鱼藤酮在3种土壤中的吸附-解吸附特性

为了综合评价鱼藤酮在土壤环境中的吸附-解吸附特性,采用批量平衡法,系统研究了鱼藤酮在砂壤土、黏壤土及壤土3种农业土壤中的吸附-解吸附行为。结果表明,鱼藤酮在3种土壤中的吸附-解吸附行为符合Freundlich模型 (R2≥0.946 8),吸附常数 (K_f-ads) 在1.52~11.39之间,吸附能力为:黏壤土 > 砂壤土 > 壤土;而解吸附常数 (K_f-des) 在1.02~4.55之间,解吸附强弱次序为壤土 > 黏壤土 > 砂壤土。鱼藤酮在砂壤土、黏壤土和壤土3种土壤中有机碳吸附常数 (K_OC) 分别为982、101 7和219,而滞后系数 (H) 分别为0.687 3、0.556 9和0.892 3,表明鱼藤酮在黏壤土及砂壤土中移动性较弱,有正迟滞作用,而在壤土中移动性较强,无迟滞作用。该研究将对鱼藤酮的环境风险评估具有一定的理论指导意义。     

Adsorption-desorption studies of alachlor, metolachlor, EPTC, chlorothalonil and pirimiphos-methyl in contrasting soils

Five soils with different organic matter contents ranging from 0.48 to 10.4% were used to study the adsorption and desorption of alachlor, metolachor, EPTC, chlorothalonil and pirimiphos-methyl in batch experiments. The isotherm shapes according to Giles classification were S-type for alachlor, metolachlor and chlorothalonil, changing to L-type for the latter as the level of soil organic matter increased, and L-type for EPTC and pirimiphos-methyl. The adsorption isotherms fitted the Freundlich equation x/m = KfCe1/n. The Kf values increased with the increase of organic matter content. The amounts of pesticides adsorbed over a range of concentrations of 0.1-20 mg litre-1 reached 63.1% for alachlor, 69.2% for metolachlor, 89.3% for EPTC, 98.4% for chlorothalonil and 96.3% for pirimiphos-methyl. The increase of the amounts desorbed with acetone indicated that the sorption of organic compounds onto organic matter occurred principally via weak London-type induction forces, or dispersion forces which are characteristics of the physical adsorption process.     

氟噻草胺与氟唑磺隆混配协同作用及在小麦田杂草防治中的应用

本文通过室内生物测定研究了氟噻草胺与氟唑磺隆对小麦及多花黑麦草的活性,田间试验测定了二者混配对阔叶杂草的防效及对小麦分蘖数的影响。室内水培法测定结果表明,氟噻草胺、氟唑磺隆对多花黑麦草有效抑制中剂量(ED50)分别为0.37mg/L和105.91mg/L,氟噻草胺与氟唑磺隆混配比例为8∶2、12∶2、16∶2、20∶2时,共毒系数(CTC)分别为94.3、239.7、198.1、156.5,表明氟噻草胺与氟唑磺隆混用具有相加或增效作用,其中以12∶2、16∶2比例混配对多花黑麦草防治增效最为显著。盆栽试验结果表明,苗前以12∶2和16∶2比例土壤封闭喷施对小麦与多花黑麦草的选择性指数为1.51和1.43;苗后3d及苗后15d茎叶喷施对多花黑麦草与小麦选择性较差,选择性指数低于1。田间测定结果表明,氟噻草胺与氟唑磺隆混配对阔叶杂草荠菜、播娘蒿、婆婆纳防效优于氟噻草胺单独使用,混配条件下株防效为85.45%~100%,鲜重防效为89.57%~100%,对小麦分蘖数无显著影响。     

液相色谱-串联质谱法研究氟噻草胺在大鼠体内组织中的分布行为

建立了大鼠组织中氟噻草胺的液相色谱-串联质谱 (LC-MS/MS) 分析方法,并对其经灌胃给药后在大鼠体内各组织中的分布行为进行了研究。大鼠组织样品经乙腈提取后,采用LC-MS/MS法测定。色谱柱为Phenomenex反向C₁₈色谱柱 (50 mm × 4.6 mm,5 μm),以体积分数为72%乙腈水溶液 (含体积分数为0.1%甲酸) 为流动相,等度洗脱,流速0.6 mL/min。质谱采用电喷雾离子源 (ESI) 及多重反应监测 (MRM) 模式,定量离子对为m/z 364.1/194.2。大鼠心、肝、脾、肺、肾、脑、肌肉、睾丸和脂肪在0.002~0.1 mg/L范围内,大肠、小肠和胃在0.10~10 mg/L范围内,氟噻草胺的质量浓度与对应的峰面积间线性关系良好 (r > 0.99)。质控样品的相对标准偏差均小于11%,基质效应在94.5%~95.6%之间,提取回收率在96%~107%之间,稳定性在95%~104%之间,均符合方法学要求。经单次灌胃给予氟噻草胺400 mg/kg后,其主要分布于大鼠的胃、大肠、小肠和肺中,各组织浓度达峰值后,随着时间延长均可从体内消除。表明氟噻草胺在动物体内分布广泛且降解迅速。本研究建立了一种可用于测定大鼠组织中氟噻草胺浓度的高效、专属、灵敏的LC-MS/MS方法,进而阐明了氟噻草胺的组织分布行为。     

Adsorption-desorption of metalaxyl as affecting dissipation and leaching in soils: role of mineral and organic components

Adsorption-desorption studies of metalaxyl in fifteen agricultural soil samples from Southern Portugal and Spain were performed following a batch equilibration method. Very high sorption was observed on a clay soil of high content in altered illite, but, when this soil was excluded from regression analysis, organic matter (OM) was the most important single soil property affecting sorption at low concentrations of metalaxyl. At higher concentrations, no correlation was observed with any soil property. The relevance of OM on sorption was also corroborated by the increase in sorption coefficients when soil OM was increased artificially by the addition of an organic amendment. Sorption studies with the colloidal fraction of selected soils also revealed the importance of mineral surfaces in metalaxyl sorption. Sorption of metalaxyl in most of the soil samples was hysteretic. Selected soil samples were incubated in the dark, sampled periodically and extracted for their fungicide content. Metalaxyl half-lives increased with sorption and OM content of the soil, and were specially high in the amended soil. Leaching studies in hand-packed columns under saturated/unsaturated flow conditions showed an inverse relation between leaching and sorption. Recoveries from the soil columns were close to 80% of the metalaxyl applied, except for the soil which OM was artificially increased, in which recovery was lower and this has been attributed to the much higher irreversibility of metalaxyl sorption in the amended soil.     

不同肥力土的土壤颗粒分布及其磷素吸附—解析规律

采用干筛法和培养实验,研究了不同肥力土的颗粒分布以及不同颗粒对磷素的吸附、解析规律。结果表明,在所筛分的5个粒径中,土以>5 mm、2～5 mm和0.25～1 mm 3个颗粒为主,随着土壤肥力提高,0.25～1 mm和1～2 mm两个粒径的土壤颗粒有明显增加。土壤颗粒由小到大变化,颗粒中磷素含量呈现由高到低的变化趋势。高肥力土壤和低肥力土壤相比,0.25～1 mm和1～2 mm两个粒径中的磷素含量分别增加40%和43%,差异达显著水平。土壤颗粒愈小对磷的吸附量越高。与土壤原样相比,<0.25 mm和0.25～1 mm两个粒径的颗粒对磷的吸附量高于土壤原样的,而1～2 mm、2～5 mm和>5 mm土壤颗粒对磷的吸附则小于土壤原样的。随着土壤颗粒径变大,磷的解析率增加。总体看来,高肥力土使中等大小土壤颗粒增多,对磷的吸附量有所减少,但对磷的解析量增大,这有助于提高磷肥的有效性,但也增加了磷素径流损失的风险。     

Adsorption,desorption and dissipation of metolachlor in surface and subsurface soils

BACKGROUND: Variations in soil properties with depth influence retention and degradation of pesticides. Understanding how soil properties within a profile affect pesticide retention and degradation will result in more accurate prediction by simulation models of pesticide fate and potential groundwater contamination. Metolachlor is more persistent than other acetanilide herbicides in the soil environment and has the potential to leach into groundwater. Reasonably, information is needed about the dissipation and eventual fate of metolachlor in subsoils. The objectives were to evaluate the adsorption and desorption characteristics and to determine the dissipation rates of metolachlor in both surface and subsurface soil samples. RESULTS: Adsorption of metolachlor was greater in the high‐organic‐matter surface soil than in subsoils. Lower adsorption distribution coefficient (K_ads) values with increasing depth indicated less adsorption at lower depths and greater leaching potential of metolachlor after passage through the surface horizon. Desorption of metolachlor showed hysteresis, indicated by the higher adsorption slope (1/n_ads) compared with the desorption slope (1/n_des). Soils that adsorbed more metolachlor also desorbed less metolachlor. Metolachlor dissipation rates generally decreased with increasing soil depth. The first‐order dissipation rate was highest at the 0–50 cm depth (0.140 week^?1) and lowest at the 350–425 cm depth (0.005 week^?1). Degradation of the herbicide was significantly correlated with microbial activity in soils. CONCLUSION: Metolachlor that has escaped degradation or binding to organic matter at the soil surface might leach into the subsurface soil where it will dissipate slowly and be subject to transport to groundwater. Copyright © 2009 Society of Chemical Industry     

Retention and degradation of metribuzin in sandy loam and clay soils of Lebanon

The retention and degradation of metribuzin herbicide were studied under two environmental conditions. Field studies were carried out on two soils, a sandy loam soil (soil A) and a clay soil (soil B). Metribuzin was applied with a jet sprayer at 1060 g a.i. ha^?1 and 1960 g a.i. ha^?1 on soils A and B respectively. Reconstituted soil columns were used to study the herbicide movement and metabolism in the two soils. Analyses of metribuzin and its metabolites were carried out using standardized methods. The results indicated a very weak capacity of adsorption of metribuzin in the two soils, and the weak adsorbed fraction is easily desorbed. Degradation and mobility of metribuzin in the field and laboratory soil columns were very intense and rapid. Soil A favoured reductive deamination whereas soil B favoured oxidative desulphuration and the respective metabolites deaminometribuzin and diketometribuzin yield the same product deaminodiketometribuzin. Both leaching by rainfall and degradation were important in the disappearance of metribuzin from the soils.     

双氟磺草胺在不同类型土壤中的吸附与淋溶特性研究

农药在土壤中的吸附和淋溶特性是评价其环境行为的重要指标。采用批量平衡法和土柱淋溶法,研究了双氟磺草胺在小麦种植区3种代表性土壤中的吸附和淋溶特性。结果表明:双氟磺草胺在安徽黏土、山东砂质壤土和河南砂质黏壤土中的吸附规律均可以较好地用Freundlich方程描述,其吸附系数(Kf)在0.39~0.62之间;土壤有机碳归一化吸附系数(Koc)在66.91~81.35之间,表明双氟磺草胺在3种土壤中均属于难吸附型;吸附自由能(ΔG)在-10.90~-10.42kJ/mol之间,均属于物理吸附。双氟磺草胺在3种土壤中的淋出率在71.7%~74.1%之间,说明其在3种土壤中的淋溶性均较强。双氟磺草胺初始添加量和腐殖酸对淋出率具有一定影响。综合试验结果,认为双氟磺草胺在3种土壤中的吸附和淋溶可能受土壤有机质含量、黏粒含量、阳离子交换量和土壤pH值等多个因素的综合影响,其对地下水的污染风险较大,因此应引起高度重视。     

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 (K_oc ≈ 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 (K_oc ≈ 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     

七种农药在3种不同类型土壤中的吸附及淋溶特性

采用振荡平衡法和土柱淋溶法研究了2,4-滴酸、丁噻隆、毒草胺、炔草酸、氟环唑、甲基磺草酮和烯啶虫胺7种农药在江西红壤、太湖水稻土及东北黑土3种不同理化性质土壤中的吸附及淋溶特性,探讨了农药性质及土壤理化性质对供试农药在土壤中吸附、淋溶行为的影响。结果表明:农药的水溶性越大,其在土壤中的吸附性越弱,淋溶性越强;农药在土壤中的吸附性与土壤pH值、有机质含量以及阳离子交换量之间有较好的相关性。土壤pH值、有机质含量以及农药性质是影响农药在土壤中淋溶及迁移的主要因素。     

Sorption of isoxaflutole by five different soils varying in physical and chemical properties

Isoxaflutole is a new pre-emergence corn herbicide which controls both grass and broadleaf weeds. Experiments were performed in the laboratory to study the sorption of isoxaflutole in five different soils (Moorhead, MN; East Monroe, CO; Ellendale, MN; South Deerfield, MA; and Chelsea, MI) using the batch equilibration technique. Total initial isoxaflutole solution concentrations for each soil were 0.05, 0.15, 0.3. 0.8, 1.5, 2.0 and 4.0 mg litre⁻¹. Analysis of [ring-¹⁴C] isoxaflutole was performed using liquid scintillation counting, and sorption data were fitted with the Freundlich model. Isotherms of isoxaflutole in all the soils were non-linear as depicted by the exponent (n < 1.0), indicating differential distribution of sorption site energies in various soils. Since the isotherms were non-linear the data fit Freundlich's isotherm well, as was indicated by high values of the regression coefficient (r²). The Freundlich sorption coefficient ranged from 0.555 to 50.0 (litre ⁿmg ^l−nkg⁻¹). Multiple regression of the sorption constant, K_F against selected soil properties indicated that organic matter content was the best single predictor of isoxaflutole sorption (r² = 0.999) followed by soil pH (r² = 0.954). Clay content of the soils did not have a high correlation with K_F values (r² = 0.453), while the sorption of isoxaflutole was not influenced by the Ca²⁺ concentration in the soil solution. Isoxaflutole sorption increased with an increase in organic matter content of soils. Sorption of isoxaflutole decreased as the soil pH increased from 4.5 to 8.5, which was depicted by the reduction of K_F values. Sorption of isoxaflutole to the soils varied with differences in binding energies. At a particular net energy value (E*), the corresponding site energy distribution [F(E*)] values followed the order, Chelsea, MI > Moorhead, MN > East Monroe, CO > South Deerfield, MA > Ellendale, MN. The negative magnitude of Gibbs free energy of sorption (ΔG ^x) indicates the spontaneity of the given sorption process in the soils from Moorhead, MN; East Monroe, CO and Chelsea, MI. © 1999 Society of Chemical Industry     

A bioassay technique to study the leaching behaviour of sulfonylurea herbicides in different soils

A bioassay procedure is described for quantitative determination of sulfonylurea herbicides in water and for studying their leaching behaviour in soils. Sunflower (Helianthus annuus L.) was found a more susceptible bioassay species than turnip (Brassica rapa L.) or lentil (Lens culinaris Medic.). The limit of quantitative detection (EC₃₀) in soil leachates was 0.12 μg 1^?1 for triasulfuron and 0.15 μg 1^?1 for metsulfuron-methyl. Leaching experiments were carried out by uniformly packing the soil in glass columns corresponding to its natural bulk density and applying simulated irrigation of 50 mm day^?1 with leachate water from untreated soil columns. Results obtained by measuring fresh weights of the true leaves of sunflowers in soil leachates showed that metsulfuron-methyl was much more mobile than triasulfuron in two soils with different sorption capacity. The BBA soil with low sorptive capacity showed very little retardation of both herbicides in the columns. The Horotiu soil with high sorptive capacity retarded triasulfuron for a long period, even under high flow conditions. Une technique d'essai biologique pour étudier l'aptitu.de au lessivage des herbicides sul-fony-lurées dans des différents sols Un protocole d'essai biologique est décrit pour la détermination quantitative des herbicides sulfonylurées dans l'eau, et pour l'étude de leur lessivage dans les sols. Le tournesol (Helianthus annuus) a été reconnu comme une espèce pour l'essai biologique plus sensible que le navet (Brassica rapa) ou la lentille (Lens culinaris). La limite de détection quantitative (EC₃₀) dans le lessivat du sol a été 0,12 μg 1^?1 pour le triasulfuron et 0,15 μg 1^?1 pour le metsulfuron methyl. Des études de lessivage ont été con-duites en mettant unifomément du sol dans des colonnes de verre de façon équivalente à la densité naturelle dans le sol et en appliquant une irrigation simulée de 50 mm jour^?1 avec de l'eau d'un lessivat de sol non traité. Les résult ats obtenus en mesurant le poids frais des feuilles vraies de tournesol dans les lessivats de sol ont montré que le metsulfuron-methyl était beau-coup plus mobile que le triasulfuron dans les 2 sols de capacités d'adsorption différentes. Le sol BBA avec une capacité d'adsorption faible a entraiîné un faible ralentissement des 2 herbicides dans les colonnes. Le sol Horotiu avec une capacité d'adsorption élevée a retardé le triasulfuron pendant une longue période, même sous des conditions de fortes précipitations. Biotestmethode zur Bestimmung des Ein-waschungsverhaltens von Sulfonyl-Harnstoff-herbiziden in unterschiedlich sorptiven Böden Eine Biotestmethode zum quantitativen Nach-weis von Sulfonyl-Harnstoffherbiziden in Was-serproben zur Bestimmung des Einwaschungs-verhaltens wurde entwickelt. Sonnenblume (Helianthus annuus L.) war unter den geprüf-ten Testpflanzen wesentlich empfindlicher als Herbstrübe (Brassica rapa L.) oder Linse (Lens culinaris Medic.). Als empfindlichste Meßgröße erwiesen sich die Echten Laubblätter der Sonnenblume. Die Nachweisgrenzen (EC₃₀-Werte) in Bodenperkolatwasser lagen bei 0,12 μg 1^?1 für Triasulfuron und 0,15 μg l^?1 für Metsulf-uron-methyl. Die Einwaschungsversuche wurden in Glassäulen durchgeführt, wobei die Böden gleichmäßig entsprechend ihrer Lagerungsdichte gepackt wurden. Die Beregnung erfolgte mit 50 mm Perkolat/Tag, das von nicht mit Herbiziden behandelten Säulenversuchen vorab gewonnen wurde. In beiden, unterschiedlich sorptiven, Böden zeigte Met-sulfuron-methyl eine stärkere Einwaschung als Triasulfuron. Im schwach sorptiven BBA-Boden wurden beide Wirkstoffe kaum retardiert, während Triasulfuron im stark sorptiven Horotiu-Boden über einen langen Zeitraum, auch unter den extremen Flußraten, zurückgehalten wurde.     

Degradation of chlorsulfuron and triasulfuron in alkaline soils under laboratory conditions

The degradation of chlorsulfuron and triasulfuron was investigated in alkaline soils (pH 7.1–9.4) spiked at 40 μg a.i. kg^–1 under laboratory conditions at 25 °C and a moisture content corresponding to 70% field capacity (–33 kPa), using high-performance liquid chromatography. Degradation data for the two herbicides did not follow first-order kinetics, and observed DT₅₀ values in surface soils ranged from 19 to 42 days and from 3 to 24 days for chlorsulfuron and triasulfuron respectively. Disappearance of both chlorsulfuron and triasulfuron was faster in non-sterile than in sterile soil, demonstrating the importance of microbes in the breakdown process. The persistence of chlorsulfuron increased with increasing depth, which can be attributed to the decline in the microbial populations down the profile. The DT₅₀ value for chlorsulfuron at 30–40 cm depth was nearly four times higher than that in the top-soil. The results obtained show that persistence of these herbicides in alkaline surface soils at 25 °C and at a moisture content of 70% field capacity is similar to those reported in other European and North American soils. The study shows that if these herbicides are contained in surface soil layers, the risk of residue carry-over under southern Australian conditions is small. However, the rate of their degradation in alkaline subsoils is very slow, and under conditions conducive to leaching their prolonged persistence in the soil profile is possible.     

Status of Mushroom Nematodes and their Management in India

Mushrooms are grown in almost all parts of India and the annual production is approximately 40,000t. Several species of naturally occurring edible mushrooms are being harvested and consumed locally in tribal and interior forest areas. However, commercially only white button and oyster mushrooms are popular. They are being cultivated under semi-scientific conditions (use of partially sterilized media and casing soil, use of implements, container etc. seldom treated with formalin, etc.) with limited inputs. Other biotic stresses, such as fungi, bacteria, insects and nematodes, cause heavy losses. Hence, the commercial productivity is much less than that of other countries. Button mushrooms are generally highly susceptible to nematode infection while oyster mushrooms are relatively resistant. Although several nematode control methods have been worked out, under Indian conditions maintenance of hygienic production conditions, prophylactic (sterilized production substrates, containers, implements, gloves, etc.) and use of plant products (leaves, non-edible oil cakes of neem, pongamiya, castor, etc.) were more successful in minimizing nematode damage to mushrooms and maximizing the yields. In this review the status of mushroom nematodes, their management and future thrust areas suitable to India conditions have been discussed.     

Water and sediment dynamics of penoxsulam and molinate in paddy fields: field and lysimeter studies

BACKGROUND: In Chile, rice is cultivated under water‐seeded and continuously flooded conditions. Because herbicide dynamics in paddy fields and non‐flooded fields is different, 3 year experiments were performed to study the dissipation of molinate and penoxsulam in water and sediment. RESULTS: In field experiments, both herbicides dissipated by 45–55% from the initial applied amounts during the first 6 h after application in all crop seasons; in lysimeter experiments, dissipation amounts were approximately 10% for penoxsulam and 16% for molinate. Penoxsulam field water DT₅₀ values varied from 1.28 to 1.96 days during the three study seasons, and DT₉₀ values from 4.07 to 6.22 days. Molinate field water DT₅₀ values varied from 0.89 to 1.73 days, and DT₉₀ values from 2.82 to 5.48 days. Sediment residues were determined 2 days after herbicide application into the paddy water, and maximum concentrations were found 4–8 days after application. In sediment, DT₅₀ values varied from 20.20 to 27.66 days for penoxsulam and from 15.02 to 29.83 days for molinate. CONCLUSIONS: Results showed that penoxsulam and molinate losses under paddy conditions are dissipated rapidly from the water and then dissipate slowly from the sediment. Penoxsulam and molinate field water dissipation was facilitated by paddy water motion created by the wind. Sediment adsorption and degradation are considered to have a secondary effect on the dissipation of both herbicides in paddy fields. Copyright © 2011 Society of Chemical Industry     

Sorption and desorption of flumioxazin to soil, clay minerals and ion-exchange resin

Flumioxazin adsorption kinetics were described using a Greenville sandy clay loam soil. Adsorption kinetics experiments showed that 72% of total herbicide was absorbed after 1 h of continuous shaking and continued to increase to 78% after 72 h. Flumioxazin adsorption was then tested on seven agriculturally important soils throughout the southern USA. Adsorption isotherms for all soils had K(f) (Freundlich distribution coefficient) values that ranged from 8.8 to 0.4, with many near 1.5. Soil organic matter content was the parameter most highly correlated with flumioxazin adsorption (r(2) = 0.95, P < 0.001). Sorption to clay minerals had K(f) values ranging from 50 for bentonite to 4.7 for kaolinite. However, normalizing K(f) for sorbent surface area revealed that aluminum hydroxide (gibbsite) possessed the greatest flumioxazin sorption per unit area. Sorption to anionic exchange resin (K(f) 676) was greater than cationic exchange resin (K(f) 42). Molecular model calculations were performed to elucidate why sorption was greater to anionic exchangers. These calculations indicated that a region of dense electronegativity exists on the 3-dione moiety of the molecule. This would lead to greater flumioxazin sorption by positively charged surface sites. Desorption isotherms from soil exhibited no effect of hysteresis. Desorption from clay minerals was very rapid and flumioxazin in solution was undetectable after three desorption steps. From these data it was concluded that flumioxazin can become readily available in soil solution with increase in soil water content.