The adsorption of glyphosate in a slurry system by 9 soils was correlated with an arbitrary single point inorganic phosphate sorption index which gave a measure of unoccupied phosphate sorption capacity, but not with total phosphate sorption capacity at pH 2.6, the level of iron and aluminium soluble in Tamm's acid oxalate or with clay content, organic matter content or pH. It is concluded that inorganic phosphate excludes glyphosate from sorption sites. The extent of adsorption was higher than, though of the same order as, that of diuron though the two are not related. From consideration of the results of previous experiments with plants grown in culture solution it is suggested that the low phytotoxicity of glyphosate applied to the soil is not due simply to high adsorption. Rather it is the result of a combination of moderate adsorption and the low intrinsic activity of this compound when made available to the root system.

The absorpticMi of urea and a number ofits derivatives by different soils was investigated using a slurr>'-type procedure. The materials could tx-listed in the following order of increasing tendancy to br ad.v)rbed: urea, fenuron, methylurea, phrnylurea, monuron, monolinuron, diuron, linuron, ncbtiron and chloroxuron. Both .V-ar>'l and '-alkyl substituents apjjcared to play a part in adsorption. Increasing chain length in tbe alkyl subsiitupnts and chloro-and chtorophenoxy siibNlitution in the aryl suljsiituent increased adsorption. There was no rfLiliunship between ixlsorption and water solubility.Organic matter content was the only soil property thai rtmld be related to adsorptive capacity. The e\'idence of Langmuir isothermal eqtiilibrJum plots suggests (hat only a fraction of the total wil surface is available for the adsorption of substituted ureas. VadsoTpiion dt rurie et dt s€s dhivis sur diffirtnts solsR^sutn^. [^'adsorption de I'uree ci d'lui certain nombre de .ses dtriv^s sur divers sols, a ii\i: t'ludiee a I'aide d'une methode dii type agitation. Consid6raiit leur tendance ^ ctre ad.sorb^es, les substances ^Uidi^es peuvcnt se ranger dans I'onlre croissant suivani; urt^c. ftfnuron, mtthylun^e, ph^nylurrfe, monuron, monolinuron. diuron, linuron, iieburon et chloroxuron. IA substitution .V-ar\lique et A-alkyliqne parait affecter I'lidsorption. l-'adsorption fut accrue par rallfingenicnt de la chaine dans les substitu^s alkyliques ei par la substitution cbloro-et chlorophinoxy-dans le 5ul>stitu6 arylique. On n'a pas trouvi de relation cntre l'adsorption ri la solubility dans IVnu.La teneur en matii-re urganique fut la seule caractdristique du sol pouvant etre reliâ sa c^pacil(^ adsorbante. L'examen des coiirbes dYquilibre isothermique de I.angmuir sugg6re qu'une partieaeulement de la surface totale du sol e. Ht disponible pour Tadsorption des ur£es substituties. Die Adsorption von llamstoff wut einiger seiner Dericale durth eine Anzaht ron Bdden Zusammenfassung. Die .\dsorptiqn von HamstofT und eine Reihe seiner Dcrivate durch verschiedene Ikxlrn wurde mit einer .\rt Schlamniverfahren unter.tucht. G«>rdnet nach zunehmender Adsorption ergab sich folgende Rt-ihcnfolge: HarnstotT. Fenuron, Methyl-, PhenylltarnstofT, Monuron, Munolinuron, Uiuron, Linuron, \eburon und C-liI()roxuron. Sowolil .V-Aryl-als auch ,\-Alkyl-Substili<>n schten einen Kinthiss aul" die Adsorption zu habcn. Zunahinc drr Kettenlangc in der AlkylsubslilutJon sowie Chlor-und Chlorphenoxysubstitution drr .Vrylsubstitutinn erhiihten die Adsorption. Zwischcn Adsorption und Wasscrloslichkeit bcstand jcdurli keine Beziehung.Der Gehalt an organischer Substanz war die einzige Bodencigenschaft, die zu drsscn adsorptiver Faliigkeit in Beziehung gebracbt werclen konntc. Die Vcrsuchc zeigen weiterhin, dass nur ein Teil der Gesamtbodenoberliache fur die .\dsorption von substituierten HarnsioHen frei ist.

A scries of adtiorption experiments was carried out in order to dcterinine if ihcrc was significant compciition for adsorption sites between diuron and water. .Adsorption of diuron was miieli lower on hydrophilic matcriaLs sucli as cellulose, chitin, aluminium oxide and a soil mineral fraclion than on the less Uydrophilie ion exchange resins, lignin, carbon and a soil organic Traction. Methylation with mcihanolic HCI or diazomethane increased adsorption by the soil organic material, bul melhylation with dimethyl sulphate did not.The soil mineral fraction adsorbed considerably more diuron from petroleum spirit solution ihan from aqueous solulion, but ihe organic mailer preparation adsorbed more from aqueous than from pclroleum solution.It was concluded ihai ihcre is competition between water and diuron for adsorption liles and that diuron is a more effective competitor at soil organic matter surfaces than at soil mineral matter surlaccs. Obsenations sur la relation entn VadsoTption du diuron et la nature de VadsorbantR^sum^. Une s<^rie d'cxp^riences d'adsorption fut eflecluie pour determiner s'il y avait competition pour les sites d'adsorption eiilre le diuron ei I'eau. Sur des substances hydrophiles tellcs que cellulose, chitinr. oxydc d'aluminc ct une fraction min^rale du sol, l'adsorption du diuron eiait plus faiblr que sur des mat<^riau.\ moins hydrophiles comme des riiiines echangt-urs d'ions, la ligninr, le carbone et une I'raciion organique du sol. La m^thylation avec HCI mcthanolique on avcc le diazom^thane accrut l'adsorption des fractions organiqucs du sol, mais la mithylation avec le sulfate do dimf^thyle fut sans effet.La fraction minirale du sol adsorbe beaucoup plus dc diuron d'une solution dans lYther de p^trole que d'une solution aqueuse, tandis que la preparation de matiire orgunique adsorbe inieux d'une solution aqueuse.On conclut qu'ii y a competition entre I'rau et le diuron pour les .sites d'ad.sorption et que le diuron est tin ronipetiteur pluseflicarc sur les surfaces tic ma ticrc organique du sol que sur les surfaces dc matiere min^rale.

Summary The persistence of isoproturon in soil in pot experiments was the same whether or not the soil contained growing wheat (Triticum aestivum L.) plants, Panllel) work with radioactive isoproturon showed that the breakdown products were the same in the presence and absence of plants. Persistence in the field was reasonably well predicted by a simulation model using the results of laboratory incubation studies and field meteorological data.

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