Undisturbed Soil Columns Research Articles

Gas transport enhancement under windy condition in poorly tilled seedbed of clayey rotational paddy field

ABSTRACT Gas exchange between soil and atmosphere governs the growth of plants and global circulation of the gaseous component of air. Enhancement of gas exchange by wind has been reported in media with large pores. In clayey paddy fields, large aggregates (clods) and inter-aggregate pores are prone to be formed by tillage. However, the effect of wind on gas transport has not been considered in such fields. This study quantified the wind-induced gas movement through the paddy soil layer composed of large clods. The applicability of the analysis using the gas diffusion equation was also verified regarding the mean clod size and wind condition. Undisturbed soil columns were taken from the ‘poorly tilled’ and ‘fairly tilled’ paddy field under the cultivation of soybean. The mean diameters of the clods were 3.4 and 1.9 cm for the ‘poorly’ and ‘fairly’ tilled columns, respectively. A repacked silica sand column was also prepared as a reference. Diffusion tests were conducted for the columns in the field under natural wind and in the laboratory under calm conditions, with CO2 as a purge gas and atmospheric oxygen as a tracer gas. The gas transfer efficiency was evaluated by and , which is the ratio of the time until the oxygen concentration reaches 50% and 90% of that in the atmosphere in the field to that in the laboratory, respectively. The results showed that gas transfer through the paddy soil layers, comprised a few centimeters of clods, under natural wind was up to 11 times quicker than under the calm conditions. The wind-induced gas exchange remained at maximum under the wind speed of more than 1.2 m s−1 at 20 cm above the soil surface in the poorly tilled soil. In contrast, in the fairly tilled soil, the effect of wind gradually increased with wind speed and finally became close to that in the poorly tilled soil at the wind speed around 2.0 m s−1. The applicability of the gas diffusion equation deteriorated as the wind speed increased from 1.2 to 2.6 m s−1 or the mean aggregate size increased from 1.9 to 3.4 cm.

Impact of land use and tillage practice on soil macropore characteristics inferred from X-ray computed tomography

Quantification of soil macropores is important to enhance our understanding of preferential flow behavior in soils. However, knowledge of 3D soil architecture for different land uses in a continental climate region is limited. X-ray computed tomography is a novel technique that can provide valuable information about the 3D features of the soil, such as connectivity, length density, and tortuosity, that largely control water flow through the macropores. In this study, X-ray computed tomography and image analysis were employed to quantify the soil macropore characteristics from four combinations of different land uses and soil tillage practices - native grassland (Nat), alfalfa (Alf), conventional till-corn (CT), and no-till corn (NT) systems. A total of 15 undisturbed soil columns, 150 mm in diameter and 500 mm in length, were collected from different fields. The macropore characteristics were distinctively different for different land use and tillage treatments, especially near the surface depth (top 100 mm). The soil macropores under CT were highly connected and concentrated mostly in the surface soil layer. In contrast, macropores under NT were larger and had well-developed pore networks. The Alf field had relatively larger and more vertically oriented macropores as compared to the Nat field. Relatively larger macroporosity and a higher number of macropores were observed in the surface of soils collected from Nat field. Macropore characteristics were mostly similar between Alf and NT treatments. The results of this study facilitate quantitative evaluation of 3D soil macropore features with significant implications for non-equilibrium flow prediction and contaminant transport modeling in soils.

Using X-ray computed tomography to quantify variability in soil macropore characteristics in pastures

Soil macropores largely control the transport of water and solutes in subsurface flows. Preferential flow via soil macropores can substantially affect water quality. Hence, it is important to quantify soil macropore characteristics and link this information with the preferential flow behavior in soils. However, whether macropore structure at one slope position within a field is different than that at another is unclear. With differences in the macropore characteristics, each slope position can contribute differently to the runoff and subsurface flows. The objective of this study was to use X-ray computed tomography (CT) and image analysis to characterize soil pore structure (> 0.75 mm diameter) at upslope, midslope, and downslope positions within a 0.40 ha pasture field. A total of 18 undisturbed soil columns (150 mm diameter and 500 mm depth) were collected from a pasture field located at the Sand Mountain Research and Extension Center, Alabama, during May 2019. The results indicated that both the macropore number and macroporosity values were lowest at the downslope position in the 0–100 mm soil layer. In contrast, a large number of macropores was observed at the downslope soils for depths below 200 mm. The lowest macroporosity values in the surface layer at the downslope position can be attributed to higher degree of trampling induced compaction due to higher soil moisture content at the downslope location, via runoff and seepage losses from the upper slopes. Likewise, it was found that using smaller diameter soil cores for sampling can cause bias in the soil macropore measurements due to considerably high coefficient of variation compared to the larger diameter soil cores. Macropore interconnectivity at the subsurface layer (100–500 mm) increased from the upslope to the downslope position, whereas at the soil surface (0–100 mm), the interconnectivity was lowest at the downslope position as compared to the upslope and midslope locations. The results of this study provide quantitative information of different soil macropore characteristics under varying topographical locations and depths in a pasture field. The relevance of topographical variation of different macropore characteristics found in this study should be tested by investigating a wider range of soil types and slopes in pastures.

Impact of olive mill wastewater (OMW) on the soil hydraulic and solute transport properties

The Mediterranean area concentrates the world’s largest production area of olive oil. The olive oil industry represents, in this basin, one of the leading sectors of the agri-food economy. Olive mill water (OMW) is the principal waste effluent produced by the olive oil industry. Due to its high pollution load, this aqueous by-product cannot be directly disposed of in domestic wastewater treatment plants (especially those with a biological treatment unit). Untreated OMW is currently used for agronomic purposes in several countries, mainly because it is rich in valuable plant nutrients. However, OMW is characterized by toxic phenols, high organic matter, high salinity, suspended solids and several other components that may have possible negative effects on chemical and physical soil properties, as well as soil biological activities. In the present research, we focused on the effects of OMW application on transport and hydraulic soil properties. Three distinct soils from a pedological point of view were selected and a series of laboratory steady-state miscible flow tests were conducted under saturated conditions, on both OMW-treated and -untreated soil columns. Tests were conducted on disturbed and undisturbed soil columns. The approach proposed by Kachanoski, based on soil impedance (Z) measurements via the time domain reflectometry (TDR) technique, was used to monitor the leaching experiments. The breakthrough curves (BTCs) exhibited different shapes that allowed the repercussions of OMW applications on soil transport behaviour to be distinguished. Several additional tests conducted on OMW-treated and -untreated soil cores to determine water retention curves (SWRCs) and saturated hydraulic conductivity Ks allowed us to infer the probable mechanisms involved in soil hydrological behaviour changes under OMW treatments. The results show that when OMW leaches into the soil immediately after its disposal there is little effect on the evaluated hydraulic and hydrodispersive properties. By contrast, we demonstrated that a short incubation period (i.e. a short contact time between OMW and soil) of 10 days is enough to exert a great influence on all the values determined (e.g. soil pore velocity v and Ks reduced by up to one order of magnitude). These effects were especially evident in undisturbed soil samples.Graphic

The Leaching of Atrazine and Plant Species Sensitivity to Atrazine using Bioassays and Chemical Analyses

ABSTRACT Atrazine, one of the most frequently applied herbicides in the world, is highly persistent, and likely to contaminate runoff and groundwater resources, determined by bioassay and chemical analyses. In the present research the two following experiments were conducted in Mazandaran Province, Iran. 1) The sensitivity of eight plant species (canola, soybean, ryegrass, wild oat, wheat, littleseed canarygrass, redroot pigweed, and corn) to atrazine residues in the laboratory of the Qaemshahr Campus of the Islamic Azad University in 2019 was determined. Bioassay and GR50 index were used to differentiate species. 2) The leaching front of atrazine in the laboratory of Mazandaran University of Medical Sciences was determined. Soil samples were collected from a 10-hectare-farm of Baykola Agricultural Research Station. The method of undisturbed soil columns was used to study atrazine leaching at three levels including control, usual dose (1.25 kg. ha−1), and high dose (2.5 kg. ha−1). The treatments were injected into soil columns inside 32-cm-high PVC pipes and after three days, 2-cm segments of the soil columns were exposed to bioassay and chemical analyses, simultaneously. In the first experiment, plants response to atrazine residues were different. Canola and corn were the most susceptible and tolerant crop species, respectively. The tolerance of other plant species to total residue, using GR50 index, was according to the following order: canola < soybean < ryegrass < wild oat < wheat < littleseed canarygrass < redroot pigweed < corn. According to the bioassay test, at the high dose of atrazine, all traits were negatively affected, and the root weight and the ratio of root to shoot weight had the highest and the lowest decrease (28% and 12% relative to control), respectively. The simultaneous investigation of canola seedling weight and atrazine concentration, at different soil depths, revealed that atrazine penetrated to the 10-cm depth, which is attributed to higher organic matter and clay content. Canola was identified as a suitable plant for atrazine bioassay. Due to the depths of weed seed distribution and leaching front of atrazine in this experiment (on average, 10 cm), the contamination of weed seed lot with herbicides can be high.

Parameterization of two‐dimensional approaches in HYDRUS‐2D: Part 2. Solute transport at the field and column scale

AbstractIn this study, a tracer field experiment was conducted to study the temporal dynamics of bromide movement in a loamy tile‐drained agricultural landscape. Moreover, tritium leaching experiments were performed on undisturbed soil columns from the same field. The HYDRUS‐2D software package was used to model water and solute transport. Three water flow models developed in Part 1—a single‐porosity approach with modified soil hydraulic functions (SP), a dual‐porosity approach (DP), and a dual‐permeability approach (DUP)—were used as a foundation for building solute transport models, of which the initial parameterization was based on a suggested hydrogeological tool from previous studies. The selected solute transport models were an SP, an SP with immobile water, a DP, a DUP, and a DUP with immobile water. The model predictions were compared against measurements of bromide concentrations in soil‐water. The DP captured the degree of the initial peaks and predicted well the shape of the observed concentrations. However, DP presented low capability to match the timing of bromide concentration peaks. In contrast, the DUP with immobile water illustrated better predictive ability by introducing an additional pore region into the matrix domain. Validation of field‐scale solute transport models was implemented using the data from the following leaching experiments. The already suggested parameterization concept was further evaluated for its capability to provide a sufficient initial representation of the internal pathways. The output from such hydrogeological studies shows that macropores and their interconnection with tile drains are key to understanding the water flow and solute transport processes in loamy structured soils.

Impact of loosening and straw addition to the subsoil on crop performance and nitrogen leaching: A lysimeter study.

Poor subsoil properties are difficult to ameliorate and detrimental to soil fertility and crop yield. The effects of loosening (L) and loosening + straw (LS) ∼60 Mg ha-1 into the subsoil (25-40cm depth) on crop yield, water flow, and the nitrogen (N) balance components under bare soil conditions and a barley (Hordeum vulgare L.) crop were investigated in an about 21-mo lysimeter study and compared with a control treatment. Undisturbed soil columns (n=12) were excavated from an agricultural field in May 2016, installed at a lysimeter station, and exposed to outdoor climatic conditions in Uppsala, Sweden, in August 2016. Spring barley ('Makof') was grown between June and September 2017. Total N leaching loads over the 21 mo were high (74-193kg ha-1 ). The LS treatment reduced the N load by 49% (P=.01) and 62% (P=.001) compared with the L and control treatments, respectively. Loosening reduced N load by 25% (P<.07) compared with the control. Emissions of N2 O were low (0.04-0.07kg N ha-1 ), and no differences were observed between treatments. Leaf relative chlorophyll content was lower in the LS treatment than in the L and control treatments (P<.05). Yield was also lowest in the LS treatment (5.8 Mg ha-1 ) and was 7 and 8.5% lower than in the control and L treatments (P>.05), respectively. These results suggest that LS can reduce N leaching. The overall effects of LS on crop performance and N removal and leaching should be further scrutinized in long-term field studies.

Effects of Rock Fragments on the Soil Physicochemical Properties and Vegetation on the Northeastern Tibetan Plateau

Stony soils are very widely distributed and contain abundant rock fragments (&amp;gt;2 mm), which impose major effects on soil properties and plant growth. However, the role of rock fragments is still often neglected, which can lead to an inadequate understanding of the interaction between plants and soil. Undisturbed soil columns were collected from three alpine grasslands on the Qilian Mountain, and the X-ray computed tomography method was applied to investigate the characteristics of rock fragments. The results showed there was significant difference in number density, volumetric content and surface area density of rock fragment among the three grasslands, and followed the order of alpine meadow &amp;gt; alpine steppe &amp;gt; alpine desert steppe. In addition, the soil organic carbon, total nitrogen, total phosphorus, available phosphorus, N-NH4+, and N-NO3− contents in fine earth all increased with increasing number density, volumetric content and surface area density but to different degrees. Furthermore, positive correlations were observed between the rock shape factor and belowground biomass (R2 = 0.531, p &amp;lt; 0.05), between the rock volumetric content and aboveground biomass (R2 = 0.527, p &amp;lt; 0.05), and between number density and Simpson’s index (R2 = 0.875, p &amp;lt; 0.05). Our findings suggest that within a certain range, the increase in rock fragment content is conducive to soil nutrient accumulation and soil water storage and circulation and changes plant features, which contributes to the growth of plants. In addition, rock fragments should be given more consideration when investigating the relationships between soil and vegetation and their response to climate change in future studies.

Effects of Astragalus sinicus combined with chemical fertilizer on nitrogen absorption and utilization of rice and nitrogen distribution and residue of Astragalus sinicus in rice-soil system.

Clarifying the pattern of nitrogen absorption and utilization of rice under the treatments of Astragalus sinicus combined with chemical fertilizer application and the pattern of absorption, utilization, distribution and residue of A. sinicus nitrogen in rice-soil system could provide basis to rational fertilization for rice planting area in southern Henan. In this study, undisturbed soil column simulation and isotope tracer technology of 15N were used to examine the differences of nitrogen uptake and utilization of rice, nitrogen nutrient balance of rice-soil system and nitrogen uptake, utilization, distribution and residue of A. sinicus nitrogen after mineralization and decomposition among seven treatments. The treatments involved 1) no fertilization (CK); 2) chemical fertilizer+22500 kg·hm-2 A. sinicus (FM1); 3) chemical fertilizer+30000 kg·hm-2 A. sinicus (FM2); 4) chemical fertilizer+37500 kg·hm-2 A. sinicus (FM3); 5) chemical fertilizer+22500 kg·hm-2 A. sinicus +lime (FM1+CaO); 6) chemical fertilizer+30000 kg·hm-2 A. sinicus lime (FM2+CaO); 7) chemical fertilizer+37500 kg·hm-2 A. sinicus +lime (FM3+CaO). Results showed that compared with CK, fertilization significantly increased nitrogen uptake of grain and rice stalks, apparent nitrogen loss, and nitrogen surplus. The grain nitrogen uptake, rice straw nitrogen uptake and nitrogen use efficiency of rice increased firstly and then decreased with the increasing A. sinicus application rates, while the apparent nitrogen loss and nitrogen surplus showed the opposite trend. The best performance was presented under the treatment of chemical fertilizer combined with 30000 kg·hm-2 of A. sinicus. Lime addition could increase grain nitrogen uptake, rice straw nitrogen uptake, and nitrogen use efficiency of rice, while reducing apparent nitrogen loss and nitrogen surplus, with the best performance of FM2+CaO. For all the treatments, the proportion of nitrogen absorbed by rice from A. sinicus was 6.3%-13.2%, while that from soil and chemical fertilizer was 86.8%-93.7%. The utilization ratio of A. sinicus nitrogen by rice was 23.8%-33.6%. The utilization ratio of A. sinicus nitrogen in different parts of rice was grain > stem and leaf > root. The residue rate of A. sinicus nitrogen in soil was 37.6%-62.4%. The loss rate of A. sinicus nitrogen was 7.8%-38.6%. Comprehensively considering nitrogen absorption and utilization of rice, nitrogen nutrient balance of rice-soil system, and the distribution situation of nitrogen from A. sinicus in rice, FM2+CaO was the optimum fertilization pattern in the study area.

Tillage-induced effects on organic carbon in earthworm casts through changes in their physical and structural stability parameters

Earthworm casts have been recognized as contributing to long-term carbon protection, but few studies have focused on the mechanism by which this is achieved. Most of the literature documenting earthworm casts revolves around the difference between the earthworm cast and natural soil, whereas little attention has been given to deciphering the effects of different tillage systems on earthworm casts. Further, whether or not an earthworm cast, like soil, affects its own organic carbon content through physical structure stability is still somewhat vague, and very little is known. The objective for this study was to determine the effect of tillage on organic carbon and physical structure stability parameters in earthworm casts. Undisturbed soil columns were collected from a 17-year tillage experiment including no tillage (NT), ridge tillage (RT) and mouldboard ploughing (MP) in Northeast China. Each column was seeded with ten earthworms (Eisenia foetida), incubated at 18 °C for 120 days and casts were collected and analysed. Both NT and RT led to significantly greater organic carbon (20.5% and 14.4%), total pore volume (54.6% and 75.6%), total pore area (45.4% and 60.4%), permeability (21.8% and 66.4%), fluid conductivity (26.2% and 31.1%), tensile strength (34.1% and 51.2%) and water resistance index (16.7% and 22.3%) in the casts compared to MP (P < 0.05), whereas water repellency showed a significant decrease (42.9% and 52.4%) (P < 0.05). Correlation analysis showed that total pore area, tensile strength and water repellency were the three most critical factors affecting organic carbon in earthworm casts (r = 0.943, 0.742, 0.762 and 0.715, 0.758, 0.743 for NT and RT, respectively). The results of tillage effects on organic carbon and physical structure stability parameters combined with Structural Equation Modelling analysis identified that NT and RT could increase organic carbon by increasing total pore area, tensile strength and water repellency in earthworm casts. These results demonstrate that tillage through physical structure stability (total pore area, tensile strength and water repellency) changes affect organic carbon in earthworm cast which are major new findings. This signifies similarity in the underlying processes by which tillage affects organic carbon and physical structure stability parameters in earthworm casts and the surrounding bulk soil. Moreover, the increased abundance of earthworms and greater organic carbon in earthworm casts under conservation tillage, suggest that earthworms enhance the conversion of residue into organic carbon and therefore enhance the long-term soil organic carbon sequestration.

Co-regulation of rainfall amount and timing on soil carbon mineralization in a typical salt marsh of the Yellow River Delta, China.

Studying the effects of rainfall regimes such as rainfall amount and timing on soil carbon mineralization is of great importance for our understanding the mechanisms underlying the stability and accumulation of soil carbon in coastal salt marshes. In this study, we examined the responses of soil carbon mineralization (CO2 and CH4 fluxes) from undisturbed soil columns to rainfall events in different seasons (dry and wet seasons) with filed experiments in a primary Suaeda salsa region in the Yellow River Delta salt-marsh wetland, which is far away from the coast and not affected by tides. The results showed that rainfall amount and timing had a significant interaction in affecting soil CO2 flux rates. During the dry season, large rainfall events significantly reduced soil CO2 flux rates but had no significant effect in the wet season, which might be closely related to the significant increase in soil water content and salinity. Rainfall amount, rainfall timing and their interactions had no significant effect on soil CH4 efflux rates. Rainfall timing and rainfall amount did not affect CH4/CO2. CH4/CO2 increased with increasing soil water content and salinity. Soil water content and soil salinity showed similar increases to increasing rainfall amount. Our results suggested that the changing rainfall regime under climate change in the future would have a great impact on soil carbon mineralization and carbon sink function by regulating soil water and salt migration in this region.

Distribution of 137Cs and 60Co in plough layer of farmland: Evidenced from a lysimeter experiment using undisturbed soil columns

ABSTRACT Radionuclide fallout during nuclear accidents on the land may impair the atmosphere, contaminate farmland soils and crops, and can even reach the groundwater. Previous research focused on the field distribution of deposited radionuclides in farmland soils, but details of the amounts of radionuclides in the plough layer and the changes in their proportional distribution in the soil profile with time are still inadequate. In this study, a lysimeter experiment was conducted to determine the vertical migration of 137Cs and 60Co in brown and aeolian sandy soils, collected from the farmlands adjoining Shidaowan Nuclear Power Plant (NPP) in eastern China, and to identify the factors influencing their migration depths in soil. At the end of the experiment (800 d), > 96% of added 137Cs and 60Co were retained in the top 0–20 cm soil layer of both soils; very little 137Cs or 60Co initially migrated to 20–30 cm, but their amounts at this depth increased with time. The migration depth of 137Cs was greater in the aeolian sandy soil than in the brown soil during 0–577 d, but at the end of the experiment, 137Cs migrated to the same depth (25 cm) in both soils. Three phases on the vertical migration rate (v) of 60Co in the aeolian sandy soil can be identified: an initial rapid movement (0–355 d, v = 219 ± 17 mm year–1), followed by a steady movement (355–577 d, v = 150 ± 24 mm year–1) and a very slow movement (577–800 d, v = 107 ± 7 mm year–1). In contrast, its migration rate in the brown soil (v = 133 ± 17 mm year–1) was steady throughout the 800-d experimental period. The migration of both 137Cs and 60Co in the two soils appears to be regulated by soil clay and silt fractions that provide most of the soil surface area, soil organic carbon (SOC), and soil pH, which were manifested by the solid-liquid distribution coefficient of 137Cs and 60Co. The results of this study suggest that most 137Cs and 60Co remained within the top layer (0–20 cm depth) of farmland soils following a simulated NPP accident, and little reached the subsurface (20–30 cm depth). Fixation of radionuclides onto clay minerals may limit their migration in soil, but some could be laterally distributed by soil erosion and taken up by crops, and migrate into groundwater in a high water table level area after several decades. Remediation measures, therefore, should focus on reducing their impact on the farmland soils, crops, and water.

Physical disturbance accelerates carbon loss through increasing labile carbon release

Labile carbon (C) is a major source of C loss because of its high vulnerability to environmental change. Yet its potential role in regulating soil organic carbon (SOC) dynamics remains unclear. In this study, we tested the effect of physical disturbance on SOC decomposition using soils from two abandoned farmlands free of management practice for more than 28 years. The soil respiration rate was measured in undisturbed and disturbed soil columns and was inversely modeled using the two-compartment model. We found that the C loss was 16.8~74.1% higher in disturbed than in undisturbed soil columns. Physical disturbance increased the total amount of labile C (C&lt;sub&gt;1&lt;/sub&gt;) loss by 136~241%, while had no effect on the kinetic decomposition rate constants of both labile (k&lt;sub&gt;1&lt;/sub&gt;) and stable (k&lt;sub&gt;2&lt;/sub&gt;) SOC decomposition. Physical disturbance fragmented the large macroaggregates into small macroaggregates, microaggregates, and free silt and clay-sized fractions. This indicates that C loss was derived from the initially protected labile C, and there was no change of SOC fraction being decomposed. Our results give insights into the understanding of the extent of labile C loss to physical disruption and demonstrate the potential effect of physical disturbance on SOC dynamics.

Effects of different agronomic practices on the selective soil properties and nitrogen leaching of black soil in Northeast China

Considering the large amount and high frequency application of concentrated fertilizer nitrogen in the Black Soil Region of Northeast China, the current laboratory/field simulation study aimed to explore the pollution risk of added nitrogen in black soil to groundwater and identify effective measures to prevent and control soil nitrogen leaching with an undisturbed soil column. The results showed that the saturated nitrogen adsorption capacities increased by 1.7%, 7.7% and 18.5% in ploughing, impervious agent (starch grafted polyacrylic acid) addition, and corn straw returning treatments, respectively, relative to the control (no-till). When the collection volume of the leaching solution reached the experimental maximum (4,000 mL), the total amount of nitrogen leaching from the control soil column (i.e., the no-tillage treatment) accounted for more than 50% of the added nitrogen, indicating a great risk of nitrogen pollution in groundwater. Compared with the no-tillage treatment, the amount of nitrogen leaching from the ploughing treatment increased insignificantly, and the amount of nitrogen leaching in the following spring in the corn straw returning treatment increased by 11.2%. The amount of nitrogen leaching decreased by 12.5% in the soil sampled in autumn of the second year. The total amount of nitrogen leaching in the soil with impervious agents decreased by 40.1%. Therefore, the permeability-reducing agent could significantly reduce underground water pollution risk posed by nitrogen leaching.

Estimation of vineyard soil structure and preferential flow using dye tracer, X-ray tomography, and numerical simulations

The appearance and distribution of soil pores have a significant influence on water flow and solute transport in the soil vadose zone. The pore system is highly variable in arable soils where crop rotation, tillage, trafficking, soil amendments, and various management practices are commonly implemented. The aim of this study was to assess the porous system and preferential flow pathways in a vineyard soil using undisturbed soil columns, and by combining laboratory and numerical methods with dye staining and X-ray imaging. It was hypothesized that the integration of various methods could reveal more information about soil structure, and flow and transport behavior of structured arable soil. Soil water retention and hydraulic conductivity curves were obtained using the evaporation method, while water flow was assessed using intermittent leaching experiments. Water flow and the transport of Brilliant Blue were simulated using HYDRUS-1D. A single-porosity model of soil hydraulic properties provided a good description of data collected during the evaporation experiments. Data collected during leaching experiments did not provide enough experimental evidence for the occurrence of nonequilibrium flow patterns and the differentiation between the single- and dual-permeability models of soil hydraulic properties. However, dye staining and X-ray imaging revealed a complex pore-architecture network with large vertical and horizontal biopores. The staining patterns (Brilliant Blue FCF) within the vertical column sections documented the extent of preferential flow. The study showed that the bi-modal character of pore structure could often be hidden when a limited number or non-adequate methods are applied for its quantification from water flow behavior. The impact of preferential pathways on dye transport can be investigated with observations and simulations. A combination of various methods enabled us to adequately assess vineyard soil structure and fine-tune the description and extent of preferential water flow.

Water and pesticide transfers in undisturbed soil columns sampled from a Stagnic Luvisol and a Vermic Umbrisol both cultivated under conventional and conservation agriculture

The main goals of conservation agriculture are to enhance soil fertility and to reduce soil degradation especially through erosion. However, conservation agriculture practices can exhibit a higher risk of contamination through vertical flows. The objectives of this study were to (i) characterise water and pesticide transfers in two different soils both managed under conventional and conservation agriculture and (ii) assess the effects of pesticide properties, soil type and agricultural system on pesticide fate. We studied the behaviour of two herbicides (nicosulfuron and mesotrione) and a molluscicide (metaldehyde) in percolation experiments in undisturbed soil columns. A series of two rain events (one with a high, the other with a low intensity) separated by a two-day flow interruption was applied three days after the pesticides and bromide application. Batch sorption coefficients, Kd, were also measured. While the Pesticides Properties Data Base (2020) indicated a decrease of sorption in the order mesotrione > metaldehyde > nicosulfuron, the measured Kd, decreased in the order mesotrione (2.3 ± 1.4 L.kg−1) > nicosulfuron (0.7 ± 0.4 L.kg−1) > metaldehyde (0.1 ± 0.1 L.kg−1). We highlighted distinct behaviour of pesticide leaching depending mainly on soil type, agricultural practices and pesticide properties. For low degree of preferential flow, pesticide leaching can be related to the sorption properties of pesticides. Nicosulfuron and mesotrione delays are more pronounced under conservation management while metaldehyde always arrived with no delay. During the high intensity rain event, on one soil type, high degree of preferential flow masked sorption effect on leaching since every pesticide arrived at the same time as the tracer and amounted to up to 21% of pesticide recovery compared to 4% on the other soil type. Conservation agriculture was found to improve the vertical transfers of water and pesticides while, on one of the studied soil type, the presence of a low conductive plough pan significantly limits water drainage.

Effect of various doses of 3,4-dimethylpyrazole phosphate on mineral nitrogen losses in two paddy soils

Nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) has been widely proposed to reduce nitrogen (N) loss and improve N availability in paddy soil. However, little knowledge exists regarding the optimum dose of DMPP required for inhibiting nitrification in different soil types. In undisturbed soil columns under greenhouse conditions, dynamics of ammonium (NH4+–N) and nitrate (NO3−–N) in floodwater and leachate, and ammonia (NH3) volatilization were studied in two paddy soils (hydragic and gleyed), amended with urea-N at 180 N kg/ha with DMPP applied at 0, 0.45, 0.675, and 0.90 kg/ha (0.25%, 0.375%, and 0.5% of urea-N, respectively). The source of DMPP was Entec® 46 (46% urea-N and DMPP at 0.5% of urea-N) that was mixed with pure urea (fertilizer mixture). DMPP application rates and soil types significantly influenced NH4+–N and NO3−–N concentrations in floodwater and leachate; however, DMPP application rates did not significantly impact NH4+–N concentrations in floodwater. Results indicate that concentrations of both NH4+– N and NO3−–N in leachate and floodwater were peaked between 10 and 20 days after fertilizer application. Increased DMPP application rates increased floodwater and leachate NH4+–N concentrations, while significantly decreasing NO3−–N concentrations in floodwater and leachate, with largest decrease seen in the 0.90-kg/ha DMPP treatment. NH3 emissions were observed after fertilizer was applied and decreased gradually, with no significant differences in response to the DMPP amount. The total N losses via leaching and NH3 emission were significantly decreased at treatments of 0.675 kg/ha and 0.90 kg/ha DMPP, and positively correlated with sand fraction in soil. Compared with the gleyed paddy soil, higher total N loss was observed in the hydragic paddy soil, which was related to the higher sand fraction of the hydragic paddy soil and the better behavior of DMPP in this soil type. Considering economic factors, mineral N concentrations in floodwater and leachate, together with N losses via leaching and volatilization, application of 0.675 kg/ha DMPP could significantly inhibit nitrification in the hydragic paddy soil while application of 0.90 kg/ha DMPP was shown to be the best choice to inhibit nitrification in the gleyed paddy soil.

Peculiar attenuation of soil toluene at contaminated coking sites

In the soil of contaminated coking sites, polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene and xylene (BTEX) are typical indicator compounds. Generally, PAHs are enriched in the topsoil layer. BTEX, with higher water solubilities and lower organic carbon-water partitioning coefficients (Koc), are distributed deeper than PAHs. However, current models have employed predictions using single compounds to mimic the migration of BTEX at contaminated coking sites. Such models have not considered the influence of the upper soil layer, where PAHs are enriched. An attempt to fill this gap was made by setting up a control soil column experiment in this study. One column was filled with undisturbed soil (column #1) and the other with PAH-contaminated soil (column #2) to simulate the theoretical and actual surface soil layers, respectively. The results showed that in column #2, the toluene gas concentration of the headspace and time required to reach steady state were notably greater than those in column #1. High-throughput sequencing revealed that there were large microbial community structure differences between the two soil columns throughout the experiment, while some genera that degrade toluene with high efficiency emerged noteworthily in column #2. This implied that the upper soil layer enriched with PAHs was conducive to the degradation of toluene vapor. Applying this finding to human health exposure assessment of toluene suggests that the potential exposure level should be reduced from the current predicted level given the unanticipated attenuation at contaminated coking sites.

Solute Dispersion of Organic Compounds on Undisturbed Soil Columns

Results of column tests performed on large undisturbed samples are presented, focusing on the behavior of the hydrodynamic dispersion coefficient ($$D_h$$). Tests were performed employing petroleum produced water from onshore facilities percolating sandy soils with different fine contents. To measure the organic content of the produced water, this work used the parameter TPH (total petroleum hydrocarbons). The obtained results show that the longitudinal dispersion coefficient ($$\alpha _L$$) varies with flow velocity ($$v_s$$) and that both the ratio between the hydrodynamic dispersion and diffusion coefficients ($$D_h/D$$) and $$\alpha _L$$ are approximately two orders of magnitude higher than the values normally found in the literature for the same type of soil. This is probably related to the fact that the organic compounds measured by TPH in the produced water are partially in dissolved form, but dispersed particles are also transported by water flow, increasing the experimental values of $$D_h$$.

Scale and REV analyses for porosity and pore connectivity measures in undisturbed soil

Soil samples with a volume of approximately 100 mL are commonly used for measuring soil properties needed to parameterize continuum models of transport processes in soils. The necessary assumption that the sampled soil volume corresponds to a representative elementary volume (REV) has only been occasionally tested. Furthermore, the few studies so far have focused on bulk properties such as porosity and bulk density and have not investigated the scale-dependence of pore-space connectivity, which is fundamental for transport properties such as the permeability of soil. In this study, we investigated the scale-dependence of morphologic properties of the soil pore-space in 25 undisturbed soil columns sampled from five different depths (8, 23, 33, 53 and 73 cm) from a field site in southern Norway (Skuterud). We conducted the analyses of scale-dependence on regions of interests of 40 × 40 × 40 mm3 from binarized X-ray images with a resolution of 40 µm. We focused our evaluation on imaged porosity and three measures of pore-space connectivity (the connection probability, the Euler-Poincaré number and the critical pore diameter). As pore network connectivity is scale-dependent and because the connectivity of large pores has a very strong impact on the soil permeability, we conducted our analyses considering three contrasting minimum pore diameters, namely 80, 250 and 500 µm.We found that the pore connectivity improved with scale, predominantly due to the presence of pores with diameters of less than 0.25 mm. This stresses the importance of image resolution in scale analyses. We moreover observed that both the mean and the standard deviation of the critical pore diameter increased with scale, which may explain why the mean and standard deviation of the saturated hydraulic conductivity are often found to increase with scale. We detected an REV range for the macroporosity between approximately 15 and 65 mm. This range decreased with an increase in the minimum pore diameter considered. However, we also found evidence contradicting the existence of the detected REV range for the macroporosity due to a lack of statistical homogeneity. No REV range could be found for the three investigated connectivity measures, probably because the evaluated scales were too small. Based on our results we conclude that larger soil samples should be used to measure soil properties and investigate processes that depend on the pore network connectivity, such as permeability or water flow and long-range solute transport. We recommend that future studies should investigate REVs for connectivity measures and investigate which REV criteria are most meaningful in a continuum modelling context. Such studies are needed to evaluate whether REVs for transport properties are common in soils. If not, flow and transport models that explicitly account for heterogeneity are necessary.