Undisturbed Lysimeters Research Articles

Evaluation of soil pesticide leaching to groundwater using undisturbed lysimeter: development of the pesticide groundwater leaching scoring system (PLS).

Groundwater pesticide safety management is essential for providing consistently safe water for humans, but such management is limited globally. In this study, we developed an accurate and convenient exposure assessment method for the safety management of pesticides in groundwater by conducting a lysimeter experiment to evaluate the leaching of 11 pesticides into groundwater. During the experimental period, flutoalanil and oxadiazon had the highest cumulative leaching amounts, 603.7 and 83.5ng, respectively. Comparative analysis of existing groundwater exposure prediction indices, including the GUS, LEACH, modified LEACH, Hornsby index, and GLI showed no correlations with the measured data (p > 0.05). To enhance the accuracy of the assessment method, we used lysimeter data and principal component analysis to determine the main factors affecting groundwater leaching, and developed the "pesticide groundwater leaching scoring system" (PLS). The soil and water half-life, which had the greatest positive impact on groundwater leaching, was set as a 10-point indicator, whereas log P was set as a 1-point indicator. In contrast, solubility in water was determined as a 5-point indicator, and organic carbon partition coefficient and vapor pressure were determined as 2.5-point indicators owing to their negative relationship. The correlation coefficient was 0.670, indicating a significant correlation with the lysimeter data (p < 0.05). Using our scoring system, we ranked 376 pesticides. As an exposure assessment method developed using actual data, the PLS is expected to be applicable to groundwater safety management.

Risk Assessment of Hydrocarbons’ Storing in Different Textured Soils in Small-Scale lysimeters

The objectives of this study are to test the penetration depth and determine the soil content in hydrocarbons’ components BTEX, PAHs, and TPH, after vertical movement of crude oil through undisturbed soils of different textures, and to assess their risk. The experiment simulates the fate of oil spills in the cold season. Three soil types were investigated: a sandy-textured eutric Arenosol, AR-eu; a loamy-textured haplic chernozem, CH-ha; and a clayey-textured, swell-shrink, Luvic Chernic Phaeozem, PH-ch-lv. Undisturbed small-scale lysimeters, 0.3 m in diameter and 1 m in length, were used. Crude oil was first applied and then water. TPH, BTEX, and PAH retention in the soils depends on soil texture. PH-ch-lv soil stored most of them in the upper horizons. TPH, BTEX, and PAH were found in different amounts as percentage from the applied ones, TPH as 48% (PH-ch-lv), and > 76% in the other two soils. BTEX was stored as 1.6% from the applied in PH-ch-lv, 5.1–5.1% in CH-ha and AR-eu soils, while PAH ranged from 15.1% in AR-eu soil to 24.8% in PH-ch-lv and 31% in CH-ha. Though subject to volatilization, chemical transformation, and bioremediation, TPH, BTEX, and PAH stored in soils present a health risk if they reach the groundwater. PH-ch-lv appears to be the most resilient soil to oil pollution. The results concern different soil textures and might be used in various countries. Future experimentation should focus on soil behavior in relation to crops, water, and certain crude oil types.

Preferential flow of surface‐applied solutes: Effect of lysimeter design and initial soil water content

AbstractUndisturbed lysimeters are widely used to study water and solute transport, where both natural and unnatural preferential flow can greatly influence leaching rates. The objective of this study was to use chemical and isotopic tracers to quantify the effect of initial soil water content and lysimeter design on preferential flows. Ten undisturbed lysimeters (900 cm2) were collected from an agricultural field, with the gap between the soil and lysimeter casing sealed with petroleum jelly for five lysimeters. Lysimeters were subjected to two rainfall simulations (3.3 cm h−1) under contrasting initial soil water contents, and leachate near the soil‐casing interface was collected separately from leachate through the bulk soil. Three‐component hydrograph separation revealed that event water comprised 21–59% of total leachate irrespective of initial soil water content and lysimeter design. Sealing the edges of the lysimeters with petroleum jelly greatly reduced but did not eliminate edge flow during rainfall simulations. Although water and solute transport were similar in both sealed and unsealed lysimeters under dry antecedent conditions due to the formation of shrinkage cracks on the soil surface, edge flow was substantially greater for the unsealed lysimeters under wet antecedent conditions. Unsealed edges under wet antecedent conditions facilitated the preferential transport of both event and pre‐event water, resulting in greater solute leaching. Using multiple tracers to contrast lysimeter designs under different initial soil water contents not only allowed for rigorous testing of a commonly used edge‐flow suppression technique but also provided new insights into preferential flow processes and patterns.

Leaching of Free and Conjugate Natural Estrogens in Soil Monoliths

Natural free estrogens found in animal manures are potent endocrine-disrupting compounds. Environmental detections can be caused by such processes as physical and chemical non-equilibrium and colloidal or conjugate facilitate transport. Antecedent or “legacy” concentrations of estrogens resident in soil may also contribute significantly to environmental detections. The objective of this study was to measure and understand the dominant causes contributing to estrogen detections in the environment from a grazed system. To achieve this objective, the effluent of undisturbed lysimeters constructed from soils of fields grazed by dairy cows (Bos taurus) was monitored for free and conjugated estrogens. Four lysimeters were dosed with urine (Urine) and four only received water (Control). Water transfer for all lysimeters was similar, and all lysimeters were near field capacity for the duration of the experiment. Rapid transport of a conservative bromide tracer suggested that preferential flow was an important physical non-equilibrium transport process. Free estrogens and conjugated estrogens (17β-estradiol (E2), estrone (E1), 17β-estradiol-17-sulfate (E2-17S), 17β-estradiol-3-glucuronide (E2-3G), estrone-sulfate (E1-S)) were detected in the source urine (E2 = 17,248 ng/L, E1 = 1006 ng/L, E2-3G = 967 ng/L, E2-17S = 886,456 ng/L, E1-S = 1730 ng/L). These same free and conjugated estrogens, in addition to estriol (E3), were all detected frequently in both Control and Urine lysimeters (detection concentration ranks: E3 > E2-17S = E2 > E2-3G = E1 = E1-3S). Total potential estrogenicity in the effluent of the Control and Urine was also similar, indicating the presence of antecedent estrogens was the dominant contribution to estrogenic detections. Additionally, the frequent detection of conjugates in the lysimeter effluent was important, because it indicated that conjugates were stable in soil but had greater potential mobility than free estrogens.

Dye Tracers Reveal Potential Edge‐Flow Effects in Undisturbed Lysimeters Sealed with Petrolatum

Core Ideas Effectiveness of petrolatum in preventing edge‐flow was assessed in lysimeters. Edge flow was observed with dye tracers in both dry and rewetted unsealed lysimeters. Petrolatum sealed edges but created a new edge where it infiltrated into the soil. Preferential flow occurred at this new edge in dry and rewetted sealed lysimeters. Maintenance of soil moisture is critical when sealing lysimeters with petrolatum. Undisturbed soil lysimeters are widely used to study water and solute transport. During or following lysimeter collection, it is common to implement measures aimed at limiting edge flow at the interface between the soil and the lysimeter casing. The objective of this study was to use dye tracers to evaluate the effectiveness of petroleum jelly in suppressing edge flow in lysimeters. Eight undisturbed square lysimeters (900 cm2) with removable spacers lining the inside of the casing were collected from an agricultural field. Spacers were removed from four lysimeters and liquefied petroleum jelly was poured into the gap created after spacer removal. The lysimeters were air dried for 150 d, after which two sealed and two unsealed lysimeters were resaturated. All lysimeters were then subjected to a 1‐h rainfall simulation (3.3 cm h−1), with dye added to the rainfall. Rewetting both sealed and unsealed lysimeters resulted in less horizontal dye coverage compared with the dry treatments due to reduced matrix–macropore interaction. Dye staining patterns for unsealed lysimeters showed that edge flow was the predominant flow pathway through the soil regardless of soil moisture status. While sealing lysimeters with petroleum jelly largely limited flow between the soil and the casing, shrinkage cracks formed during drying that coincided with the extent of petroleum jelly infiltration into the soil. This new hydrophobic edge served as a preferential flow pathway in the sealed lysimeters under both dry and rewetted conditions. Findings suggest that maintaining adequate soil moisture before and after petroleum jelly addition is critical to avoid preferential flow along the hydrophobic edge in sealed lysimeters.

Characteristics of hydrophobic and hydrophilic acid fractions in drainage waters of undisturbed soil lysimeters

Dissolved organic matter (DOM), a heterogeneous mixture of low concentrations of organic matter draining from soils, plays a significant role in soil C cycling and in nutrient and pollutant transport. DOM from undisturbed soil profiles has rarely been studied. Hydrophobic acids (Ho) and hydrophilic acids (Hi), the major components of DOM, were recovered, using XAD-8 and XAD-4 resins in series, from waters draining in winter and in spring periods from well-drained and poorly drained Irish grassland soil profiles in lysimeters. Waters were collected from 45 soil undisturbed lysimeters at the Teagasc Research Centre, Johnstown Castle, Wexford, Ireland. Four Irish representative soils had been collected as undisturbed 1.0-m-deep monoliths, transported to the experiment site and arranged randomly in an experimental facility. Water collections were carried out in winter and spring periods. The DOM was isolated and fractionated using an XAD-8 and XAD-4 resins in-tandem procedure, and hydrophobic acids (Ho) and hydrophilic acids (Hi) were isolated. The amounts of DOM recovered in the winter period were much greater than those in the spring period, and the soil types had only minor influences on the DOM concentrations recovered. The Ho and Hi fraction contents ranged from 62 to 90 and 10 to 28%, respectively, of the total DOM content extracted. The Hi acids were most enriched in 13C, and considered to reflect greater microbial inputs. The neutral sugar (NS) contents for the Ho and Hi fractions were in the range of 15 to 52 μg mg−1, with the Hi fraction most enriched. The amino acids (AAs) for the Ho and Hi fractions varied from 0.6 to 2.4%, and the total AAs and NS of the Ho acids were well correlated. The DOM fractions from the drainage waters contained much less AAs and NS than the corresponding fractions in the parent soils. The solid- and liquid-state NMR data indicated organic structures with low aromaticity, significant amounts of carbohydrate and with lesser amounts of peptide structures, and with long-chain methylene (CH2)n and methine (-CH-) groups. The application of a variety of wet chemistry and of spectroscopy procedures has given a more in-depth awareness of the compositions of the DOM in the drainage waters from four different soils in 1.0-m-deep lysimeter arrangements. Based on wet chemistry analyses, and FTIR and liquid- and solid-state NMR spectrometry, it is clear that there are some differences between the compositions of the DOM fractions recovered. Alkyl functionalities dominated the structures. These included significant amounts or O-alkyl (predominantly carbohydrate), and with lesser (and variable amounts in the different fractions) aromatic structures (to which aromatic amino acid components were considered to be significant contributors), and with no evidence for lignin-derived structures The results suggest that, during residence in the soil solution, microbiological processes transform the SOM components released into products that are greatly different from their materials of origin in the SOM.

Interpreting in situ Soil Water Characteristics Curve under Different Paddy Soil Types Using Undisturbed Lysimeter with Soil Sensor

The soil water characteristics curve (SWCC) represents the relation between soil water potential and soil water content. The shape and range of SWCC according to the relation could vary depending on soil characteristics. The objective of the study was to estimate SWCC depending on soil types and layers and to analyze the trend among them. To accomplish this goal, the unsaturated three soils were considered: silty clay loam, loam, and sandy loam soils. Weighable lysimeters were used for exactly measuring soil water content and soil water potential. Two fitting models, van Genuchten and Campbell, were applied. Two models entirely fitted well the measured SWCC, indicating low RMSE and high R2 values. However, the large difference between the measured and the estimated was found at the 30 cm layer of the silty clay loam soil, and the gap was wider as soil water potential increased. In addition, the non-linear decrease of soil water content according to the increase of soil water potential tended to be more distinct in the sandy loam soil and at the 10 cm layer than in the silty clay loam soil and at the lower layers. These might be seen due to the various factors such as not only pore size distribution, but also cracks by high clay content and plow pan layers by compaction. This study clearly showed difficulty in the estimation of SWCC by such kind of factors. Parameters obtained from the Campbell and van Genuchten models and goodness-of-fit results.

Phosphorus Leaching in Soils Amended with Animal Manures Generated from Modified Diets

New dietary modifications for dairy (reducing P content in feed) and poultry (addition of feed additives such as phytase) aim to reduce P excretion in manures. Our objective was to investigate if dietary changes were effective at reducing P leaching loss on land application of manures. We used 54 undisturbed lysimeters (30 cm diameter, 50 cm deep) collected from three typical mid-Atlantic soils. Lysimeters received 85 kg total P ha from fertilizer (superphosphate), dairy manures generated from low- or high-P diets, or broiler litters generated from normal diet or reduced P- and phytase-amended diets. Lysimeters were irrigated with 50 mm of water each week for 9 wk. The major forms of P in the leachate were dissolved (dissolved unreactive > dissolved reactive P [DRP]) rather than particulate (total particulate P). The higher P solubility (100%) in superphosphate resulted in greater leaching of DRP, whereas the lower P solubility (<30%) in dairy manures or broiler litters resulted in lower DRP leaching from soils. Preferential flow in two soils caused greater DRP leaching; this effect was more pronounced in the superphosphate-amended than in the manure/litter-amended lysimeters. The dairy and poultry dietary modification was effective at reducing the amount of P in manures and litters. However, the application of treatments at similar P rate (85 kg ha) resulted in the addition of a higher amount of manure (54-66%) in lysimeters that received low-P dairy manure-amended and phytase-amended broiler litter, which then controlled P leaching from soils.

Managing Phosphorus Leaching in Mid‐Atlantic Soils: Importance of Legacy Sources

Core Ideas Higher P leaching from P‐saturated mid‐Atlantic soils. Preferential flow caused more P leaching in fine‐textured soils. Matrix flow reduced P leaching from coarse‐textured soils. Use both P saturation ratio and flow pathways to predict the risk of P leaching. Application of phosphorus (P) inputs to soils saturated with legacy P can significantly increase the risk of P leaching and deteriorate water quality. Our objectives were to quantify the effect of soil type and extent of P saturation on P leaching and determine the suitability of a rapid, inexpensive soil P saturation test for use in P leaching risk assessment protocols. We collected 18 undisturbed lysimeters (30‐cm diameter, 50 cm deep), using a tractor‐mounted corer, from three typical mid‐Atlantic soils in Delaware, where P leaching is a concern. The soils were selected on the basis of Mehlich‐3 P saturation ratio (M3‐PSR) of optimum (&lt;0.10) to environmental (&gt;0.15) thresholds. Lysimeters were irrigated with the equivalent of 50 mm of water each week for a total of 16 wk. Concentrations of dissolved reactive P (DRP) and total P in leachate were not significantly different between optimum and environmental M3‐PSR lysimeters before fertilizer application (Weeks 1–8). However, concentrations of DRP and total P significantly increased after fertilizer application at 85 kg P ha−1 (Weeks 9–16) in the environmental M3‐PSR lysimeters. Among three soils in both M3‐PSR categories, concentrations and loads of P leached were higher from the Matapeake silt loam and Pocomoke sandy loam due to preferential leaching that limited contact of flowing water and P with the soil P‐fixing constituents (Fe, Al, and Ca), while P leaching was lower from Woodstown sandy loam due to matrix flow that resulted in greater interaction of water and P with the soil constituents. These results provide clear evidence of a greater risk of P leaching from P‐saturated soils with preferential flow pathways and show that the M3‐PSR along with information about preferential flow pathways should be used to predict the risk of P leaching.

Parameterizing a Dynamic Architectural Model of the Root System of Spring Barley from Minirhizotron Data

The development of models describing water and nutrient fluxes to and through 3‐D spatially resolved root structures in soils brings along the need to predict or describe the root architecture and root growth in detail. However, detailed data to calibrate and validate such architecture and growth models is typically not available. Here, we investigate the sensitivity of the root architecture model RootTyp to changes in its model parameters and reconstructed the root system architecture of barley (Hordeum vulgare L.) growing in an undisturbed lysimeter using minirhizotron images at four different depths. Root arrival curves from a series of minirhizotron images were used to parameterize RootTyp using a range of realistic architectures. We adjusted a simple architecture to the data, which contained only long primary roots starting from the seed. This simple model unfortunately could not reproduce the observed increase of root density with depth. The model was subsequently improved by allowing root branching and elongation to be horizon‐dependent and by making reiteration of root tips possible. Reiteration is an alternative form of branching, where secondary roots can become as long and thick as primary roots. Our results show that minirhizotron data do not contain enough information to warrant identification of the parameters governing these processes, as the additional parameters act similarly on data characteristics as the initial ones. Therefore, different experimental techniques should be combined to constrain the model parameters better in the future.

Impact of soil water regime on degradation and plant uptake behaviour of the herbicide isoproturon in different soil types

The environmental fate of the worldwide used herbicide isoproturon was studied in four different, undisturbed lysimeters in the temperate zone of Middle Europe. To exclude climatic effects due to location, soils were collected at different regions in southern Germany and analyzed at a lysimeter station under identical environmental conditions. 14C-isoproturon mineralization varied between 2.59% and 57.95% in the different soils. Barley plants grown on these lysimeters accumulated 14C-pesticide residues from soil in partially high amounts and emitted 14CO 2 in an extent between 2.01% and 13.65% of the applied 14C-pesticide. Plant uptake and 14CO 2 emissions from plants were inversely linked to the mineralization of the pesticide in the various soils: High isoproturon mineralization in soil resulted in low plant uptake whereas low isoproturon mineralization in soil resulted in high uptake of isoproturon residues in crop plants and high 14CO 2 emission from plant surfaces. The soil water regime was identified as an essential factor that regulates degradation and plant uptake of isoproturon whereby the intensity of the impact of this factor is strongly dependent on the soil type.

Impact of tillage on solute transport in a loamy soil from leaching experiments

Soil tillage practices can affect water flow and solute transport processes dynamically in space and in time. However, the relationship between tillage practices and flow and transport in soils is not yet well understood. Within this paper, we analyze the short term impact of the conversion from conventional mouldboard ploughing (CT) to reduced disc harrowing (RT) on the solute transport process within a loamy soil. Solute breakthrough experiments at two flow rates were performed on 2 undisturbed lysimeter collected in a CT and RT field plot. Solute transport parameters were estimated using transfer function theory. Important differences in solute transport were observed between the RT and the CT treatments. The CT treatment exhibited a rapid, more homogeneous and less dispersive solute transport as compared to the RT treatment. These results are explained by the changes in soil structure due to tillage and compaction. The dominant transport was identified as being a stochastic-convective process in both lysimeters. The similarity of the mixing regime for the two soil columns can be explained by preferential solute trajectories activated within structural macropores as a result of the high flow rates applied. We show that the relationship between tillage practices and transport is complex, not only scale and time dependent but also influenced by the boundary conditions and tillage practices.

Modeling water flow and bacterial transport in undisturbed lysimeters under irrigations of dairy shed effluent and water using HYDRUS-1D

HYDRUS-1D was used to simulate water flow and leaching of fecal coliforms and bromide (Br) through six undisturbed soil lysimeters (70 cm depth by 50 cm diameter) under field conditions. Dairy shed effluent (DSE) spiked with Br was applied to the lysimeters, which contained fine sandy loam layers. This application was followed by fortnightly spray or flood water irrigation. Soil water contents were measured at four soil depths over 171 days, and leachate was collected from the bottom. The post-DSE period simulations yielded a generally decreased saturated water content compared to the pre-DSE period, and an increased saturated hydraulic conductivity and air-entry index, suggesting that changes in soil hydraulic properties (e.g. via changes in structure) can be induced by irrigation and seasonal effects. The single-porosity flow model was successful in simulating water flow under natural climatic conditions and spray irrigation. However, for lysimeters under flood irrigation, when the effect of preferential flow paths becomes more significant, the good agreement between predicted and observed water contents could only be achieved by using a dual-porosity flow model. Results derived from a mobile-immobile transport model suggest that compared to Br, bacteria were transported through a narrower pore-network with less mass exchange between mobile and immobile water zones. Our study suggests that soils with higher topsoil clay content and soils under flood irrigation are at a high risk of bacteria leaching through preferential flow paths. Irrigation management strategies must minimize the effect of preferential flow to reduce bacterial leaching from land applications of effluent.

Modeling Transport of Microbes in Ten Undisturbed Soils under Effluent Irrigation

The HYDRUS‐1D mobile–immobile water model (MIM) was used to evaluate the transport of fecal coliforms, Salmonella bacteriophage, and Br in 10 soils. At a flux of 5 mm h−1, a pulse of dairy shed effluent was applied to 30 large undisturbed lysimeters, followed by water irrigation. Soil types included clayey gley soil, clay loam, silt loam, silt loam over gravels, fine sandy loam, dune sand soil, pumice soil, and allophanic soil. Except for dune sand, modeling results showed lower mobile water contents and dispersivities for microbes than for Br, indicating the exclusion of microbes from smaller pores. The MIM‐derived removal rates were in the order: volcanic soils &gt; greywacke‐derived silt loams &gt; granular young sandy soils, and were the most variable in clayey gley loam and silt loam over gravels. Microbial reduction was 100% in allophanic soil, 16 to 18 log m−1 in pumice soil (where the unit log is the log10 reduction in maximum concentration compared with the original concentration), and was lowest in clayey gley soil (0.1–2 log m−1). For most of the other soils, the reduction was 2 to 3 log m−1, except for 9 to 10 log m−1 for fecal coliforms in a fine sandy loam. The detachment rate was only 1% of the attachment rate, indicating irreversible attachment of microbes. Soil structure (macroporosity) appeared to play the most important role in the transport of microbes and Br, while soil lithology had the greatest influence on attenuation and mass exchange. The general pattern of predicted mobile water content agrees with the measured macroporosity, which is positively related to leaching vulnerability but negatively related to dispersivity.

Influence of organic amendments on diuron leaching through an acidic and a calcareous vineyard soil using undisturbed lysimeters

The influence of different organic amendments on diuron leaching was studied through undisturbed vineyard soil columns. Two composts (A and D), the second at two stages of maturity, and two soils (VR and Bj) were sampled. After 1 year, the amount of residues (diuron + metabolites) in the leachates of the VR soil (0.19–0.71%) was lower than in the Bj soil (4.27–8.23%), which could be explained by stronger diuron adsorption on VR. An increase in the amount of diuron leached through the amended soil columns, compared to the blank, was observed for the Bj soil only. This result may be explained by the formation of mobile complexes between diuron and water-extractable organic matter (WEOM) through the Bj soil, or by competition between diuron and WEOM for the adsorption sites in the soil. For both soils, the nature of the composts and their degree of maturity did not significantly influence diuron leaching.

Evaluation of probabilistic modelling approaches against data on leaching of isoproturon through undisturbed lysimeters

This study evaluated probabilistic modelling approaches against data on leaching of isoproturon through two contrasting soil types. Leaching through undisturbed lysimeters from a sandy loam (Wick series) and a moderately structured clay loam (Hodnet series) was investigated in seven replicates. The variability of soil properties and of sorption and degradation of isoproturon was estimated by taking 6–14 samples within the areas of lysimeter extraction in the field. Normal distributions were assigned to Koc and DT50 and a large number of values for these two parameters were sampled from each distribution. Parameter values were used to simulate movement of isoproturon through the lysimeters with the preferential flow model MACRO. Uncertainty in output distributions was compared with the variability of measured data. A constrained probabilistic assessment varying only degradation and sorption properties was sufficient to match the observed variability in cumulative leaching from the coarse-textured Wick soil (CV = 79%). Variation of pesticide properties alone could not match observed variability in cumulative leaching from the structured Hodnet soil (CV = 61%) and variability in a number of soil properties was incorporated. For both soils, constrained probabilistic approaches where only the top few most sensitive model inputs were varied were sufficient to match or exceed observed variability.

Construction and Performance of Large Soil Core Lysimeters

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

Lysimeter study to investigate the effect of rainfall patterns on leaching of isoproturon.

The influence of five rainfall treatments on water and solute leaching through two contrasting soil types was investigated. Undisturbed lysimeters (diameter 0.25 m, length 0.5 m) from a sandy loam (Wick series) and a moderately structured clay loam (Hodnet series) received autumn applications of the radio-labelled pesticide isoproturon and bromide tracer. Target rainfall plus irrigation from the end of November 1997 to May 1998 ranged from drier to wetter than average (235 to 414 mm); monthly rainfall was varied according to a pre-selected pattern or kept constant (triplicate lysimeters per regime). Leachate was collected at intervals and concentrations of the solutes were determined. Total flow (0.27-0.94 pore volumes) and losses of bromide (3-80% of applied) increased with increasing inputs of water and were larger from the Wick sandy loam than from the Hodnet clay loam soil. Matrix flow appeared to be the main mechanism for transport of isoproturon through the Wick soil whereas there was a greater influence of preferential flow for the Hodnet lysimeters. The total leached load of isoproturon from the Wick lysimeters was 0.02-0.26% of that applied. There was no clear variation in transport processes between the rainfall treatments investigated for this soil and there was an approximately linear relationship (r2 = 0.81) between leached load and total flow. Losses of isoproturon from the Hodnet soil were 0.03-0.39% of applied and there was evidence of enhanced preferential flow in the driest and wettest treatments. Leaching of isoproturon was best described by an exponential relationship between load and total flow (r2 = 0.62). A 45% increase in flow between the two wettest treatments gave a 100% increase in leaching of isoproturon from the Wick soil. For the Hodnet lysimeters, a 35% increase in flow between the same treatments increased herbicide loss by 325%.

Chemical availability of 137Cs and 90Sr in undisturbed lysimeter soils maintained under controlled and close-to-real conditions

Chemical availability of 137Cs and 90Sr was determined in four undisturbed soils in a lysimeter study three and four years after deposition to the soil surface. The study was part of a larger project on radionuclide soil–plant interactions under well-defined conditions. The soil types were loam, silt loam, sandy loam and loamy sand, and were representatives of important European soil and climatic conditions. The lysimeters were installed in greenhouses with climatic and hydrological control, and were contaminated with 137Cs and 90Sr in an aerosol mixture simulating fallout from a nuclear accident. Soil samples were taken from several depths in each soil in 1997 and 1998 and the samples were sequentially extracted with H 2O, NH 4Ac, NH 2OH·HCl, H 2O 2 and HNO 3. Extractability of 137Cs decreased in the order: HNO 3>Residual⩾NH 4Ac>H 2O 2⩾NH 2OH·HCl⩾H 2O. More than 80% was found in the acid digestible or residual fractions, and 11–17% in labile fractions. Soil type differences were small. Extractability of 90Sr decreased in the order: NH 4Ac>NH 2OH·HCl>HNO 3>H 2O 2≈H 2O. 31–58% was found in easily available fractions. Differences between soil types were quite small. The results suggest that availability of 137Cs for plant uptake and migration is low, whereas availability of 90Sr is rather high.

Leaching of pesticides and a bromide tracer through lysimeters from five contrasting soils

In each of two seasons, undisturbed lysimeters 0.8 m in diameter and 1.05 m in length taken from five soil types were cropped with winter wheat. They received autumn applications of the pesticides isoproturon and linuron as well as a bromide tracer and spring applications of dimethoate and MCPA. Leachate was collected at regular intervals and concentrations of the various solutes determined. Rainfall from December to March was 290 and 191 mm in the first and second seasons, respectively. Both springs were exceptionally dry with less than 50% of the mean April-to-June rainfall of 138 mm. Total flow from the lysimeters ranged from 335 to 477 mm (and from 0.78 to 3.95 pore volumes) over the two seasons. Leaching to drainage of bromide highlighted soils where preferential flow was influential with total losses ranging from 24% of applied for a strongly structured, alluvial clay loam to 79% for an unstructured sand. Leaching to drainage of isoproturon (Koc ≈ 100 ml g−1) was observed from all but a peat soil with losses greater (0.31–1.01% of applied) from the clay loam and a deep medium loam, where patterns of leaching clearly indicated preferential flow mechanisms, than from the sand and a light loam over gravel (0.04–0.18% of applied) where a broad breakthrough curve indicated that matrix flow was more important. Linuron (Koc ≈ 500 ml g−1) was detected in occasional samples of leachate from the clay loam, the light loam over gravel and the medium loam during the first season only (maximum loss 0.12% of applied). The sandy soil, often considered most vulnerable to leaching, gave the smallest total losses of pesticide of the four mineral soils, whilst significant preferential flow in the deep, medium loam was believed to result from a compacted topsoil. Neither of the spring-applied pesticides was detected in the leachate, as flow following application was very small and relatively slow. © 2000 Society of Chemical Industry