Formation and persistence of metabolites of imazamethabenz-methyl in a sandy loam soil

The fate of imazamethabenz-methyl was studied in a sandy loam soil after application in spring to winter wheat (Triticum aestivum L.). Imazamethabenz-methyl and its metabolite 2 (2-(4, 5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-1H-imidazol-2-yl)-4-methylbenzoic acid, in mixture with the 5-methylbenzoic acid isomer) were further transformed into the metabolites 3 (2-(4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-¹H-imidazol-2-yl)-l,4-benzenedicarboxylic acid, in mixture with the 1,5-benzenedicarboxylic acid isomer), and 4 (1,2,4-benzenetricarboxylic acid, in mixture with the 1,2,5-isomer). Meta-bolites 3 and 4 reached maximum concentration levels in the 0–13 cm layer corresponding to 14–17% and 9–14% of the imazamethabenz-methyl dose, respectively. These maxima were reached between 105 and 177 days after application. Imazamethabenz-methyl metabolism was slower in plots treated with organic fertilizers than in untreated plots. After 196 days the concentrations of all metabolites in the 0–13 cm layer had declined to, at most, 0.01 mg kg^?1. There was no carry-over of residues that could be phytotoxic to the next crop. Formation et persistance dés metabolites de l'imazaméthabenz-méthyl dans un sol sablolimoneux La métabolisation de l'imazaméthabenz-méthyl a étéétudiée dans un sol sablo-limoneux après application sur une culture de froment d'hiver (Triticum aestivum L.) L'imazaméthabenz-méthyl et son métabolite 2 (2-(4,5-dihydro-4-methyl-4-(l-methylethyl)-5-oxo-^?1H-imidazol-2-yl)-4-methylbenzoïque acide, en mélange avec 1'isomère 5-methylbenzoïque acide) sont trans-formés ultérieurement en métabolites 3 ((2-(4,5-dihydro-4-methyl-4- (l-methylethyl)-S- oxo -^?1H-imidazol-2-yl)-l,4-benzenedicarboxylique acide, en mélange avec l'isomère 1,5-benzenedicar-boxylique acide) et 4 (1,2,4-benzenetricarboxy-lique acide, en mélange avec le 1,2,5- isomère). Les concentrations dans la couche de sol de 0–13 cm de profondeur des métabolites 3 et 4 at-teignent des maximums qui correspondent re-spectivement à 1,4–17% et 9–14% de la dose initiate en imazamethabenz-methyl. Ces concentrations maximales sont atteintes entre les 105 et 177 jours qui suivent 1'application. La métabolisation de rimazaméthabenz-méthyl est plus lente dans les parcelles trailées par des fetilisants organiques, que dans les parcelles non traitées par ces fertilisants. Après 196 jours, les concentrations de tous les métabolites dans la couche de sol de 0–13 cm ont diminué jusqu' à 0.01 mg kg^?1 ou moins. Dans ces conditions, en fin de culture il n'est pas resté dans le sol de résidus qui auraient pu être phytotoxiques à la culture suivante. Bildung und Persistenz von Metaboliten des Imazamethabenz-methyl in einen sandigen Lehmboden Nach der Applikation von Imazamethabenz-methyl in Winterweizen (Triticum aestivum L.) wurde sein Abbau untersucht. Das Herbizid und seine Metaboliten 2, die isomeren 2-(4, 5-Dihydro-4-methyl-4 (1-methylethyl)-5-oxo-¹ Himidazol-2-yl)-und -5-methylbenzoesäure, wurden weiter zu den Metaboliten 3, die isomeren-1,4-und-l,5-benzendicaboxylsäure, und 4, die isomeren 1,2,4- und 1,2,5-benzentricarboxylsäure, transformiert. Die Metaboliten 3 und 4 hatten ihre höchste Konzentration in 0 bis 13 cm Bodentiefe und entsprachen 14 bis 17 % bzw. 9 bis 14 % der Imazamethabenzmethyl-Dosis. Diese Maxima wurden zwischen 105 und 177 d nach der Applikation erreicht. In organisch gedüngten Parzellen war der Abbau langsamer als in ungedüngten. Nach 196 d war die Konzentration aller Metaboliten in 0 bis 13 cm Bodentiefe auf höchstens 0,01 mg kg¹ zurückgegangen, so daß für die Folgekultur keine phytotoxischen Rückstände mehr vorlagen.     

Influence of surfactants on the leaching of bentazone in a sandy loam soil

BACKGROUND: Surfactants are very often used for more efficient pesticide spraying, but knowledge about their influence on the leaching potential for pesticides is very limited. In the present study, the leaching of the herbicide bentazone [3‐isopropyl‐1H‐2, 1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide] was measured in columns with sandy loam soil with or without the addition of a non‐ionic surfactant, octylphenol ethylene oxide condensate (Triton X‐100, Triton), and an anionic surfactant, sodium dodecylbenzenesulfonate (SDBS), and in the presence of both surfactants (SDBS + Triton). RESULTS: The mobility of bentazone (B) increased in the following order: B + Triton (slowest) < B + SDBS + Triton < B < B + SDBS (fastest). When Triton X‐100 was applied to the soil together with bentazone, the leaching of bentazone in the soil decreased significantly compared with leaching of bentazone without the addition of surfactant. SDBS and Triton X‐100 neutralised their influence on the leaching speed of bentazone in the soil columns when both surfactants were applied with bentazone. CONCLUSION: From the study it can be concluded that, depending on their properties, surfactants can enhance or reduce the mobility of bentazone. By choosing a non‐ionic surfactant, bentazone mobility can be reduced, giving time for degradation and thereby reducing the risk of groundwater pollution. Copyright © 2009 Society of Chemical Industry     

三种拟除虫菊酯类农药在砂土和壤土中的淋溶行为

采用土柱淋溶法和气相色谱法研究了3种拟除虫菊酯类农药三氟氯氰菊酯、联苯菊酯和高效氯氰菊酯在热带地区主要土壤类型砂土和壤土中的淋溶特性。结果表明:3种拟除虫菊酯类农药在砂土和壤土中主要残留于第1段土壤 (0～5 cm) 中,且驻留量随土壤深度增大而减少。三氟氯氰菊酯、高效氯氰菊酯和联苯菊酯在砂土中的R_i值分别为52.86%、94.73%和83.19%,在壤土中的R_i值分别为54.70%、77.28%和55.33%,均大于50%。根据农药在土壤中的淋溶性等级划分标准,3种药剂均属于难淋溶农药,不易对地下水造成污染。本研究结果可为热带地区土壤和地下水中农药污染修复提供参考。     

Field degradation of the herbicide metribuzin and its degradation products in a Manitoba sandy loam soil*

The degradation of the herbicide metribuzin (4-amino-6 r-butyl-3-(methylthio)-1, 2, 4-tnazin-5-(4H)one) applied at 1 and 2 kg/ha at times equivalent to pre-emergence (12 June), post-emergence (5 July), and pre-harvest (15 August), has been investigated in Almasippi very line sandy loam at Carman, Manitoba. Gas-liquid chromatographic analytical results showed that metribuzin degraded during the growing season, and that residue levels immediately prior to freeze-up (25 October) were in general less than 10% of applied metribuzin independent of application date, and were largely unchanged the following spring. The metabolites and photoproduct of metribuzin were present in maximum amounts near 13 July for the first two treatment dates, a time closely following maximum soil temperature readings, and these compounds in turn degraded almost completely by freeze-up. The following spring only very low levels were detected. Under the conditions described, metribuzin and its degradation products degraded to low levels and should not provide a carryover problem the next growing season.     

适用不同粒径含盐砂壤土水分扩散率的通用模式

针对土壤盐分较重的砂壤土确定土壤水分扩散率D（θ）的问题,采用室内非稳定流水平土柱法对新疆石河子121团灌区膜下滴灌棉田不同粒径砂壤土水分扩散率及土壤盐分运移进行了研究。结果表明：粒径为1.0~2.0 mm的砂壤土水分扩散率最大,而且变化比较迅速,其次是0.5~1.0 mm的砂壤土,最小的是<0.5 mm的砂壤土,随着土壤粒径的减小,土壤水分扩散率逐渐降低;随着土壤含盐率的增大土壤水分扩散率减少。得出以土壤体积含水率为变量而且还考虑土壤含盐率的综合通用模式,该通用模式较为符合实际情况,并能够较好地反映同一容重、相同水平距离情况下粒径不同时含盐砂壤土的土壤水分扩散率的变化。     

Persistence and binding of DDT and gamma-HCH in a sandy loam soil under field conditions in Delhi,India

Persistence and binding capacity of [¹⁴C]p, p′-DDT and [¹⁴C]y-HCH were studied for one year in a sandy loam soil of Delhi, India, after surface treatment during monsoon, winter and summer seasons under field conditions. Both DDT and HCH dissipated more rapidly under the Indian subtropical climate than reported for temperate regions. In all three seasons, both insecticides dissipated most rapidly during the initial 60 days. However, in the final six months there was very little change in the residue levels. After one year, the final soil burden of DDT varied from 33 to 36% and of HCH from 14 to 15% of the initial concentrations in the different experiments. HCH bound more with the soil as, out of the total residues present after one year, more than 75% of HCH was in bound form compared with only 24% of DDT. The observed time for 50% initial dissipation of DDT ranged from 60 to 120 days, while in the case of HCH it varied from 30 to 45 days. However, the rate of loss of residues which persisted for more than 6 months was equivalent to a half-life of between 500 and 10000 days for DDT, and between 700 and 2000 days for HCH, thus illustrating the very long persistence of aged residues. Since degradation of both insecticides was apparently minimal, the data indicate that dissipation of DDT and HCH was largely due to volatilisation.     

Bromoxynil degradation in a Mississippi silt loam soil

BACKGROUND: The objectives of these laboratory experiments were: (1) to assess bromoxynil sorption, mineralization, bound residue formation and extractable residue persistence in a Dundee silt loam collected from 0–2 cm and 2–10 cm depths under continuous conventional tillage and no‐tillage; (2) to assess the effects of autoclaving on bromoxynil mineralization and bound residue formation; (3) to determine the partitioning of non‐extractable residues; and (4) to ascertain the effects of bromoxynil concentration on extractable and bound residues and metabolite formation. RESULTS: Bromoxynil K_d values ranged from 0.7 to 1.4 L kg^?1 and were positively correlated with soil organic carbon. Cumulative mineralization (38.5% ± 1.5), bound residue formation (46.5% ± 0.5) and persistence of extractable residues (T_1/2 < 1 day) in non‐autoclaved soils were independent of tillage and depth. Autoclaving decreased mineralization and bound residue formation 257‐fold and 6.0‐fold respectively. Bromoxynil persistence in soil was rate independent (T_1/2 < 1 day), and the majority of non‐extractable residues (87%) were associated with the humic acid fraction of soil organic matter. CONCLUSIONS: Irrespective of tillage or depth, bromoxynil half‐life in native soil is less than 1 day owing to rapid incorporation of the herbicide into non‐extractable residues. Bound residue formation is governed principally by biochemical metabolite formation and primarily associated with soil humic acids that are moderately bioavailable for mineralization. These data indicate that the risk of off‐site transport of bromoxynil residues is low owing to rapid incorporation into non‐extractable residues. Published 2009 by John Wiley & Sons, Ltd     

Application of bispyribac‐sodium provides effective weed control in direct‐planted rice on a sandy loam soil

An increasing water crisis, as well as the unavailability and high cost of labor, in Pakistan has forced rice‐growers to plant rice directly into the field. However, severe weed infestation causes disastrous effects on the productivity of this rice system. In this study, three herbicides (pendimethalin, penoxsulam and bispyribac‐sodium) were evaluated for weed control in direct‐planted rice on a sandy loam soil. Weedy check and weed‐free plots were established for comparison. Weed infestation decreased the rice yield by 75.2%. However, the application of herbicides suppressed the weed infestation, with a simultaneous increase in the rice yield. The postemergence application of bispyribac‐sodium was the most effective herbicide in reducing the total weed density and dry weight over the weedy check, followed by penoxsulam and pendimethalin, respectively. Bispyribac‐sodium increased the number of productive tillers, 1000‐grain weight, number of grains per panicle and grain yield over the control, as well as improved the water productivity and economic returns of direct‐planted rice. The weeds' proliferation increased the number of unproductive tillers and decreased the plant height. In conclusion, the postemergence application of bispyribac‐sodium can be used effectively to control weeds, increase water productivity and improve the economic returns and yield of direct‐planted rice on a sandy loam soil in Pakistan.     

Gross nitrogen transformations and N_2O emission sources in sandy loam and silt loam soils

The soil type is a key factor influencing N(nitrogen) cycling in soil; however, gross N transformations and N_2O emission sources are still poorly understood. In this study, a laboratory ~(15)N tracing experiment was carried out at 60% WHC(water holding capacity) and 25℃ to evaluate the gross N transformation rates and N_2O emission pathways in sandy loam and silt loam soils in a semi-arid region of Heilongjiang Province, China. The results showed that the gross rates of N mineralization, immobilization, and nitrification were 3.60, 1.90, and 5.63 mg N/(kg·d) in silt loam soil, respectively, which were 3.62, 4.26, and 3.13 times those in sandy loam soil, respectively. The ratios of the gross nitrification rate to the ammonium immobilization rate(n/ia) in sandy loam soil and silt loam soil were all higher than 1.00, whereas the n/ia in sandy loam soil(4.36) was significantly higher than that in silt loam soil(3.08). This result indicated that the ability of sandy loam soil to release and conserve the available N was relatively poor in comparison with silt loam soil, and the relatively strong nitrification rate compared to the immobilization rate may lead to N loss through NO_3~– leaching. Under aerobic conditions, both nitrification and denitrification made contributions to N_2O emissions. Nitrification was the dominant pathway leading to N_2O production in soils and was responsible for 82.0% of the total emitted N_2O in sandy loam soil, which was significantly higher than that in silt loam soil(71.7%). However, the average contribution of denitrification to total N_2O production in sandy loam soil was 17.9%, which was significantly lower than that in silt loam soil(28.3%). These results are valuable for developing reasonable fertilization management and proposing effective greenhouse gas mitigation strategies in different soil types in semiarid regions.     

The influence of tillage on the weed flora in a succession of winter wheat crops on a clay loam soil and a silt loam soil

Weed populations were monitored for 4 years on two experiments designed to compare the effect of different primary tillage treatments on winter wheat (Triticum aestivum L.) cropping. Ploughing was compared with deep and shallow tine cultivation and with no tillage on both a clay loam and a silt loam over chalk. Soil-acting residual herbicides were used to control weeds, especially Alopecurus myosuroides Huds. and Avena fatua L. Dicotyledonous weeds were uncommon on the clay loam but on the silt loam, in a year when no residual herbicide was used, they were most numerous where the soil was disturbed most. In other years there was little difference in the number emerging. Six species were reduced in number by reduced cultivation or no tillage, whilst four species, including two grasses, were increased. At both sites, A. myosuroides was more numerous on direct drilled and tine cultivated plots than on ploughed. Herbicides gave good control on the silt loam but failed to control the weed on the clay loam. On the clay loam, A. fatua was most numerous on tine cultivated plots and a combination of herbicides and roguing produced a decline in the population.     

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.     

Formulation affecting alachlor efficacy and persistence in sandy soils

BACKGROUND: The development of controlled‐release formulations of alachlor to extend the period of weed control was studied. This extended duration reduces the need for high herbicide application rates that could lead to environmental contamination. For this purpose, the influence of formulation, as well as the influence of soil characteristics, on alachlor efficacy and persistence in soil of a commercial formulation (CF) and different ethylcellulose microencapsulated formulations (MEFs) was evaluated. RESULTS: Higher alachlor rates yielded an enhanced initial herbicidal activity. The prolonged release of alachlor provided by the MEFs resulted in a higher herbicidal efficacy and a longer period of weed control compared with the effects of CF in the two soils tested (at 40 days after treatment, oat growth inhibition for CF and MEFs was 1.96% and 93.5% respectively). Soil characteristics strongly influenced alachlor efficacy and weed control by MEFs. The highest alachlor efficacy and persistence were observed in the soil with lowest microbial activity and clay and organic matter content. CONCLUSIONS: The use of MEFs can be advantageous because they permit the maintenance of the desired concentration of the herbicide in the soil for longer periods of weed control. Copyright © 2009 Society of Chemical Industry     

Effect of dalapon-sodium on nitrification and denitrification in a tropical loam soil

A loamy soil treated with dalapon-sodium was incubated under aerobic or anaerobic conditions with added ammonium or nitrate nitrogen respectively. The incubated dalapon-sodium treated soil and controls were analysed periodically for NH₄+N and NO₃^-N. Results indicated that the herbicide retarded nitrification and denitrification by up to 8 and 12 weeks respectively. Effet du dalapon-sodium sur la nitrification et la dénitrification dans un sol de limon tropical Un sol de limon traité avec du dalapon-sodium a été mis en incubation dans des conditions aérobies ou anaérobies avec addition d'azote ammoniacal ou nitrique respectivement. Le sol traité avec du dalapon-sodium et mis en incubation a été analysé périodiquement, ainsi que les témoins, pour NH₄^+N et NO₃^-N. Les résultats ont montré que l'herbicide retardait la nitrification et la dénitrification respectivement jusqu’à 8 et 12 semaines. Wirkung von Dalapon-Na auf Nitrifikation und Denitrifikation in einem tropischen Lehmboden Einem mit Dalapon-Na behandelten Lehmboden wurde Ammon- bzw. Nitratstickstoff zugesetzt und unter aeroben bzw. anaeroben Bedingungen gelagert. Der mit Dalapon-Na behandelte Boden und die entsprechenden Kontrollen wurden periodisch auf NH₄⁺- und NO₃^--Stickstoff untersucht. Die Ergebnisse zeigten, dass das Herbizid die Nitrifikation um bis zu 8 und die Denitrifikation bis zu 12 Wochcn verzögerte.     

The microbial biodegradation of paraquat in soil

The microbial degradation of [¹⁴C]paraquat using cultures from two agricultural soils was investigated. The experiments were carried out in the absence of light, under aerobic conditions. Degradation was rapid, with 50% mineralisation to [¹⁴C]carbon dioxide occurring within three weeks. HPLC, capillary electrophoresis and mass spectroscopy confirmed that the majority (>85%) of the remaining radiochemical in solution was [¹⁴C]oxalic acid, and that no paraquat remained.     

The phytotoxicity of various herbicides in two sandy loam soils and the effect of liming

The phytotoxicity of five soil-acting herbicides was investigated in two sandy loam soils and that of a further five herbicides in one of these soils. The effect of liming on phytotoxicity was also examined. Metoxuron, fenuron, metribuzin and fluometuron were more active in Boddington Barn soil than in Bledington soil. Prometryne was similar in effect in both soils. Liming significantly increased the effect of metoxuron in Boddington Barn soil and metoxuron, atraton, difenoxuron and metribuzin in Bledington soil. Monolinuron was less toxic in limed Bledington soil. Reasons for these differences have not been determined.     

Behaviour and persistence of trifluralin in soil

The growth response of sorghum to trifluralin, on various soils and soil mixtures, was significantly correlated with organic matter (ranging from <0–1% to 20–4%) but not with clay content (ranging from 3% to 63%). However, in soils with a similar, low organic matter content, the activity of trifluralin increased with increasing clay content. No correlation was found between phytotoxicity of trifluralin and lime content of soils. The persistence of trifluralin incorporated in soil was examined by repeated reseedings of sorghum. Phytotoxicity lasted longer in soil dried and mixed at each interval between seedings than in soil left undisturbed; after 2 months about 50% of the original 4 ppm trifluralin remained in undisturbed soil vs 60 % in repeatedly mixed soil. The rate of degradation, after 2 months of incubation at 50% field capacity, increased with temperatures from 10°to40° the concentration of trifluralin required for a given growth reduction was approximately eight times greater after incubation at 40° than at 10°C. Comportement et persistattce de la trifluraline dans le sol Les effets de Ia trifluraline sur la croissance du sorgho cultivé dans divers sols ou mélanges de sol se sont révlés être en corrélation significative avec la matiere organique (entre < 0,1 % et 20,4 %) mais pas avec la teneur en argile (de 3 % A 63 %). Toutefois dans les sols contenant un taux analogue et faible de matiére organique, l'activité de la trifluraline s'est accrue en même temps que Ia leneur en argile. Aucune corrélation n'a été constatée entre la phytotoxicité de la trifluraline et la teneur en calcaire des sols. La persistance de la trifluraline incorporée dans le sol a été examinée au moyen de ressemis répétés de sorgho. La phytotoxicité dura plus longtemps dans le sol séché et remuéà chaque intervalle entre les semis que dans le sol non travaillé; au bout de 2 mois, 50% environ des 4 ppm de trifluraline apportés à. I'origine restaient dans le sol non remué contre 60% dans le sol plusieurs fois remué. Le taux de degradation, aprés deux mois d'inciibation à 50% de la capacityé au champ, augmenta avec la température de 10°à 40°C; la concentration de trifturaline nécessaire pour obtenir une réduction de croissance donnée fut approximativement huit fois plus grande aprés incubation. à 40° qu'aprés incubation à 10°C. Verhalten und Perststenz von Trifluralin im Boden Die Wachstumsreaktion von Hirse gegenubcr Trifluralin in verschiedenen Böden und Bodenmischungen war signifikant mit dem Gehalt an organischer Substanz (<0–1 %–20–4%) korreliert, nicht aber mit dem Tongehalt (von 3%-63%). Jedoch nahm in Böden mit annähernd gleich niedrigen Gehalten an organischer Substanz die Wirksamkeit von Trifluralin mit steigendeni Tongehalt zu. Zwischen der Phytotoxizität von Trifluralin und dem Kalkgehalt der Böden wurde keine Korrelation gefunden. Die Persistenz von in den Boden eingearbeitetem Trifluralin wurde durch wiederholte Einsaat von Hirse untersucht. Die Phytotoxizität dauerte im Boden, der jeweils zwischen den Einsaaten getrocknet und gemischt worden war, langer an als im nicht derartig behandelten Boden. Nach 2 Monaten waren im letzteren Boden ungefähr 50% der ursprüinglichen 4 ppm Trifluralin verblicben gegenüber 60% im wiederholt durchmischten Boden. Nach 2 Monatlen Inkubation bei 50% Feldkapazität stieg die Abbaurate, wenn die Temperatur von 10° auf 40°C stieg; die für eine gegebene Wachstumsreduktion benötigte Trifluralinkonzentration war bei 40° annShernd achtfach grösser als bei 10°C.     

Behavior and persistence in soil of benefin

The phytotoxicity of benefin, as assessed by sorghum on various soils and soil mixtures, was significantly correlated with the organic matter content but not with the clay or lime content of the soils. After 1 month of incubation no significant activity remained from 2 ppm benefin, and after 2 months only slight activity remained from 4 ppm. Benefin was less persistent than trifluralin and more persistent than nitralin.