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Controlled‐release fertilizers (CRFs) have the potential to deliver crop production and environmental benefits through better control of applied nitrogen (N) in cropping systems. Whereas N release from CRFs can be impacted by several factors, there has been a widely held view that soil water has little effect on N release from polymer‐coated CRFs. Past research has often studied the soil water effect as a function of soil water content. This limits the transferability of results. In this study we measured N release from a polymer‐coated urea (PCU) and a polymer‐sulfur–coated urea (PSCU) using undisturbed soil cores at set matric potentials. Soil matric potential had a significant effect on N release from PCU. Release at −1,000 kPa was delayed by up to 30 d compared with −10 kPa. Optical stereo microscopy clarified that this was linked to differences in the rate of water absorption. Theoretical considerations demonstrate that these relatively large differences could not be explained by the effect of soil matric potential on vapor flow. It is possible that soil matric potential interacted with the properties of the coating to change its permeability or the involvement of liquid flow. The effect of soil water on N release from PSCU was less clear. The magnitude of the soil water effect is, therefore, product‐specific and dependent on coating properties. The soil matric potential provided a consistent description of release patterns between soils with contrasting soil water retention characteristics. Soil water effects should hence be studied as a function of soil matric potential.

Agricultural grass cultivars bred for increased forage yield commonly have extensive root systems. As roots are an important input of organic matter into the soil, it follows that such cultivars could lead to important increases in soil organic carbon (SOC), but this, and the mechanisms involved, are poorly understood with little empirical field evidence. We assessed the effect of two cultivars, Lolium perenne L. cv. ‘AberMagic’ and L. perenne L. × Festuca pratensis Huds. cv. ‘Prior’, in comparison with mixed-species permanent pasture (‘Pasture’) in a field experiment on temperate alluvial soil in the southwest UK. Root and SOC stocks, and specific plant-derived lipids as mechanistic biomarkers for shoot and root inputs of C, were measured on intact 1-m volumetric soil cores collected on four dates in 2013-2015. Total grass yields were greater for both grass cultivars (40-43 Mg ha–1) than Pasture (39 Mg ha–1), and by 2015 root stocks in the upper 0.1 m were significantly greater by more than 4.7 Mg ha–1. At 0.1-0.3 m depth, SOC stocks (per 0.1-m depth) were significantly greater under the two grass cultivars (24-50 Mg ha–1) compared to Pasture (18-32 Mg ha–1). In the full 1-m profile, mean SOC stocks were 137, 133 and 110 Mg ha–1 for AberMagic, Prior and Pasture, respectively, matching root biomass distribution. Odd-chain n-alkane concentrations were significantly greater for shoots than roots (274 vs. 64 mg kg–1, respectively), and roots had significantly greater concentrations than shoots of even-chain hydroxy fatty acids (1829 vs. 305 mg kg–1, respectively) and diacids (317 vs. 93 mg kg–1, respectively). This confirmed lipids as candidate biomarkers for distinguishing shoot and root inputs into the soil, with the latter being the dominant source of SOC. Based on the observations of increased forage yield and SOC stock, high-yielding forage grass cultivars can contribute to future strategies for climate-smart agriculture in grassland-dominated temperate regions.

Autoclaved-citrate extractable (ACE) soil protein is included in some soil health assessments as a biological indicator. Furthermore, soil protein contents may be related to the ability of a soil to make nitrogen (N) available for plants by mineralization. The main objective of this study was to evaluate the correlation between ACE protein and potential net N mineralization in undisturbed soil cores from 57 fields in California under annual crops. Total N in the soils ranged from 0.65 to 12.5 g kg⁻¹, and the sites represented eight Soil Taxonomy orders. Soil ACE protein concentrations ranged from 1.0 to 45.2 g kg⁻¹ soil. Although the correlation between ACE protein and potential net N mineralization was positive, ACE protein explained only 21% of the variability in potential net N mineralization across all sites, which was less than total N. Under the assumption that proteins contain 16% N, ACE protein-N accounted for 28% of total N across all sites. However, in some soils with a high total N content, ACE protein accounted for up to 67% of total N. Because autoclaving is expected to denature some proteins, these values seem very high and are likely caused by the interference of coextracted humic substances. Our results do not suggest that ACE protein is a better predictor of potential net N mineralization than total soil N, which may be at least partly due to an apparent interference of coextracted humic substances with the protein assay.

X-ray radiography is a suitable approach to study water dynamics in undisturbed soil. However, beam hardening impairs the deduction of soil moisture changes from X-ray attenuation, especially when studying infiltration of water into cylindrical soil columns. We developed a calibration protocol to correct for beam hardening effects that enables the quantitative determination of changing average water content in two-dimensional projections. The method works for a broad range of materials and is easy to implement. Moreover, we studied the drift of X-ray attenuation values due to the detector latency and eliminated its contribution to the quantitative analysis. Finally we could visualize the dynamics of infiltrating water into undisturbed cylindrical soil samples.

There is concern that accelerating sea-level rise will exceed the vertical growth capacity of coastal-wetland substrates in many regions by the end of this century. Vertical vulnerability estimates rely on measurements of accretion and/or surface-elevation-change derived from soil cores and/or surface elevation tables (SETs). To date there has not been a broad examination of whether the multiple timescales represented by the processes of accretion and elevation change are equally well-suited for quantifying the trajectories of wetland vertical change in coming decades and centuries. To examine the potential for timescale bias in assessments of vertical change, we compared rates of accretion and surface elevation change using data derived from a review of the literature. In the first approach, average rates of elevation change were compared with timescale-averaged accretion rates from six regions around the world where sub-decadal, decadal, centennial, and millennial timescales were represented. Second, to isolate spatial variability, temporal comparisons were made for regionally unique environmental categories within each region. Last, comparisons were made of records from sites where SET-MH stations and radiometric measurements were co-located in close proximity. We find that rates vary significantly as a function of measurement timescale and that the pattern and magnitude of variation between timescales are location-specific. Failure to identify and account for temporal variability in rates will produce biased assessments of the vertical change capacity of coastal wetlands. Robust vulnerability assessments should combine accretion rates from multiple timescales with the longest available SET record to provide long-term context for ongoing monitoring observations and projections.

Groundwater recharge estimation is a critical quantity for sustainable groundwater management. The feasibility and robustness of recharge estimation was evaluated using physical-based modeling procedures, and data from a low-cost weather station with remote sensor techniques in Southern Abbotsford, British Columbia, Canada. Recharge was determined using the Richards-based vadose zone hydrological model, HYDRUS-1D. The required meteorological data were recorded with a HOBO(TM) weather station for a short observation period (about 1 year) and an existing weather station (Abbotsford A) for long-term study purpose (27 years). Undisturbed soil cores were taken at two locations in the vicinity of the HOBO(TM) weather station. The derived soil hydraulic parameters were used to characterize the soil in the numerical model. Model performance was evaluated using observed soil moisture and soil temperature data obtained from subsurface remote sensors. A rigorous sensitivity analysis was used to test the robustness of the model. Recharge during the short observation period was estimated at 863 and 816 mm. The mean annual recharge was estimated at 848 and 859 mm/year based on a time series of 27 years. The relative ratio of annual recharge-precipitation varied from 43% to 69%. From a monthly recharge perspective, the majority (80%) of recharge due to precipitation occurred during the hydrologic winter period. The comparison of the recharge estimates with other studies indicates a good agreement. Furthermore, this method is able to predict transient recharge estimates, and can provide a reasonable tool for estimates on nutrient leaching that is often controlled by strong precipitation events and rapid infiltration of water and nitrate into the soil.

Summary This study investigated the potential for visible–near-infrared (vis–NIR) spectroscopy to predict locally volumetric soil organic carbon (SOC) from spectra recorded from field-moist soil cores. One hundred cores were collected from a 71-ha arable field. The vis–NIR spectra were collected every centimetre along the side of the cores to a depth of 0.3 m. Cores were then divided into 0.1-m increments for laboratory analysis. Reference SOC measurements were used to calibrate three partial least-squares regression (PLSR) models for bulk density (ρb), gravimetric SOC (SOCg) and volumetric SOC (SOCv). Accurate predictions were obtained from averages of spectra from those 0.1-m increments for SOCg (ratio of performance to inter-quartile (RPIQ) = 5.15; root mean square error (RMSE) = 0.38%) and SOCv (RPIQ = 5.25; RMSE = 4.33 kg m−3). The PLSR model for ρb performed least well, but still produced accurate results (RPIQ = 3.76; RMSE = 0.11 Mg m−3). Predictions for ρb and SOCg were combined to compare indirect and direct predictions of SOCv. No statistical difference in accuracy between these approaches was detected, suggesting that the direct prediction of SOCv is possible. The PLSR models calibrated on the 10-cm depth intervals were also applied to the spectra originally recorded on a 1-cm depth increment. While a bigger bias was observed for 1-cm than for 10-cm predictions (1.13 and 0.19 kg m−3, respectively), the two populations of estimates were not distinguishable statistically. The study showed the potential for using vis–NIR spectroscopy on field-moist soil cores to predict SOC at high depth resolutions (1 cm) with locally derived calibrations.

Premise of the study Identifying roots to species is challenging, but is a common problem in ecology. Fluorescent amplified fragment length polymorphisms (FAFLPs) can distinguish species within a mixed sample, are high throughput, and are inexpensive. To broaden the use of this tool across ecosystems, unique size profiles must be established for species, and its limits identified. Methods Fragments of three noncoding cpDNA regions were used to create size profiles for 193 species common to the western Canadian boreal forest. We compared detection success among congeners using FAFLPs and Sanger sequencing of the trnL intron. We also simulated and experimentally created communities to test the influence of species richness, cpDNA regions used, and extraction/amplification biases on detection success. Results Of the 193 species, 54% had unique size profiles. This value decreased when fewer cpDNA regions were used. In simulated communities, ambiguous species identifications were positively related to the species richness of the community. In mock communities, some species evaded detection owing to poor extraction or amplification. Sequencing did not increase detection success compared to FAFLPs for a subset of 24 species across nine genera. Discussion We recommend FAFLPs are best suited to confirm rather than discover species occurring belowground.

The amount of mineral N remaining after cash crops informs agronomic and conservation practices. Few studies investigate mineral N below 30 cm, yet deeper N is more at risk for leaching to groundwater. We found, on average, 253 kg ha of mineral N, 115 kg ha in the NO–N form, remaining after summer cash crop growth in the mid-Atlantic region. Of this residual mineral N, 55% was 90 to 210 cm deep. More residual NO–N remained after soybean than after corn. These substantial pools of mineral N remaining deep in the soil profile after productive cash crops, even unfertilized soybean, suggest that practices should be designed to scavenge residual N from deep soil layers in the fall, before it is lost over winter.

Root systems are important for global models of below-ground carbon and nutrient cycling. Notoriously difficult sampling methods and the fractal distribution of root diameters in the soil make data being used in these models especially susceptible to error resulting from under-sampling. We applied the concept of species accumulation curves to root data to quantify the extent of under-sampling inherent to minirhizotron and soil coring sampling for both root uptake and carbon content studies. Based on differences in sample size alone, minirhizotron sampling missed approximately one third of the root diameters observed by soil core sampling. Sample volumes needed to encounter 90% of root diameters averaged 2481 cm(3) for uptake studies and 5878 cm(3) for root carbon content studies. These results show that small sample volumes encounter a non-representative sample of the overall root pool, and provide future guidelines for determining optimal sample volumes in root studies.

Summary Uncertainty surrounds belowground plant responses to rising atmospheric CO2 because roots are difficult to measure, requiring frequent monitoring as a result of fine root dynamics and long-term monitoring as a result of sensitivity to resource availability. We report belowground plant responses of a scrub-oak ecosystem in Florida exposed to 11 yr of elevated atmospheric CO2 using open-top chambers. We measured fine root production, turnover and biomass using minirhizotrons, coarse root biomass using ground-penetrating radar and total root biomass using soil cores. Total root biomass was greater in elevated than in ambient plots, and the absolute difference was larger than the difference aboveground. Fine root biomass fluctuated by more than a factor of two, with no unidirectional temporal trend, whereas leaf biomass accumulated monotonically. Strong increases in fine root biomass with elevated CO2 occurred after fire and hurricane disturbance. Leaf biomass also exhibited stronger responses following hurricanes. Responses after fire and hurricanes suggest that disturbance promotes the growth responses of plants to elevated CO2. Increased resource availability associated with disturbance (nutrients, water, space) may facilitate greater responses of roots to elevated CO2. The disappearance of responses in fine roots suggests limits on the capacity of root systems to respond to CO2 enrichment.

Aim To determine if recurrent fire accounts for bamboo-dominated forests that cover about 180,000 km2 of western Amazonia. Location Western Amazonia, including Los Amigos and Cocha Cashu, Peru, and Acre, Brazil. Methods We identified bamboo (B+) and closed-canopy forests (B−) using a combination of MODIS imagery, Landsat TM imagery and field surveys. Local-scale and landscape-scale patterns of historical bamboo dynamics were analysed by collecting soil cores from B+ and B− sites across three regions. Soil charcoal within cores was used to document previous fire, and phytoliths were employed to reconstruct vegetational patterns through time. Results Fire occurred in B+ and B− sites with approximately equal frequencies in each region sampled. Between regions, fire signals were most prevalent at Los Amigos, with Cocha Cashu and Acre sites typically containing only trace amounts of charcoal. Vegetational state remained constant through time in both B+ and B− forests of Cocha Cashu and Acre. The persistence of bamboo through time is less clear at Los Amigos, with bamboo presence changing both spatially and temporally. Main conclusions Fire does not appear to be the driving mechanism behind current bamboo distributions, although it may facilitate bamboo invasion. Once established in an area, bamboo persistently dominates the vegetation structure over historical time-scales at some sites (Cocha Cashu and Acre), but not at others (Los Amigos), which is likely to be a function of patch origin. Increasing human activity, including fire and deforestation, combined with predicted Amazonian drought, may allow bamboo to expand from its current distribution and replace typical Amazonian closed-canopy forests. These structural changes in the forests have important implications for carbon storage, as Amazonian forests are currently the largest terrestrial carbon sink in the world.

Although confined and perched light nonaqueous phase liquids (LNAPLs) have previously been recognized, the majority of technical LNAPL literature focuses on unconfined LNAPL. Little information exists regarding the appropriate use of LNAPL distribution and transmissivity data to distinguish between confined, perched, and unconfined LNAPL hydrogeological scenarios. This paper describes three case histories that illustrate how the observed behavior of LNAPL can be used to identify the hydrogeologic condition of LNAPL at a given site and improved methods for calculating LNAPL drawdown based on these hydrogeologic conditions. The assessment methodology uses routinely available data such as fluid gauging, boring lo, laser-induced fluorescence, visual observations of soil cores, and LNAPL baildown testing. Identification of the correct LNAPL hydrogeologic condition results in more accurate LNAPL conceptual site models, improved estimates of LNAPL recovery rates and volumes, more appropriate technology applications, and improved accuracy of LNAPL remediation metrics such as LNAPL transmissivity.

The responses of aboveground parts of the forest to changes in environmental factors and stand age is well studied, but the same is not true for the belowground parts of the forest. Two plantation black locust (Robinia pseudoacacia L.) forest sites were taken in the Loess Plateau of China, one in the drier, infertile, more sandy area of the middle Loess Plateau, and another in the wetter, fertile, more clay-filled area of the southern Loess Plateau. At each site, both a younger (8-year-old) plantation stand and an older (30-year-old) plantation stand were included to study the effects of soil physicochemical properties and stand age on the fine root (

Two collections of Pauropoda (Myriapoda) from soil cores in high-country subalpine and alpine tussock grassland in New Zealand contained 757 specimens representing 11 species, eight of which are recognised as new to science, including two representing new genera. The following new taxa are described here by the first author: Ataktopauropus Scheller gen. n. for Ataktopauropus adaios Scheller sp. n., Decapauropus orestes Scheller sp. n., Decapauropus undulatus Scheller sp. n., Nesopauropus upsilon Scheller sp. n., Pauropus otagoensis Scheller sp. n., Pounamupauropus Scheller gen. n. for Pounamu- pauropus bartonae Scheller sp. n. and Stylopauropoides vesica Scheller sp. n. (all seven species in family Pauropodidae), and Borneopauropus neozelandicus Scheller sp. n. (family Brachypauropodidae). The genera Nesopauropus Scheller and Borneopauropus Scheller are reported from New Zealand for the first time.

Several methods are used for the extraction of soil solution. The objective of this study was to find out to what extent the different extraction methods yield complementary or equivalent information. Soil solutions were sampled once at 10 different forest sites in Germany, with 4 sampling points per site, using 5 different extraction methods. Concentrations of the major ions in the 1:2 extracts and the equilibrium soil-pore solutions (obtained from percolation of field-fresh soil cores) were generally lower than in desorption solutions, suction-cup solutions, and saturation extracts. Surprisingly, the latter three methods generally yielded equivalent results. However, possible systematic differences between these methods could have been masked by the high small-scale spatial variability within the sites.

Scientists estimate seed abundances to calculate seasonal carrying capacities and assess wetland management actions for waterfowl and other wildlife using soil core samples. We evaluated recovery of known quantities of moist-soil seeds from whole and subsampled experimental core samples containing 12 seed taxa representing small, medium, and large size classes. We recovered 86.3% (SE = 1.8) of all seeds added to experimental cores; 8.3% (SE = 1.2) of seeds were destroyed during the sieving process and 5.4% (SE = 1.2) were not recovered by observers. Recovery rates varied by seed size, but not seed quantity or disproportionate ratios of seed-size classes. Overall seed recovery rates were similar between subsampled ( = 81.2%, SE = 3.6) and whole—processed core samples ( = 86.3%, SE = 1.8). We used recovery rates to generate size-specific, taxon-specific, and constant correction factors and applied each to actual core sample data. Size-specific correction factors increased seed mass estimates in the...

We investigate the flow rate dependency of solute transport within an undisturbed monolithic soil core, collected in an Inceptisol. Through a series of nine controlled steady-state solute breakthrough experiments, flow rate dependency of solute transport was elucidated using the general transfer function (GTF) modeling theory. We first observed that the apparent dispersion coefficient increases with depth and flow rate. We also observed that the flow regime is rather a convective–dispersive (CD) process at low flow rates and a stochastic–convective (SC) process at high flow rates. At intermediate flow rates, the flow regime could not be described with either CD or SC processes. To better understand the mechanisms of altering flow regime at intermediate flow rates, a dye tracer experiment was conducted. Results show that preferential flow is initiated at intermediate flow rates. We hypothesize that the mixing of solutes between stream tubes decreases when flow rate increases, due to the decrease of the tortuosity of solute flow paths and the initiation of preferential flow through macropores.

This study investigated the degree to which human activities through urbanization influence heavy metal concentrations in a suburban landscape in Ankeny, IA. Residential areas from different years in nine time periods of development were identified from aerial photos. Soil cores were collected from the center of the front yard of 10 randomly selected homes. Cores were subdivided into 0- to 5-, 5- to 10-, and 10- to 20-cm increments from a composite of five cores. The soils were analyzed for organic C, pH, and total Cd, Co, Cr, Cu, Ni, Pb, and Zn. Results showed that organic C increased and pH decreased with time, and that there was a general decreasing trend in heavy metal concentrations from the pre-1939 period until 1983-1990, after which there was a sharp increase in the concentrations of most of the metals. The mean Cu concentration ranged from 21 mg kg(-1) for the pre-1939 time period of development to 14.9 mg kg(-1) for the recent period of development (2003-2005). Nickel concentrations increased significantly with depth with means of 21.3 mg kg(-1) at depth 0 to 5 cm, 22.5 mg kg(-1) at depth 5 to 10 cm, and 23.0 mg kg(-1) at depth 10 to 20 cm. The concentrations of heavy metals were significantly intercorrelated, except Zn, suggesting their coexistence as mineral constituents or common contamination source. The concentrations of Cu and Pb in some locations could be due to anthropogenic inputs or higher organic matter content in soils adjacent to older homes. There appears to have been a source that caused an increase in Cd, Cr, Co, Cu, Pb, and Ni concentrations in soil adjacent to homes built between 1983 and 1990.

Capacitance probes (CP) based on responses to electromagnetic properties in soil are widely used for monitoring soil volumetric water content (θ v ), but proper calibration is necessary to obtain reliable results. The objectives of this study were to: (i) compare errors in evaluating θ v when using soil-specific equations as opposed to the manufacturer's default equation; (ii) compare the CP calibration equations obtained in the laboratory and in the field; and (iii) evaluate the accuracy of CP under field conditions using soil-specific equations as opposed to the manufacturer's default equation. Laboratory and field calibrations were conducted by fitting statistical relationships between readings from CP and θ v measured from soil cores. The accuracies of the obtained calibration equations were evaluated under field conditions during two irrigation cycles. In both calibration studies, the manufacturer's default equation consistently overcalculated θ v (RMSE > 0.044 m 3 m-3 ) , whereas custom CP calibration equations provided accurate θ v determinations (RMSE < 0.028 m 3 m -3 ). Even when θ v was overestimated, the manufacturer's default equation was able to reproduce θ v dynamics during irrigation. Therefore, if users are interested in relative differences in θ v , they may use the manufacturer's default equation. If absolute values are needed, however, soil-specific calibration is required. The accuracy of CP in monitoring θ v under field conditions was slightly better using the laboratory calibration equation (RMSE = 0.019 m 3 m -3 ) rather than the field calibration equation (RMSE = 0.023 m 3 m -3 ). The use of a laboratory calibration is recommended given that it is easily reproducible, facilitates work planning, and minimizes uncertainties.

Soil water content is often determined using various permittivity sensors. The Hydra Probe reports both the real (e') and imaginary (e") components of complex permittivity (e*) and estimates electrical conductivity (σ'). Previously, a 12-wire probe was used with a vector network analyzer to determine e' and e" and σ' and σ" in undisturbed soil cores. The purpose of this study was to compare results from the Hydra Probe and the 12-wire probe for fluids as well as for soil samples taken from six locations, to better understand the interrelations of e', e", and σ' from the Hydra Probe. Undisturbed soil cores were collected from an Iowa prairie and adjacent soybean [Glycine max (L.) Merr.] field, an Iowa forest and adjacent soybean field, Idaho burned and unburned sites, Colorado grassland and dryland wheat (Triticum aestivum L.) sites, Ohio grassed areas, and Texas rangeland and an irrigated field. Because of their density, some of the Texas samples were sieved and repacked. The reported σ', e', and e" values of fluids were compared between the two measurement systems and with theoretical values. Because the theoretical values for soils are not known, the measured values were compared between systems. Both probes showed σ', e', and e" close to the theoretical values for fluids. In soils, we showed that an adjustment was needed in the calculated σ' from the Hydra Probe to account for dielectric relaxation. The soil σ' of the Hydra Probe matched σ' from the 12-wire probe better after the adjustment was made.

ConservaƟ ve solute transport experiments were conducted at a fi eld plot and on an undisturbed soil core from the same site. The hydraulic and solute transport properƟ es were extensively characterized so that the data could be analyzed from a determinisƟ c perspecƟ ve. To invesƟ gate the infl uence of scale and conceptual model on solute transport in the relaƟ vely homogeneous upper soil profi le of the fi eld site, breakthrough curves that were collected at diff erent depths in the undisturbed column and in the fi eld experiments were compared and analyzed. The mobile-immobile model provided a physically realisƟ c descripƟ on of the column data that was largely independent of the transport distance, and upscaling from the undisturbed core to the fi eld plot was relaƟ vely successful. Mean and variance of the Br − travel Ɵ mes were controlled by plot-scale variability in soil water content and heterogeneity, which was overcome by averaging the concentraƟ on values from four locaƟ ons at the same depth and Ɵ me, and analyzing the Br − transport behavior as a one-dimensional process. Diff erences between the measured and simulated mass balances, average concentraƟ on, and the variaƟ ons in concentraƟ on were predicted reasonably well across depth and Ɵ me. Although predicƟ on of the exact concentraƟ on informaƟ on at a given point was not achieved, this study demonstrates that areaaverage Br − transport in a heterogeneous vadose zone can be determinisƟ cally quanƟ fi ed.

Prior research has shown a log-log correlation between ex situ air permeability (k a ) measured at a matric potential of -50 and -100 cm H 2 O and saturated hydraulic conductivity (K sat ) in agricultural soils. We examined the applicability of a previously established log k a vs. log K sat predictive relation in unburned and burned woodland-chaparral and coniferous soils. Specifically, we measured in situ k a in the field using the soil corer air permeameter (SCAP) and measured laboratory K sat on soil cores. To determine postfire soil physical changes, K sat was transformed into water permeability, k w. Then k a and k w were compared in unburned and burned soils. The median k a was lower and median k w was higher in burned than unburned woodland-chaparral soils. The median k a and k w were both lower in burned than unburned coniferous soils. Despite these effects, the 95% prediction interval of the predictive relation includes 80% of the burned soils and 83% of all desert soils. The RMSE values of the predicted log K sat and measured log K sat were 0.371, 0.552, 0.588, and 0.511 m d -1 for unburned and burned woodland-chaparral and unburned and burned coniferous soils, respectively. In comparison, the RMSE for the predicted and measured log K sat was 0.654 m d -1 for an agricultural data set. The overall RMSE for unburned and burned soils including the agricultural soils was 0.551 m d -1 . This suggests that the predictive relation is applicable for unburned and burned desert soils for in situ k a measurements.

We investigated the erodibility of surface casts produced by an anecic earthworm of the Colombian savannahs by means of indoor rain simulations. The kinetic energy applied to samples, 21.62 J minute (-1) m (-2), was estimated to be equivalent to 41% of the energy of the more intense period of a local storm. The erodibility of casts was assessed at different stages of their ageing along with the effects of repeated wetting-drying cycles. Bare soil cores and soil cores of the same size with a cast on their surface (soil + cast) were used as controls. Saturated hydraulic conductivity (HC) was measured to test whether casts enhance soil water permeability. Fresh, almost liquid, individual casts were completely dispersed by a 2-hour rainfall simulation at a dispersion rate of 0.9 +/- 0.5% of sample minute (-1). After 5 hours drying at 32 degrees C and 79% relative humidity, casts were as moist as fresh casts (non-significant Mann-Whitney U-test) but had a solid appearance and were no longer dispersed by raindrop impact. Under simulated rainfall, dry casts were very slowly fragmented into large aggregates (> 5 mm). The HC of casts was increased by repeated cycles of wetting and drying but unaffected by length of air-drying and natural ageing, and averaged 7 (3, n=6), 20 (3, n= 7) and 32 (1, n = 45) cm hour (-1) for bare soil, soil + cast and all casts, respectively (standard error, sample size). Except for bare soil, these values were greater than the greatest rainfall intensities recorded locally. The consequences for soil erosion, nutrient losses and water infiltration are discussed.

Three-dimensional ground-penetrating radar (3D GPR) was used to investigate the subsurface structure of ice-wedge polygons and other features of the frozen active layer and near-surface permafrost near Barrow, Alaska. Surveys were conducted at three sites located on landscapes of different geomorphic age. At each site, sediment cores were collected and characterised to aid interpretation of GPR data. At two sites, 3D GPR was able to delineate subsurface ice-wedge networks with high fidelity. Three-dimensional GPR data also revealed a fundamental difference in ice-wedge morphology between these two sites that is consistent with differences in landscape age. At a third site, the combination of two-dimensional and 3D GPR revealed the location of an active frost boil with ataxitic cryostructure. When supplemented by analysis of soil cores, 3D GPR offers considerable potential for imaging, interpreting and 3D mapping of near-surface soil and ice structures in permafrost environments. Copyright © 2007 John Wiley & Sons, Ltd.

Disk infiltrometers are widely used to determine saturated and near-saturated soil hydraulic conductivity. Previous studies have recommended applying a high-permeability material to the undisturbed soil surface to establish a complete hydraulic bond between the disk and the infiltration surface. Other studies have shown that the use of the contact material affects the infiltration, and hence also the determination of saturated and near-saturated conductivity. In this study, we tested a new type of infiltrometer (that we call a hood infiltrometer), which might overcome these problems. Instead of requiring a disk and contact material, it places a water-filled hood, open side down, onto the soil surface. In this study, repeated hood and disk infiltrometer field tests in conjunction with time-domain reflectometry (TDR) measurements were performed at the same location to compare the performance of the two types of infiltrometer. Furthermore, we extracted undisturbed soil cores to measure the hydraulic functions in the lab. The measured hood and disk data were analyzed using Wooding's solution and by numerical parameter optimization technique using uni- and bimodal hydraulic functions. Running the disk infiltrometer with a contact layer provided saturated hydraulic conductivities that were 10 times smaller than corresponding values measured by the hood infiltrometer. We attributed these differences to smearing, sealing, and clogging of pores, which led to additional flow impedances in the soil surface layer. We were able to show, however, that the combined use of hood and disk infiltrometers in conjunction with TDR enabled hydraulic characterization of the soil from saturation to dry conditions.

We hypothesized the seed biomass available to migrating waterfowl would be higher in spring- versus fall-flooded wetlands. To test this hypothesis we conducted an experiment using 5 pairs of wetland impoundments in northern Missouri, USA (2000–2002). We strategically assigned one impoundment of each pair to either a fall or spring treatment group. We estimated seed biomass in fall and in spring by clipping seed heads and collecting soil cores at 20 random locations within each impoundment. We placed exclosures near each fall sample site in spring-flooded impoundments to estimate seed loss from granivorous birds and rodents. Despite similar biomass in fall between treatments (P = 0.64), overwinter seed loss was greater in fall-flooded (79%; 1,324 ± 195 kg/ha) than in spring-flooded (31%; 653 ± 130 kg/ha) impoundments (P = 0.009). Considering barnyard grass or millet (Echinochloa spp.) only, seed loss was higher in fall-flooded than in spring-flooded impoundments (P = 0.05). Spring biomass estimate...

Soybean [Glycine max (L.) Merr.] yield in claypan soils varies systematically with soil properties and landscape position. This is likely caused by soil interactions with soybean roots. Field observations of soybean root distribution are needed to reveal its effect on yield variability. This study examined profi le distributions of soybean root length density (RLD) and average root diameter (ARD) as a function of landscape position, depth to claypan (DTC), apparent soil electrical conductivity (EC a ), clay-maximum translated depth (D t ), and other soil properties. A landscape of claypan soils was sampled postharvest at two sites near Centralia, MO, in 2001. Roots were washed from soil cores in 15-cm layers (15–120 cm) and measured with image analysis. Root length density and ARD were signifi cantly related to landscape position, DTC, D t , and EC a . Predictions of RLD and ARD were best from 15 to 60 cm, the depths with the greatest infl uence from claypan soil morphology. Soil profi le distributions of base cations, P, and pH matched root density profi les. Soybean roots were inhibited in E horizons above the claypan and stimulated 20 to 40 cm below it. Soybean roots below the claypan had about 20 to 30% smaller diameter. We conclude that DTC and rapid estimators of claypan morphology, such as EC a , can be used to predict soybean root distribution in claypan soil landscapes.

We investigated seasonal root production and root turnover of fertilized and wellwatered monocultures of Phalaris for 2 years using minirhizotrons installed in six newly designed temperature gradient tunnels, combined with sequential soil coring. Elevated atmospheric CO2 treatments were combined with two cutting frequencies and three warming scenarios: no warming, 13.0/13.0 and 12.2/14.01C (day/night) atmospheric warming. The elevated CO2 treatment increased both new and net root length production primarily when combined with atmospheric warming, where the constant warming treatment had a greater positive effect than the increased night-time warming treatment. Responses to elevated CO2 were greater when the swards were cut more frequently and responsiveness varied with season. For Phalaris swards, 17% of total net primary productivity went belowground. On account of root turnover, only one-third of the new roots produced in the year following establishment could be expected, on average, to be recovered from soil cores. The interaction between the effects of CO2 and warming, combined with the differential effects of the two warming treatments, has important implications for modelling belowground responses to projected climate change.

Soil organic carbon (SOC) sequestration is an important process to mitigate CO 2 emissions. Our objectives were to determine the rates of C sequestration and to determine if the SOC pool was at or approaching equilibrium in plots under long-term (24-yr) conservation (CT) and disk tillage (DT) management. The plots were Norfolk loamy sand (fine-loamy, kaolinitic, thermic, Typic Kandiudult) and were under a row crop rotation. All plots received annual subsoiling, while only plots under DT were surface disked. Soil cores were collected to 90 cm deep. After 24 yr, the only significant increase in SOC occurred in CT plots at a 0- to 5-cm depth. The SOC pool in plots under DT was at a near-steady state, while the SOC pool under CT was not at equilibrium. This supports the conclusion that CT is an effective countermeasure to offset atmospheric CO 2 emissions.

Field experiments are essential for elucidating the processes involved in N 2 O production during soil freezing/thawing (FT) cycles, but laboratory simulations can provide the advantage of controlled conditions. Past studies have used disturbed or undisturbed soil cores placed in a controlled temperature environment, so that FT occurred from the external surface to the inside of the core (omni-directional method, OD). A new method of soil FT for simulating field conditions more dosely in the laboratory was developed and its effect on N 2 O fluxes evaluated. Three methods were examined: OD, uni-directional (UD) with the soil column surrounded by filled-in soil, and a variant of UD with water accessible to the base of the core (UDW). The rate of soil cooling with time was significantly faster and similar at all depths (-0.29°C h -1 ) for OD, than for UD or UDW methods (-0.16°C h -1 at 1 cm, -0.10°C h -1 at 20 cm). This differential cooling resulted in a significant change in soil temperature with depth for UD and UDW methods 0.125°C cm -1 during freezing and -0.35°C cm -1 during thawing, but of only 0.04 and -0.02°C cm -1 for the OD method. Comparison with field temperature data indicated that the UD and UDW method more closely resembled the gradual top-to-bottom freezing of soil layers that occurs in field conditions (changes of -0.20°C h -1 at 1 cm; -0.05°C h -1 at 20 cm). Gravimetric water content in the frozen layer 0 to 20 mm in the UDW (60.6 g kg -1 ) was significantly higher than in UD (44.4 g kg -1 ) and OD (37.6 g kg -1 ) soil columns. Fluxes of N 2 O during thawing were significantly affected by the incubation method used, probably due to the intensity and duration of freezing, and the water content prevalent under each method with OD (13 ng N 2 O-N m -2 s -1 ) > UDW (4.8 ng N 2 O-N m -2 s -1 ) > UD (2.1 ng N 2 O-N m -2 s -1 ). We conclude that the UD (and UDW) method allows for manipulation of FT in soil columns gradually layer-by-layer providing the conditions needed to link the site of N 2 O production in the soil profile with surface N 2 O fluxes in laboratory studies.

The ability of two nitrogen cycle models, of contrasting complexity, to predict N mineralization from a range of grassland soils in the UK, was evaluated. These were NCYCLE, a simple mass balance model of the N cycle in UK grasslands, and CENTURY, a more complex model simulating long-term C, N, P & S dynamics in grassland ecosystems. The models were tested using field measurements of net N mineralization from a range of grassland soils (differing in soil type, history & management practice), obtained over a 2 year period using a soil core incubation technique. This method was considered to measure the total net release of mineral N from the soil organic matter over a specified time, including N which may have been recycled several times. NCYCLE consistently under-estimated mineralization rates at all sites. By contrast, there was some correlation between CENTURY predictions of net N mineralization and field measurements. This may have reflected the different abilities of the two models to simulate N recycling. Neither model, however, was able to predict adequately the effect of cultivation and reseeding on net N mineralization.

We used the soil-core translocation method to investigate the effect of increased temperature on above- and below-ground phytomass and organic matter in cool alpine areas. The translocation of undisturbed soil cores from a high alpine site (2525 m a.s.l.) to an alpine site near the timberline (1895 m a.s.l.) achieved an effective artificial warming of 3.3 K. From a methodological point of view, the translocation of soil cores was performed successfully. Soil cores moved to a new site at the same altitude showed no change in above- and below-ground vegetation, bulk density, and soil skeleton. At both sites, soils were Haplic Podzols with a similar chemistry and clay mineralogy. At the lower elevation site, however, podzolization processes seemed to be more pronounced. As a consequence, the translocation of the soil cores probably led to a disturbance of the actual steady state that had been established after about 10,000–13,000 years of soil formation. This might have affected the adaptability of the vegetation system. Therefore, it cannot be fully excluded that the experimental design influenced the results. Translocation of soil cores from a very cool to a warmer site led to a distinct decrease in above-ground phytomass (about –45%) over the experimental period of two years. Below-ground phytomass significantly decreased (up to –50%) in the topsoil (0–5 cm) after artificial warming. Possible mechanisms are that roots reduced photosynthesis and hence C flow below-ground, a reduction of soil moisture that would have led to root death (not a very probable cause, however) or an abrupt change in the radiation duration and flux which affected root growth (also not very probable). Fast climate change exceeded the ability of the above-ground and below-ground phytomass to adapt quickly. Whether the decrease in phytomass was a short-term or a long-term response to climate warming remains uncertain. Based on a gradient study (climosequence at the same locality), we hypothesize that the decreased plant productivity might be a short-term effect. Experimentelle Untersuchung von Klimaanderungen und ihren Auswirkungen auf die oberirdische und unterirdische Phytomasse durch Translokation von Bodensaulen Um die Auswirkungen erhohter Temperaturen auf die ober- und unterirdische Biomasse und die organische Substanz im Boden zu studieren, wurden Bodensaulen von einem hoher gelegenen, alpinen Standort (2525 m u. M.) an einen tiefer gelegenen Standort (1895 m u. M.) versetzt. Diese Translokation simuliert einen kunstlichen Temperaturanstieg von 3,3 K. In methodischer Hinsicht kann das Experiment als gelungen betrachtet werden. Bodensaulen, die in unmittelbare Nahe des Ausgangsstandorts (2525 m u. M.) versetzt wurden, zeigten gegenuber dem Referenzzustand keine Veranderungen hinsichtlich der ober- und unterirdischen Biomasse, Bodendichte und Skelettgehalt. Beide Standorte waren durch Podsole charakterisiert mit einer ahnlichen Bodenchemie und -mineralogie. Beim tiefer gelegenen Standort war die Podsolierungserscheinung jedoch etwas ausgepragter. Die Versetzung der Bodensaulen vom hoher zum tiefer gelegenen Standort und somit auch eine Versetzung in ein leicht anderes chemisch-mineralogisches Milieu fuhrte moglicherweise zu einer Storung des sich nach rund 10000–13000 Jahren etablierten Quasi-Gleichgewichtszustandes. Dieser Umstand konnte auch das Anpassungsvermogen der Vegetation beeinflusst haben. Somit kann nicht vollstandig ausgeschlossen werden, dass die experimentelle Ausfuhrung die Resultate beeinflusste. Die Translokation von Bodensaulen von einem kalteren in ein warmeres Klima fuhrte zu einer ausgepragten Abnahme der oberirdischen Phytomasse (–45 %). Nach erfolgter kunstlicher Erwarmung verminderte sich auch die Menge an unterirdischer Phytomasse in der obersten Bodenschicht um rund –50 %. Mogliche Mechanismen, die zu einem Absterben der Wurzeln gefuhrt haben, sind eine verminderte Photosynthese und damit verbunden ein verminderter Kohlenstofftransport in die unterirdische Phytomasse, eine Abnahme der Bodenfeuchte (ein eher wenig wahrscheinlicher Grund) oder eine abrupte Anderung der Strahlungsdauer und somit -menge (auch eher weniger wahrscheinlich), welche das Wurzelwachstum direkt beeinflusste. Ein schneller Klimawandel uberstieg offensichtlich die Anpassungsfahigkeit der Vegetation. Ob nun die Abnahme der Phytomasse ein kurz- oder eher langfristiger Effekt war, kann nicht definitiv geklart werden. Aufgrund einer Klimasequenz im gleichen Untersuchungsgebiet gehen wir aber davon aus, dass die gemessenen Effekte eher einen kurz- bis mittelfristigen Charakter haben.

Movement of nutrients from livestock manure handling sites has the potential to negatively impact the environment. This study was conducted using electromagnetic induction (EMI) measurements to develop apparent soil electrical conductivity (EC(a)) maps to identify regions of nutrient buildup beneath an abandoned compost site. A trailer-mounted EM-38 coupled with a global positioning satellite system was towed across an area used for composting of feedlot manure. The resulting EC(a) maps were compared with known locations of compost rows confirming the alignment of row locations with high EC(a) regions. The identified rows were cored and compared with the region between the rows. The identified rows with a compost history demonstrated significant (P < 0.05) increases in soluble salts (1.6 times greater), NO3 (6.0 times greater), and Cl (2.0 times greater) compared with the area between the rows at a 1.5-m depth. Image processing techniques were used to display yearly changes that were associated with nutrient movement and transformations in the soil beneath the site. Correlations between EMI measurements and soil core analyses for NO3-N, Cl, and EC provided ancillary support for the EMI methods. The use of EMI for mapping of sites having a history of livestock waste application was effective in delineating high nutrient buildup areas and for observing spatial EC(a) changes over time.

Forest soils are often deep andlor coarse-textured, which does not always lend itself to easy unbiased sampling. Two important Pacific Northwest (PNW) forest soil series that are deep and coarse-textured were studied to evaluate methods of estimating soil C: (i) a loamy sand glacial outwash soil (Indianola series, mixed, mesic Dystric Xeropsamments) and (ii) a very gravelly sandy loam glacial outwash soil (Everett series, sandy-skeletal, isotic, mesic Vitrandic Dystroxerepts). Four methods were compared for estimating soil C, including: (i) large pit (0.5 m 2 ) excavation, (ii) dug pit with 54-mm hammer-core bulk-density sampling, (iii) 31-mm soil push sampler, and (iv) clod method. Coarse (>2 mm) fragments were also collected, processed, and analyzed for soil C. Extending soil sampling deeper than 15 cm increased soil C estimates by as much as 120%. The pit excavation method with sand-displacement volume measurements, which is by far the most labor-intensive and time-consuming, was considered the standard by which other methods were compared, as it didn't contain any obvious biases. Soil core methods overestimated the 50%) of the Everett soil. Including C analysis of the >2-mm soil fraction increased soil C estimates by 170% for the Everett series soil (due to organic C contained in the rocks; there were no carbonates) but did not substantially increase the estimate in the Indianola series soil.

Intact soil cores from a montane tropical rain forest site in the Atherton Tablelands (Kauri Creek) and from a lowland tropical rain forest site in the Coastal Lowlands (Bellenden Ker), Queensland, Australia were investigated during different hygric seasons for the magnitude of gross nitrification rates using the Barometric Process Separation technique (BaPS). Pronounced seasonal variations of gross nitrification rates were found at both sites with highest values during the transition period between dry and wet season (montane site: 24.0 mg N (kg SDW)—1 d—1; lowland site: 13.1 mg N (kg SDW)—1 d—1) and significantly lower rates of gross nitrification during the dry and wet season. Rates of gross nitrification were always higher at the montane site than at the lowland site, but the opposite was found for N2O emissions. The results indicated that the high losses of N2O at the lowland tropical rain forest site may be contributed largely by high denitrification activity due to its wetter and warmer climate as compared to the dryer and colder climate at the montane tropical rain forest site. This conclusion was supported by analysis of cell numbers of microbes involved in N-cycling. Higher numbers of denitrifiers were present at the lowland site, whereas higher numbers of nitrifiers were found at the montane site. Nitrifikationsaktivitat in tropischen Regenwaldboden im kustennahen Tiefland und in den Atherton Tablelands, Queensland, Autralien Mit Hilfe der Methode zur Barometrischen Prozess Separation (BaPS) wurden Brutto-Nitrifikationsraten intakter Bodenkerne von einem Bergregenwald-Standort auf den Atherton Tablelands (Kauri Creek) und einem Tieflandregenwald (Bellenden Ker) in den Coastal Lowlands, Queensland, Australien, wahrend unterschiedlicher Jahreszeiten bestimmt. An beiden Standorten konnte ein ausgepragter saisonaler Verlauf der Brutto-Nitrifikationsraten festgestellt werden, mit maximalen Werten wahrend des Ubergangs von Trocken- zur Regenzeit (Bergregenwald: 24,0 mg N (kg SDW)—1 d—1; Tieflandregenwald: 13,1 mg N (kg SDW)—1 d—1) und signifikant niedrigeren Werten in der Trocken- und Regenzeit. Wahrend die Brutto-Nitrifikationsraten am Bergregenwald-Standort zu allen Jahreszeiten hoher als am Tieflandregenwald-Standort waren, ergab sich fur die Hohe der N2O-Emissionen ein umgekehrter Trend. Die Ergebnisse zeigen, dass in Folge des deutlich feuchteren und warmeren Klimas am Tieflandregenwaldstandort die im Vergleich zum trockeneren und kuhleren Bergregenwald-Standort wesentlich hoheren N2O-Verluste auf eine hohere Aktivitat der Denitrifikation zuruckzufuhren sind. Analysen zur Abundanz von am Stickstoffkreislauf beteiligten Mikroorganismen unterstutzen diese Feststellung. Ein Vergleich beider Standorte zeigte hohere Zellzahlen der Denitrifizierer am Tieflandregenwald-Standort, wahrend am Bergregenwald-Standort die Population der nitrifizierenden Mikroorganismen groser war.

A method was developed to obtain large undisturbed soil cores and instrument those cores to collect vadose zone leachate data under agricultural field conditions. Twenty undisturbed soil core lysimeters were constructed at an irrigated-field site in southeastern North Dakota. Construction of the undisturbed lysimeters consisted of utilizing a steel cutting bit to collect large (0.61-m diam. by 1.68-m deep) soil cores in sections of polyvinyl chloride (PVC) pipe, installing a leachate collection system, installing time domain reflectometry (TDR) soil moisture probes, and then finally placing them below grade so normal farming practices could continue. The described method of core collection is an improvement over other methods in that the cutting bit is reusable, the resulting core is larger and deeper than other methods, no heavy static weights are required, and it is not necessary to expose a free-standing soil column. Leachate quality and quantity data is reported for 1990 through 1995 and compared favorably with larger, reconstructed profile lysimeters on the same site. Overall, the lysimeters functioned as intended for the first 6 yr of operation; however, two developed leaks and rodents damaged another. Possible sidewall flow was observed and may be avoidable in future designs.

Animal welfare considerations have stimulated the development of outdoor piglet (Sus scrofa) production systems, but the high levels of nutrients excreted suggest that nutrient losses from this system may be high. This study first described the spatial distribution of denitrification activity in a 5- x 5-m grid within and outside a paddock immediately after the sows (32 sows ha -1 for 6 mo) were removed in October 1997, and again the following March. Denitrification rates averaged 0.01 kg N ha -1 d -1 outside, and 0.5 kg N ha -1 d -1 inside the paddock in October, while the corresponding figures in March were 0.01 and 0.1 kg N ha -1 d 1 . The highest denitrification rates were observed around the feeder, and this was also the case for concentrations of dissolved organic C and inorganic N in the soil. A statistical model that included both soil parameters and distance to feeder and huts gave the best description of the variability, but there was no significant autocorrelation between sampling points. In a second phase, seasonal variation of denitrification activity within a paddock (12 sows ha -1 yr -1 ) was quantified; 10 soil cores were sampled along a transect 11 times between March 1998 and February 1999. There was a significant positive effect of dissolved organic carbon (DOC) on denitrification at

Forest management practices may alter soil properties, but experimental evaluation of treatment effects is often difficult because large soil variability yields poor statistical sensitivity. This study was conducted to determine if pretreatment soil sampling enhances our ability to detect treatment differences in Pacific Northwest forests. We used statistical simulation and data from 271 pretreatment 30-cm-deep soil cores taken from 70- to 100-yr-old post-fire Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stands at the Siskiyou National Forest in southwestern Oregon. At this site, an unmanipulated control and six treatments of overstory species and woody debris are being established on 6-ha plots and replicated in three blocks. If only post-treatment measurements were made, the minimum detectable difference (MDD) between extreme treatments would be 26 to 57% of current soil C and N concentrations (g kg -1 ) and masses (kg m -2 ), with C generally having smaller relative MDDs than N. In contrast, if the differences between post- and pretreatment were evaluated, relative MDDs for C properties would remain the same, but those for N would decrease by as much as one-half because N has greater pretreatment variability among plots than C. Masses of C and N, which incorporate information about rock volume and either soil mass or bulk density, have relative MDDs as small as one-half of those associated with concentrations. Evaluation of other sites is required to determine if these observations are consistent for forests in general and, thus, applicable to the design of sampling strategies in large-scale experiments.

Accurate soil mapping at a fine scale is needed for site-specific farming, research on solute transport, and many other applications requiring detailed analysis of both the depth and thickness of soil horizons. Soil mapping techniques currently used are too costly to address the spatial variability of soil mapping units. We propose the use of a profile cone penetrometer (PCP) to assist in mapping soil properties at a landscape scale. Data collected with the PCP show clear changes in soil properties with depth, and were confirmed using profile descriptions from soil pits as well as 4.3-cm-diam soil cores. Combining three-dimensional PCP data with soil attribute information will provide a rapid and effective means to digitally update soil surveys and improve the efficiency and cost effectiveness of sampling techniques.

Summary We have developed a predictive model of denitrification in soils, NEMIS, based on data from a cultivated field composed of denitrification rates measured on undisturbed soil cores and the corresponding soil water-filled pore space, nitrate content and respiration. This model is a multiplicative combination of a potential denitrification rate measured under standard conditions defined in this paper, and dimensionless functions of nitrate content, water-filled pore space and temperature. The model was applied to two further databases obtained independently of its definition. Significant correlation was observed between the simulated and measured denitrification rates. The sensitivity of NEMIS to systematic variations of the input variables and of the coefficients included in the dimensionless functions was tested using these databases. NEMIS seems to be a very useful tool particularly adapted for interpolating a small number of denitrification measurements from a simple database composed of soil potential denitrification rate and the evolution of soil water-filled pore space, nitrate content and temperature. Its main limitation is its high sensitivity to the water-filled pore space from which denitrification starts to occur and which is included in the water function. NEMIS, un modele predictif de la denitrification a l'echelle de la parcelle cultivee Resume NEMIS, un modele predictif de la denitrification dans les sols, a ete defini a partir d'une base de donnees obtenue dans un sol cultive et composee de vitesses de denitrification mesurees sur des echantillons de sol non remanies et les valeurs correspondantes de taux de saturation en eau, de teneur en nitrates et de vitesses de respiration. Ce modele est une combinaison multiplicative entre une vitesse potentielle de denitrification mesuree dans des conditions standardisees definies dans ce papier et de fonctions sans dimension de la teneur en nitrates, du taux de saturation en eau et de la temperature du sol. Ce modele a ensuite ete utilise sur deux jeux de donnees independantes et des correlations significatives ont ete observees entre mesures et simulations. La sensibilite du modele lors de variations systematiques du niveau des variables d'entree ainsi que des coefficients inclus dans les fonctions sans dimension a ete testee sur ces jeux de donnees. NEMIS apparait comme un outil tres utile d'interpolation entre quelques points de mesures de denitrification a partir d'un jeu de donnees relativement simple comprenant le potentiel de denitrification du sol et l'evolution du taux de saturation en eau, de la teneur en nitrates et de la temperature du sol. La principale limite de NEMIS est sa grande sensibilite au taux de saturation en eau du sol a partir duquel le processus de denitrification commence a fonctionner.

exploitable by plant roots (Scott et al., 1988a). Similarly, the more continuous the macropores are, the more The role of macropores in soil and water processes has motivated freely gases can interchange with the atmosphere. Conmany researchers to describe their sizes and shapes. Several approaches have been developed to characterize macroporosity, such tinuous macropores also have a direct effect on water as the use of tension infiltrometers, breakthrough curve techniques, infiltration and solute transport in soil. image-analysis of sections of soils, and CAT scanning. Until now, According to Sutton (1991), the size of pore openings efforts to describe macropores in quantitative terms have been concen- is more important for plant growth than is the overall trated on their two-dimensional (2-D) geometry. The objective of soil porosity. Although existing pores constrain the penthis study is to nondestructively quantify the three-dimensional (3etration of roots, they provide favorable conditions for D) properties of soil macropores in four large undisturbed soil colroot growth. Several studies have shown that the presumns. The geometry and topology of macropore networks were determined using CAT scanning and 3-D reconstruction techniques. Our ence of continuous macropores in soil significantly beneresults suggest that the numerical density of macropores varies be- fits root growth (Bennie, 1991). One of the most importween 13 421 to 23 562 networks/m 3

The transport of the herbicide chlortoluron (3-(3-chlor-p-tolyl)-1,1-dimethylurea) was monitored in Northern Germany in a sandy soil between November 1994 and March 1995. On a 0.86-ha grid, soil cores were taken down to a depth of 0.3 m and analyzed for total chlortoluron concentrations at 0.03-m intervals. A bromide (Br - ) transport experiment was carried out at the same site. Thirty-three, 61, and 136 d after application, corresponding to 54, 115, and 305 mm of precipitation, chlortoluron was found almost exclusively in the upper two, four, and six layers, respectively. In these layers, coefficients of variation (CVs) varied from about 50 to >200%. At the first sampling, about 1% of applied chlortoluron was detected in the layer just above the plow-sole. Mean travel depths of chlortoluron were distinctly more variable than those of Br - , showing no spatial correlation. The retardation factor of chlortoluron, expressing its displacement relative to that of Br - , considerably increased during the experiment, on the average from 11.5 at the first sampling to 26.3 at the third sampling. Only then, the local mean travel depths of chlortoluron showed a significant (positive) correlation with those of Br and a significant (negative) correlation with organic C contents. Sorption kinetics of chlortoluron were investigated in laboratory sorption-desorption (SD) experiments at 3 and 20°C. Sorption-desorption isotherms showed pronounced hysteresis. The influence of experimental temperature was small. The collected data are intended as a basis to evaluate the ability of different modeling approaches to represent pesticide displacement at the field scale.

Summary Transport of gas in soil depends on the paths available through the porous system. We determined the rate of diffusion of air through a core of silty-clay soil experimentally. After the experiment, the core was impregnated with resin and sectioned at 100 μm. From the images of the sections, the porous structure was reconstructed in three dimensions with a 100-μm resolution and gas diffusion was simulated in it. We computed the self-diffusion to describe gas diffusion. The experiment and simulation were compared using tortuosity, which is the ratio between the self-diffusion coefficient calculated in air and the coefficient calculated in the reconstructed sample. The results showed that the experimentally measured tortuosity (2.3) and the numerically calculated tortuosity (1.75) were similar. This suggests that the self-diffusion propagator is useful for simulating self-diffusion in a numerical three-dimensional reconstructed sample and that the scale chosen for the reconstruction of the sample (100 μm) was suitable for this particular soil. Resume Les proprietes de transfert en phase gazeuse des sols ont eteetudiees sur un sol limono-argileux. A l’issue de l’experience, l’echantillon a ete impregne avec une resine polyester puis sectionne en coupes seriees. A l’aide des images numerisees des coupes, l’echantillon a ete reconstruit en trois dimensions. Nous avons ensuite simule le processus de diffusion gazeuse dans l’echantillon reconstruit a l’aide du propagateur de diffusion. Experience et simulation ont ete comparees a l’aide de la tortuosite, rapport entre le coefficient de diffusion gazeuse dans l’air et celui dans le sol. Les resultats montrent que la tortuosite mesuree experimentalement (2,3) et la tortuosite calculee numeriquement (1,75) sont proches. Ceci prouve que l’utilisation du propagateur de diffusion est justifiee pour la simulation du processus de self-diffusion dans un echantillon tridimensionnel reconstruit et que l’echelle choisie pour la reconstruction (100 μm) s’avere pertinente pour l’etude de la diffusion gazeuse dans ce sol.

Laboratory determination of soil hydraulic characteristics (HC) is performed on cylindrical confined soil cores, while resin-coated small natural aggregates are prevalent for determining the Soil Shrinkage Characteristic Curve (SSCC). Because of the different geometry and volume of clods and cores, incorporation of shrinkage in HC of clay soils could be affected by the use of SSCC determined on natural aggregates or on confined cores. The objectives of this study were (i) to investigate differences between the SSCC obtained on resin-coated natural aggregates (volume V = 20-30 cm 3 ) and on cylindrical confined cores having a volume (650 cm 3 ) close to that of cores used for HC laboratory determination, (ii) to test the performance of different models proposed for analytical interpretation of the SSCC, and (iii) to derive regression equations predicting the SSCC from routinely measured soil physical properties. Using twenty-one Sicilian soils of variable shrink-swell behavior, we found significantly larger specific volume (n ), indicating less shrinkage, in the cylindrical confined cores. The investigation also proved the good fitting of a two-line model to the measured SSCC and the possibility to predict the basic shrinkage line from the clay content. These results suggest that incorporation of shrinkage in HC of clay soils should be based on the SSCC measured or predicted on cores with geometry and dimensions as those used for routine laboratory measurement of HC.

Unsystematisch verteilte Bodenbelastungen mit polychlorierten Dibenzo-p-dioxinen und Dibenzofuranen (PCDD/PCDF) waren Anlas fur die Durchfuhrung einer Stadtbodenkartierung in Rheinfelden (Baden). Diese teilweise sehr hohen Belastungen liesen sich nicht allein durch atmospharischen Eintrag aus ansassigen Industriebetrieben erklaren. Zur Ermittlung des Ausmases der Bodenbelastungen wurde als Methode die fallbezogene Stadtbodenkartierung gewahlt. Der Stadtbodenkartierung lag nach Voruntersuchungen als Arbeitshypothese zugrunde, das in Rheinfelden erhohte PCDD/PCDF-Bodenbelastungen an erkennbare Partikel gebunden im Boden vorliegen und deshalb durch eine bodenkundliche Gelandeaufnahme erfasbar sind. An etwa 3700 Bohrpunkten erfolgte eine Bodenansprache. Durch die flachendeckende, parzellenscharfe Kartierung konnten (hoch)bela-stete von wenig bzw. unbelasteten Bereichen abgegrenzt werden. Es wurden etwa 720 Bodenproben entnommen und auf Schwermetalle untersucht. An 140 Proben wurden die PCDD/PCDF-Gehalte bestimmt. Durch die Analytik wurde bestatigt, das im speziellen Falle Rheinfeldens PCDD/PCDF-Belastungen uber 100 ng I-TFQ/kg nahezu ausschlieslich in den als stark anthropogen gestort eingestuften Boden zu finden waren, Diese Boden waren erkennbar mit solchen Beimengungen verunreinigt, die auf erhohte PCDD/PCDF-Gehalte hinweisen und durch die Gelandeaufnahme erfasbar sind. Eine eindeutige Beziehung zwischen angenommenen Leitparametern (Ba, Hg. Pb) und PCDD/PCDF konnte nicht nachgewiesen werden. Die Methode einer solchen bclastungsfallspezifisuh modifizierten Stadtbodenkartierung ist grundsatzlich fur die Erkundung aller fla-chenhaften Bodenbelastungen geeignet, die an feldbodenkundliche Merkmale gekoppelt sind. Sie kann im Einzelfall eine effiziente und kostensparende Erkundungsmethode darstellen. Estimation of elevated soil contamination with polychlorinated Dibenzo-p-dioxins and Dibenzofurans by soil mapping in the field The evidence of irregular occurring soil contamination with polychlorinated dibenzo-p-dioxines and dibenzofuranes (PCDD/PCDF) have led to the pilot project ‘Mapping of urban soils at Rheinfelden (Baden)’. The contaminations have been partly very high and could not be explained by atmospheric deposition. The mapping of urban soils at Rheinfelden was based on the hypothesis, that elevated concentrations of PCDD/PCDF are bound to visible particles in the soil and therefore should be found by soil mapping in the field. About 3700 soil cores including soil description have been registered. By high resolution mapping of the whole area based on sampling of each — even the smallest — property it was possible to distinguish between highly contaminated and not or only low contaminated areas. 140 Samples have been analysed for PCDD/PCDF content while 720 soil samples have been taken in order to analyse heavy metal content. Our results showed that PCDD/PCDF contaminations above 100 ng I-TEQ/kg (toxicity equivalents) were only found in soils with strong anthropogenic influence. These soils have been contaminated with visible admixtures leading to elevated PCDD/PCDF concentration. There was no strong correlation between the key parameters (Ba, Hg. Pb) and the PCDD/PCDF contents. Generally contaminations with areal relevance could be detected by the used modified mapping of urban soils. In this case this method was an efficient and cost-reducing tool of detection.

To predict the effects of water or leachate infiltration into unsaturated field soils requires measurements of both the field-saturated hydraulic conductivity (K fs ) and the matric flux potential (Φ m ). Measurement of these soil parameters commonly requires steady-state infiltration rates, which, in the slowly permeable clay liners that are found underlying municipal landfills, can require several weeks or months to be attained. The transient, capillary-dominated, early-time method of determining K fs and Φ m has been found to provide a much faster, yet still reliable estimate of these flow parameters. Here, an analytical solution was utilized for early-time, one-dimensional infiltration under the conditions of an initial constant head followed by a falling-head phase. Six laboratory trials were conducted using precisely compacted clay cores to determine K fs and Φ m during both early-time and steady-state flow domains. The results of these trials showed a favorable comparison between these two techniques, with the early-time constant-head and falling-head methods producing K fs estimates that were 60 and 75% of their respective steady-state values. This suggests that the early-time determination of K fs and Φ m on slowly permeable media has a definite practical advantage over lengthy steady-state analyses. A new, expeditious procedure for determining steady-state K fs values of highly compacted soil cores, involving use of a Mariotte-equipped pressure plate chamber, was also developed and validated.

Soil probes are hammered into the soil to sample uniform, undisturbed soil cores, and can also be used to dig uniform holes for permanent installation of devices to monitor soil moisture and soil solution composition. Extracting soil probes becomes increasingly difficult at increasing depths, particularly when the soil is dry, frozen, or has a cohesive consistency. The construction and operation of a device for extracting soil probes is described. The device can be constructed from inexpensive and universally available galvanized pipe and pipe joints, and a 25 mm width x 2 m length nylon strap. The device can be used to extract other soil sampling equipment that requires upward vertical force. A single person can generate over 1000 kg of upward force on the probe without excessive effort. Use of the probe does not strain the back, which is an important consideration as back injuries are a serious concern with manual soil probe extraction.