Infiltration Experiments Research Articles

Effects of Textural Layering on Water Regimes in Sandy Soils in a Desert-Oasis Ecotone, Northwestern China

Textural layering of soil plays an important role in distributing and regulating resources for plants in many semiarid and arid landscapes. However, the spatial patterns of textural layering and the potential effects on soil hydrology and water regimes are poorly understood, especially in arid sandy soil environments like the desert-oasis ecotones in northwestern China. This work aims to determine the distribution of textural layered soils, analyze the effects of different soil-textural configurations on water regimes, and evaluate which factors affect soil water infiltration and retention characteristics in such a desert-oasis ecotone. We measured soil water content and mineral composition in 87 soil profiles distributed along three transects in the study area. Constant-head infiltration experiments were conducted at 9 of the soil profiles with different texture configurations. The results showed that textural layered soils were patchily but extensively distributed throughout the study area (with a combined surface area percentage of about 84%). Soil water content in the profiles ranged from 0.002 to 0.27 g/cm3 during the investigation period, and significantly and positively correlated with the thickness of a medium-textured (silt or silt loam) layer (p < 0.001). The occurrence of a medium-textured layer increased field capacity and wilting point and decreased available water-holding capacity in soil profiles. Burial depth of the medium-textured layer had no clear effects on water retention properties, but the layer thickness tended to. In textural layered soils, smaller water infiltration rate and cumulative infiltration, and shallower depths of wetting fronts were detected, compared with homogeneous sand profiles. The thickness and burial depth of medium-textured layers had obvious effects on infiltration, but the magnitude of the effects depended on soil texture configuration. The revealed patterns of soil textural layering and the potential effects on water regimes may provide new insight into the sustainable management of rainfed vegetation in the desert-oasis ecotones of arid northwestern China and other regions with similar environments around the world.

Sequential and coupled inversion of horizontal borehole ground penetrating radar data to estimate soil hydraulic properties at the field scale

Horizontal borehole ground penetrating radar (GPR) measurements can provide valuable information on soil water content (SWC) dynamics in the vadose zone, and hence show potential to estimate soil hydraulic properties. In this study, the performance of both sequential and coupled inversion workflows to obtain soil hydraulic properties from time-lapse horizontal borehole GPR data obtained during an infiltration experiment were compared using a synthetic modelling study and the analysis of actual field data. The sequential inversion using the vadose zone flow model HYDRUS-1D directly relied on SWC profiles determined from the travel time of GPR direct waves using the straight-wave approximation. The synthetic modelling study showed that sequential inversion did not provide accurate estimates of the soil hydraulic parameters due to interpretation errors in the estimated SWC near the infiltration front and the ground surface. In contrast, the coupled inversion approach, which combined HYDRUS-1D with a forward model of GPR wave propagation (gprMax3D) and GPR travel time information, provided accurate estimates of the hydraulic properties in the synthetic modelling study. The application of the coupled inversion approach to measured borehole GPR data also resulted in plausible estimates of the soil hydraulic parameters. It was concluded that coupled inversion should be preferred over sequential inversion of time-lapse horizontal borehole GPR data in the presence of strong SWC gradients that occur during infiltration events.

Inverse Infiltration Modeling of Dike Covers Made of Dredged Material Using PEST and AMALGAM

A variety of studies recently proved the applicability of different dried, fine-grained dredged materials as replacement material for erosion-resistant sea dike covers. In Rostock, Germany, a large-scale field experiment was conducted, in which different dredged materials were tested with regard to installation technology, stability, turf development, infiltration, and erosion resistance. The infiltration experiments to study the development of a seepage line in the dike body showed unexpected measurement results. Due to the high complexity of the problem, standard geo-hydraulic models proved to be unable to analyze these results. Therefore, different methods of inverse infiltration modeling were applied, such as the parameter estimation tool (PEST) and the AMALGAM algorithm. In the paper, the two approaches are compared and discussed. A sensitivity analysis proved the presumption of a non-linear model behavior for the infiltration problem and the Eigenvalue ratio indicates that the dike infiltration is an ill-posed problem. Although this complicates the inverse modeling (e.g., termination in local minima), parameter sets close to an optimum were found with both the PEST and the AMALGAM algorithms. Together with the field measurement data, this information supports the rating of the effective material properties of the applied dredged materials used as dike cover material.

An improved genetic algorithm for determining modified water-retention model for biochar-amended soil

Biochar has been globally recognized as a soil amendment to ameliorate the degraded soil structures. We investigated the different biochar percentages contributed to the changes in soil water retention, soil infiltration, and water-holding capacity of one dimensional scale. Besides, infiltration models were compared, and an improved genetic algorithm (GA) combined with multi-objective optimization and elitist strategy was proposed to upgrade the modified van-Genuchten (VG) model. Results indicated that observed cumulative infiltration displayed reductions by 14.06%, 46.62%, and 71.78% for the soil mixed with 5%, 10%, and 15% biochar, respectively, relative to the pure soil. The Kostiakov model was more effective than the Philip model in predicting cumulative infiltration. Furthermore, the constructed modified VG model based on the inversed hydraulic parameters was capable of predicting soil moisture at suction less than 2070 kPa (i.e., 1.38 times wilting point) but caused an underestimation beyond it. This research has the potential to replace the soil water retention curve (SWRC) measurement by one-dimensional infiltration experiment with parameters inversed from the improved GA combined with a modified VG model. It is time-saving and efficient during the SWRC study.

Tailored Liquid Phases for Enhanced Sintering of Advanced PM - Steels

The application of “masteralloys” as alloying carriers in Powder Metallurgy (PM) steels enables the introduction of highly oxygen‑sensitive alloying elements for advanced PM‑steels, by using a tailored liquid phase. The characteristics of the liquid and its interaction with the iron base powder are determining factors for final microstructure and dimensional behaviour. In this study, theoretical calculations and experimental findings are presented for the masteralloy systems Fe_Mn_Si_C, Fe_Cr_Si_C and Fe_Mn_Cr_Si_C. Lowered melting temperatures and narrow melting temperature intervals could be achieved. The interaction between Fe base material and the masteralloys was studied by infiltration and DTA experiments. It was found that by adjusting the C and Si content in the masteralloy, liquids with widely varying properties could be obtained. This might be a key for tailoring microstructures, properties and dimensional stability of advanced PM‑steels.

Investigation on the lateral anti-seepage capacity of a vertical soil sand layer (VSSL) in a sunken lawn

The use of a sunken lawn is an emerging Low Impact Development (LID) technique to effectively control storm runoffs. However, the random infiltration of rainwater that occurs due to the construction of a sunken lawn in an area of collapsible loess seriously threatens the safety of buildings around it. Setting up a vertical soil sand layer (VSSL) structure next to a sunken lawn as an anti-permeate method has been proposed in this study. To analyze the lateral anti-seepage effects of a VSSL, a sunken lawn model around a building was established based on soil physical parameters, and water seepage in the sunken lawn was investigated using a infiltration experiment and HYDRUS-2D software. The results show that the anti-seepage effects of a VSSL can significantly reduce the average wetting front migration length and water content at the observation points behind the sand layer. The Nash-Sutcliff Efficiency (NSE) index was used to evaluate the accuracy and reliability of the HYDRUS-2D model. The values of the NSE index obtained were greater than 0.82 (varied between 0.82 and 0.98) which confirmed the applicability of the HYDRUS-2D software in accurately describing the hydraulic behavior of the lateral anti-seepage effects of the VSSL in a sunken lawn. Simulation infiltration tests showed that, on the side of the VSSL, the wetting front migration length was reduced by 55.5% on average, and the water content of the observation points behind the sand layer was reduced by 40.5%, increasing the stability of the loess around the building infrastructure. The results are of value in practical applications, such as for devising engineering or non-engineering measures to avoid loess collapsibility around sunken lawns.

Comparative Non-Darcian Modeling of Subsurface Preferential Flow Experimental Observations in a Riparian Buffer

HighlightsHigh ecohydrological activity drives macropore prevalence in riparian buffers.An abundance of macropore flow (MF) was confirmed in a field riparian buffer in Kenya.Source-response (SR) and multilayer kinematic diffusive wave (MKDW) MF models are compared.A novel MKDW modeling framework efficiently identifies and predicts preferential flow in riparian buffers.Abstract. The significant ecohydrological activity typical of riparian buffers makes them potential hotspots of macropores, i.e., structured preferential flow pathways, through the soil vadose zone. The prevalence of these preferential pathways can allow transported contaminants to bypass the soil matrix and quickly reach a seasonal shallow water table and the adjacent surface waterbody. This quick transport can ultimately limit the role of riparian buffers for runoff pollution control. Currently, there are no management tools that incorporate macropore flow (MF) when assessing riparian buffer performance. The objective of this study was to experimentally quantify and mathematically simulate macropore flow and arrival time in a riparian buffer under field conditions. Three infiltration experiments were conducted with a grid of 20 time-domain transmission (TDT) dielectric soil moisture sensors along a field riparian buffer transect in Kenya to quantify the presence of macropore flow and to test two non-Darcian soil MF models, including the source-responsive (SR) model and the modified kinematic-dispersive wave (MKDW) model developed in this study, by adding a user-defined multilayer convection scheme and a new hysteresis function between water flux and content. The abundance of MF in the riparian buffer was corroborated experimentally. Modeling results showed that the MKDW model was an efficient (average NSE of 0.937 and 0.721 for calibration and testing, respectively), flexible, and robust method to identify and represent non-linear and non-sequential MF signals at any soil depth and antecedent conditions. The SR model was computationally inexpensive and provided good calibration results (NSE = 0.867) but required piecemeal recalibration of the travel time and maximum water content at each layer and yielded lower performance in testing. The Akaike (AIC) and Bayesian (BIC) information criteria showed that MKDW outperformed SR when accounting for the trade-off between model complexity and efficiency. The results support further research focused on independent characterization of model parameters at the field scale, and the inclusion of MKDW in holistic riparian buffer management and decision-support tools such as VFSmod. Keywords: Kinematic-dispersive wave, Macropore flow, Numerical modeling, Preferential flow, Riparian vadose zone.

Corrigendum to: Soil hydraulic properties estimation from one‐dimensional infiltration experiments using characteristic time concept

Corrigendum to: Soil hydraulic properties estimation from one‐dimensional infiltration experiments using characteristic time concept

Experimental Study of Rainfall Infiltration in an Analog Fracture‐matrix System

In this study, an experimental apparatus was developed to investigate unsaturated infiltration in an analog fracture‐matrix system. Fracture and adjacent matrix is simulated by sands with various particle sizes. Four rainfall infiltration experiments were performed on the analog fracture‐matrix system at a constant rainfall rate of 100 mm/h. The process of rainfall infiltration is measured by a combination method of tensiometers and quick moisture apparatus. The measured results reveal that fracture‐matrix interactions certainly exert influences on the hydraulic behaviour of unsaturated fractured matrix, and the fluid flow mainly infiltrates along the nonuniform paths within the matrix. Moreover, it is observed that the influences are greater when using a coarser sand to mimic the fracture. Specifically, the wetting phase in the matrix moves faster than that in the fracture; the fracture, therefore, acts as a vertical capillary barrier, but there exists lateral water exchange from the matrix to the fracture. Overall, this study has demonstrated the importance of fracture/matrix interactions, which should be considered when dealing with unsaturated flow through permeable matrices.

Quantifying the Importance of Preferential Flow in a Riparian Buffer

HighlightsRiparian buffers and vegetative filter strips are uniquely susceptible to preferential flow.An innovative method is proposed to partition infiltration into matrix and macropore domains.Riparian buffer matrix and plot-scale infiltration experiments were simulated with HYDRUS-1D and VFSMOD.Preferential flow accounted for 32% to 47% of infiltration depending on hydrologic conditions.Preferential flow mechanisms should be incorporated into riparian buffer design tools and models.Abstract. Riparian buffers are uniquely susceptible to preferential flow due to the abundance of root channels, biological activity, and frequent wetting and drying cycles. Previous research has indicated such susceptibility and even measured the connectivity of preferential flow pathways with adjacent streams and rivers. However, limited research has attempted to partition the riparian buffer infiltration between matrix and preferential flow domains. The objectives of this research were to develop an innovative method to quantify soil matrix infiltration at the plot scale, develop a method to partition infiltration into matrix and macropore infiltration at the plot scale, and then use these methods to quantify the significance of macropore infiltration at a riparian buffer site. This research further demonstrated the importance of considering preferential flow processes in design tools and models to evaluate riparian buffer effectiveness. Sprinkler and runon field experiments were conducted at an established riparian buffer site with sandy loam soil. Trenches were installed and instrumented with soil moisture sensors along the width of the riparian buffer (i.e., along the flow path toward the stream) for detecting non-uniform flow patterns due to preferential flow. Riparian buffer parameters, including soil hydraulic parameters, were estimated using HYDRUS-1D for the sprinkler experiments and VFSMOD for the runon experiments. This research partitioned the infiltration into matrix and preferential flow domains by assuming negligible exchange of water between the soil matrix and preferential flow pathways in comparison to the magnitude of soil matrix flow. For these experimental conditions with 0.20 to 0.48 L s-1 of runon and initial soil water contents of 0.29 to 0.32 cm3 cm-3, preferential flow accounted for at least 27% to 32% of the total runon water entering the riparian buffer. This corresponded to approximately 32% to 47% of the total infiltration. While increasing the riparian buffer plot soil hydraulic conductivity in single-porosity models can adequately predict the total infiltration and therefore the surface outflow from the buffer, design tools and models should specifically consider preferential flow processes to improve predictive power regarding the actual infiltration processes and correspondingly the non-equilibrium flow and solute transport mechanisms. Keywords: Flow partitioning, HYDRUS, Matrix flow, Preferential flow, Riparian buffer, VFSMOD.

Rain Transmission Losses Assessment in Arid Environment, Egypt: Numerical and Experimental Study

In water-scarce regions, Transmission Losses Assessment from rainfall is required for the Numerical and Experimental Study of groundwater recharge. This Study is an attempt to assess Transmission Losses and the infiltration rate at Wadi El-Assiuti, Egypt, field infiltration experiments were conducted to measure the infiltration and porosity at the target area, such as using a double-ring infiltrometer. Determination and Quantify the infiltration rate of the soil is very vital as input parameters of the hydrological modeling, irrigation planning and other natural or man-made Processes. Steady state infiltration rates have been determined in selected sites of Wadi El-Assiuti. Accurate determination of infiltration rates is fundamental for trustworthy prediction of surface runoff and groundwater recharge. Double ring infiltrometer was used to measure infiltration rate at selected sites. An important part of the study was the accurate and consistent measurement of infiltration rates‥ The infiltration rate was calculated according to the installation and operating instruction for the double ring in ASTM 2003. Final infiltration rates were 18 cm h−1, for the first observation site, 24.2 cm h−1for the second site and 59 cm h−1for the third site. The analysis indicated that the soil for the three selected areas is sandy soil. Infiltration rates were taken at 0 to70 minutes of 10 minutes intervals. The infiltration rate at the third site is high compared to the other two selected sites. After performing the experiments, soil samples have been gathered and analyzed in the laboratory for porosity analysis. The results of this study can therefore be applied in the prediction of saturated hydraulic conductivity of the surface layers and groundwater recharge, and in developing or selecting the most efficient irrigation methods. The results from this work have been also involved in a numerical hydrological model to estimate the Transmission Losses form rainfall at Wadi El-Assiuti using Hydro-BEAM.

Structural control of the non-ionic surfactant alcohol ethoxylates (AEOs) on transport in natural soils.

Surfactants, after use, enter the environment through diffuse and point sources such as irrigation with treated and non-treated waste water and urban and industrial wastewater discharges. For the group of non-ionic synthetic surfactant alcohol ethoxylates (AEOs), most of the available information is restricted to the levels and fate in aquatic systems, whereas current knowledge of their behavior in soils is very limited. Here we characterize the behavior of different homologs (C12-C18) and ethoxymers (EO3, EO6, and EO8) of the AEOs through batch experiments and under unsaturated flow conditions during infiltration experiments. Experiments used two different agricultural soils from a region irrigated with reclaimed water (Guadalete River basin, SW Spain). In parallel, water flow and chemical transport were modelled using the HYDRUS-1D software package, calibrated using the infiltration experimental data. Estimates of water flow and reactive transport of all surfactants were in good agreement between infiltration experiments and simulations. The sorption process followed a Freundlich isotherm for most of the target compounds. A systematic comparison between sorption data obtained from batch and infiltration experiments revealed that the sorption coefficient (Kd) was generally lower in infiltration experiments, performed under environmental flow conditions, than in batch experiments in the absence of flow, whereas the exponent (β) did not show significant differences. For the low clay and organic carbon content of the soils used, no clear dependence of Kd on them was observed. Our work thus highlights the need to use reactive transport parameterization inferred under realistic conditions to assess the risk associated with alcohol ethoxylates in subsurface environments.

Pretreatment of diesel-contaminated hydrophobic soil using surfactant and sodium hexa-metaphosphate (Na-HMP) to improve infiltration of aqueous phase remedial agents in unsaturated soil

The remediation of diesel-contaminated hydrophobic soil is difficult due to the inability of aqueous phase remedial agents to infiltrate the soil. This novel laboratory study enhanced the gravity-driven infiltration of water and oxidant solution into the hydrophobic soil by pretreatment. For this purpose, the hydrophobic soil was pretreated (partially liquid saturating) using 0.1% sodium hexa-metaphosphate (Na-HMP) and 0.5% alpha olefin sulfonate (AOS). The diesel-contaminated soil (34,167 ± 560 mg TPH/kg) was partially saturated with 0.5 pore volumes of Na-HMP and surfactant mixture solution. The infiltration experiment of the pretreated soil was conducted by pouring a solution (water/oxidant) provided from the Marriott reservoir over the digital balance. This study did not observe any natural infiltration of water or oxidant reagent into the diesel-contaminated soil. After the pretreatment, the cumulative infiltration of water to the pretreated soil increased to 5.17 cm after 40 min. The natural infiltration occurred due to the dispersion of soil particles and reduction of hydrophobicity by the Na-HMP and AOS, respectively. Widened soil pores were observed after pretreatment using the scanning electron microscopy (SEM) analysis. The infiltration of 5% Na2S2O8 solution was 5.80 cm after 40 min when the diesel-contaminated soil was pretreated with 0.1% Na-HMP and 0.5% AOS. Pretreatment using Na-HMP and AOS can enhance the remediation of highly hydrophobic and low-permeability soils. This finding can provide an insight into enhancing the soil remediation efficiency by increasing the gravity-driven uniform delivery of the remediation agent into the undisturbed soil. Graphical abstract

Enhanced Removal of Contaminants of Emerging Concern through Hydraulic Adjustments in Soil Aquifer Treatment

Water reclamation through the use of soil aquifer treatment (SAT) is a sustainable water management technique with high potential for application in many regions worldwide. However, the fate of contaminants of emerging concern (CECs) during the infiltration of treated wastewater during SAT is still a matter of research. This study investigates the removal capacity of 27 CECs during SAT by means of infiltration experiments into a 6 m soil column. Additionally, the influence of the hydraulic operation of SAT systems on the removal of CECs is investigated by changing the wetting and drying cycle lengths. Sixteen out of 27 CECs are efficiently removed during SAT under various operational modes, e.g., bezafibrate, diclofenac and valsartan. For six substances (4-methylbenzotriazole, amidotrizoic acid, benzotriazole, candesartan, hydrochlorothiazide and sulfamethoxazole), removal increased with longer drying times. Removal of amidotrizoic acid and benzotriazole increased by 85% when the drying cycle was changed from 100 to 444 min. For candesartan and hydrochlorothiazide, removal improved by 35%, and for 4-methylbenzotriazole and sulfamethoxazole, by 57% and 39%, respectively. Thus, enhanced aeration of the vadose soil zone through prolonged drying times can be a suitable technique to increase the removal of CECs during SAT.

Heterogeneity in outcomes of repeated instances of percolation experiments.

We investigate the heterogeneity of outcomes of repeated instances of percolation experiments in complex networks using a message-passing approach to evaluate heterogeneous, node-dependent probabilities of belonging to the giant or percolating cluster, i.e., the set of mutually connected nodes whose size scales linearly with the size of the system. We evaluate these both for large finite single instances and for synthetic networks in the configuration model class in the thermodynamic limit. For the latter, we consider both Erdős-Rényi and scale-free networks as examples of networks with narrow and broad degree distributions, respectively. For real-world networks we use an undirected version of a Gnutella peer-to-peer file-sharing network with N=62568 nodes as an example. We derive the theory for multiple instances of both uncorrelated and correlated percolation processes. For the uncorrelated case, we also obtain a closed-form approximation for the large mean degree limit of Erdős-Rényi networks.

Performance evaluation of organoclays for the amoxicillin retention in a dynamic context

The hydraulic conductivity of diverse organoclays was determined through percolation experiments and compared to a raw Na-montmorillonite (Na-Mt). The incorporation of surfactants even at low content drastically changes the hydraulic conductivity with a large increase of about two order of magnitude in contrast to that of Na-Mt (10−12 m s−1). Batch kinetics and equilibrium adsorption experiments confirmed the proper affinity of organoclays to a zwitterion antibiotic: the amoxicillin (AMX) which was quickly adsorbed (at a time below 30 min) at large amounts (up to 1.4 × 10−3 mol g−1). However, in percolation conditions, the significant increase of the permeability led to a short interaction time between the organoclays and the pharmaceutical. In contrast to Na-Mt for which it took age to get only one drop of AMX, leachates, resulting of a percolation through organoclays, were collected for a time below 10 min, not enough sufficient to ensure a proper removal of an antibiotic with concentration reduced by 5–80% of the initial solution.

The impermeability effect of soil air on the ponding infiltration experiment of soil column

The agricultural flood irrigation in Jingyang South Platform, Shaanxi Province caused the rise of groundwater level, which induced a large number of loess landslides. The study of water movement in unsaturated loess under irrigation is the premise of revealing the mechanism of loess landslide. In this paper, the changes of matric suction, volume moisture content and air pressure with time at different depths of unsaturated undisturbed loess are measured by indoor soil column water infiltration test. Air pressure at each point of the soil rises to about 98 Pa in a short time after the test beginning, and keeps small fluctuation up and down during the test. At the end of the experiment, the air pressure at each point of the soil returns to zero in a short time after the upper water accumulation is eliminated. During the test, the change of infiltration rate has a significant corresponding relationship with the exhaust phenomenon at the top of the soil column, and the air resistance significantly reduces the infiltration rate of water.

Can structure data obtained from CT images substitute for parameters of a preferential flow model?

Modeling preferential flow in soils is still a challenge for the scientific community working on water resources. Indeed, it is an issue to determine the functional parameters of models dedicated to water flow, that are currently obtained by fitting processes, whereas their relationships with soil structure remain poorly known. Improved models are expected from a better understanding of the links between functional and structural parameters, which can be achieved thanks to recent developments in imaging methods such as X-ray Computed Tomography (CT). The paper seeks to improve a dual-porosity model, coupling matrix flow (by Richards equation) and preferential flow (by a Kinematic Dispersive Wave), by substituting some model parameters, usually obtained by inversion of experimental data, by those assessed from CT images of the soil structure. Thus, two versions of the model are compared, the “classical” and the “advanced” one including parameters determined using the 3D images of the sample structures. To compare model versions with real situations, infiltration experiments were conducted in lab on two different soils at two initial water contents. An X-ray medical scanner allowing acquisitions of large soil volumes (≈1700 cm3) with a voxel size of 400 µm was used to image the sample structures. Then, we derived two geometrical parameters from the macroporosity network: the percolating macroporosity and a characteristic dimension of this macropore network, the mean inter-macropore distance. The sensitivity analysis conducted on the classical version of the model showed that the kinematic coefficient and the dimensional parameter of the porous medium are the two main contributors to the cumulated drainage whatever the initial condition. Although experimental data are better simulated by the classical version of the model, drainage dynamics is also well simulated by the advanced version. However, differences between the model versions that are small for both soils at field capacity become significant for the dried state (mean initial matric potential of −3.5 m). This emphasizes the crucial effect of the sink-source term and in particular the complex effect of the dimensional parameter that it contains. Indeed, difficulties to simulate properly water exchange between porosity domains are encountered for both versions of the model. We conclude that empirical parameters that were up to now fitted from experiments could be deduced from geometrical indicators computed from CT images and that owning to these first results the applied methodology is promising to achieve a better understanding and modeling of preferential flow processes and to improve model predictability.

ToxA, a significant virulence factor involved in wheat spot blotch disease, exists in the Mexican population of Bipolaris sorokiniana

Spot blotch, caused by the pathogen Bipolaris sorokiniana, is an important foliar disease of wheat in warm and humid regions worldwide. The fungal virulence factor ToxA interacts with Tsn1 in wheat and leads to a susceptible reaction. ToxA has been found in B. sorokiniana populations of Australia, the USA, and India, and here we report its occurrence in Mexico, based on analysis of a collection of 196 Mexican isolates of B. sorokiniana. The isolates were collected from experimental stations and farmers’ fields in nine states of Mexico, during the period from 1992 to 2017. A PCR assay with the ToxA-specific marker was conducted, and the results revealed the presence of ToxA in 20 isolates (10.2%). Culture filtrate infiltration experiments confirmed that all the 20 isolates were able to induce necrosis reaction on Glenlea, a wheat genotype with Tsn1. This is the first report on the occurrence of ToxA in Mexican B. sorokiniana population, which is key information for breeding wheat for resistance against spot blotch.

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.