Herbicide Leaching Research Articles

Urea Fertilizer and pH Influence on Sorption Process of Flumetsulam and MCPA Acidic Herbicides in a Volcanic Soil.

The aim of this study was to evaluate the influence of urea fertilizer and pH on the sorption process of two acidic herbicides, flumetsulam (2',6'-difluoro-5-methyl[1,2,4]triazolo[1,5-a]pyrimidine-2-sulfonanilide) and MCPA (4-chloro--tolyloxyacetic acid), on an Andisol. Urea reduced the adsorption of MCPA but not that of flumetsulam. The Freundlich parameter of MCPA decreased from 8.5 to 5.1 mg L kg. This finding could be attributed to an increase in dissolved organic C due to an initial increase in soil pH for urea application. The higher acidic character of MCPA compared with that of flumetsulam produced a greater hydrolysis of urea, leading to a further pH increase. A marked effect of pH on the adsorption of both herbicides was observed. The organic C distribution coefficient () values for flumetsulam were in the range of 74 to 10 L kg, while those of MCPA were in the range of 208 to 45 L kg. In the kinetic studies, the pseudo-second-order model appeared to fit the data best ( > 0.994). The initial adsorption rates () ranged from 20.00 to 4.59 mg kg h for flumetsulam and from 125.00 to 25.60 mg kg hfor MCPA. Both herbicides were adsorbed rapidly during the first stage of the sorption process, and the rates of sorption were dependent on pH. The application of the Elovich and Weber-Morris models led us to conclude that mass transfer through the boundary layer and, to a lesser degree, intraparticle diffusion were influenced by the chemical character of the herbicide. These results suggest that urea application could increase leaching of acid herbicides in soils.

MOBILIDADE DO SULFENTRAZONE EM SOLOS COM DIFERENTES CARACTERÍSTICAS FÍSICAS E QUÍMICAS

RESUMO O conhecimento dos fatores que influenciam a lixiviação dos herbicidas no solo é fundamental para sua utilização de forma segura, do ponto de vista técnico e ambiental. Neste trabalho, avaliou-se a mobilidade do sulfentrazone em quatro solos provenientes de uma área de reflorestamento da região Sul do Brasil (Planossolo Háplico, Argissolo Vermelho, Cambissolo Húmico e Neossolo Regolítico) e um Latosso Vermelho-Amarelo da Zona da Mata de Minas Gerais. As amostras de solo foram coletadas na profundidade de 0-20 cm e caracterizadas física e quimicamente. Os substratos foram colocados em colunas e, posteriormente, aplicou-se, nos topos delas, 1,0 kg ha-1 do herbicida, seguido de uma chuva simulada de 60 mm. Após a drenagem da água, foram semeadas ao longo da coluna sementes da espécie Sorghum bicolor , como planta bioindicadora da presença do sulfentrazone; 21 dias após o plantio, foi realizada a avaliação visual da intoxicação das plantas de sorgo e a coleta da parte aérea delas para determinação da matéria seca. O delineamento utilizado foi o inteiramente casualizado, em esquema de parcelas subdivididas. As colunas preenchidas com cada um dos solos constituíram as parcelas, e as 10 profundidades da coluna (0-5, 5-10, 10-15, 15-20, 20-25, 25-30, 30-35, 35-40, 40-45 e 45-50 cm), as subparcelas, mais uma testemunha sem herbicida para cada solo. Os teores de argila e matéria orgânica e o pH de cada solo influenciaram na mobilidade do sulfentrazone; solos com menores teores de argila e matéria orgânica apresentaram maior potencial de lixiviação desse herbicida.

Carboxymethyl starch/montmorillonite composite microparticles: Properties and controlled release of isoproturon

Preparation of novel high substituted carboxymethyl starch-based microparticles containing sodium montmorillonite (MMT) by crosslinking with Al3+ was described. For preparing nanocomposite granules carboxymethyl starch (CMS) from native potato starch as well as CMS from amylopectin has been used. The hydrophilic CMS/MMT composite systems were used for herbicide, i.e. isoproturon encapsulation (ca. 75% encapsulation efficiency). The herbicide release rate from CMS/MMT composites in water was significantly reduced when compared to commercial isoproturon: 95% released after ca. 700h and ca. 24h, respectively. Leaching in soil from composite systems was relatively slower than release in water. After a series of eight irrigations leached about 10% of isoproturon loaded. The CMS/MMT carriers could reduce the potential leaching of herbicide and beneficially reduce pollution of the environment.

Herbicide and Mulch Interactions: A Review of the Literature and Implications for the Landscape Maintenance Industry

Use of organic mulch is one of the most common methods of weed control in landscape planting beds and provides other benefits, including improved soil characteristics, increased growth of ornamental plants, and enhanced property aesthetics. In the landscape maintenance industry, it is common to apply mulch and herbicides concurrently to landscape beds to provide long-term, broad-spectrum weed control. It is known that herbicides behave differently when applied to different soil types and organic materials; however, research is lacking concerning which herbicides are most effective with different mulch materials in the landscape. Determining the most effective herbicide–mulch combinations could potentially improve weed control, reduce labor costs from hand weeding, and mitigate negative environmental impacts resulting from off-site herbicide movement. The objective of this paper is to review the research that has been conducted pertaining to various mulch–herbicide combinations in the landscape and in other areas of agricultural production while also identifying key knowledge gaps that should be addressed in future research. Review of the literature suggests satisfactory weed control can be achieved with high mulch depths (≥ 7 cm) regardless of herbicide use, and herbicide–mulch interactions become more pronounced as mulch depth decreases. Additionally, future research is needed to determine which herbicides are best suited for different mulch types to improve weed control and potentially reduce environmental impacts, including herbicide leaching and runoff into urban and suburban waterbodies.

Quantidade de chuva e lixiviação do herbicida metribuzin através de planta bioindicadora

RESUMO Objetivou-se, neste trabalho, avaliar o potencial de lixiviação do herbicida metribuzin com precipitações pluviométricas naturais, em dois solos com texturas contrastantes, argiloso e médio arenoso, em condições de campo, através de planta bioindicadora. Colunas de PVC foram introduzidas nos dois solos. Manteve-se a integridade original do solo durante a coleta das amostras, que ocorreu após o acúmulo das precipitações em um intervalo estipulado ao ambiente entre 30-40, 60-80 e 100-120 mm de chuva. As colunas foram separadas com corte longitudinal para a semeadura da espécie bioindicadora (25 plantas). Após a semeadura avaliações de fitotoxicidade das plantas bioindicadoras foram realizadas aos 5, 7, 10 e 12 dias após a semeadura, através de uma escala de notas de 0 a 100%. A lixiviação do herbicida metribuzin foi dependente da precipitação recebida para os dois tipos de solo estudados. A eficácia da planta bioindicadora dependeu do tipo de solo e da precipitação. A metodologia de utilização de plantas bioindicadoras mostrou-se eficiente para avaliação da mobilidade de herbicida no perfil do solo.

Leaching Behavior of Two Pendimethalin Formulations in a Soilless Growing Medium

Pendimethalin is commonly applied for PRE weed control in container nursery production. Field and laboratory trials were conducted to determine herbicide effectiveness and leaching of two pendimethalin formulations in pine bark, the primary component used in the growing medium of container-grown plants in the South. The microencapsulated (ME) formulation of pendimethalin gave lower control of southern crabgrass and leached deeper than the emulsifiable concentrate (EC) formulation in pine bark. The EC formulation controlled southern crabgrass 93% compared with only 70% with the ME formulation at 4.48 kg ai ha−1. After applying 3.4 kg ai ha−1pendimethalin and 17.8 cm of irrigation water, the ME formulation showed greater leaching into the 3- to 6- and 6- to 9-cm depths than the EC formulation on the basis of a southern crabgrass bioassay. Using a microwave extraction method, only 0.91 mg kg−1pendimethalin was found in the 3- to 6-cm pine bark depth compared with 4.0 mg kg−1for the ME formulation. Below the 6-cm depth, no pendimethalin was detected when the EC formulation was applied, but 0.5 ppm was found for the ME formulation. No pendimethalin was detected in effluent collected from irrigation water for the EC; however, 3.0 mg kg−1was collected from leachate for the ME formulation. Pendimethalin ME is leaching much deeper than the EC formulation in the pine bark profile, which results in lower weed control. This extensive leaching of ME formulation may be due to capsule movement with the irrigation water, combined with a delayed release of pendimethalin, which then binds to the pine bark much lower in the container profile.

Comparison of three pesticide fate models with respect to the leaching of two herbicides under field conditions in an irrigated maize cropping system

The ability of three models (PEARL, MACRO and PRZM) to describe the water transfer and leaching of the herbicides S-metolachlor and mesotrione as observed in an irrigated maize monoculture system in Toulouse area (France) was compared. The models were parameterized with field, laboratory and literature data, and pedotransfer functions using equivalent parameterization to better compare the results and the performance of the models. The models were evaluated and compared from soil water pressure, water content and temperature data monitored at 0.2, 0.5 and 1m depth, together with water percolates and herbicide concentrations measured in a tension plate lysimeter at 1m depth. Some hydraulic (n, θs) parameters and mesotrione DT50 needed calibration. After calibration, the comparison of the results obtained by the three models indicated that PRZM was not able to simulate properly the water dynamic in the soil profile. On the contrary, PEARL and MACRO simulated generally quite well the observed water pressure head and volumetric water content at the three different depths during wetting periods (e.g. irrigated cropping period) while a poorest performance was obtained for drying periods (fallow period with bare soil and beginning of crop period). Similar water flow dynamics were simulated by PEARL and MACRO in the soil profile although in general, and due to a higher evapotranspiration in MACRO, PEARL simulated a wetter soil than MACRO. For the whole simulated period, the performance of all models to simulate water leaching at 1m depth was poor, with an overestimation of the total water volume measured in the lysimeter (ranging from 2.2 to 6.6 times). By contrast, soil temperature was properly reproduced by the three models. The models were able to simulate the leaching of herbicides at 1m depth in similar appearance time and order of magnitude as field observations. Cumulative observed and simulated mesotrione losses by leaching were consistently higher than the observed and simulated losses of the less mobile herbicide, S-metolachlor. In general, PRZM predicted the highest concentrations for both herbicides in the leachates while PEARL simulated the observed herbicide concentrations better than MACRO and PRZM.

Long-term effects of olive mill waste amendment on the leaching of herbicides through undisturbed soil columns and mobility under field conditions

Olive mill waste has recently been proposed for use as soil amendment in Mediterranean environments because of its potential for soil carbon sequestration, improving the soil’s quality and productivity. MCPA and S-metolachlor are herbicides applied worldwide in agricultural soils. They readily leach down to lower soil depths. The aim of this study was to evaluate the impact of oiled and de-oiled olive mill waste amendments (OW and DW, respectively) on the sorption, leaching through undisturbed soil columns, and movement and persistence of MCPA and S-metolachlor under real field conditions, in a sandy clay loam soil with low organic matter content which had received addition of these wastes for nine years. The soil had been amended with 30 and 60Mgha−1yr−1 of OW (OW30 and OW60) and 27 and 54Mgha−1yr−1 of DW (DW27 and DW54). The OW or DW addition resulted in significantly enhanced sorption and sorption irreversibility for both herbicides. Compared with unamended soils, leaching losses of the herbicides were reduced in the undisturbed soil columns by 84 and 97% of the applied MCPA and by 85 and 92% of the applied S-metolachlor for the OW60 and DW54 amended soils, respectively, despite the greater volume of soil macropores in OW and DW-amended soils. Under field conditions, slower vertical movement was observed for MCPA and especially for S-metolachlor in the OW- and DW-amended than in the unamended soil profiles. While the OW and DW addition extended the field persistence of S-metolachlor, increasing its half-life from 53 to 69 and 63 days for unamended, OW60, and DW54 soils, respectively, MCPA dissipation was not significantly affected by these amendments. The results suggest that previous laboratory persistence studies performed in unamended, OW, and DW-amended soils might have underestimated the real half-lives of herbicides in the field. Both OW and DW addition could be beneficial in reducing the mobility of MCPA and S-metolachlor in agricultural soils with low organic matter content, thus, decreasing the risk of groundwater contamination by these herbicides.

The Role of Sugarcane Residues in the Sorption and Leaching of Herbicides in Two Tropical Soils

Sugarcane is a major crop in Brazil that generates huge amounts of organic residues that are usually left deposited in, or applied to the soil, and thereby affect the behavior of herbicides. This study assessed the effects of sugarcane residues (straw, ash, and compost) and residence time (“aging”) on the sorption of alachlor and diuron in two contrasting soils (LVd and LVAd), as well as the effects of these residues on the leaching of alachlor. Adding straw and compost had no effect, whereas adding ash significantly increased sorption of both herbicides. Aging (28 days) increased apparent sorption distribution coefficients (K d,app values) by 1.2 to 2.3 times. Straw and ash amendments resulted in less leaching of alachlor (<1.0 % of the applied amount) than compost or control soil (~6 % of the applied amount). The straw retained ~80 % of the applied alachlor during leaching. Although this may be overrated due to an artifact of the methodology adopted, alachlor retention in the straw could not be predicted by the use of K d,app. The transport potential of alachlor may be overestimated if aging and sugarcane straw management are not factored into the models.

Effect of fly ash on metsulfuron-methyl sorption and leaching in soils

This investigation was undertaken to determine the effect of amendment of two fly ashes [Kota and Inderprastha (IP)] on sorption behavior of metsulfuron-methyl in three Indian soil types. Kota fly ash (5%) did not show any effect on herbicide sorption while IP fly ash significantly enhanced the sorption. Further studies on metsulfuron-methyl sorption-desorption behavior in 0.5, 1, 2, and 5% IP fly ash-amended soils suggested that effect of fly ash varied with soil type and better effect was observed in low organic carbon content soils. The sorption-desorption isotherms fitted very well to the Freundlich sorption equation and, in general, slope (1/n) values less than unity were observed. Metsulfuron-methyl sorption in the IP fly ash-amended soils showed strong correlation with the fly ash content and compared to the Freundlich sorption constant (K f), K FA values (sorption normalized to fly ash content) showed less variation. Metsulfuron-methyl leaching studies suggested greater retention of herbicide in the application zone in IP fly ash-amended soils, but effect varied with soil type and no herbicide leaching was observed in 5% fly ash-amended soils. The study suggested that all coal fly ashes are not effective in enhancing the sorption of metsulfuron-methyl in soils. However, one which enhanced herbicide sorption, could play an important role in reducing its leaching losses.

Reduced Herbicide Leaching by in Situ Adsorption of Herbicide–Micelle Formulations to Soils

Aiming to reduce herbicide leaching, "in situ" adsorption of herbicide-micelle formulations to soils was explored. Sulfentrazone or metolachlor were solubilized in cationic micelles, and these herbicide-micelle formulations were applied to sandy and alluvial soils. Sulfentrazone adsorption to the soils was negligible; however, its adsorption via its solubilization in micelles and their adsorption to the soil was significant and in good agreement with the Freundlich and Langmuir models. Adsorption of solubilized herbicide to the sandy soil was higher than to the alluvial soil. The low ratio between the surfactant concentration and the cation exchange capacity (CEC) of the alluvial soil brought upon micelle decomposition and reduction in herbicide adsorption. Therefore, an optimized ratio between surfactant and soil CEC was chosen to maximize herbicide retention. Even upon adding relatively low loadings of surfactant (0.075-0.3% w/w soil), herbicide leaching through the soils was significantly reduced (2-5-fold) in comparison with the commercial formulations.

Spatial variation in herbicide leaching from a marine clay soil via subsurface drains

BackgroundSubsurface transport via tile drains can significantly contribute to pesticide contamination of surface waters. The spatial variation in subsurface leaching of normally applied herbicides was examined together with phosphorus losses in 24 experimental plots with water sampled flow-proportionally. The study site was a flat, tile-drained area with 60% marine clay in the topsoil in southeast Sweden. The objectives were to quantify the leaching of frequently used herbicides from a tile drained cracking clay soil and to evaluate the variation in leaching within the experimental area and relate this to topsoil management practices (tillage method and structure liming).ResultsIn summer 2009, 0.14, 0.22 and 1.62%, respectively, of simultaneously applied amounts of MCPA, fluroxypyr and clopyralid were leached by heavy rain five days after spraying. In summer 2011, on average 0.70% of applied bentazone was leached by short bursts of intensive rain 12 days after application. Peak flow concentrations for 50% of the treated area for MCPA and 33% for bentazone exceeded the Swedish no-effect guideline values for aquatic ecosystems. Approximately 0.08% of the glyphosate applied was leached in dissolved form in the winters of 2008/2009 and 2010/2011. Based on measurements of glyphosate in particulate form, total glyphosate losses were twice as high (0.16%) in the second winter. The spatial inter-plot variation was large (72–115%) for all five herbicides studied, despite small variations (25%) in water discharge.ConclusionsThe study shows the importance of local scale soil transport properties for herbicide leaching in cracking clay soils. © 2013 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Bentonite and anthracite in alginate-based controlled release formulations to reduce leaching of chloridazon and metribuzin in a calcareous soil

The leaching of herbicides through soil can be minimized using controlled release formulations (CRFs). In this research, bentonite and anthracite have been used as modifying agents in alginate-based CRFs prepared with chloridazon and metribuzin. These CRFs have been evaluated in a calcareous soil. The Kf and Koc values obtained from sorption experiments in soil have demonstrated a high leaching potential for both herbicides, mainly for metribuzin. Release kinetics in soil have showed that the control of release rate of chloridazon and metribuzin was possible by using bentonite and anthracite in CRFs, being this effect greater when we use anthracite as modifying sorbent. Using an empirical equation, the time taken for 50% of the active ingredient to be released (T50(soil)) was calculated. T50 values ranged between 2.88d for metribuzin-bentonite alginate-based granules and 14.37d for chloridazon-anthracite alginate-based granules, being the release rate higher in metribuzin CRFs than in those prepared with chloridazon, which has lower water solubility. Besides, a linear correlation between T50 values in water and soil was obtained. Mobility experiments carried out in a calcareous soil have shown that the use of CRFs reduces the presence of herbicides in the leachate compared to technical products, mainly for chloridazon. We found that one could design a right profile in the release rate of active ingredients from CRFs in each agro-environmental situation, and thus prevent the environmental pollution derived from the use of chloridazon and metribuzin.

Effectiveness of low-temperature biochar in controlling the release and leaching of herbicides in soil

Biochars, being good sorbents of organic compounds, can reduce the mobility of pesticides in soil and subsequent pollution to groundwater, but may also impact on the efficacy of soil-applied herbicides. The aim of this study is to seek a potential solution to this problem. We prepared a wood biochar at a relatively low heat treatment temperature (350 °C), and used it as an adsorptive carrier for incorporating the herbicides 2,4-D and acetochlor, and also as a soil amendment. Release experiment through a thin soil layer and leaching experiment through a soil column were used to evaluate the effectiveness of the biochar for controlling the release and leaching of herbicides in soil. The release experiments demonstrated that the low-temperature biochar could control the release of herbicides in soil, and the leaching experiments showed that this biochar significantly reduced the leached amount of herbicides by 1/2 ~ 3/4, depending on the depth (5 ~ 15 cm) of biochar-amended topsoil. High retention of herbicides in the biochar-amended topsoil was observed. The results suggest that the low temperature biochar, if applied properly in soil, may be useful for extending the efficacy of herbicides while controlling their potential pollution.

Mobilidade do ametryn em latossolos brasileiros

O conhecimento dos fatores que influenciam a lixiviação dos herbicidas no solo possibilita o uso seguro do produto do ponto de vista ambiental, além de ser fundamental para que se façam recomendações tecnicamente corretas. Objetivou-se com este trabalho avaliar a lixiviação do ametryn em quatro solos brasileiros, com diferentes características físico-químicas, e comparar o método cromatográfico com o biológico em estudos de mobilidade desse herbicida. Os substratos avaliados foram: Latossolo Vermelho-Amarelo (LVA) pH 5,40 e pH 6,11, Latossolo Vermelho-Amarelo húmico (LVAh) pH 4,8 e pH 6,24, Latossolo Vermelho (LV) pH 5,00 e pH 6,06 e Latossolo Amarelo (LA) pH 6,30 e 10 profundidades na coluna (0-5, 5-10, 10-15, 15-20, 20-25, 25-30, 30-35, 35-40, 40-45 e 45-50 cm), mais uma testemunha de cada substrato sem aplicação do herbicida, com quatro repetições. Os substratos foram colocados em colunas devidamente preparadas para estudos de mobilidade. A espécie Cucumis sativus foi utilizada como bioindicadora da presença do ametryn. Concluiu-se que os teores de matéria orgânica e pH dos solos avaliados foram as características que mais interferiram na mobilidade do ametryn e que o ensaio biológico se mostrou eficiente como indicador da lixiviação desse herbicida nas colunas. Comprovou-se que o método biológico por bioensaios pode ser utilizado como método preliminar ou complementar ao método instrumental, visando à confirmação de resultados e, ou, redução de custos e tempo das análises.

Use of Rice Straw Biochar Simultaneously as the Sustained Release Carrier of Herbicides and Soil Amendment for Their Reduced Leaching

The sustained release and reduced leaching of herbicides is expected for enhancing their efficacy and minimizing their pollution. For this purpose, the rice straw biochar made at a relatively low temperature (350 °C) (RS350) was used simultaneously as the carrier for incorporating herbicides besides as the soil amendment. In this way, the sustained release of herbicides acetochlor and 2,4-D was obtained in the release experiments, due to the high and reversible sorption by RS350 biochar. Besides, the RS350 biochar significantly reduced the leached amount of herbicides by 25.4%-40.7% for acetochlor, and by 30.2%-45.5% for 2,4-D, depending on the depth (50 or 100 mm) of biochar-amended soil horizon. The high retention of both herbicides in the biochar-amended topsoil makes it possible to extend their efficacy. The results suggest a potential way of using low temperature biochars to reduce the leaching of herbicides without impacting their efficacy.

Sorption of fluorinated herbicides to plant biomass-derived biochars as a function of molecular structure

Biochars produced at different heat treatment temperatures (HTT) are molecularly distinct and thus expected to show variable sorbent characteristics. We investigated the difference in sorption behavior of norflurazon (NORO) and fluridone (FLUN) to biochars from wood and grass feedstocks produced at different HTT. Amorphous biochars (HTT=400°C) exhibited the highest sorption parameter (KOC) for the two herbicides, emphasizing the importance of amorphous structural arrangement of aromatic moieties in these chars. Negative correlation between biochar aromaticity and isotherm nonlinearity (n) suggests that the n values were related mainly to total aromatic C content, not to that in the individual phases. Sorption of FLUN and NORO to low-temperature biochars (HTT=400°C) was about 1100 times and 6400 times greater, respectively, than a sediment sample, confirming that applications of low-temperature biochars to arable soils may reduce the mobility of FLUN and NORO, thus preventing unwanted herbicide leaching and subsequent contamination of sensitive water bodies.

Effects of physicochemical soil properties of five agricultural soils on herbicide soil adsorption and leaching

Once pesticides reach the soil, there are several factors that affect their soil behavior. To identify the principal soil and herbicide properties that control their adsorption and leaching, a study of five Chilean agricultural and forest soils was performed. Simazine, diuron, terbuthylazine and MCPA were applied to the top of 45-cm tall by 12-cm diameter disturbed soil columns, filled with either an Andisol, Ultisol, Entisol or one of two Inceptisol soils. After herbicide applications, each lysimeter received 24 mm of simulated rain every 24 hours for five days. Once water percolation stopped, the lysimeters were divided into five sections and herbicide concentrations were quantified using High Pressure Liquid Chromatography. Relationships between soil physicochemical properties, herbicide sorption (adsorption and desorption) and herbicide leaching were determined. All herbicides exhibited the least depth reached from the Andisol soil (10 cm) and the highest from the Ultisol soil (45 cm). The principal soil property that affected herbicide adsorption was the soil organic carbon content, specifically the fulvic acid-humins fraction. Soil leaching was related to the inverse of soil adsorption (1/Kd), cation exchange capacity, humic substances content and herbicide pKa. These results suggest that it is possible to develop simple quantitative models to predict the soil-leaching properties of pesticides

Lixiviação de sulfentrazone, isoxaflutole e oxyfluorfen no perfil de três solos

O destino de herbicidas aplicados em pré-emergência das plantas daninhas varia de acordo com o solo. Dessa forma, objetivou-se avaliar a lixiviação dos herbicidas sulfentrazone, isoxaflutole e oxyfluorfen no perfil de três solos. As doses de 0,5 e 0,75 kg ha-1 de sulfentrazone, 0,113 e 0,169 kg ha-1 de isoxaflutole e 0,72 e 1,08 kg ha-1 de oxyfluorfen foram aplicadas na superfície de colunas de PVC de 30 cm de altura preenchidas com três solos: um franco-arenoso e dois argilosos com teores alto (9,0 dag kg-1) e baixo (4,4 dag kg-1) de matéria orgânica. Após a aplicação, foram simuladas duas chuvas de 40 mm cada, com intervalo de 24 horas, respeitando o período de infiltração em cada solo. A lixiviação dos herbicidas ao longo do perfil dos solos foi verificada pelo método de bioensaio utilizando plantas de sorgo (Sorghum bicolor). A atividade herbicida do sulfentrazone e a movimentação no perfil dos solos foram elevadas na maior dose aplicada. A maior movimentação descendente do produto, na dose de 0,75 kg ha-1 de sulfentrazone, foi constatada no solo de textura franco-arenosa até 27,5 cm, seguido pelos solos de textura argilosa com baixo e alto teor de matéria orgânica até 25 e 17,5 cm, respectivamente. Verificou-se elevado potencial de lixiviação do isoxaflutole, ultrapassando a profundidade de 22,5 cm nos três solos estudados e nas duas doses aplicadas, diferentemente do oxyfluorfen, que permaneceu adsorvido nas camadas superficiais dos solos. Ao comparar os solos, maior atividade herbicida e movimentação ocorreram naquele de textura franco-arenosa. Em relação aos herbicidas, o isoxaflutole apresentou maior mobilidade do que o sulfentrazone, enquanto o oxyfluorfen mostrou baixo potencial de lixiviação.

A field study of the impact of different irrigation practices on herbicide leaching

Agricultural practices, such as subsurface drainage, irrigation and tillage, may significantly affect pesticide leaching and, consequently, the risk of groundwater contamination. The aim of the present study was to investigate the impact of different irrigation systems on herbicide leaching to shallow groundwater through direct monitoring at the field scale in northern Italy over a 3-year period. Concentrations of the herbicide terbuthylazine (TBA) and its metabolite desethylterbuthylazine (DES) were monitored on 10 farms cropped with maize and irrigated by sprinkler, basin and border systems. Considering the results grouped according to the different irrigation systems, the mean TBA and DES concentrations was lower than the arbitrary non-health based legal limit of 0.1 μg/L using sprinkler and border systems, while it was 0.19 and 0.30 μg/L respectively for TBA and DES using basin systems. However, since many factors other than the irrigation systems can contribute to pesticide leaching and in a field study it is impossible to discriminate between all the different variables, the concentrations of both compounds were simulated with and without irrigation using the model MACRO 5.1 in order to gain a deeper understanding of the role of irrigation on leaching. First, the groundwater table depth, which was measured daily in all fields, was used to calibrate the model and thus achieve a good soil hydrology calibration. To assess the performance of the model the root mean squared error (RMSE) was used. RMSE ranged from 0.2 to 0.5 m, showing that a satisfactory hydrology calibration was obtained. Afterward, the solutes were modelled and the results showed that under non-irrigated conditions, concentrations of both compounds would be very low. These findings validate the hypothesis that careful selection of agricultural practices, such as the type of irrigation, can reduce pesticide leaching.