Changes In Bulk Density Research Articles

Tine options for alleviating compaction in wheelings

Repeated trafficking and harvesting operations lead to high levels of compaction in inter-row wheelings used in asparagus (Asparagus officinalis) production. This reduces soil porosity and infiltration resulting in water ponding on the soil surface. Even on gently sloping land this can result in runoff generation and an increased risk of soil erosion. A winged tine (WT) is currently used by a leading asparagus grower to loosen compacted inter-row wheelings. In order to test the effectiveness of this tine for alleviating compaction and implications for runoff and soil erosion control, it was evaluated alongside several other tine configurations. These were a narrow tine (NT); a narrow tine with two shallow leading tines (NSLT); a winged tine with two shallow leading tines (WSLT); and a modified para-plough (MPP). Testing was conducted under controlled conditions on a sandy loam soil in the Soil Management Facility at Cranfield University, Bedfordshire, UK. Tine performance was assessed at 3 depths (175, 250 and 300mm) by draught force; soil disturbance (both above and below ground); specific draught for a given level of soil disturbance; surface roughness; and estimated change in soil bulk density. The effectiveness of tines for compaction alleviation and potential for mitigating runoff and soil erosion varied with depth. The most effective tines were found to be the MPP NSLT and the WSLT at 175mm, 250mm and 300mm depth, respectively.

Quantification of biochar effects on soil hydrological properties using meta-analysis of literature data

The use of biochar as a soil amendment had been increasingly advocated for its effects on carbon sequestration and greenhouse gas emission mitigation as well as on improvement of soil fertility. However, lack of a general assessment of biochar effects on soil physical properties made it difficult for the recommendations for its practical use for soil quality improvement in global agriculture. In this study, we performed a meta-analysis of literature data published by October 2015 and quantified biochar effects on selected soil physical properties. The literature data covered a range of feedstocks, pyrolysis temperature, soil and experimental conditions. Results showed that biochar amendment significantly improved all the soil physical properties tested. On average, soil bulk density was significantly reduced by 7.6% whereas soil porosity significantly increased by 8.4%, aggregate stability by 8.2%, available water holding capacity (AWC) by 15.1% and saturated hydraulic conductivity by 25.2%. Furthermore, the changes in soil bulk density were negatively correlated to porosity and AWC. In addition, these effects were greater in coarse textured soils than in fine textured soils. While the size of biochar effect on soil physical properties varied with the amount of biochar added, changes in bulk density only was correlated to application rates of crop residue and wood biochar. Overall, biochar amendments could likely improve soil hydrological properties though varying with biochar and soil conditions. Use of biochar thus could offer a viable option to improve moisture storage and water use efficiency for soils poor in organic carbon in arid/semiarid zones. More studies on dynamics of soil hydrological behaviors following biochar amendment should be deserved in field conditions for a sound understanding of biochar's potential in world agriculture.

USING DIFFERENT TYPES OF SUBSOILER SHARES TO IMPROVE THE PRODUCTIVITY OF COMPACTED SOILS

Soil compaction is an environmental problem and has been recognized as the main form of soil degradation in some Mediterranean areas. Soil compaction may increase soil strength and compacted soil layers can affect root growth and crop productivity. The aim of the present work was to investigate the effect of using different types of sub-soilers shanks and shares on physical soil properties, seed germination and crop productivity of faba bean (vicia faba). The experiment was carried out at El- Hamam district area- Matrouh in sandy loam soil. The soil was characterizes by hard pan compaction down to 40 cm. Parameters such as changes in soil penetration resistance, bulk density, hydraulic conductivity and soil moisture content were measured. The results revealed that the highest increase of soil penetration resistance and lowest hydraulic conductivity due to the soil compaction occurred in non treated soil with sub-soilers. The seed germination and yield of faba bean increased with decreasing soil penetration resistance. A positive action was detected between using fit equipped mole behind different shanks and shares of the sub-soilers used on both soil penetration resistance, and hydraulic conductivity. The ability to eliminate soil compaction could be useful on agricultural field in the South district of El Hamam canal area by using sub-soiler with mole fit equipped behind shank as well as decreased the effect of the hard pans and improve soil properties such as soil penetration resistance and hydraulic conductivity. The deep tillage gained that the lowest energy requirements were recorded either without using the fit mole equipped or with using single point share with straight shank. However using the curved shank - winged share with mole achieved the highest seed germination values and crop yield as compared with other treatments.

Impact of wheeled and tracked tractors on soil physical properties in a mixed conifer stand

Damage to forest soil caused by vehicle traffic mainly consists of soil compaction, displacement, and rut formation. Severity of the damage depends on vehicle mass, weight of the carried loads, ground morphology, and soil properties, such as moisture. This paper investigates the impacts of two types of vehicles (tracked or wheeled tractor), traffic intensities (one or five skidding cycles) and soil moisture (24% or 13% by weight) on compaction of a loam textured soil in a mixed conifer stand of central Italy. Changes in porosity, bulk density, shear and penetration resistances were analyzed. The latter three parameters were significantly higher in the trafficked soil portions than in the undisturbed ones in all treatments, while the opposite was true for porosity. The impact on soil bulk density and porosity was stronger for the wheeled tractor working on moist soil, while no significant effect of soil moisture was recorded for the tracked tractor. Shear and penetration resistances increased as a consequence of traffic, depending on both tractor type and soil moisture. The largest impact on shear resistance was recorded for the wheeled tractor on moist soil, while significant differences in penetration resistance were observed only between tracked and wheeled tractors in dry soil conditions. In order to preserve soil quality during logging activities, we recommend to operate under dry soil conditions and to limit vehicle movement on existing or new planned trails.

Changes in Properties of Cement and Lime Mortars When Incorporating Fibers from End-of-Life Tires

This paper studies the addition of fibers from end-of-life tires to commercial mortar mixtures. Two different types of mortar, one lime-plastic and other cement-fluid, are mixed with different percentage of fibers ranging from 0% to 1%. The changes in bulk density, consistency, compressive and flexural strength, dynamic Young modulus and water absorption are studied. According to the results, consistency is the property that shows more relevant changes for an addition of 0.25% fibers. Consistency is related to workability and affects the water absorption and the Young modulus values. On the contrary, bulk density and mechanical properties did not change with the addition of fibers. The results prove that this fiber, considered a waste from recycling of end-of-life tires, can be used in commercial mixtures without losing strength. On the other hand, mortar workability limits the amount of fibers that can be included in the mixture and this parameter determines the performance of the mortar.

Comparison of Results of Impedance Spectroscopy Methods with Results of Impact-echo Method in Investigation of High-temperature-degraded Concrete

The growth in the transport industry results in more accidents, which often include fire in locations with the concrete structures, which also effects its lifetime and its functionality. After any case of fire loading it is required to verify structure's condition. One way how to assess the risks connected with further usage of the structures after being exposed to the fire is the non-destructive testing. This paper is dealing with non-destructive measurement of changes of electric parameters of the cement based mortars subjected to the high temperatures. Prismatic samples with dimensions of 40×40×160mm were prepared from water, Portland cement CEM I 42.5 R and quartz sand (in a ratio 1:3), with water/cement ratio 0.46. Samples were intentionally degraded by high temperature in range of 200–1200°C (200°C step) and the changes in bulk density, flexural tensile strength and electric properties (loss factor tan δ (f), the imaginary component impedance ImZ (f) and the real part of component impedance ReZ (f) were monitored. Two methods were used for testing of electric properties – Impedance spectroscopy and Impact-echo method. The obtained results were compared and suitability of used methods was assessed.

Impacts of Switchgrass-Loblolly Pine Intercropping on Soil Physical Properties of a Drained Forest

Intercropping switchgrass ( L.) with managed loblolly pine ( L.) has been proposed as an alternative source of bioenergy feedstock that does not require conversion of agricultural cropland. Different management practices may alter soil physical properties (SPP), which could influence productivity, hydrologic and biogeochemical processes. Therefore, we investigated the effect of switchgrass-loblolly pine intercropping on the SPP of a poorly drained forest soil in eastern North Carolina using three management regimes: young loblolly pine stand (PINE), switchgrass-pine intercropping (PSWITCH), and a 38-year-old loblolly pine stand (REF). Measurements of SPP were conducted before and after the third annual harvesting operation using intact soil cores taken from three points within each of three replicated plots and at three depths: 0-15 cm, 15-30 cm, and 30-45 cm. Pre- and post-harvest values of SPP in PSWITCH were not significantly different. Compared to PINE, changes in bulk density and in both total porosity and saturated hydraulic conductivity in PSWITCH were significant only in the top 30 and 15 cm of soil, respectively. Volume drained and drainable porosity in PSWITCH decreased significantly at water table depths ≤45 cm. Cumulative effects of V-shearing for switchgrass seedbed preparation and the first and second harvest operations may have caused structural changes to the surface soil layer in PSWITCH that subsequently resulted in the measured differences in SPP between PSWITCH and PINE. We suggest that soil disturbance should be minimized during field operations to lessen the adverse effects on SPP, and models used to quantify impacts of management practices and land use change on the hydrology and biogeochemistry of managed forests should consider SPP changes caused by management regimes.

Study on Movement of Water and Salt through Soil Column and Utilization of Hydrus-1D Program to Simulate Five Scenarios of Crop Production in Salt Affected Paddy Soil

<p class="zhengwen"><span lang="EN-GB">An experiment was conducted on the purpose to study movement of water and salt through soil column. Salt-affected paddy soil was assessed for its relevant transport parameters consisting of the hydraulic and the solute transport parameters. The hydraulic parameters included soil hydraulic conductivity (K<sub>s</sub>) and the van Genuchten’s parameters (θ<sub>s</sub>, θ<sub>r</sub>, α, and n). In this experiment the solute transport parameters was referred to the coefficient of Langmuir’s isotherm which consisted of k<sub>d</sub> and η. Experience showed that hydraulic parameters were sensitive to changes of soil bulk density (ρ<sub>b</sub>). Therefore pedotransfer functions describing the relations between these parameters with ρ<sub>b</sub> were established. Straight line functions were found for θ<sub>s</sub> and n, exponential functions were found for α and K<sub>s</sub>, and logarithmic function was found for θ<sub>r</sub>. Packing the soil in the physical column inevitably caused horizontal differentiation of different ρ<sub>b</sub>. Bulk density of each layer was estimated by analysis of water flow through soil column at steady-state. Then ρ<sub>b</sub> of each layer was calculated from the relation K<sub>s</sub> (ρ<sub>b</sub>). After the ρ<sub>b</sub> was known the van Genuchten’s parameters were calculated from the pedotransfer functions. A physical column of 4 inches diameter and 50 cm length was constructed. Sodium chloride solution EC 6 dS/m was fed on soil surface during the process of salinization and the feeding solution was changed to fresh water during the process of desalinization. Breakthrough solution was analyzed for Na concentration and the breakthrough curves were constructed. The relevant parameters as well as initial and boundary conditions were fed into Hydrus-1D on the purpose to simulate the breakthrough curves. Statistical comparison results using t-test and RMSE suggested that Hydrus-1D could be used successfully to monitor transport of water and salt through soil column.</span></p><p class="zhengwen"><span lang="EN-GB">Five scenarios concerning water and solute transport through soil profile under rice and mung bean cropping were simulated using Hydrus-1D. Simulation results suggested that continuous flooding was the most efficient way to leach soluble salts down to ground water. Wet/dry irrigation scheme for rice production could drain salts only when rice crop was in the first period of growth where crop water uptake was small. During later stages of growth concentration profile of Na remained almost unchange indicating negligible downward movement of salts. Leaving the soil to dry naturally during the dry season caused upward accumulation of salt to the degree smaller than cultivating mung bean since water content and hence the diffusion coefficient of the soil were higher and more favorable for upward salt diffusion than in the former case. Inserting the capillary rise hindering soil layer underneath mung bean root zone was found to retard upward diffusion of salt to the degree comparable to leaving the soil to dry naturally.</span></p>

Compressibility and equivalent bulk modulus of shelled corn

An oedometer was used to measure changes in bulk density of shelled corn at different compression pressures and moisture contents. An equivalent confining pressure (ECP) was introduced to quantify the compression action in grain bins by considering non-uniformity and variability of compression pressures. Two models were developed for predicting bulk density and bulk modulus, respectively, as functions of ECP and moisture content. It was found that the uncompressed bulk density of shelled corn (before applying compression pressure) decreased with grain moisture and the relationship could be adequately described by a linear equation in the moisture range from 12.6 to 17.1% wb (wet basis). Shelled corn was more compressible at higher moisture content. However, bulk density approached to the same maximum value as compression pressure increased regardless of moisture content. In other words, moisture content had little effect on the maximum compressed bulk density. The equivalent bulk modulus of shelled corn increased with compression pressure and decreased with moisture content. The predicted bulk density and bulk modulus values were in good agreement with the experimental data.

Microstructural evolutions, elastic properties and mechanical behaviors of W/Cr Co-doped Bi4Ti3O12 ceramics

For Aurivillius phase Bi4Ti3−xWxO12+x+0.2wt.% Cr2O3 (BTWx-C, x=0–0.1) ceramics prepared by a conventional ceramic process, plate-like grains with random orientations are formed there. The aspect ratio of grains increases after the doping of W for ceramics, at the same time the bulk density of ceramics decreases. The change of Poisson's ratio may be related to the change of bulk density, whilst the change of bond strength could be responsible for the change of Young's modulus. The large-grained samples tend to possess a lower frequency constant but a higher elastic compliance, as well as a lower hardness. Especially, a larger grain size provides a higher fracture toughness for the sample at x=0.05 due to the mechanism of crack deflection. The stress–strain curves of BTWx-C ceramics under a uniaxial compression load are characterized as three stages: linear elastic deformation, ferroelastic domain switch and microcrack propagation. The microcrack propagation along grain boundaries results in the final axial flerry of ceramics. Additionally, the fracture strength of ceramics may be largely influenced by the internal stress resulted from the paraelectric–ferroelectric phase transformation during sintering.

Bulk Density and Carbon Concentration Variance Influence on Soil Carbon Stock Measurements

Soil carbon (C) storage is generally expressed as a mass of C per unit area measured to a specific depth. This practice is not ideal as the soil surface can fluctuate for several reasons including compaction, tillage, and shrink/swell of clays. This change in bulk density may cause the calculated C stocks in a soil to change from one sampling period to the next. In soils with high shrink/swell capacities, the bulk density has the potential to change regardless of soil management. This could present limitations to efforts to monitor changes in C stocks in high shrink/swell soils. Therefore, a study was conducted in two soils with shrink/swell capacity, in which they were sampled to a depth of 90 cm at two or three different moisture conditions and analyzed for bulk density and organic C at 10-cm increments. Profile C stocks were analyzed using the conventional “fixed depth” method and also with a “fixed mass” method. The analysis showed that under moist conditions the swelling of clays did not decrease bulk density. On the contrary, moist conditions generally resulted in elevated bulk density values. This resulted in significant differences in C stocks within depth increments where the variation in C concentration was low. Differences in profile C stocks, as determined using the fixed depth method, caused by differences in bulk density were removed by using the fixed mass method of calculating C stocks. The fixed mass method provided measurements of C stocks, which vary only as a result of variation in C concentrations.

Effects of different irrigation regimes on soil compaction in a winter wheat–summer maize cropping system in the North China Plain

An adjusted irrigation regime may help to minimize the risk of soil compaction, which is a major yield constraining factor in global crop production, constituting a serious issue in the winter wheat–summer maize double cropping system of the North China Plain. Thus this study aimed to evaluate the natural changes of soil penetration resistance (PR) and soil bulk density (BD) caused by freezing/thawing (FT) and wetting/drying (WD) cycles. This was tested under full irrigation (FI) and deficit irrigation (DI) over three double cropping seasons from 2011 to 2014, following a conventional tillage sequence of shallow, deep and shallow tillage before the first, second and third season, respectively. The results showed that in the deeper soil layer FT during winter reduced the PR by 22.9%, 34.7% and −18.7% under FI for the three seasons, respectively. The values under DI were 4.5%, 8.0% and −33.8% for the three seasons, respectively. However the compaction alleviating effects due to FT were only of temporary nature. Furthermore FI caused a stronger recompaction after deep tillage compared to DI, mainly attributed to increased slumping of soil. On the contrary DI reduced the BD by 8.4% in the deep soil layer by fostering intensive cycles of WD over the three double cropping seasons. Results also showed that DI resulted in a higher physical quality of subsoil, expressed by the value of S, compared to FI. It was concluded that irrigation intensity should be reduced after deep tillage to minimize and slow down subsequent recompaction.

Splash erosion of clay–sand mixtures and its relationship with soil physical properties: The effects of particle size distribution on soil structure

Large quantities of disturbed soils and residues derived from engineering constructions have provided material resources for soil erosion and geological disasters, which is becoming a serious problem in China. To date, studies on the erosion mechanism of these soils in a wide particle size distribution (PSD) are limited, and the relationships between soil PSD and physical characteristics are not explicit. Here, we analyzed the effects of PSD on structural and mechanical parameters and attempted to quantify their relationships by blending silty clay soil and engineering sand as clay–sand mixtures with various sand mass proportions ranging from 0 to 90% at a 10% increment in a wet and a dry mixing type (MT). In addition, the effect of PSD on splash erosion was measured under simulated rainfall. Changes of bulk density and porosity of soil mixtures (for clay contents more than 13%) with clay content displayed apparent differences separately in the wet and dry mixing types mainly due to the deformation and reorganization of soil grains. Internal friction angle φ and cohesion c of saturated soils showed a parabolic trend and an exponential increase with clay content respectively, while cohesion c was better quantified by particle fractal dimension D than clay content. Shear strength indexes in the wet mixing type were generally larger than those in the dry mixing type when clay content was larger than 13%. Splash erosion temporal variation was significantly affected by PSD, MT, rainfall duration (RD) and their interaction effects (PSD×MT, PSD×RD), among which MT was the most prominent source of variation (F=99.97, p<0.001). Stepwise multiple regression analysis indicated that splash erosion rate was negatively correlated with cohesion (p<0.001) and the coefficient of variations (CVs) of splash erosion rate were positively related with non-capillary porosity (p<0.01). Simple equations were proposed for predicting physical parameters (bulk density ρ, porosity e, φ, c, splash erosion rate) as a function of soil PSD characteristics. These obtained results are useful to supplement the erosion knowledge of disturbed soils, facilitate soil erosion prediction and provide technical guidelines for soil and water conservation in engineering construction areas.

Design and Calibration of the Unilateral Sensitive Soil Moisture Sensor

Reliable and affordable moisture sensors with a simplified calibration process for obtaining the water content information of soil/soilless substrates were limited. In this paper, an unilateral sensitive capacitive soil moisture sensor, based on the improved ECH2O sensor probe structure, was presented. Through simulating the relationship between the ratio of plate space and plate width (a/b) and probe sensitivity, sensitive depth, respectively, the size of the sensor was determined with ANSYS first. Capacitance measurement circuit based on resonant principle was then designed. The relationship between the output of the sensor and the soil water content calibration model (β parameter model), was investigated. As a result, we proposed a two-step calibration β method. Experimental results showed that β parameter model appropriately described the relationship between the output and the soil water content, the minimum correlation coefficient R 2 = 0.9554 in the soil, peat, perlite, and vinegar residue. The measurement error of β parameter model was <;0.025 units except in perlite. The error caused by the change of bulk density was <;0.025 units in peat and vinegar residue. Therefore, the two-step calibration β method is suitable for calibrating the sensor.

Towards sound comparisons of soil carbon stocks: A proposal based on the cumulative coordinates approach

The study of changes in soil organic carbon (SOC) stocks as a result of land use or climate change requires sound criteria to compare SOC stocks in different plots. Just comparing SOC stored down to a standard depth (often, 30cm) is prone to errors, owing to the changes in soil bulk density due to shifts in SOC content or the soil compaction due to heavy machinery. To solve this problem several approaches have been suggested. Jenkinson proposed in 1971 the concept of ‘equivalent soil depth’, the depth to which a soil should be sampled to reach a certain amount of fine mineral earth. Here we present a procedure which combines that concept with the modern cumulative coordinates approach (CCA). Our method involves sampling soils down to a given depth (30cm) with a volumetric core sampler which maintains the profile structure, and divide the obtained core in depth layers (0–5, 5–15 and 15–30cm). Each layer is studied separately for its stone and gravel content, fine earth (<2mm) and coarse organic fragments. From these data we calculate the cumulative (with depth) amounts of fine earth (<2mm), soil organic carbon (SOC), and fine mineral earth (FME), i.e. the fine earth corrected for organic matter. Then, SOC and FME are plotted together and fitted to a double-exponential equation, to obtain the amount of SOC (kgm−2) accumulated in the uppermost Y kgm−2 of FME. As an example, we apply this approach to the comparison of SOC stocks in four plots differing in land use (crop, old forest, and recent pine stands), and also as to their stoniness and bulk density. Essentially, instead of comparing SOC stocks on a depth basis — amount of C stored in the uppermost Y cm of soil, for instance 30cm — we propose to compare SOC stocks on a fine mineral earth basis — amount of C stored by the uppermost Y kgm−2 of FME. The value we propose is Y=300kgm−2 of FME. Such an approach automatically corrects for the compression or expansion of soil due to heavy machinery, or the changes in bulk density due to the shifts in SOC content, thus making contrasting plots directly comparable. It is less clear, nevertheless, the usefulness of CCAs to compare SOC stocks in plots strongly differing as to their stoniness.

Considering the soil compaction status on logging areas in a Hyrcanian forest

This paper deals with the issue of soil compaction during timber harvesting operations on cutting areas. Soil compaction was assessed following the logging operation in Darabkola forest area by measuring soil bulk density. In this research, a completely random sampling method was used to assess the resulting changes in soil bulk density. Soil bulk density was measured using bulk density sampler on felling, bucking, delimbing and control areas. The results showed that the bulk density value in the top soil layer increased with increasing tree volume and was not dependent on the terrain slope on the felling area. Also, there was a significant relationship between the bulk density value of felling area and tree volume. Further analysis showed that there was no significant relationship between bulk density values on felling, bucking, delimbing and control areas. It was shown that careful harvesting planning, restriction, skidding and directional felling limited the soil compaction and helped the soil conservation.

The role of rock fragments in crack and soil structure development: a laboratory experiment with a Vertisol

SummaryA large number of factors that influence soil surface cracking behaviour in swell‐shrink soils have been studied, but there are few studies on the influence of rock fragments on crack development. Effects of rock fragments have been investigated with reference to the soil pore system but they have mainly been studied indirectly through measurements of water flow and/or bulk density changes. A laboratory experiment was carried out with repacked soil samples that were prepared by adding rock fragments of three different sizes (2–4, 4–8 and 12–16 mm) to a Vertisol at two different rates (10 and 25% by volume). Soil image analysis procedures were applied in order to describe quantitatively the network of surface cracks and the pore system to a depth of 8 cm below the surface, which developed after wetting‐drying cycles. Mean values and standard deviations of surface crack or pore widths decreased with the increase in rock fragment content and the decrease in rock fragment size, while the density of the ‘skeleton’ of the crack and pore networks increased. Rock fragments also induced vertical homogenization of the soil structure. The number of rock fragments was a key factor in determining some crack network characteristics, inducing inverse variations in mean width and skeleton density of the crack or pore network. Overall results suggested that rock fragments acted as triggering points for crack and pore development in Vertisols. The findings of this work provide a contribution to the understanding of the mechanisms of crack network and soil structure development that are induced by stones in swell‐shrink soils.

Biogeochemical indicators of peatland degradation – a case study of a temperate bog in northern Germany

Abstract. Organic soils in peatlands store a great proportion of the global soil carbon pool and can lose carbon via the atmosphere due to degradation. In Germany, most of the greenhouse gas (GHG) emissions from organic soils are attributed to sites managed as grassland. Here, we investigated a land use gradient from near-natural wetland (NW) to an extensively managed (GE) to an intensively managed grassland site (GI), all formed in the same bog complex in northern Germany. Vertical depth profiles of δ13C, δ15N, ash content, C / N ratio and bulk density as well as radiocarbon ages were studied to identify peat degradation and to calculate carbon loss. At all sites, including the near-natural site, δ13C depth profiles indicate aerobic decomposition in the upper horizons. Depth profiles of δ15N differed significantly between sites with increasing δ15N values in the top soil layers paralleling an increase in land use intensity owing to differences in peat decomposition and fertilizer application. At both grassland sites, the ash content peaked within the first centimetres. In the near-natural site, ash contents were highest in 10–60 cm depth. The ash profiles, not only at the managed grassland sites, but also at the near-natural site indicate that all sites were influenced by anthropogenic activities either currently or in the past, most likely due to drainage. Based on the enrichment of ash content and changes in bulk density, we calculated the total carbon loss from the sites since the peatland was influenced by anthropogenic activities. Carbon loss at the sites increased in the following order: NW &lt; GE &lt; GI. Radiocarbon ages of peat in the topsoil of GE and GI were hundreds of years, indicating the loss of younger peat material. In contrast, peat in the first centimetres of the NW was only a few decades old, indicating recent peat growth. It is likely that the NW site accumulates carbon today but was perturbed by anthropogenic activities in the past. Together, all biogeochemical parameters indicate a degradation of peat due to (i) conversion to grassland with historical drainage and (ii) land use intensification.

Comparison of Different “S-index” Expressions to Evaluate the State of Physical Soil Properties

The S-index describes the absolute value of slope at the inflection point of the water retention curve (WRC) and it is a popular tool for the indirect descriptionofthesoil physical-hydraulicconditions.It can be calculated as a function of van Genuchten (VG) parameters by four different expressions based on (a) the use of arithmetic or ln-transformed axis of pressure head h and (b) the use of volumetric h or gravimetric W soil water content (the four expressions are obtained from the dh/dh,dW/dh,dh/d(lnh) and dW/ d(lnh) derivatives). The aim of the study is to test the ability of the four S-index expressions to rank soil physical-hydraulic (SPH) indicators such as fractions of porosity, bulk density and saturated hydraulic conductivity. WRCs of an artificial soil, which was subjected to flooding and extensive destruction of macroporosity, and WRCs from the twelve USDA soil classes were used in the analysis. The results showed that the expressions of dh/dhand dW/dhdisplay higher correlations versus the SPH indicators in comparison to dh/d(lnh) and dW/d(lnh). The expressions based on the gravimetric approach such as dW/dh and dW/ d(lnh) do not contain the parameter of bulk density while the expressions based on the ln-transformed axis ofhdo not contain the parameteraof VG model. Even though dh/dh and dW/dh showed similar performance, the first one is suggested as the safest approach to describe SPH indicators for non-deformable soils because its theoretical background is more consistent and more relevant to porosity attributes which are always described in terms of volume and not of mass, whereas the second one is suggested for the case of deformable soils in order to avoid errors introduced by the changes of bulk density.

Sensitivity of LEACHN Model Predictions to Changes in Nitrogen Transformation Rate Constants and Bulk Density

LEACHN is a deterministic model that could be used as a decision support tool to simulate NO 3 -N (nitrate-N) movement through the soil profile in order to make management decisions (i.e., when and how much effluent to apply on land) at effluent-irrigated land disposal sites. However, using this model as a “black box” is not satisfactory, and an in-depth understanding of how the model works is essential before the model is used by the operators and managers of land treatment systems. This article provides a brief description of LEACHN, the N (nitrogen) cycle and soil hydrological properties in LEACHN, and an assessment of LEACHN. This article also provides the key findings of a previous study as background knowledge for the current study. The main focus of this article is to investigate the sensitivity of LEACHN predictions to changes in N transformation rate constants, i.e., K min (mineralization), K nit (nitrification), and K den (denitrification), at field scale, and also to explore the effect of changes in soil bulk density on leachate NO 3 -N concentrations and amount of N leached. This study shows that LEACHN was sensitive to K min values, and this parameter had a significant impact on soil humus-N and the amount of NO 3 -N leached. The total amount of NO 3 -N leached was slightly affected by K nit values. However, the K den value had no significant impact on the total amount of NO 3 -N leached. This analysis also highlighted the need for accurate measurements of bulk density as inputs to the LEACHN model. The optimized LEACHN model (using the best N transformation rate constants values) was tested successfully for two field data sets.