Measurement and simulation of the movement and degradation of atrazine and metribuzin in a fallow soil

The movement and persistence of atrazine and metribuzin, in a sandy loam soil following application in spring, was simulated using two models. The first model, based on the physical laws describing water and solute movement and using measured values of soil hydraulic properties, underestimated herbicide mobility in the soil and predicted too rapid drying of the deeper soil layers. The accuracy of the simulations was improved by empirically reducing the measured hydraulic conductivities by a factor of 4. This probably reflects the difficulties of obtaining reliable measurements of soil hydraulic properties. A second and simpler model, which simulated water and herbicide movement using mobile and immobile water categories, accurately predicted soil water contents. It tended to underestimate herbicide movement at short times after application, and to overestimate movement later in the experiments. A comparison of different methods of simulating herbicide degradation showed that prediction of degradation rates in the field from laboratory data can be unsatisfactory with some compounds.     

Effects of microbial inhibitors on the degradation rates of metamitron,metazachlor and metribuzin in soil

Rates of carbon dioxide evolution and degradation rates of metamitron, metazachlor and metribuzin were measured in two soils in the presence of three microbial inhibitors. The nonselective microbial inhibitor sodium azide reduced both carbon dioxide evolution and the rate of loss of all three herbicides in both soils, although the reduction in degradation rate of metamitron was small. The antibacterial antibiotic novobiocin enhanced carbon dioxide evolution from both soils but had variable effects on the rates of herbicide degradation. It inhibited degradation of metazachlor and metribuzin, and in one of the soils its effects on metazachlor degradation were similar to those of sodium azide. Novobiocin inhibited degradation of metamitron to a small extent in one soil only. The antifungal antibiotic cycloheximide also enhanced carbon dioxide evolution from both soils. In general, its effects on herbicide degradation were similar to those of novobiocin, although the extent of inhibition was usually less pronounced. The results are discussed in terms of the relative involvement of microorganisms in degradation of the three herbicides.     

The influence of soil properties on the rates of degradation of metamitron,metazachlor and metribuzin

The rates of degradation of metamitron, metazachlor and metribuzin were measured in 12 mineral soils and the first order rate constants were compared with soil properties by regression analysis. Rates of metamitron degradation were best described by a multiple regression involving the silt content of the soil and the fraction of the total herbicide content which was available in the soil solution. Metazachlor degradation was best described by a multiple regression involving the sand content of the soil, the availability of the herbicide in the soil solution and soil microbial respiration. There was evidence that metribuzin degradation in any one soil was closely related to microbial activity, and rate constants per unit microbial respiration were derived for each soil. These rate constants were best described by a multiple regression involving the Freundlich adsorption constant and the sand content of the soils. The best regression equations for each herbicide were tested against observed degradation rates in an additional group of six soils. The calculated rates compared favourably with those observed for both metamitron and metazachlor, but with metribuzin, there was good agreement with one soil only.     

Some physicochemical and environmental factors affecting transformation rates and sorption of the herbicide metamitron in soil

In addition to the molecular structure of a pesticide, environmental conditions may influence its persistence through their effect on the growth and activity of pesticide-degrading micro-organisms. As a result, transformation rates may decrease rapidly when a compound is leached into subsoil. Metamitron sorption isotherms were determined and incubation series were set up for a sandy loam soil, simulating single and combination effects that occur during transport of metamitron into subsoils. K_OC values increased with increasing depth from 185 to 700 litre kg⁻¹. A combination of conditions that are unfavourable for microbial activity, such as low temperature (5°C), low concentrations (0·5 mg kg⁻¹) and a large sorbed fraction (K_OC = 700) resulted in half-lives of over one year. Oxygen inhibition decreased the transformation rate of metamitron from 0·058 to 0·019 day⁻¹. In order of significance, the transformation of metamitron appears to be a function of temperature, oxygen availability and sorption to organic carbon. Increasing doses did not change transformation rates significantly, although different transformation pathways were observed.     

Absorption, translocation and metabolism of metamitron in Chenopodium album

BACKGROUND: In recent years, common lambsquarters (Chenopodium album L.) populations from sugar beet fields in different European countries have responded as resistant to the as‐triazinone metamitron. The populations have been found to have the same D1 point mutation as known for atrazine‐resistant biotypes (Ser₂₆₄ to Gly). However, pot experiments revealed that metamitron resistance is not as clear‐cut as observed with triazine resistance in the past. The objectives of this study were to clarify the absorption, translocation and metabolic fate of metamitron in C. album. RESULTS: Root absorption and foliar absorption experiments showed minor differences in absorption, translocation and metabolism of metamitron between the susceptible and resistant C. album populations. A rapid metabolism in the C. album populations was observed when metamitron was absorbed by the roots. The primary products of metamitron metabolism were identified as deamino‐metamitron and metamitron‐N‐glucoside. PABA, known to inhibit the deamination of metribuzin, did not alter the metabolism of metamitron, and nor did the cytochrome P450 inhibitor PBO. However, inhibition of metamitron metabolism in the presence of the cytochrome P450 inhibitor ABT was demonstrated. CONCLUSION: Metamitron metabolism in C. album may act as a basic tolerance mechanism, which can be important in circumstances favouring this degradation pathway. Copyright © 2011 Society of Chemical Industry     

不同残膜量对土壤水分运移的影响及模拟

为解决绿洲区残膜污染,结合已有研究,根据农田残膜量与覆膜年限的关系,设计了9种残膜量处理(0、50、80、132、160、264、396、792、1 320 kg·hm~(-2)),利用室内土柱模拟试验,对不同处理的土壤水分湿润锋运移距离、运移速率、累积蒸发量、蒸发速率、土壤含水率进行监测分析并进行模型模拟,探究残膜量对土壤入渗和蒸发的影响以及模型模拟精度。结果表明:随着残膜量增加,湿润峰运移距离呈减小趋势,较CK减少2.76%～8.66%(P0.05),0～5 h内的平均运移速率较CK减少0.4%～19.5%(P0.05),总体呈幂函数降低趋势;随残膜量增加,累积蒸发量逐渐减小,较CK减少5.04%～38.92%(P0.05),蒸发速率呈降低趋势,而随着蒸发时间增长,蒸发速率也呈幂函数降低趋势;各残膜处理0～10 cm土层土壤平均含水率比10～20 cm土层降低1.51%～3.08%(P0.05),残膜破坏了土壤水分分布的均衡性。通过评价模型的结果显示,各处理拟合结果的决定系数R~2均大于0.988。随着残膜量的增加,RRMSE值出现差异,CRM值趋近0,CE值出现波动变化,模型拟合的结果呈现先变好后变差。     

Evaluation of a simulation model for prediction of herbicide movement and persistence in soil

The movement and persistence of residues of propyzamide, linuron, isoxaben and R-40244 were measured in a sandy loam soil in field experiments prepared in spring and autumn. None of the herbicides moved to depths greater than 12 cm in the soil during the winter period, following application in autumn, and none moved more than 6 cm in the soil, following application in spring. The general order of persistence of total soil residues was isoxaben > linuron = R-40244 > propyzamide. Appropriate constants to describe the moisture and temperature dependence of degradation were derived from laboratory incubation experiments and used with measurements of the strengths of adsorption of the different herbicides by the soil, in a computer model of herbicide movement. The model, in general, gave good predictions of total soil residues, but overestimated herbicide movement, particularly in winter. Measurements of herbicide desorption from the soil at intervals, during a laboratory incubation experiment, demonstrated an apparent increase in the strength of adsorption with time. When appropriate allowance was made for these changes in adsorption in the computer model, improved predictions of the vertical distribution of the herbicide residues were obtained.     

Adsorption,decomposition and movement of oxamyl in soil

A study was conducted of the behaviour of oxamyl in Israeli soils of varying clay and organic matter contents. The adsorption isotherms for oxamyl were linear, and the adsorption coefficient (K_d) could be correlated to the clay content of the soils, as well as to the organic matter content of the soil. Oxamyl adsorption was underestimated by using published correlations between the adsorption and the chemical properties of pesticides, such as their solubility or octan-1-ol-water partition coefficient. The decomposition of oxamyl in soils followed first-order kinetics. The half-life ranged from 4 to 33 days in a Bet Dagan soil. The reaction rate increased with increasing moisture content of the soil until field capacity was reached, at which point it levelled off. The Arrhenius relationship was followed, with degradation proceeding more rapidly at higher temperatures. In several soils of varying composition, which were kept at field capacity, no difference in the degradation rates was observed. Oxamyl was applied to a Bet Dagan soil from a point source in a single pulse, as a split application, and on a continuous basis. The distribution patterns of oxamyl under the various treatments differed significantly. After the single-pulse application, oxamyl was leached out of the emitter zone. While the split application decreased the oxamyl-free zone, the best results were obtained by continuous application, which gave a nearly uniform distribution of oxamyl in the soil.     

Conversion and leaching of aldicarb in soil columns

Aldicarb was applied to soil columns in the laboratory which were leached by artificial rainfall. Concentrations of aldicarb, its sulphoxide and its sulphone in the effluent were measured by gas-liquid chromatography. The measured results were analysed in some detail using a computation model. Aldicarb and its oxidation products were very mobile in soil, a fact which could be well described after introducing very low sorption coefficients in the computation model. Aldicarb itself was converted at a high rate following first order kinetics (half-life about 2 days). The best approximations obtained for the rate constant of sulphoxide conversion in two soils were about 0.03 and 0.06/day respectively (half-lives 23 and 12 days). Only a rather wide range of possible values could be obtained for the rate at which sulphone was decomposed.     

Adsorption-leaching study of the herbicides metamitron and chloridazon

Freundlich isotherms were obtained for the adsorption equilibrium of the herbicides metamitron and chloridazon with the components of a representative soil in a pesticide concentration range of 10-1000 γg ml^?1 for metamitron and 10-500 μg ml^?1 for chloridazon. The mobility of these herbicides through soil columns was also studied using the displacement technique described by Davidson (Soil Sci. Soc. Amer. Proc., 32 (1968) 629). The experiment was carried out simultaneously in three columns, two of which were fed with solutions of the herbicides while the third was used as a control. The herbicide solutions flowed down by gravity and were collected at the outlet at different times. The herbicide content of these outlet solutions was determined by Differential Pulse Polarography.     

Leaching behaviour of azoxystrobin and metabolites in soil columns

BACKGROUND: Azoxystrobin [methyl (E)‐2‐{2‐[6‐(2‐cyanophenoxy)pyrimidin‐4‐yloxy]phenyl}‐3‐methoxyacrylate], a strobilurin fungicide, is a broad‐spectrum, systemic and soil‐applied fungicide. Azoxystrobin has been registered for rice cultivation in India, but no information is available on its leaching behaviour in Indian soils. Therefore, leaching behaviour of azoxystrobin was studied in packed and intact soil columns under different irrigation regimes. RESULTS: Azoxystrobin did not leach out of the 300 mm long columns after 126 and 362 mm rainfall. After percolating water equivalent to 362 mm rainfall, azoxystrobin leached down to 10–15 cm (packed columns) and 15–20 cm (intact columns) depth. Azoxystrobin was not detected in the leachate from the packed column leached with 94.5 mL water every week (140 mm rainfall per month) during the 28 weeks of the study period. However, azoxystrobin acid, formed by azoxystrobin degradation, was detected in the leachate after 18 weeks. At the end of the study, azoxystrobin had leached down to 5–10 cm depth, and only 60% of initially applied azoxystrobin was recovered from the soil. CONCLUSION: The results indicate that azoxystrobin is fairly immobile in sandy loam soil, but azoxystrobin acid, a major metabolite of azoxystrobin, is quite mobile and may pose a threat of soil and groundwater contamination. Copyright © 2009 Society of Chemical Industry     

Fate of the herbicides glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron in two Finnish arable soils

The fate of five herbicides (glyphosate, glufosinate-ammonium, phenmedipham, ethofumesate and metamitron) was studied in two Finnish sugar beet fields for 26 months. Soil types were sandy loam and clay. Two different herbicide-tolerant sugar beet cultivars and three different herbicide application schedules were used. Meteorological data were collected throughout the study and soil properties were thoroughly analysed. An extensive data set of herbicide residue concentrations in soil was collected. Five different soil depths were sampled. The study was carried out using common Finnish agricultural practices and represents typical sugar beet cultivation conditions in Finland. The overall observed order of persistence was ethofumesate > glyphosate > phenmedipham > metamitron > glufosinate-ammonium. Only ethofumesate and glyphosate persisted until the subsequent spring. Seasonal variation in herbicide dissipation was very high and dissipation ceased almost completely during winter. During the 2 year experiment no indication of potential groundwater pollution risk was obtained, but herbicides may cause surface water pollution.     

Sulcotrione versus atrazine transport and degradation in soil columns

A soil column experiment under outdoor conditions was performed to monitor the fate of 14C-ring-labelled sulcotrione, 2-(2-chloro-4-mesylbenzoyl)cyclohexane-1,3-dione and atrazine, 6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine, in water leachates and in the ploughed horizon of a sandy loam soil. Two months after treatment, the cumulative amounts of herbicide residues leached from the soil were 14.5% and 7% of the applied radioactivity for sulcotrione and atrazine, respectively. Maximum leachate concentrations for each herbicide were observed during the first month following application: 120 and 95 microg litre(-1) for sulcotrione and atrazine respectively. After 2 weeks, 78% of the sulcotrione and atrazine was extractable from the soil, whereas after two months only 10 and 4%, respectively, could be extracted. The maximum sulcotrione content in the first 10 cm of soil was identical with that of atrazine. For both molecules, the content of non-extractable residues was low, being around 15%. Sulcotrione seems to be more mobile than atrazine but the consequences for water contamination are similar since lower doses are used.     

The relative movement and persistence in soil of chlorsulfuron, metsulfuron-methyl and triasulfuron

Summary. Adsorption and degradation rates of triasulfuron in 8 different soils were negatively correlated with soil pH and were generally lower in subsoils than in soils from the plough layer. The half-life at 20°C varied from 33 days in a top soil at pH 5·8 to 120 days in a subsoil at pH 7·4. Adsorption distribution coefficients in these two soils were 0·55 and 0·19, respectively. Movement and persistence of residues of chlorsulfuron, triasulfuron and metsulfuron-methyl were compared in a field experiment prepared in spring 1987. Triasulfuron was less mobile in the soil than the other two compounds. Residues of all three herbicides were largely confined to the upper 40–50 cm soil 148 days after application. With an initial dose of 32 g ha⁻¹, residues in the surface soil layers were sufficient to affect growth of lettuce and sugar-beet sown approximately one year after application. Laboratory adsorption and degradation data were used with appropriate weather data in a computer model of herbicide transport in soil. The model gave good predictions of total soil residues during the first five months following application, and also predicted successfully the maximum depth of penetration of the herbicides into the soil during this period. However, more herbicide was retained close to the soil surface than was predicted by the model. The model predicted extensive movement of the herbicides in the soil during winter but did not predict that residues sufficient to affect crop growth could be present in the upper 15–20 cm soil after one year.     

Persistence and movement of ethofumesate in soil*

Persistence of ethofumesate [(±)2-ethoxy-2.3-dihydro-3,3-dimethylbenzofuran-5-yl-methansulphonate] in soil was associated with soil temperature. Ethofumesate applied at 4.5 kg/ha in November persisted about twice as long in soil as that applied the following March. In another field study, 88–91% of the herbicide had dissipated after 24 weeks in sandy loam soil, compared to 72–77% in loam soil when it was applied at rates of 2.2, 3.4, 4.5, and 9.0 kg/ha. The rate of degradation was independent of the initial rate of chemical applied. The time required for 50% of the herbicide to dissipate in sandy loam and loam soils was 7.7 and 12.6 weeks, respectively. The movement of ethofumesate in these two soils over a 24-weeks sampling period was confined mainly to the upper 7.5 cm of the soil profile.     

Behaviour of metamitron and hydroxy-chlorothalonil in low-humic sandy soils

The behaviour of the herbicide metamitron and of the main transformation product, hydroxy-chlorothalonil (HTI), of the fungicide chlorothalonil was studied to assess the risk of leaching from low-humic sandy soil. The adsorption of metamitron corresponded to a K_om value of about 60 dm³ kg⁻¹ (moderate adsorption). The half-life of metamitron in soil at 15 °C was only three days, presumably due to adaptation of the micro-organisms. In the autumn, the residue of metamitron in the soil profiles corresponded to less than 1% of the cumulative dosage. The half-life of chlorothalonil at 15 °C was about 12 days and about 45% of it was transformed to HTI. The adsorption of HTI to the soils corresponded to a K_om value of 260 dm³ kg⁻¹. The incubation study (15 °C) showed the transformation of HTI in the soils to be very slow. The amounts of HTI remaining in the soil profiles in the autumn corresponded to 4 and 16% of the cumulative dosage of chlorothalonil. In winter, the HTI residue decreased by 40% relative to the autumn level. Occasionally, HTI could be detected in the upper ground-water level (at a depth of about 1 m), at an average concentration of 0.1 to 0.2 µg dm⁻³. © 1999 Society of Chemical Industry     

基于Hydrus-2D的红壤区涌泉根灌自由入渗土壤水分运移数值模拟

针对Hydrus-2D软件在红壤区涌泉根灌土壤水分运移模拟的适用性问题,依据非饱和土壤水动力学理论,并结合红壤区涌泉根灌土壤水分运动特征建立了涌泉根灌土壤水分的入渗模型,利用Hydrus-2D软件对模型进行求解,并对湿润锋运移距离以及土壤含水率的模拟值和实测值进行了对比验证。结果表明:在灌水结束时,Hydrus-2D软件对竖直向下方向湿润锋的模拟值和实测值之间相对误差为5.21%,水平方向湿润锋的模拟值和实测值之间相对误差为-7.28%,且湿润锋模拟值和实测值的相关系数(R²)均大于0.980,RMSE均在1.300 cm以内,F检验P值也均大于0.05;在灌水结束时,距离灌水器不同距离处土壤含水率剖面分布的模拟值和实测值基本一致,均表现为随着土层深度的增加而先增大后减小,在距离灌水器不同位置处,Hydrus-2D软件对剖面土壤含水率的模拟值和实测值之间的相对误差均在±10%以内,且土壤含水率的模拟值和实测值相关系数(R²)均大于0.990,RMSE在0.030 cm³·cm^-3以内,F检验P值也均...     

不同灌水量对土壤氮磷钾养分移动的影响

在大田条件下，采用三室隔膜木箱试验研究了不同灌水量对土壤氮磷钾养分移动的影响。结果表明：灌水和施肥均有利于NO3^-－－N向根面迁移，而且在距根面0－5mm内NO3^－－－N有明显的累积现象：NH4^ －－N则相反，靠近根面土层出现最大亏缺率，随距根面距离的增加亏缺率减小，水分对NH4^ －－N迁称有明显影响的范围为0－30mm，大于30mm效果减弱；灌水量大，施肥充足，土壤磷、钾的扩散范围和扩散强度大，反之则小。     

生物炭用量对模拟土柱氮素淋失和田间土壤水分参数的影响

利用土柱模拟试验和田间试验,把由果树废枝干制备的生物炭以0,20,40,60 t·hm^-2和80 t·hm^-2的用量施入土壤,以探明不同用量的生物炭对土壤硝铵态氮素淋失和土壤水分的影响。结果表明,施用生物炭可降低土壤NH₄⁺-N和NO₃^--N累积淋溶量,其中用量为80 t·hm^-2处理较对照分别降低了41%和18.6%（P＜0.05）;NO₃^--N淋溶主要集中在前三次,其淋溶量占总量的97.3%～98.8%,生物炭能增加NO₃^--N在土壤中的滞留时间,延缓淋失;在整个淋洗过程中,氮素主要以NO₃^--N的形式淋失,其累积淋溶量占NO₃^--N、NH₄⁺-N淋溶总量的97.3%～98.14%;施用生物炭种植春玉米后,土壤含水率和总孔隙度增加不显著。     

Effect of vegetation on the longevity,mobility and activity of fipronil applied at the termiticidal rate in laboratory soil columns

BACKGROUND: Termiticides are applied at concentrations much higher than those used in agricultural settings. The longevity of fipronil has not yet been examined at the rates used for termite control, nor has the compound's movement in the soil been addressed. RESULTS: Fipronil was detected in the eluates of treated soil cones, increasing initially and then decreasing to a steady concentration of about 1 µg mL^?1. In larger PVC pipe plots, fipronil in the top treated soil depth (0–7.5 cm) dissipated more rapidly (half‐life of 11–13 months) than in treated soil at the next treated depth (7.5–15 cm; half‐life of 20–29 months). The presence of vegetation had no significant effect on the mobility, longevity or movement into untreated depths. Treated soil remained toxic to termites throughout the duration of the study. Fipronil moved into the 15–22.5 cm soil depth in sufficient concentration to cause 100% mortality to eastern subterranean termites in 3 day bioassays. CONCLUSION: Fipronil remains in treated soil at levels toxic to termites for at least 30 months. Movement of the active ingredient was observed in sufficient amounts to kill termites in non‐treated soil directly below the treated soil. Published 2010 by John Wiley & Sons, Ltd.