Evidence for the Accelerated Degradation of Isoproturon in Soils

The herbicide isoproturon was degraded rapidly in a sandy loam soil under laboratory conditions (incubation temperature, 15°C; soil moisture potential, -33 kPa). Degradation was inhibited following treatment of the soil with the antibiotic chloramphenicol, but unaffected by treatment with cycloheximide, thus indicating an involvement of soil bacteria. Rapid degradation was not observed with other phenylurea herbicides, such as diuron, linuron, monuron or metoxuron incubated in the same soil under the same experimental conditions. Three successive applications of isoproturon to ten soils differing in their physicochemical properties and previous cropping history induced rapid degradation of the herbicide in most of them under laboratory conditions. There were, however, no apparent differences in ease of induction of rapid degradation between soils which had been treated with isoproturon for the last five years in the field and those with no pre-treatment history. A mixed bacterial culture able to degrade isoproturon in liquid culture was isolated from a soil in which the herbicide degraded rapidly.     

Anwendung von Isoproturon, allein und in Kombination mit anderen Wirkstoffen, im Nachauflauf-Winter (NA-W) und Nachauflauf-Frühjahr (NA-F) zu Winterweizen und Wintergerste

Use of isoproturon, alone and in combination with other compounds, post-emergence in winter and spring on winter wheat and winter barley Isoproturon, alone and combined with dinoseb acetate and bifenox, was applied post-emergence in winter and spring to winter barley and winter wheat. The experiment was on two sites (sandy and clay soils) and lasted for two years. Although after winter application the initial herbicide level in the soil was higher than after spring treatment, there were no differences at the end of the growing season. The DT₅₀ (time to 50% disappearance) value for isoproturon was between 12 and 33 days in both years for both soils and the DT₉₀ value varied from 34 to 68 days. Soil residues of isoproturon were not affected by the presence of the other compounds. Winter application gave better weed control and higher crop yields.     

Rapid mineralisation of the herbicide isoproturon in soil from a previously treated Danish agricultural field

Mineralisation of the phenylurea herbicide isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) and two of its known metabolites, 3-(4-isopropylphenyl)-1-methylurea (monodesmethyl-isoproturon) and 4-isopropylaniline, was studied in Danish agricultural soils with or without previous exposure to isoproturon. A potential for rapid mineralisation of isoproturon and the two metabolites was present in soils sampled from three plots within an agricultural field previously treated regularly with the herbicide, with 34-45%, 51-58% and 33-36% of the added [phenyl-U-14C]isoproturon, [phenyl-U-14C]monodesmethyl-isoproturon and [phenyl-U-14C]4-isopropylaniline metabolised to [14C]carbon dioxide within 30 days at 20 degrees C. In contrast, such extensive mineralisation of these three compounds was not observed within this period in soils sampled from two other agricultural fields without previous treatment with isoproturon. The mineralisation patterns indicated growth-linked metabolism of the three compounds in the previously exposed soils, and doubling times for [14C]carbon dioxide production ranged from 1.6 to 3.2, 1.0 to 2.1 and 1.3 to 1.7 days for isoproturon, monodesmethyl-isoproturon and 4-isopropylaniline, respectively. The ability to mineralise [phenyl-U-14C]isoproturon to [14C]carbon dioxide was successfully sub-cultured to a fresh mineral medium which provided isoproturon as sole source of carbon and nitrogen. One of the soils sampled from an agricultural field not previously treated with isoproturon showed accelerated mineralisation of [phenyl-U-14C]4-isopropylaniline toward the end of the experiment, with a doubling time for [14C]carbon dioxide production of 7.4days. This study indicates that the occurrence of rapid mineralisation of the phenyl ring of isoproturon to carbon dioxide is related to previous exposure to the herbicide, which suggests that microbial adaptation upon repeated isoproturon use may occur within agricultural fields.     

Effect of long‐term field application of pendimethalin: enhanced degradation in soil

The effect of long‐term application of pendimethalin in a maize–wheat rotation on herbicide persistence was investigated. Pendimethalin was applied at 1.5 kg AI ha⁻¹ separately as one or two annual applications for five consecutive years in the same plots. Residues of pendimethalin were determined by gas chromatography. Harvest‐time residues of the herbicide decreased gradually over the years and at the end of five years less than 3% of applied pendimethalin was recovered from soil as against 18% in the first year. Residues were found distributed in the soil profile up to 90 cm depth at the end of the experiment with peak distribution of 0.03 µg g⁻¹ in the surface layer of soil treated with 10 herbicide applications. The minimum distribution was, however, in the deepest soil (75–90 cm) profile. Some of the metabolites of pendimethalin ie dealkylated pendimethalin derivative, partially reduced derivative and cyclized product were also traced in surface and sub‐surface soils up to 90 cm. A study of the rate of degradation of pendimethalin in field‐treated soils under laboratory conditions revealed faster degradation compared to control soils. Only the surface soil (0–15 cm) showed this enhanced degradation of the herbicide, which could be due to the adaptability of the aerobic micro‐organisms to degrade pendimethalin. Microbes capable of degrading herbicide were isolated, identified and pendimethalin degradation was confirmed in nutrient broth. © 2000 Society of Chemical Industry     

The interaction between planting depth of four winter wheat cultivars, Alopecurus myosuroides Huds. and Bromus sterilis L. and their susceptibility to post-emergence applications of isoproturon and chlorotoluron

Seeds of four winter wheat cultivars, Slejpner, Galahad, Avalon and Penman, were sown at depths ranging from 6–75 mm in soil in pots, and isoproturon or chlorotoluron was then applied to the soil surface. For chlorotoluron-treated plants (both pre- and post-emergence) the dose required to produce a 50% effect (ED₅₀) was unaffected by depth of planting. In contrast, for isoproturon applied pre-emergence, the ED₅₀ for both Avalon and Slejpner was strongly affected by sowing depth. Although chlorotoluron was much more active in a second experiment when applied post-emergence to Slejpner wheat, the ED₅₀ for both herbicides increased with greater depth of sowing. Protection of wheat from isoproturon damage by deeper planting was enhanced if the adsorption capacity of the soil was raised from K_d 0.5 to 2.0 by incorporation of activated charcoal in the soil. Isoproturon entry into plants (as measured by the effect on rate of photosynthesis) was slower in those that had been sown deeper and were growing in more adsorptive soils, but there was no obvious relationship between these observations and isoproturon distribution in the soil profile. In nutrient culture the four wheat cultivars responded similarly to a range of doses of isoproturon. The chlorotoluron-sensitive cultivars, Slejpner and Galahad, were damaged by much lower doses of chlorotoluron than were Avalon and Penman. Bromus sterilis L. responded similarly to wheat with regard to its interaction with isoproturon and planting depth. Alopecurus myosuroides Huds., however, was less damaged by isoproturon when the zone above the seed was protected from the herbicide by growing the shoot through a plastic straw.     

Effect of cropping cycles and repeated herbicide applications on the degradation of diclofop-methyl, bentazone, diuron, isoproturon and pendimethalin in soil

A greenhouse study was conducted to investigate the ability of four crops (wheat, corn, oilseed rape and soybean) to influence the degradation of bentazone, diclofop-methyl, diuron, isoproturon and pendimethalin in soil. The present study showed that microbial biomass-carbon was significantly higher in planted soils than in bulk soil, especially with wheat and corn, after several cropping cycles. The biomass in corn and soybean planted soils was adversely affected by bentazone but recovered after three cropping cycles. In wheat-planted soils, diclofop-methyl application resulted in persistent increase of the amount of microbial biomass. Bentazone did not show accelerated degradation even after five successive treatments, differing from diclofop-methyl, for which two applications were sufficient to enhance significantly its rate of degradation. Enhanced degradation of diclofop-methyl was even more pronounced in wheat-planted soil. The rates of mineralisation of diuron, isoproturon and pendimethalin were not affected after the first cropping cycle, but were significantly increased in planted soils after five cropping cycles. The results confirm that plants may promote pesticide degradation in soil by stimulating biodegradation processes. In the case of diclofop-methyl, stimulation of accelerated degradation was observed.     

Anwendung von Isoproturon, allein und in Kombination mitanderen Wirkstoffen, im Nachauflauf–Winter (NA–W) und Nachauflauf–Frühjahr (NA–F) zu Winterweizen und Wintergerste

Use of isoproturon, alone and in combination with other compounds, post–emergence in winter and spring, on winter wheat and winter barley. II. Side effects on dehydrogenase activity, nitrogen transformation and straw decomposition in the soil The effect of isoproturon, alone and combined with dinoseb acetate and bifenox, on dehydrogenase activity, nitrogen transformations and straw decomposition following post–emergence application in winter and spring to winter wheat and winter barley was studied over two years at two sites. Isoproturon caused limited transient stimulation and inhibition of dehydrogenase activity, maximum 40%, and nitrogen turnover, 70–90%. Dinoseb acetate reduced general metabolic activity by up to 30%. Ammonium and nitrite concentrations were at times more than 100% higher than control values. In the laboratory, with temperature, soil moisture and sampling times similar25 to those in the field, isoproturon caused reductions in dehydrogenase activity in only a few cases but dinoseb acetate reduced the activity by up to 50%. The herbicide effects were clearer in a sandy than in a clay soil. The effect of time of application on the response of soil microbial activity to herbicides was evident only in the field.     

春麦田除草剂的应用与杂草群落演替

作者采用定点定位试验,对春麦田除草剂应用与杂草群落演替趋势进行研究。结果表明:在杂草群落多样性麦田,小麦连作并分别连续5年施用同一种除草剂,原杂草群落中占优势的靶标杂草得以控制,而非靶标杂草和抗、耐药性杂草因失去竞争和制约对象而猖獗发展,发生量较原来增加几倍至几十倍,并形成优势种群,对小麦造成新的更严重的危害。一种除草剂在同田块连续施用4年,由于杂草群落演替,抗、耐药杂草兴起,除草效果显著下降而失去其使用意义。作者提出除草剂配套使用、轮用、混用等措施,并配合以合理的轮作制度,以减轻杂草群落长期受到单一的定向选择性压力。     

土壤处理防治小麦田杂草节节麦药剂筛选

节节麦是我国冬小麦田中的一种恶性杂草.本文通过室内生物测定和田间药效试验筛选了有效防治节节麦的土壤处理剂,为冬小麦田节节麦的化学防治提供理论依据.温室试验结果发现:氟噻草胺、草酮和异丙隆对节节麦毒力较高,GR5(0值分别为37.2、15.7和349.3 g/hm2,均低于各自田间推荐剂量,但其在小麦与节节麦之间的选择...     

Spatial variability in 14C-herbicide degradation in surface and subsurface soils

The spatial variability in mineralization of atrazine, isoproturon and metamitron in soil and subsoil samples taken from a 135-ha catchment in north France was studied. Fifty-one samples from the top layer were taken to represent exhaustively the 31 agricultural fields and 21 soil types of the catchment. Sixteen additional samples were collected between depths of 0.7 and 10 m to represent the major geological materials encountered in the vadose zone of the catchment. All these samples were incubated with 14C-labelled atrazine under laboratory conditions at 28 degrees C. Fourteen selected surface samples which exhibited distinctly different behaviour for atrazine dissipation (including sorption and mineralization) were incubated with 14C-isoproturon and 14C-metamitron. Overall soil microbial activity and specific herbicide degradation activities were monitored during the incubations through measurements of total carbon dioxide and 14C-carbon dioxide respectively. At the end of the incubations, extractable and non-extractable (bound) residues remaining in soils were measured. Variability of herbicide dissipation half-life in soil surface samples was lower for atrazine and metamitron (CV < 12%) than for isoproturon (CV = 46%). The main contributor to the isoproturon dissipation variability was the variability of the extractable residues. For the other herbicides, spatial variability was mainly related to the variability of their mineralization. In all cases, herbicide mineralization half-lives showed higher variability than those of dissipation. Sorption or physicochemical soil properties could not explain atrazine and isoproturon degradation, whose main factors were probably directly related to the dynamics of the specific microbial degradation activity. In contrast, variability of metamitron degradation was significantly correlated to sorption coefficient (K(d)) through correlation with the sorptive soil components, organic matter and clay. Herbicide degradation decreased with depth as did the overall microbial activity. Atrazine mineralization activity was found down to a depth of 2.5 m; beyond that, it was negligible.     

Enhanced degradation of some soil-applied herbicides

In a field experiment involving repeated herbicide application, persistence of simazine was not affected by up to three previous doses of the herbicide. With propyzamide, there was a trend to more rapid rates of degradation with increasing number of previous treatments. Persistence of linuron and alachlor was affected only slightly by prior applications. In a laboratory incubation with soil from the field that had received four doses of the appropriate herbicide over a 12–month period, there was again no effect from simazine pretreatments on rates of loss. However, propyzamide, linuron and alachlor all degraded more rapidly in the previously treated than in similar untreated soil samples. Propyzamide, linuron, alachlor and napropamide degradation rates were all enhanced by a single pretreatment of soil in laboratory incubations, whereas degradation rates of isoproturon, metazachlor, atrazine and simazine were the same in pretreated and control soil samples.     

Practical experiences with a system for site-specific weed control in arable crops using real-time image analysis and GPS-controlled patch spraying

Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Primarily, spatial information allows a potential reduction in herbicide use, when post‐emergent herbicides are only applied to field sections with high weed infestation levels. This paper presents a system for site‐specific weed control in sugar beet, maize, winter wheat, winter barley, winter rape and spring barley. The system includes on‐line weed detection using digital image analysis, computer‐based decision making and Global Positioning System‐controlled patch spraying. In a 2‐year study, herbicide use with this map‐based approach was reduced in winter cereals by 6–81% for herbicides against broad leaved weeds and 20–79% for grass weed herbicides. Highest savings were achieved in cereals followed by sugar beet, maize and winter rape. The efficacy of weed control varied from 85% to 98%, indicating that site‐specific weed management will not result in higher infestation levels in the following crops.     

Influence of topsoil tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil

Twelve lysimeters with a surface area of 0.5 m² and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural tilth or a finer topsoil tilth. The influence of topsoil tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h^?1 over a 4‐week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4‐week period. Leaching losses of the three herbicides were monitored for a subsequent drainage event. Analysis of covariance showed a significant effect of topsoil tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer tilth. However, generation of the fine tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains. © 2001 Society of Chemical Industry     

Simulation of atrazine persistence in Spanish soils

The persistence of atrazine was monitored in three fields at different sites in Spain during two consecutive years (1990 and 1991). Laboratory assays for determining the influence of temperature and soil moisture content on the rate of herbicide degradation were carried out on soil samples from the same fields. The degradation constants derived from these assays, together with weather records for the period of the field experiments, were used in a computer program which simulated herbicide persistence in the field. Some adjustments were made to adapt the model to Spanish conditions. The model predicted with reasonable accuracy the persistence of the herbicide in two soils, although there was a tendency to overestimate the residues at early dates. Discrepancies between predicted and measured residues were greater in the third soil, due to rapid initial losses that were not predicted by the program. In this case, the agreement was improved if the program was run taking time zero to be one month after herbicide application. Possible reasons for these discrepancies are discussed.     

Evidence for the enhanced biodegradation of napropamide in soil

In laboratory incubations, the time to 50% loss of napropamide was approximately 60; 21 and 8 days in soil treated for the first, second and third time respectively. In a survey of soils from commercial fields, there was evidence that enhanced biodegradation of the compound had been induced by normal field applications—in some soils by a single previous treatment. Confirmation of the observations of rapid rates of loss in pre-treated soil was obtained in experiments with three formulations of napropamide. The rate of degradation in enhanced soils was unaffected by treatment of the soils with the antifungal antibiotic cycloheximide, but was inhibited by the antibacterial antibiotic chloramphenicol. Mixed bacterial cultures able to degrade the herbicide were obtained from three rapid-degrading soils by enrichment culture. Isolates from two of them were able to degrade the herbicide in pure culture. These bacteria have, as yet, not been characterised.     

Evidence for 2,4‐D mineralisation in Mediterranean soils: impact of moisture content and temperature

BACKGROUND: The 2,4‐D degradation ability of the microbiota of three arable Mediterranean soils was estimated. The impact of soil moisture and temperature on 2,4‐D degradation was investigated. RESULTS: The microbiota of the three soils regularly exposed to 2,4‐D were able rapidly to mineralise this herbicide. The half‐life of 2,4‐D ranged from 8 to 30 days, and maximum mineralisation of ¹⁴C‐2,4‐D ranged from 57 to 71%. Extractable ¹⁴C‐2,4‐D and ¹⁴C‐bound residues accounted for less than 1 and 15% respectively of the ¹⁴C‐2,4‐D initially added. The highest amounts of ¹⁴C‐2,4‐D bound residues were recorded in the soil with the lowest 2,4‐D‐mineralising ability. Although all three soils were able to mineralise 2,4‐D, multivariate analysis revealed that performance of this degrading microbial activity was dependent on clay content and magnesium oxide. Soil temperature affected the global structure of soil microbial community, but it had only a moderate effect on 2,4‐D‐mineralising ability. 2,4‐D‐mineralising ability was positively correlated with soil moisture content. Negligible 2,4‐D mineralisation occurred in all three soils when incubated at 10 or 15% soil moisture content, i.e. within the range naturally occurring under the Mediterranean climate of Algeria. CONCLUSION: This study shows that, although soil microbiota can adapt to rapid mineralisation of 2,4‐D, this microbial activity is strongly dependent on climatic parameters. It suggests that only limited pesticide biodegradation occurs under Mediterranean climate, and that arable Mediterranean soils are therefore fragile and likely to accumulate pesticide residues. Copyright © 2009 Society of Chemical Industry     

Adsorption of isoproturon,diuron and metsulfuron-methyl in two soils at high soil:solution ratios

Rates of degradation of isoproturon, diuron and metsulfuron-methyl were measured in two soils incubated at two temperatures (5 and 25 °C) with soil moisture at a matric potential of ?5 kPa. Rates of change in soil solution concentration were also measured after extraction of water from the soil using a centrifugation technique. The data, in general, indicated a more rapid rate of decline in aqueous-phase concentrations of herbicide than in total soil concentrations, and hence a progressive increase in partition coefficient in favour of the adsorbed phase^. In all of the incubations, however, adsorption of the herbicide was initially less than that measured using standard equilibration techniques that involved shaking with large volumes of solution relative to weights of soil. This may be explained by the ready availability of more adsorption sites in the shaken systems. With isoproturon and diuron, the changes in adsorption with time were similar at the two incubation temperatures. This indicates that the apparent changes in adsorption with these two compounds were not caused by preferential degradation in the soil solution, but by a slow equilibration with adsorption sites. The results with the weakly adsorbed compound metsulfuron-methyl, however, suggested the possibility of preferential degradation in the solution phase because, when degradation was slow, the absolute amounts adsorbed remained constant or increased slightly, even although solution concentrations declined. Implications of the results for pesticide behaviour in soils in the field are discussed.     

Secondary dispersal, spatial dynamics and effects of herbicides on reproductive capacity of a recently introduced population of Bromus sterilis in an arable field

An arable field was subdivided and subjected to either deep inversion ploughing or non‐inversion cultivation after viable seeds of Bromus sterilis had been sown into oilseed rape stubble. After sowing in isolated plots distributed within the field, sequences of cropping treatments for the establishment of two successive winter wheat crops were applied. Each subfield was split into an uphill and a downhill direction for soil cultivation. The field had a 10° slope. In the season following seed introduction, 2.6% of the introduced seeds had successfully germinated and established in the non‐inversion cultivation regime, when no effective graminicide was applied. Ploughing eradicated B. sterilis. Using differential global positioning system (DGPS) mapping of the whole field population, emerged plants were observed up to 8.7 m (uphill treatment) and 21.3 m (downhill treatment) of their initial source. The median distance seeds were transported was 2.3 m uphill and 4.8 m downhill. Post‐emergence application of the herbicide propoxycarbazone slightly reduced weed density and seed weight, and almost halved weed seed production. Application of fenoxaprop‐P‐ethyl was followed by higher density of plants, tillers and seeds of B. sterilis. Seed viability was unaffected by herbicide use. Thus, in the second wheat crop following seed rain, the weed population was dispersed more widely in the field, such that 20–30% of seeds were dispersed more than 5 m distance from the first year's foci of infestation. The relevance of soil cultivation to secondary dispersal of B. sterilis is discussed.     

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.     

The photochemical decomposition of the herbicide isoproturon

The photochemical degradation of the herbicide isoproturon in aqueous and non-aqueous solutions and in soils has been investigated. Four new photometabolites were formed in non-aqueous solution and three in soil. These were characterised by spectroscopic methods and identified by comparison with authentic synthetic samples such as 3-(4-isopropylphenyl)-1-methylurea; 3-(4-isopropylphenyl)urea; 4,4′-diisopropylazobenzene and 4,4′-diisopropylazoxybenzene. The pathway of formation of these photo products is depicted.