Soil metabolism of the herbicide napropamide in cereals, maize, sugar beet and vegetable field replacement crops

The metabolism of the herbicide napropamide has been studied in the field in the soil of replacement crops (cereals, corn, sugar beet, potato and several vegetables). Napropamide was soil applied in the autumn and the soil left fallow during the winter. Crops were sown in April of the following year and simulated the replacement crops that are grown in the event of failure of the first autumn-sown crop. Trials were made twice, i.e. during the 1987-1988 and 1988-1989 crop seasons. The soil metabolism of napropamide was also studied in a rose nursery. Napropamide was transformed by microbiological processes in the soil into the corresponding monoethylamide and acid. These compounds did not generally accumulate in the soil, and their individual concentrations did not exceed that of residual napropamide during the observed growing seasons. The kinetics, metabolic pathways and agricultural implications of the herbicide are briefly discussed.     

Soil dissipation of the herbicide isoxaben after use in cereals

The soil dissipation of the herbicide isoxaben was studied in field trials in Belgium in winter cereals treated with green manure, cow manure or pig slurry before sowing. Wheat was sown and the soil sprayed with 125 g isoxaben ha^?1 in October. Soil samples were analysed by GLC. Isoxaben dissipated with first-order kinetics over the first 6 months with half-lives of 2.9, 4.0, 4.8 and 6.6 months in unamended plots, and plots treated with green manure, cow manure and pig slurry respectively. The organic fertilizer treatments thus increased the isoxaben soil persistence. After 6 months, the organic fertilizer effect was less pronounced, leading to isoxaben soil concen-trations in all treatments becoming similarly low. Isoxaben at 75 gha^?1 applied to winter wheat or barley in the spring gave dissipation half lives of 2.1 and 2.4 months, leading to isoxaben soil residues at the beginning of August of 15–21 p.p.b., similar to levels resulting from the autumn appli-cation. The isoxaben soil residues remaining after harvest would be too low to damage a rotational crop. The rates of isoxaben soil dissipation were greater in the spring and summer seasons than during the winter. The dissipation rates of autumn-applied isoxaben were also studied in spring-sown sugar beet and the effects on a variety of springsown rotational crops were investigated. Dissipation dans le sol de I'herbicide isoxaben en culture de céréales La dissipation dans le sol de I'herbicide isoxaben a étéétudiée dans des essais de plein champ, en Belgique, en culture de céréales d'hiver ayant eu avant le semis un engrais vert, un apport de fumier de vache ou de lisier de pore. Le blé a été semé et le sol traité avec 125 g d'isoxaben ha^?1en octobre. Les échantillons ont été analysés par GLC. L'isoxaben s'est dégradé pendant les pre-miers mois avec des demi-vies respectives de 2,9, 4,4,8 et 6,6 mois dans les parcelles sans amende-ments, les parcelles avec engrais vert, fumier et lisier. Les amendements organiques ont augmenté la persistance de l'isoxaben dans le sol. Après 6 mois, l'effet des amendements organiques a été moins prononcé, aboutissant à des concentrations d'isoxaben basses et voisines pour tous les traitements. L'isoxaben a 75 g ha^?1 appliquéà du blé d'hiver et de l'orge au prin-temps a donné des demi-vies de 2,1 et 2,4 mois, aboutissant à des résidus d'isoxaben dans le sol début août de 15–21 ppb, comparables aux taux resultant d'une application automnale. Les résidus d'isoxaben dans le sol restant après la moisson seraient trop faibles pour endommager une culture suivante. Le taux de dégradation dans le sol de l'isoxaben a été plus é1evé au prin-temps et en été qu'en hiver. Le taux de dégrada-tion de l'isoxaben appliqué en automne a étéégalement étudié sur des betteraves semées au printemps et les ef fets sur plusieurs cultures dans le cadre de la rotation ont étéétudiés. Rückstandssituation von Isoxaben im Boden nach Applikation in Getreide Die Rückstandssituation des Herbizids Isoxaben im Boden wurde in Freilandstudien in Wintergetreide nach Gründüngung, Ausbringung von Stallmist bzw. Schweinegülle untersucht. Das Herbizid wurde im Oktober im Nachsaatverfahren mit 125 g Isoxaben ha^?1 angewandt, und die Bodenproben wurden gaschromatographisch analysiert. Das Herbizid wurde über die ersten 6 Monate nach einer Kinetik 1. Ordnung mit “Halbwertszeiten” von 2,9 Monaten im Ausgangsboden, 4,0 Monaten nach der Gründung und 4,8 bzw. 6,6 Monaten in der Stallmist-bzw. Gülle- Variante abgebaut. Durch die organischen Düngungen wurde also die Persistenz des Herbizids im Boden erhöht. Nach 6 Monaten lieβ die Wirkung der Dünger nach, so daβ vergleichbar niedrige Rückstände gefunden wurden. Bei der Nachauflaufbehandlung von Winterweizen und -gerste im Frühjahr mit 75 g Isoxaben ha^?1 lagen die Werte für einen 50% igen Rückgang der Ausgangskonzentration bei 2,1 bzw. 2,4 Monaten, und es ergaben sich Anfang August vergleichbar hohe Werte von 15 bis 21 ppb wie bei den Herbstbehandlungen. Diese Rückstände würden zu keinen Schäden an Nachbaukulturen führen. Die Verlustraten waren prozentual über Winter geringer als im Frühjahr. Sie wurden auch in Zuckerrüben untersucht, desgleichen ihre Wirkung auf verschiedene im Frühjahr angebaute Nachbaukulturen.     

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.     

Atrazine soil metabolism in maize fields treated with organic fertilizers

The metabolism of atrazine in soil was studied in two maize fields located in regions with different soil types. Treatments were cow manure or pig slurry (50 tonnes each ha^-1) applied once either in March or in November before sowing, or green manure incorporated in March. Control plots were not treated with organic fertilizers. Atrazine at 0.75 or 1.0 kg a.i. ha^-1 was applied after sowing. In the 0-12 cm soil layer, the main atrazine metabolites found were deethylatrazine and hydroxyatrazine. Low concentrations of deisopropylatrazine and 6-chloro-1, 3, 5-triazine-2, 4-diamine were also observed. During the 4 months after sowing, the organic fertilizers decreased the rate of atrazine degradation, but subsequently there were no differences between treated and control plots. At harvest, the concentrations of atrazine and its metabolites were very low and similar in all plots. The organic fertilizers thus did not cause atrazine metabolites to accumulate in soil. In addition, atrazine and its metabolites were never detected below 12 cm in any of the plots.     

Sulcotrione soil persistence and mobility in summer maize and winter wheat crops

Sulcotrione soil persistence in spring maize ( Zea mays L.) crops grown on a sandy loam soil was greater at pH 5·5 and 6·0 (soil half-life T _1/2≈58 days) than at pH 7·1 ( T _1/2 = 44 days). Sulcotrione was also applied as recommended on a summer maize crop at the five- to six-leaf growth stage, grown on a sandy loam soil. Sulcotrione soil half-life was 44 days, and the herbicide remained mainly in the 0- to 5-cm surface soil layer during the cropping period, in spite of the high water solubility and the heavy rains at the end of August; lower sulcotrione concentrations (10–18% of the total during the 2-month period after sulcotrione application) were detected in the 5- to 10-cm surface soil layer. The herbicide was applied pre-emergence to winter wheat ( Triticum aestivum L.) at four sites that differed in their soil texture and composition: loamy sand, sandy loam, loam and clay loam. Persistence was greater in the soils containing more organic matter. In soils having similar organic matter contents, persistence was lower in the soil containing more sand relative to loam and clay. During the winter crops, sulcotrione moved down to the 10- to 15-cm soil layer, in spite of the fact that the rains were lower in winter than in summer. Sulcotrione most generally was not detected in the 15–20 cm soil layer of the maize and winter wheat crops.     

Soil biodegradation of imazamethabenz-methyl and its acid metabolite in wheat crops and in sugar beet replacement crops

The effect of three organic fertilizers, green manure, pig slurry, and cow manure on the rate of soil degradation of imazamethabenz-methyl under field conditions was investigated in a wheat (Triticum aestivum) crop sown in November. The herbicide was applied in March, 5 months after incorporation into the soil of the fertilizers. The half-life of imazamethabenz-methyl in the soil was 35 days in control plots, and 55, 66 and 85 days respectively in plots treated with green manure, pig slurry, and cow manure. In the same plots the half-lives of the sum of imazamethabenz-methyl and its herbicide acid metabolite were 61,98,127 and 172 days, respectively. The organic fertilizers thus increased the soil persistence of imazamethabenz-methyl and its acid metabolite, i.e. the product generated by hydrolysis of the methyl ester function of imazamethabenz-methyl. Towards the end of the cropping period, residues of both compounds became low in both fertilizer-treated and control plots. Soil degradation of imazamethabenz-methyl was also studied in sugar beet (Beta vul-garis) replacement crops sown in April into land treated in November of the preceding year (as could occur with a treated winter wheat crop which subsequently failed). The rate of degradation in the sugar beet replacement crop was about half that of the same treatment applied in spring wheat. Dégradation biologique dans le sol de rimazaméthabenz-méthyle et de son métabolite acide dans des cultures de hlé et de betterave à sucre de remplacement L'effet de trois fertilisants organiques (engrais vert, lisier de pore et fumier de bovin) sur la dégradation dans le sol de l'imazaméthabenz-méthyle a été etudié au champ dans une culture de blé (Triticum aestivum) semé en novembre. L'herbicide a été appliqué en mars, 5 mois après l'incorporation des fertilisants. La demi-vie de rimazaméthabenz-méthyle dans le sol était 35, 55, 66 et 85 jours, respectivement dans les témoins et dans les parcelles ayant reçu l'engrais vert, le lisier de porc et le fumier de bovin. Dans les mêmes parcelles, la demi-vie de la somme de l'imazaméthabenz-méthyle et de son métabolite acide herbicide étaient respectivement 61, 98, 127 et 172 jours. Les fertilisants organiques ac-croissaient done la persistance dans le sol de rimazaméthabenz-méthyle et de son métabolite acide, c'est à dire le produit issu de l'hydrolyse de sa fonction méthylester. A la fin de la période culturale, les résidus de ces deux composés étaient faibles dans toutes les parcelles. La dégra-dation dans le sol de l'imazaméthabenz-méthyle a été aussi étudiée dans la betterave à sucre (Beta vulgaris) implantée comme culture de remplacement en avril dans un sol traité en novembre de 1'année précédente (cette situation peut se ren-contreren casde retournement d'un blé d'hiver). La vitesse de dégradation de l'imazaméthabenz-méthyle dans la culture de betterave à sucre était environ moitié moindre que chez le blé de printemps. Biodegradation von Imazamethabenz-methyl und seinem sauren Metaboliten im Boden in Weizen und Zuckerrübe als Ersatzkultur Die Wirkung von 3 organischen Düngern (Gründüngung, Schweinegülle und Stallmist) auf die Abbaurate von Imazamethabenz-methyl unter Feldbedingungen wurde in im November gesätem Weizen (Triticum aestivum) untersucht. Das Herbizid wurde im Mai ausgebracht, 5 Monate nach der Einarbeitung der Dünger. Die ‘Halbwertszeit’ für den Abbau des Herbizids im Boden war in der Vergleichsparzelle 35 Tage und in den organisch gedüngten Parzellen 55,66 bzw. 85 Tage. Für das Herbizid und seinen sauren Metaboliten zusammen lagen die ‘Halbwertszeiten’ in denselben Parzellen bei 61, 98, 127 bzw. 172 Tagen. Demnach verlängerten die organischen Dünger die Persistenz des Herbizids und seines Metaboliten (Hydrolyseprodukt der Methylesterfunktion) im Boden. Gegen Ende der Vegetationsperiode gingen die Rückstände der beiden Stoffe in allen Parzellen zurück. Det Abbau wurde auch auf Flächen untersucht, die nach einer Behandlung im November des Vorjahres mit Zuckerrübe (Beta vulgaris) bestellt waren (so als ob sie nach einem Ausfall der Weizenkultur eingesetzt würde). Die Abbaurate in dieser Ersatzkultur war etwa halb so hoch wie nach einer gleichen Behandlung in Sommerweizen.     

Soil metabolism of flupyrsulfuron in winter wheat crops

The sulfonylurea herbicide flupyrsulfuron was applied post‐emergence in March at the rate of 10 g a.i. ha^?1 on winter wheat crops. In the 0–8 cm surface soil layer of the crops grown on sandy loam and loam soils, the flupyrsulfuron half‐life was 64 and 40 days respectively. Flupyrsulfuron and its metabolites were not detected during both crops or 1 month after crop harvest in the 8–15 and 15–20 cm soil layers. Soil degradation of flupyrsulfuron successively generated the cyclization products 1‐(4,6‐dimethoxypyrimidine‐2‐yl)‐2,4‐diketo‐7‐trifluoromethyl‐1,2,3,4‐tetrahydropyrido[2,3‐d]pyrimidine 2 and N‐(4,6‐dimethoxypyrimidine‐2‐yl)‐N‐(3‐methoxycarbonyl‐6‐trifluoromethylpyridine‐2‐yl)‐amine 3 , which were the main metabolites of flupyrsulfuron in soil. Hydrolysis of 3 successively generated N‐(4,6‐dimethoxypyrimidine‐2‐yl)‐N‐(3‐car‐ boxylic acid‐6‐trifluoromethylpyridine‐2‐yl)‐amine 4 and N‐(4‐methoxy‐6‐hydroxypyrimidine‐2‐yl)‐N‐(3‐carboxylic acid‐6‐trifluoromethylpyridine‐2‐yl)‐amine 5 . Low and temporary concentrations of 2‐sulfonamido‐3‐carbomethoxy‐6‐trifluoromethyl‐pyridine 6 and 2‐amino‐4,6‐dimethoxypyrimidine 7 were observed. Bioassays with sugarbeet as test plants indicated that 2, 3, 4, 5, 6 and 7 had herbicide activities corresponding to 100%, 80%, 75%, 75%, 75% and 15% of that of flupyrsulfuron respectively. The metabolites thus extended the herbicidal protection given by flupyrsulfuron and explain the high herbicidal protection given by the low dose of flupyrsulfuron applied. One month after the harvest of the winter wheat, no more significant residue of flupyrsulfuron or of its metabolites was detected in soil.     

Influence of application rate and manure amendment on cnloridazon dissipation in the soil

Plots of a sugar beet field in Belgium were treated pre-emergence with 1.3, 1.95 or 2.6 kg a.i. ha^-1 chloridazon. Some of these plots had been amended 1 month before sowing with 50 1 ha^-1 cow manure. Soil samples were taken al regular intervals and analysed by gas-liquid chromatography and gas-liquid chromatography combined with mass spectrometry. During the first month following chloridazon application, soil dissipation followed apparent first-order kinetics with soil half-lives being independent of the dose, and were 37 days in the non-manured plots and 96 days in the manured plots. After the first month, rates of chloridazon soil dissipation increased, giving the same residual chloridazon soil concentration of c. 0.25 mg a.i, kg^-1 in all plots 1.8 months after application. Residual levels remained at this concentration up to the third month after application, and then disappeared, leaving no delectable soil residues at harvest. Chloridazon soil dissipation thus occurred according to unusual kinetics.