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afXer the fourth, sixth and seventh application was generally similar to the untreated control. In these samples, nitraic content appeared to be correlated negatively with remaining weed number; the conirol thus contained less niiraie than efficient herbicidal treatments. Soil samples taken after the seventh application of bromacil, diuron, fluometuron, neburon and simazine. which contained appreciable rcsiduul concentrations, did not show signilicant dilTerences from control, in an in viiro nitrification test.Ten herbicides, bromacil, chlorthal-dimethyl, dlphenaniid, diuron, fluometuron, neburon, promelryne, pyrazon, simazine aod trifluralin at two doses were repeatedly sprayed, in autumn and in spring, for 4 consecutive years on noncultivated, sprinkler-irrigated field plots. Herbicidal effect was assessed at 1-2 month intervals on the natural weed population and after each observation a paraquat-I diquat spray destroyed emerged weeds. The response of various weed species to herbicides varied markedly but a herbicideinduced shift in the composition of weed population did not occur, presumably because of the paraquat treatment.The overall phytotoxicity to weeds present was, in decreasing order: diuron, bromacil, simazine, triflitralin, prometryne, neburon, fluometuron, pyrazon, diphenamid, chlortlial-dimethyl. Persistence of herbicides was in decreasing order: diuron = bromacil, simazine, neburon (at higher rate), fluometuron, trifluralin. prometryne. Control produced by pyrazon improved with the number of applications, but that of diphenamid and chlorthat-dimethyl remained weak and short. After repeated applications, the activity of these herbicides increased or remained at similar level, but in no case decreased.Soil samples were taken 5 months after each application and bioassayed. Phytoto.Kic residues were detected beneath the disturbed top-soil from bromacil, diuron, fluometuron and simazine after the first application, and from neburon after the second application; residues from trifluralin were found in the top soil only after the fifth application. After the seventh spraying, residues of bromacil were found in the 45-60-cm soil layer.Ammonia content in soil samples taken from treated plots * Contributioti from The Volcani Center, Agricultural Research Organization, Bet Dagan, Israel. 1973 Series, No. 181-E. Effects d'applications repit4es de di.K herbicides agissant par le sol sur une population de mauvaises herbes, i^accumulation des risidus et la nitrification.

Summary: Résumé: Zusammenfassung 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 jeweil...

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Gamma radiation of 3 megarads was applied to undiluted commercial formulations and aqueous solutions of 3-(3,4 dichlorophenyl)-1,1-dimethylurea (diuron), 1,1-dimethyl-(3-a,a,a-trifluoro-m-tolyl)-urea fluometuron),N,N-dimethyl-2,2-diphenylacetamide (diphenamid), 2,4-bis (isopropylamino)-6-(methylthio)-s-triazine (prometryne), dimethyl tetrachloroterephthalate (DCPA),a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) and sodium chlorate. The effect of radiation on herbicidal activity was assessed with bioassays. Radiation did not affect the bioactivity of undiluted or 50% solutions of any of the tested herbicides but decreased appreciably the activity of 100-ppm solutions of fluometuron, diphenamid, and prometryne. Diluted 100 and 10-ppm solutions of trifluralin lost part of their activity during storage in plastic containers and, in addition, following irradiation. It was not clear whether the decrease in activity observed in the 100-ppm solution of diuron was due to irradiation or to storage. No reduction in bioactivity was produced following irradiation of 100 and 10-ppm solutions of DCPA or 1% and 10% solutions of sodium chlorate.