Publisher Summary The behavior of pesticides in soils has been the subject of research long before pollution became a byword. In recognition that soil is the ultimate sink for most widely used pesticides, and given the impetus of recent public awareness of the quality of our environment, the past decades have marked much progress in the understanding of the fate and behavior of pesticides in soils. A strong case for the continued use or precipitate abandonment of agricultural pesticides is inappropriate. It is reasonable, however, to note the vitally important role pesticides have assumed in increasing the quantity and quality of foodstuffs, timber, and ornamental plants; in improving animal health; and in combating certain diseases transmitted to man. This chapter reviews the behavior of pesticides in soils from the standpoint of processes affecting pesticides (physicochemical and metabolic), the effect of pesticides on the soil microbiota, and the implications of these processes on persistence, bioactivity, and plant uptake. Adsorption, the most influential process affecting pesticides in soils, depends on both soil and pesticide properties. Other significant soil factors include total surface area, water content, temperature, and pH. Pesticide properties that are relevant include overall chemical character and configuration, dissociation constant, water solubility, charge distribution, and molecular size. Movement of the pesticides occurs by leaching, volatilization, or runoff. The importance of photodecomposition as a process degrading pesticides in soils is uncertain. Generally, photolysis occurs more readily for compounds in solution, with soil inhibiting the reaction.

Behavior of Pesticides in Soils

Publisher Summary This chapter discusses the effects of pesticides on the microflora in general and on the microorganisms responsible for the major biological processes. The use of pesticides in agriculture leads to changes in the soil microflora. In the major biological cycles, nitrification and cellulolysis seem to be the phases that are most affected by pesticides. In the case of the nitrifying bacteria, their frailty, added to their specialization, results in a greater sensitivity, Moreover, the effects of pesticides on the biological life of soils seem to appear more often under precarious environmental conditions that impede the growth of microorganisms. At normal field rates and with short-term applications, the effects are generally more limited. Methods of evaluating the effects of pesticides must be refined and improved. A better quantification by means of new biological methods, such as measurement of the biomass and radiorespirometry, would provide more precise information.

Effects of Pesticides on The Soil Microflora

Summary: Resume: Zusammenfassung

The effect of repeated applications of 2,4-D and MCPA in a long-term field experiment on their subsequent degradation was investigated. The herbicides had been applied annually since 1954, Comparisons were made with plots treated once and then retreated the following year. Repealed applications of the two herbicides resulted in a reduction in degradation lime from 10 weeks for 2,4-D and 20 weeks for MCPA after one application to 4 and 7 weeks respectively after 19 years of annual application. In spite of an increased capability of the soil microflora lo degrade 2,4-D and MCPA 9 months after a previous treatment. no change in numbers of organisms capable of utilizing the substances as carbon sources were found in treated plots as compared with the control. It is obvious that there is a cross adaptation between 2,4-D and MCPA. It seems most likely that two different ‘enrichment’ been induced, each capable of decomposing both herbicides, but with different efficiencies.



Effet d'applications repetee de 2,4-D et de MCPA sur leur degradation dans le sol



L'effet d'applications repetee de 2.4-D et de MCPA sur leur degradation uleerieure a eteetudie dans une experience au champ de longue duree. Les herbicides ont ete appliques chaque annee depuis 1954. Des comparaisons ont ete effectuees avec des parcelles traiees une fois et traitees a nouveau l'annee suivante. Les applications repetees des deux herbicides ont provoque une reduction du temps de degradation qui est passe de 10 semaines pour le 2,4-D et 20 semaines pour le MCPA apres une seule application, a 4 et 7 semaines respectivement, apres 19 annees d'applications annuelles. En depit d'une capacite accrue de la microflore du sol a degrader le 2.4-D et le MCPA, neuf mois apres un traitement prealable, aucun changement n'a ete constate dans le nombre des organismes capables d'utiliser les produits comme sources de carbone dans les parcelles traitees, par rapport au temoin. II est evident qu'il y a une adaptation croisee entre le 2,4-D et le MCPA. II apparait tres probable que deux ‘enrichissements’ de Hores ont ete induits, chacun d'eux etant capable de decomposer les deux herbicides mais avec des efficacites differentes.



Die Wirkung wiederholter Behandlungen von 2.4- D und MCPA auf ihren Abbau im Boden



Die Wirkung wiederholter Anwendungen von 2,4-D und MCPA auf ihren Abbau wurden in einem Freiland-Versuch untersucht. Die Herbizide wurden jahrlich, sell 1954 ange-wendet. Es wurden Vergleiche mil Parzellen angcstellt, die zum erstenmal und im folgenden Jahr nochrnaK bchandelt worden waren. Die widerholien Behandlungen mit den beiden Herbiziden bewirkte elne Verringerung der Ab-bauzeit von 10 Wochen fur 2,4-D und 20 Wochen fiir MCPA nach einer Behandlung, auf 4 bzw. 7 Wochen nach 19 Jahren jahrlicher Anwendung. Trotz der erhohten Ffihigkeit der Bodenmikroflora 2,4-D und MCPA neun Monate nach einer vorhergehenden Behandlung abzubauen, war die Zahl der Organismen, die diese Herbizide als Kohlensloffquelle verwerten konnen, in den behandelten und unbehandelten Parzellen gleich gross. Zwischen 2.4-D und MCPA existiert ofVensichtlich elne Kreuz-Adaplalion. Sehr wahrscheinlich wurden zwei versehiedene ‘enrichment’-Floren induziert, von der jede in der Lage ist beide Herbizide, aber mit unterschiedlicher Effizienz, Hbzubauen.

The effect of repeated applications of 2,4‐D and MCPA on their breakdown in soil

The production and usage of herbicides have increased dramatically in recent years. Consequently there is growing concern about the effects of these chemicals on the environment, particularly the possible long-term effects on soil fertility which may result from disturbance of the soil microflora. This review considers the recent developments in the study of the interactions between herbicides and microorganisms, and discusses the problems of evaluating the results of such studies with a view to determining or predicting possible short-term or long-term effects which may be of practical significance.

Herbicides and soil microorganisms.

Greenhouse and laboratory experiments showed that the biological activity of EPTC (S-ethyl dipropylthio- carbamate) + R-25788 (N,N-diallyl-2,2-dichloroacetamide) was lost more rapidly in soils if they had been previously treated with this herbicide. Treatments which reduced or eliminated the microbial activity in the soil restored the herbicide activity in 'problem' soils. A combination of 2 kg/ha of the insecticide fensulfothion (diethyl-4- methyl- sulphinyl phenyl phosphorothionate) with EPTC + R-25788 also restored the biological activity of the herbicide. Field trials confirmed the decreased biological activity with repeated use of EPTC + R-25788; other herbicides recommended for grass weed control in corn (Zea mays L.) performed satisfactorily in these 'problem' soils. The performance of EPTC + R-25788 was improved by a rotation away from it for one season (using another herbicide) but the- level of activity was still below that obtained in a soil treated with EPTC + R-25788 for the first time. A new formulation of EPTC + R-25788 containing a herbicide extender R-3 3865 (0,O-diethyl-O-phenyl phosphorothioate) was not affected by the enhanced microbiological breakdown and provided effective season-long weed control in the 'problem' soils. Additional index words. Thiocarbamates, microbiological degradation, persistence, Zea mays, herbicide extenders.

Decreased activity of EPTC + R-25788 following repeated use in some New Zealand soils.

Zusammenfassung. Es wird uber die Abbaugeschwindigkeit von DNOC und 2,4-p in eistmals und in langjahrig wiederholt behandeltem Boden berichtet. Der langjahng wiederhoh behandelte Boden stammte aus einem Feldversuch, in dem diese Herbizide in 12 Jahren 12 mal zur Unkrautbekampfung in Getreide angewandt wurden. Wenn Boden der DNOC-Parzellen 7 Monate nach seiner letzten Behandlung erneut mit DNOC versetzt wurde, war gegenuber erstmals behandeltem kein Unterschied in der Abbaugeschwindigkeit festzustellen. Wurde Boden der 2,4-D-Parzcllen 8 Monate nach der letzten Applikation wieder mit 2,4-D versetzt, verlicf der Abbau des Herbizids schneller als im Boden der zum erstenmal mit dem Herbizid behandelt worden war.



Effet d'un traitement a long terme avec le DNOC et le 2,4-D sur leur degradation dans le sol



Resume. La degradation du DNOC et du 2,4-D a eteetudiee dans un sol traite pour la premiere fois et dans un sol provenant de parcelles en plein champ qui ont recu des traitements annuels durant une periode de dotize ans pour le desherbage des cereales. Quand le sol provenant des parcelles traitees au DNOC fut examine sept mois apres la derniere application, il ne fut pas constate de difference dans le taux de degradation par rapport ausol traits pour la premiere fois. La degradation du 2,4-D dans lesol provenant des parcelles traitees et examine huit mois apres la derniere application fut plus rapide que dans le sol des parcelles traitees pour la premiere fois.



The effect of long-Urm treatment with DNOC and 2,4-D on their breakdown in soil



Summary. The breakdown of DNOC and 2,4-D was studied in soil treated for the first time and in soil from field plots which had received annual treatments over a period of 12 years for weed control in cereals. When soil from DNOC-treated plots was tested 7 months after the last application, there was no difference in the rate of breakdown from that in soil treated for the first time. The breakdown of 2,4-D was more rapid in soil from the treated plots, tested 8 months after the last application, than in soil from plots treated for the first time.

K. Hurle Und

Papers

Untersuchungen uber den einfluss langjahrig wiederholter anwendung von dnoc und 2,4‐d auf ihren abbau im boden