in the surface horizons of two semiarid tropical soils (an Oxisol and an Alfisol) using particle‐size, density, and magnetic separations. The inorganic phases of fractionated materials were examined using chemical extraction and x‐ray diffraction. Organic matter associated with the sand fraction accounted for 21 to 30% of soil C, mostly as coarse, floating material. This coarse material was more abundant in the Alfisol. One‐half the organic C of both soils was associated with the silt‐sized fraction, which contained a substantial portion of microaggregates resistant to sonication. Carbon in silt‐sized aggregates was mainly stabilized by association with poorly crystalline oxides and by aggregation with crystalline oxides and clays. The C as light matter (<1.8 g cm‐3) liberated from silt‐size microaggregates by successive sonication treatments accounted for ≈23% of total soil C for both soils. The SOM in the <1.8 g cm‐3 fraction seemed younger and less decomposed than the organic materials in the temperate soil fractions with similar density and equivalent sizes. In clays, C was concentrated in fractions of intermediate magnetic susceptibility, whereas both the highly magnetic fraction of predominantly well‐crystallized Fe and the nonmagnetic fraction were C poor. The study points to the important role of particle size and crystallinity of Fe oxides and of microaggregation between oxides, organic matter, and other minerals in stabilizing tropical soil organic matter.
Seasonal Distribution of Nitrous Oxide Emissions from Soils in the Parkland Region
Authors: Lemke R. L. , Izaurralde R. C. , Nyborg M. 
Published: July 2010

AbstractThe temporal variability of soil‐derived N2O emissions presents a major challenge to the accurate quantification of N2O‐N losses from agroecosystems. We characterized the seasonal distribution of N2O emissions from two agricultural sites in the Parkland region of Alberta during 1993 and 1994. Treatments studied were fallow, and spring wheat (Triticum aestivum L.) with and without urea fertilizer, under conventional till management. Gas samples were collected from vented static soil chambers and were analyzed for N2O with a gas chromatograph equipped with a 63Ni electron capture detector. Soil water content and concentrations of NO‐3‐N, NH+4‐N, and water‐soluble organic C (WSOC) were measured several times during the season. A brief burst of N2O emission was recorded at both sites during and immediately following spring snow melt. A second period of activity occurred between mid‐June and mid‐July. Between 16 and 60% of estimated annual N2O‐N loss occurred during spring thaw, while >80% of cumulative annual N2O‐N loss had occurred by mid‐July. Mean soil NO‐3‐N concentration explained up to 65% of the temporal variability in geometric mean N2O emissions. A multiple regression model that included fall soil concentrations of NO‐3‐N, NH+4‐N, and WSOC explained 94% of the variability in estimated cumulative N2O‐N loss during the following spring thaw. Most N2O‐N losses in the Parkland region appear to occur during spring thaw and early summer; therefore, sampling schedules need to focus on these time periods. Management practices that minimize N availability during spring thaw may be an effective mitigation strategy for this region.
Direct vs. Indirect Nitrogen‐15 Approaches to Estimate Nitrogen Contributions from Crop Residues
Authors: Stevenson F. C. , Walley F. L. , van Kessel C. 
Published: July 2010

AbstractThe benefit of including a legume in a cropping system often has been attributed, in part, to N2 fixation and the additional N that legume residues can supply to the succeeding crop. In this study, we estimated the N contribution from pea (Pisum sativum L.) to a succeeding wheat (Triticum aestivum L.) crop directly, using 15N‐labeled crop residues, and indirectly, using the A value. The A value provides an index of soil N availability and was used to indirectly estimate the N contribution of crop residues to the subsequent crop. Pea‐wheat and wheat‐wheat rotations were established at four sites using a small‐plot research approach and at one site using a landscapescale research approach. Nitrogen‐15‐labeled residue and 15N‐labeled fertilizer were applied to unlabeled areas within each rotation following the first growing season. When estimated directly using 15N‐labeled residues, pea residue contributed 10 kg N ha‐1 to the subsequent wheat crop, whereas wheat residue contributed only 3 kg N ha‐1. According to indirect estimates of N contribution, the A value in the second year of the pea‐wheat rotation was, on average, 119 kg N ha‐1 higher than for the wheat‐wheat rotation. The difference in A values was equivalent to an additional contribution from pea, relative to wheat residues, of 4 kg N ha‐1 in the small‐plot study and 38 kg N ha‐1 in the landscape‐scale study. The direct approach considers only the N contribution from the aboveground portion of the previous crop residues. In contrast, indirect estimates of the N contribution from crop residues based on the A value includes the contribution of all belowground N sources and the influence of non‐N rotation effects, such as root diseases, on the ability of a succeeding crop to access soil N reserves.
Iron Oxides Erodibility Interactions for Soils of the Memphis Catena
Authors: Rhoton F. E. , Römkens M. J. M. , Lindbo D. L. 
Published: July 2010

AbstractIn the Memphis catena, the well‐drained Memphis (fine silty, mixed, active, thermic Typic Hapludalfs) is more erodible than the moderately well‐drained Loring (fine silty, mixed, active, thermic Oxyaquic Fragiudalfs) and Grenada (fine silty, mixed, active, thermic Glossic Fragiudalfs). We hypothesized that soil wetness and Fe oxide status affects the erodibility of these soils. Samples (<2 mm) of A‐ and B‐horizons, collected from representative pedons at five locations, were characterized for standard physical and chemical properties. Simulated rainfall was applied (64 mm h‐1) to additional samples (<8 mm) in a rainfall simulator pan that had a 0.6 m × 0.6 m test area. Water dispersible clay (WDC) and soil loss averaged 7.2% and 9.21 Mg ha‐1 for Memphis, 6.8% and 8.85 Mg ha‐1 for Loring, and 6.1% and 8.71 Mg ha‐1 for Grenada. Sediment Feo, Fed, and Feo/Fed ratios were about 0.80, 1.5, and 0.50 times that of the soil, respectively. Correlation coefficients (r) for WDC and soil loss vs. Fe oxide variables exceeded 0.90 in some horizons, whereas, organic C (OC) and % clay were generally <0.60. However, OC vs. % sediment <53 µm had r values of 0.87 compared to 0.59 for some Fe oxide variables. Regression models derived for WDC and soil loss had Fe oxide parameters as principal variables in the best fit models and coefficients of determination that ranged from 0.208 to 0.922 (significant at P ≤ 0.01). Results suggest that Fe oxides are more important than OC and clay content for determining the erodibility of these soils, particularly Feo/Fed ratios which are negatively correlated with WDC and soil loss.
Nitrate‐Nitrogen, Soluble, and Bioavailable Phosphorus Runoff from Simulated Rainfall After Fertilizer Application
Authors: Gascho G. J. , Davis J. G. , Hook J. E. , Wauchope R. D. , Dowler C.C. , Johnson A. W. , Truman C. C. , Sumner H. R. 
Published: July 2010

AbstractRunoff from crop land can enhance eutrophication of fresh water and hypoxia in sea water. We simulated rain at 25 mm hr‐1 for 2 hr, 8 d prior and 1, 14, 29, 49 and 108 d after fertilization and planting of corn (Zea mays L.). Experimental sites received 50 kg N, 45 kg P, and 125 kg K ha‐1 as granulated fertilizer broadcast and incorporated to a depth of 150 mm. An additional 118 kg N ha‐1 was surface‐banded as solution fertilizer at Day 28, which was 1 d prior to the Day 29 rain. The study was conducted for 2 yr on a Tifton loamy sand (fine‐loamy, siliceous, thermic Plinthic Kandiudults) with a slope of 4.5%, on micro‐ (5.57 m2) and meso‐scale (622 m2) plots. Runoff was equal for the two scales of plots. There were greater runoff losses of soluble‐P from meso‐ (1.4 kg ha‐1) than from micro‐plots (1.0 kg ha‐1). Nitrate‐N losses averaged 2.7 kg ha‐1 and bioavailable‐P losses were 2.3 kg ha‐1. Greatest NO3‐N and soluble‐P losses occurred the day after application of the soild fertilizer, whereas bioavailable‐P loss was greatest at Day 14 and 29. No increase in NO3‐N losses was found 1 d after the application of urea ammonium nitrate solution, possibly indicating that liquid fertilizers are not as susceptible to runoff losses as solid fertilizers. Results of this study should encourage the use of small plots, thereby saving research time and expense and provide data useful for estimating losses at similar sites.
Evaluation of the Test‐Mineral Method for Studying Minesoil Geochemistry
Authors: Monterroso C. , Macías F. 
Published: July 2010

AbstractThe test‐mineral method was evaluated as a means of assessing the chemical environment and soil processes in mine soils. This study was carried out on lignite mine tailings at As Pontes (northwestern Spain). The spoils are heterogeneous and mainly consist of carbonaceous and noncarbonaceous clays and slates, often containing pyrite. Vermiculite was used as a reference mineral and placed in ionpermeable polyamide bags that were then buried in various reclaimed minesoils. One bag was recovered from each soil after 13, 26, and 52 wk and analyzed for pH, elemental composition, exchangeable cations, cation‐exchange capacity (CEC), extractable Al and Fe, and mineralogy (x‐ray diffractometry [XRD], differential thermal analysis [DTA], and thermogravimetry [TGA]). Vermiculite rapidly underwent geochemical and mineralogical changes (in <13 wk). The greatest changes took place in soils developed from minespoils rich in sulfides; exchangeable Na on the vermiculite was replaced with Ca, Mg, Al, or H and there was an important decrease in CEC due to interlayer Alpolymerization. This behavior is typical of an acid environment. By contrast, the CEC of vermiculite in the low‐sulfide soils did not change and exchangeable Na (principal cation in original vermiculite) was displaced by Ca, with virtually no involvement of other cations. This test vermiculite proved to be an excellent indicator of the chemical environment of minesoils.
Refinement of the Anion Exchange Membrane Method for Soluble Phosphorus Measurement
Authors: Cooperband L. R. , Gale P. M. , Comerford N. B. 
Published: July 2010

AbstractThe proper use of anion exchange membranes (AEMs) to assess phosphorus availability in situ requires a more thorough understanding of their function under a wide range of soil biophysical conditions. We evaluated the ability of AEMs to sorb selected organic P compounds, determined possible interference of low‐molecular‐weight organic acids and humic substances on AEM‐P sorption, and assessed the efficiency of AEM‐P sorption in the presence of wetland sediments and soil‐sediment microbes. We collected soils, swamp water, and sediments from a cypress swamp‐pine flatwoods ecosystem in north central Florida. Membranes recovered nearly 100% of both ortho and organic P in a study using aqueous solutions of ortho P and organic P compounds. Membrane sorption of ortho P with varying concentrations of oxalate and protocatechuate was close to 100%. There was a reduction of 15 µg P per membrane when AEMs were placed inside low‐molecular‐weight‐cutoff dialysis tubing (<1000 MWCO) in P‐spiked swamp water; however, there was no significant tubing effect in non‐spiked swamp water. In an experiment exploring effects on AEM‐P sorption of P additions to swamp water with or without sediments, AEMs recovered six times more P than measured in non‐spiked swamp water with sediments. When swamp water was treated with chloroform, AEMs sorbed an equal or greater amount of ortho P than ortho P measured in swamp water with no AEMs. Results suggest that AEMs can be used to measure soluble and readily desorbable P in low‐P status soils and sediments with organic acids.
Microbial Utilization of Heterocyclic Nitrogen from Atrazine
Authors: Bichat F. , Mulvaney R. L. , Sims G. K. 
Published: July 2010

AbstractRadiotracer studies have provided indirect evidence that heterocyclic N in atrazine [2‐chloro‐4(ethylamino)‐6‐(isopropylamino)‐1,3,5‐triazine] may be utilized by microorganisms as a source of N; however, no data are available from investigations using 15N as a tracer. Studies were conducted to examine microbial utilization of atrazine ring‐15N in soil and pure cultures of Pseudomonas sp. strain ADP, Agrobacterium radiobacter J14a, or bacterium M91‐3. Atrazine [U‐15N‐ring] was synthesized from labeled urea. To investigate the effect of exogenous N on atrazine degradation, pure cultures were supplemented with unlabeled atrazine and labeled N as (NH4)2SO4, KNO3, urea, or glycine. Under C‐limiting conditions, cells of Pseudomonas sp. strain ADP incorporated side chain‐N into biomass and liberated ring‐N as NH4. When N was limiting, ring‐N was also recovered in biomass. Degradation of atrazine by Pseudomonas strain sp. ADP and A. radiobacter was unaffected by the presence of exogenous N, whereas no degradation occurred with bacterium M91‐3 in media containing urea or NH4‐N. The fate of double‐labeled [U‐14C, U‐15N‐ring]‐atrazine (15 mg kg‐1) was examined after incubation of a Bloomfield soil (sandy, mixed, mesic Psammentic Hapludalf) amended with NH4‐ or NO3‐N (75 mg kg‐1), with or without an inoculum of Pseudomonas sp. strain ADP (1.06 × 1013 cells kg‐1). In uninoculated soil, mineralization of atrazine‐14C was inhibited by inorganic N, whereas in the inoculated soil, 87% of the atrazine was mineralized, regardless of the N treatment. The C/N ratio was much lower for amino acids isolated from soil than for the atrazine ring, suggesting preferential assimilation of N over C by microorganisms.
Influence of Cropping Intensity and Nitrogen Fertilizer Rates on In Situ Nitrogen Mineralization
Authors: Kolberg R. L. , Westfall D. G. , Peterson G. A. 
Published: July 2010

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

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

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

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

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

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