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Abstract  

Adsorption of the herbicide terbuthylazine by a soil from the Jezreel Valley was investigated by thermo-IR-spectroscopy. The adsorption took place mainly by the clay mineral montmorillonite. The adsorbed molecule was hydrogen bonded via the aniline groups to water molecules which were coordinated to the exchangeable metallic cations. When the sample was thermally treated at 115°C interlayer water was evolved, part of the herbicide decomposed and the other part became directly coordinated to the exchangeable metallic cations. The decomposition product contained a CO group.

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samples. Pesticides monitored for this study were atrazine, terbuthylazine and their metabolites. GAC Norit 1240 W was purchased from Cabot Corporation and Filtrasorb 400 was purchased from Chemviron Carbon. The characteristics of this GAC are presented in

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In a pot experiment the effects of the length of incubation period and the pre-emergence application of terbutryn/terbuthylazine at 2.80 kg a.i. ha-1 or post-emergence application of bentazone at 2.88 kg a.i. ha-1 on the nitrogenase activity in intact pea plants were measured in situ by the acetylene reduction assay. An incubation period of 10 min resulted in the highest nitrogenase activity. As the length of the incubation period increased to 30 or 60 min the total as well as the specific nitrogenase activity decreased. Terbutryn/terbuthylazine decreased the total nitrogenase activity at all three (i.e. vegetative, flowering and seed-filling) stages, whereas bentazone resulted in a significant decrease at the flowering stage only. However, terbutryn/terbuthylazine-treated plants had the highest specific nitrogenase activity both at the flowering and seed-filling stages.

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Effects of one pre-emergence herbicide (terbutryn/terbuthylazine) and one post-emergence herbicide (bentazone) along with unweeded and hand-weeded controls on weeds and on the nodulation, nitrogenase activity, nitrogen content, growth and yield of pea (Pisum sativum) were studied. Terbutryn/terbuthylazine was applied pre-emergence @ 1.40, 2.80 and 5.60 kg/hawhereas bentazone was sprayed 6 weeks after sowing @ 1.44, 2.88 and 5.76 kg/h. Terbutryn/terbuthylazine controlled all the weeds very effectively, whereas bentazone did not control some weeds such as Polygonum aviculare, Poa annua and Elymus repens. The herbicides decreased the number of nodules, the dry weight of nodules, the nitrogenase activity, the shoot dry weight, the nitrogen content in the straw and seeds, and the seed yield of peas, the effects generally being higher at higher rates of application. The adverse effects of herbicides on these parameters might be due to their effects on plant growth, as both the herbicides are known to adversely affect photosynthesis. Nitrogenase activity did not correlate well with plant-N content or shoot dry weight. However, there was a strong relationship between plant biomass and plant-N content, which suggests that researchers can rely on these parameters for studying the effects of treatments on nitrogen fixation, rather than measuring nitrogenase activity.

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The effects of the pre-emergence application of terbutryn/terbuthylazine at 1.40 and 2.80 kg a.i./ha and prometryn at 1.70 and 3.40 kg a.i./ha and the post-emergence application of bentazone at 1.44 and 2.88 kg a.i./ha were studied on nodulation, root and shoot growth in two pea varieties, namely Rex and Guido. Of these the lower rates are the recommended rates for field application. Bentazone even at the recommended rate decreased nodule dry weight, whereas all three herbicides at double the recommended rate (except terbutryn/terbuthylazine in Rex) decreased the number and dry weight of nodules. Terbutryn/terbuthylazine and bentazone decreased root dry weight to a greater extent, whereas prometryn had only a slight effect. Shoot growth was adversely affected by all three herbicides in both the varieties, but prometryn and bentazone had less adverse effects in Rex than in Guido. Compared to the recommended rate, the herbicides had a greater adverse effect on nodulation at double the recommended rate.

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Összehasonlító vizsgálatokat végeztünk 13 gyomirtó szer hatóanyagán azok fotobomlási folyamatainak tanulmányozására. Mivel a spontán alapfolyamatok megfigyelése volt a célunk, nem használtunk adalékanyagokat. Bár a természetben a növényvédő szerek számtalan, a bomlásukat befolyásoló anyaggal találkoznak, a kutatás e fázisában ezeknek a hatásoknak a vizsgálata nem volt célunk. A vizsgálatok alapján felvázoltuk az egyes hatóanyagok bomlási sémáját és a bomlás időbeli lefutását. Megállapítottuk, hogy valamennyi vizsgált vegyület jól mérhető fotoaktivitást mutatott vizsgálati körülményeink között, valamint hogy a legtöbb vegyület bomlásterméke kevésbé környezetidegen, mint az eredeti vegyület volt.

Nem hagyhatjuk azonban figyelmen kívül, hogy természetes körülmények között a talajban számos egyéb folyamat is lejátszódik, a vizsgált vegyületek — elsősorban bázikus jellegű — nitrogénatomján a mikrobiális folyamatok hatására N-oxidáció is bekövetkezhet. Ez egyrészt közvetlenül nitrozovegyületek kialakulásához vezethet, amelyek már magukban is igen toxikusak és karcinogének. A talajban előforduló nitrit- és különösen a nagy mennyiségű nitrátionokkal ezek a nitrozovegyületek tovább is reagálhatnak, és ez a folyamat a fokozottan agresszív karcinogén N-nitrózaminok keletkezéséhez vezethet. Mivel ezek a folyamatok talajtípus függőek, további vizsgálatuk elengedhetetlen.

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