Interactions between 14C-labelled atrazine and the soil microbial biomass in relation to herbicide degradation

A laboratory incubation experiment was set up to determine the effects of atrazine herbicide on the size and activity of the soil microbial biomass. This experiment was of a factorial design (0, 5, and 50 g g^–1 soil of non-labelled atrazine and 6.6×10³ Bq g^–1 soil of ¹⁴C-labelled atrazine) x (0, 20, and 100 g g^–1 soil of urea-N) x (pasture or arable soil with a previous history of atrazine application). Microbial biomass, measured by substrate-induced respiration and the fumigation-incubation method, basal respiration, incorporation of ¹⁴C into the microbial biomass, degradation of atrazine, and ¹⁴C remaining in soil were monitored over 81 days. The amount of microbial biomass was unaffected by atrazine although atrazine caused a significant enhancement of CO₂ release in the non-fumigated controls. Generally, the amounts of atrazine incorporated into the microbial biomass were negligible, indicating that microbial incorporation of C from atrazine is not an important mechanism of herbicide breakdown. Depending on the type of soil and the rate of atrazine application, 18–65% of atrazine was degraded by the end of the experiment. Although the pasture soil had twice the amount of microbial biomass as the arable soil, and the addition of urea approximately doubled the microbial biomass, this did not significantly enhance the degradation of atrazine. This suggests that degradation of atrazine is largely independent of the size of the microbial biomass and suggests that other factors (e.g., solubility, chemical hydrolysis) regulate atrazine breakdown. A separate experiment conducted to determine total amounts of ¹⁴C-labelled atrazine converted into CO₂ by pasture and arable soils showed that less than 25% of the added ¹⁴C-labelled atrazine was oxidised to ¹⁴CO₂ during a 15-week period. The rate of degradation was significantly greater in the arable soil at 24%, compared to 18% in the pasture soil. This indicates that soil microbes with previous exposure to atrazine can degrade the applied atrazine at a faster rate.     

Lumbricid macrofauna alter atrazine mineralization and sorption in a silt loam soil

Atrazine is a widely used herbicide and is often a contaminant in terrestrial and freshwater ecosystems. It is uncertain, however, how the activity of soil macrofauna affects atrazine fate and transport. Therefore, we investigated whether earthworms enhance atrazine biodegradation by stimulating herbicide degrading soil microflora, or if they increase atrazine persistence by facilitating herbicide sorption. Short (43 d) and medium term (86 d) effects of the earthworms Lumbricus terrestris and Aporrectodea caliginosa on mineralization, distribution, and sorption of U-ring-¹⁴C atrazine and on soil C mineralization was quantified in packed-soil microcosms using silt loam soil. A priming effect (stimulation of soil C mineralization) caused by atrazine supply was shown that likely lowered the earthworm net effect on soil C mineralization in atrazine-treated soil microcosms. Although earthworms significantly increased soil microbial activity, they reduced atrazine mineralization to ¹⁴CO₂-C from15.2 to 11.7% at 86 d. Earthworms facilitated formation of non-extractable atrazine residues within C-rich soil microsites that they created by burrowing and ingesting soil and organic matter. Atrazine sorption was highest in their gut contents and higher in casts than in burrow linings. Also, gut contents exhibited the highest formation of bound atrazine residues (non-extractable atrazine). Earthworms also promoted a deeper and patchier distribution of atrazine in the soil. This contributed to greater leaching losses of atrazine in microcosms amended with earthworms (3%) than in earthworm-free microcosms (0.003%), although these differences were not significant due to high variability in transport from earthworm-amended microcosms. Our results indicated that earthworms, mainly by casting activity, facilitated atrazine sorption, which increased atrazine persistence. As a consequence, this effect overrode any increase in atrazine biodegradation due to stimulation of microbial activity by earthworms. It is concluded that the affect of earthworms of atrazine mineralization is time-dependent, mineralization being slightly enhanced in the short term and subsequently reduced in the medium term.     

The influence of nitrogen on atrazine and 2,4-dichlorophenoxyacetic acid mineralization in grassland soils

The influence of fertilizer N on the mineralization of atrazine [2-chloro-4(ethylamino)-6(isopropylamino)-s-triazine] and 2,4-D (2,4-dichlorophenoxyacetic acid) in soils was assessed in microcosms using radiometric techniques. N equivalent to 0, 250, and 500 kg N as NH₄NO₃ ha^-1 was added to three grassland soils. Compared to the control, the 250- and 500-kg treatments suppressed mineralization of atrazine by 75 and 54%, respectively, and inhibited mineralization of 2,4-D by 89 and 30%, respectively. Active fungal biomass responded to the N treatments in an opposite manner to herbicide mineralization. Compared to the control, the 250- and 500-kg treatments increased the active fungal biomass by more than 300 and 30%, respectively. These results agree with other observations that N can suppress the decomposition of resistant compounds but stimulate the primary growth of fungi. The degree of suppression was not related to the amount of N added nor to the inherent soil N levels before treatment. The interaction between the N additions and the active fungal biomass in affecting herbicide mineralization suggests that N may alter microbial processes and their use of C sources and thus influence rates of herbicide degradation in the field.     

竹炭固定化微生物对土壤中阿特拉津的降解研究

采用环境友好材料竹炭为主要载体,壳聚糖和海藻酸钠为辅助载体,固定从污泥中分离出的阿特拉津降解菌株,研究不同固定材料对降解菌生长的影响,以及固定化微生物对土壤中阿特拉津的降解效果.结果表明,竹炭对阿特拉津降解菌具有较强的吸附固定能力,且竹炭粒径越小,固定化效果越好.利用壳聚糖和海藻酸钠交联并加固阿特拉津降解菌,增大了固定化空间,显著增加了降解菌的生物量,并提高了阿特拉津的降解效率.1％壳聚糖+5％海藻酸钠+竹炭+降解菌颗粒对阿特拉津降解菌的固定化效果最佳,施用该微生物固定化颗粒28天后,砂姜黑土及红壤中阿特拉津残留率分别为48.07％和47.23％.     

How increasing availabilities of carbon and nitrogen affect atrazine behaviour in soils

 The effect of increasing amounts of glucose and mineral N on the behaviour of atrazine was studied in two soils. One had been exposed to atrazine under field conditions (adapted soil), the other had not (non-adapted soil), resulting, respectively, in an accelerated degradation of atrazine in the adapted soil and in a slow degradation of the herbicide in the non-adapted soil. The dissipation of ¹⁴C-atrazine via degradation and formation of non-extractable "bound" residues was followed during laboratory incubations in soils supplemented or not with increasing amounts of glucose and mineral N. In both soils, glucose added at rates of up to 16 g C kg^–1 soil did not modify atrazine mineralization but increased the formation of bound residues; this was probably due to the retention of atrazine by the growing microbial biomass. Atrazine dealkylation was enhanced when a large amount of glucose was added. In both soils, the addition of the largest dose of mineral N (2.5 g N kg^–1 soil) decreased atrazine mineralization. The simultaneous addition of glucose and mineral N enhanced their effects. When the largest doses of mineral N and glucose were added, atrazine mineralization stopped in both soils, and the proportion of bound residues increased. Glucose and mineral N additions influenced atrazine mineralization to a greater extent in the adapted soil than in the non-adapted one, as revealed by ANOVA, although glucose addition had a greater effect than N. The competition for space and nutrients between atrazine-degrading microorganisms and the total heterotrophic microflora probably contributed to the decrease in atrazine mineralization. Received: 9 June 1998     

Effect of long-term liquid pig manure application on atrazine mineralization in a soil cultivated with maize

Soil samples were collected in plots from a field experiment in maize monoculture receiving 0, 60 and 120 m³ ha^-1 liquid pig manure (LPM) for 19 years. Soils were sampled from the 0- to 20-cm layer in August and October 1997 and in June, July and September 1998. Subsurface samples were also evaluated in September 1998. Laboratory soil radiorespirometry was used to evaluate atrazine mineralization using [U-ring-¹⁴C]-atrazine mixed with commercially available product. The effect of atrazine dose (50, 100 and 500 mg atrazine kg^-1 soil) was evaluated on soils sampled in August 1997. For the other sampling dates, the soils were spiked with 50 mg atrazine kg^-1 soil. No LPM dose effect on atrazine mineralization was obtained in the different experiments. Increasing atrazine dose to 500 mg kg^-1 decreased significantly the mineralization rate (R_i) and the maximum of atrazine mineralized (MAX), while the time needed to mineralize 50% of MAX (DT-50%) was not significantly affected. Sampling time had a significant effect on atrazine mineralization. Atrazine mineralization in the soils sampled in June 1998 showed lower R_i and MAX than in the soils sampled at the other dates. Atrazine mineralization in subsurface soils (20–60 cm) was very variable and quite high in some samples. This may be due to atrazine pre-exposure in subsoils resulting from atrazine deep movement by preferential flow.     

Microbial biomass and C mineralization in agricultural soils as affected by atrazine addition

This study examines the effects of atrazine on both microbial biomass C and C mineralization dynamics in two contrasting agricultural soils (organic C, texture, and atrazine application history) located at Galicia (NW Spain). Atrazine was added to soils, a Humic Cambisol (H) and a Gleyic Cambisol (G), at a recommended agronomic dose and C mineralization (CO₂ evolved), and microbial biomass measurements were made in non-treated and atrazine-treated samples at different time intervals during a 12-week aerobic incubation. The cumulative curves of CO₂–C evolved over time fit the simple first-order kinetic model [Ct = Co (1 − e ^−kt )], whose kinetic parameters were quantified. Differences in these parameters were observed between the two soils studied; the G soil, with a higher content in organic matter and microbial biomass C and lower atrazine application history, exhibited higher values of the total C mineralization and the potentially mineralizable labile C pool than those for the H soil. The addition of atrazine modified the kinetic parameters and increased notably the C mineralized; by the end of the incubation the cumulative CO₂–C values were 33–41% higher than those in the corresponding non-added soils. In contrast, a variable effect or even no effect was observed on the soil microbial biomass following atrazine addition. The data clearly showed that atrazine application at normal agricultural rates may have important implications in the C cycling of these two contrasting acid soils.     

Adsorption of atrazine and metolachlor in three soils from Blue Creek wetlands, Waterville, Ohio

Atrazine and metolachlor are extensively used pesticides in agricultural activities in northwest Ohio. Adsorption coefficients are often used to model pesticide fate and transport. Many physical-chemical parameters, such as organic matter, clay content, pH, and ionic strength, affect pesticide adsorption. Adsorption kinetics and adsorption isotherms were studied by batch experiment. Effects of humic acid, solution pH, and ionic strength on atrazine and metolachlor adsorption were also approached. After 24 h, both atrazine and metolachlor reached adsorption equilibrium in three local soils. Adsorption isotherms were described by Freundlich equations. The Freundlich coefficient (Kf) ranged from 0.14 to 4.47 (L kg^–1) for atrazine, and 0.04 to 5.30 (L kg^–1) for metolachlor. Adsorption capacity decreased in the order Sloan loam > Del Rey loam > Ottokee fine sand. Koc values varied considerably for both pesticides: metolachlor > in Sloan loam, atrazine metolachlor in Del Rey loam, and atrazine > metolachlor in Ottokee fine sand. In addition to organic matter content, clay played a key role in adsorption in the Del Rey loam and Ottokee fine sand. Higher adsorption was observed at pH 5 for both pesticides. As pH decreased to 3 and increased to 11, adsorption decreased. Adsorption increased as ionic strength increased.     

Degradability of atrazine, cyanazine, and dicamba in methanogenic enrichment culture microcosms using sediment from the Pearl River of Southern China

Degradation of three herbicides, atrazine, cyanazine and dicamba, was assessed in laboratory microcosms incubated under simulated methanogenic conditions using sediment from Pearl River of Southern China as an inoculum. Atrazine was much more resistant to degradation than cyanazine and dicamba over 300 days of incubation. Biodegradation of cyanazine and dicamba was further substantiated by establishment of enrichment transfer cultures in which the degradation of the respective herbicide was accelerated by the active microorganisms. Degradation of cyanazine initially involved the removal of chlorine and the two side chains, while that of dicamba was O-demethylation reaction forming 3,6-dichlorosalicyclic acid. Results suggest that biodegradation of xenobiotics can be established through enrichment culture transfer technique, and further mechanism of degradation and microorganisms involved can be elucidated.     

Microbial mineralization of atrazine and 2,4-dichlorophenoxyacetic acid in riparian pasture and forest soils

Microbial biomass and mineralization of atrazine [2-chloro-4(ethylamino)-6(isopropylamino)s-triazine] and 2,4-D (2,4-dichlorphenoxyacetic acid) were examined in the top 10 cm of riparian pasture soils and in the litter layer and top 10 cm of mineral soils of riparian forest ecosystems. The riparian forest litter had higher levels of active and total fungal biomass than forest or pasture mineral soils in winter, spring, and fall. Active bacterial biomass was higher in forest litter than in forest and pasture mineral soils in spring and autumn, and higher in forest mineral soils than in pasture soils in summer. Total bacterial biomass was higher in forest mineral soils than in pasture soils during all seasons. In spring, it was also higher in forest litter than in pasture soils. Atrazie and 2,4-D mineralization in pasture soils was exceeded by that in forest litter in spring and autumn and by that in forest mineral soils in summer and autumn. There was no correlation between either active or total fungal and bacterial biomass with pesticide degradation.     

除草剂莠去津和灭草松单用和混用在土壤中的降解

The application of a mixture of bentazone （3-isopropyl-1H-2,1,3-benzothiadiazin-4（3H）-one-2,2-dioxide） and atrazine （6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine） is a practical approach to enhance the herbicidal effect. Laboratory incubation experiments were performed to study the degradation of bentazone and atrazine applied in combination and individually in maize rhizosphere and non-rhizosphere soils. After a lag phase, the degradation of each individual herbicide in the non-autoclaved soil could be adequately described using a first-order kinetic equation. During a 30-d incubation, in the autoclaved rhizosphere soil, bentazone and atrazine did not noticeably degrade, but in the non-autoclaved soil, they rapidly degraded in both non-rhizosphere and rhizosphere soils with half-lives of 19.9 and 20.2 d for bentazone and 29.1 and 25.7 d for atrazine, respectively. The rhizosphere effect significantly enhanced the degradation of atrazine, but had no significant effect on bentazone. These results indicated that biological degradation accounted for the degradation of both herbicides in the soil. When compared with the degradation of the herbicide applied alone, the degradation rates of the herbicides applied in combination in the soils were lower and the lag phase increased. With the addition of a surfactant, Tween-20, a reduced lag phase of degradation was observed for both herbicides applied in combination. The degradation rate of bentazone accelerated, whereas that of atrazine remained nearly unchanged. Thus, when these two herbicides were used simultaneously, their persistence in the soil was generally prolonged, and the environmental contamination potential increased.     

Combined effect of bioaugmentation and bioturbation on atrazine degradation in soil

Earthworms, because they change soil physical and chemical properties, are efficient engineers that act on soil microbial community and activity. Thus they may drive pollutant biodegradation in soil such as atrazine mineralization. We hypothesized that earthworms modify the abundance of indigenous soil bacteria and the fate and activity of atrazine-degraders in the soil they engineer by bioturbation. Two bacterial strains were used as bioaugmentation agents: Pseudomonas sp. ADP and Chelatobacter heintzii, which have acquired the capacity to metabolize atrazine by carrying plasmidic atz A, B, C, D, E, F and atzA, B, C, trzD genes, respectively. We analyzed the interactions between earthworms (Lumbricus terrestris) and the indigenous and atrazine-degrading (indigenous and inoculated) bacterial communities by quantifying the 16S rRNA and the atzA gene sequence copies numbers, respectively, in different earthworm microsites. The kinetics of atrazine mineralization were measured to link the bacterial community changes with the degradation function. Digestion by earthworms significantly impacted the number of indigenous bacteria and atrazine mineralization in bioaugmented soils. Regarding the fate of the two atrazine-degraders tested, Pseudomonas sp. strain ADP survived better within the 10 days of experiment than C. heintzii in the bulk soil but the surviving fraction of C. heintzii was still metabolically active and able to mineralize atrazine. A positive “burrow-lining” effect on the atzA sequence copies number was observed in soil whether bioaugmented with C. heintzii or not (i.e. native indigenous atzA) thereby indicating that burrow-linings form a specific ‘hot spot’ for atrazine-degraders. The present study is the first to report the role of earthworms in selecting native catabolic key-genes in soil (indigenous atzA). This catabolic gene selection through earthworm soil bioturbation could be important in sustaining the degradation (detoxification) function of soil.     

Influence of nitrogen on atrazine and 2, 4 dichlorophenoxyacetic acid mineralization in blackwater and redwater forested wetland soils

 Microcosms were used to determine the influence of N additions on active bacterial and fungal biomass, atrazine and dichlorophenoxyacetic acid (2,4-D) mineralization at 5, 10 and 15 weeks in soils from blackwater and redwater wetland forest ecosystems in the northern Florida Panhandle. Active bacterial and fungal biomass was determined by staining techniques combined with direct microscopy. Atrazine and 2,4-D mineralization were measured radiometrically. Treatments were: soil type, (blackwater or redwater forested wetland soils) and N additions (soils amended with the equivalent of 0, 200 or 400 kg N ha^–1 as NH₄NO₃). Redwater soils contained higher concentrations of C, total N, P, K, Ca, Mn, Fe, B and Zn than blackwater soils. After N addition and 15 weeks of incubation, active bacterial biomass in redwater soils was lower when N was added. Active bacterial biomass in blackwater soils was lower when 400 kg N ha^–1, but not when 200 kg N ha^–1, was added. Active fungal biomass in blackwater soils was higher when 400 kg N ha^–1, but not when 200 kg N ha^–1, was added. Active fungal biomass in redwater soils was lower when 200 kg N ha^–1, but not when 400 kg N ha^–1, was added. After 15 weeks of incubation 2,4-D degradation was higher in redwater wetland soils than in blackwater soils. After 10 and 15 weeks of incubation the addition of 200 or 400 kg N ha^–1 decreased both atrazine and 2,4-D degradation in redwater soils. The addition of 400 kg N ha^–1 decreased 2,4-D degradation but not atrazine degradation in blackwater soils after 10 and 15 weeks of incubation. High concentrations of N in surface runoff and groundwater resulting from agricultural operations may have resulted in the accumulation of N in many wetland soils. Large amounts of N accumulating in wetlands may decrease mineralization of toxic agricultural pesticides. Received: 26 June 1998     

Nitrogen mineralization and nitrification in soils treated with ammonium sulfate and Nutrasweet sludge

Abstract

NutraSweet sludge, a by‐product of the manufacture of the artificial sweetener aspartame, contains about 40% of its nitrogen (N) in inorganic form and the rest mostly in the form of L‐phenylalanine. Although this sludge is often applied to land as fertilizer, the exact management strategy for its optimum use has not been clear. We conducted a laboratory study to compare the evolution of inorganic N contents and nitrification in two soils treated with NutraSweet sludge and ammonium sulfate at rates of 0, 25, 50, 100, and 150 mg N kg^‐1. Four days after application, the inorganic N recovered from the sludge ranged from 67 to 105%, indicating a fast rate of mineralization. At 25 and 50 mg N kg^‐1, the overall recovery of inorganic N from NutraSweet sludge was higher than from ammonium sulfate, whereas the converse was true at higher application rates. In Dothan soil with an initial pH of 5.5, nitrate‐N as percentage of the N applied was higher in samples with NutraSweet sludge than in those with ammonium sulfate. The opposite effect was observed in Tifton soil, which had an initial pH of 6.8. Due to the fast release of inorganic N from NutraSweet sludge, the material should be managed as an inorganic, ammoniacal N fertilizer.     

土壤有机复合物降解的动力学模型

A set of equations in suggested to describe the kinetics of degradation of organic ompounds applied to soils ad the kinetics of growth of the inolved microorganisms:-dx/dt=jx kxm dm/dt=-fm gxm where x is the concentration of organic compound at time t,m is the numer of microorganisms capable of degrading the organic compound at time t,while j,k,f and g are positive constants,This model can satisfactorily be used to explain the degradation curve of organic compounds and the growth curve of the involved microorganisms.     

Cross-enhancement of accelerated biodegradation of organophosphorus compounds in soils: Dependence on structural similarity of compounds

Rates of degradation of seven organophosphate nematicides and insecticides were examined in two soils known to show accelerated biodegradation of fenamiphos and one soil known to show accelerated biodegradation of chlorpyrifos. The results indicated that several organophosphate insecticides and one nematicide were susceptible to cross-enhanced degradation in the soil showing accelerated biodegradation of chlorpyrifos. No cross-enhancement was observed in the two soils showing accelerated degradation of fenamiphos. Fumigation resulted in the complete inhibition of pesticide degradation in all soils. The data suggested that the cross-enhancement of selected pesticides in chlorpyrifos-degrading soil was dependent on the structural similarity of the compounds. Mechanisms of degradation of pesticide in soil support this hypothesis, where structurally similar compounds (diazinon, parathion, coumaphos and isazofos) were hydrolysed by microbial activity in chlorpyrifos-degrading soil but the degradation products were accumulated. Enhanced degradation of chlorpyrifos and fenamiphos was found to be stable in the laboratory condition for a period of one year.     

壤和堆肥中四环素类抗生素的检测方法优化及其在土壤中的降解研究

在对土霉素（OTC）、四环素（TC）和金霉素（CTC）3 种四环素类抗生素的高效液相色谱（HPLC）检测分析方法以及在土壤和堆肥中的提取方法进行改进和优化的基础上,采用该方法进行了 3 种抗生素在土壤中的降解试验。结果表明,选用 Agilent Eclipse XDB-C8（4.6150 mm,5 m）色谱柱,以 0.01 mol/L草酸/乙腈/甲醇（79/10.5/10.5,v/v/v）为流动相,紫外检测波长 268 nm,流速 1.0 mL/min,进样量 5 L,采用外标法定量,可使 3 种四环素类抗生素在 20 min 内全部洗脱并达到基线分离; 在 0~10 mg/L 范围内,抗生素浓度与峰面积呈显著的线性关系,相关系数（r）均 0.999。土壤和堆肥样品中的 OTC、TC 和 CTC可用1 mol/L NaCl/0.5 mol/L 草酸/乙醇（25/25/50,v/v/v）混合溶液提取,其回收率在 76.0%~92.5% 之间。加入到土壤中的抗生素在 25℃下避光培养 49 d 后,在壤土和红土中的降解率分别是 67%~72% 和 36%~46%,对应的半衰期分别为 2630 d 和 4675 d,说明抗生素在壤土中比红土中容易降解。此外,3种抗生素在壤土中的半衰期没有显著性差异,而在红土中 CTC 和 TC 的降解速率显著高于 OTC。     

阿特拉津在土壤, 矿物质及堆肥中的吸附, 运输和转化

Atrazine is a widely used herbicide for controlling weeds on both agricultural and nonagricultural land,which is equally detected in water supplies beyond safe concentrations.Although the presence of atrazine metabolites is an indication of herbicide degradation,some of them still exhibit toxicity,greater water solubility and weaker interaction with soil components than atrazine.Hence,studies with atrazine in the environment are of interest because of its potential to contaminate drinking water sources.Data on atrazine availability for transport,plant uptake,and microbial degradation and mineralization are therefore required to perform more comprehensive and realistic environmental risk assessments of its environmental fate.This review presents an account of the sorption-desorption phenomenon of atrazine on soil and other sorbents by revisiting the several mechanisms of atrazine-sorbent binding reported in the literature.The retention and transport of atrazine in soils;the influence of organic matter on atrazine sorption;the interactions of atrazine with humic substances,atrazine uptake by plants,atrazine bioccumulation and microbial degradation;atrazine transformation in composting environments;and finally atrazine removal by biosorption are discussed.     

Tillage and cover effects on soil microbial properties and fluometuron degradation

This research concerns the influence of no tillage (NT) or conventional tillage (CT) and a ryegrass (Lolium multiforum Lam.) cover crop in a cotton (Gossypium hirsutum L.) production system on soil and ryegrass microbial counts, enzyme activities, and fluometuron degradation. Fluorescein diacetate hydrolysis, aryl acylamidase, and colony-forming units (CFUs) of total bacteria and fungi, gram-negative bacteria, and fluorescent pseudomonads were determined in soil and ryegrass samples used in the degradation study. Fluometuron (14C-labelled herbicide) degradation was evaluated in the laboratory using soil and ryegrass. The CT and NT plots with a ryegrass cover crop maintained greater microbial populations in the upper 2 cm compared to their respective no-cover soils, and CT soils with ryegrass maintained greater bacterial and fungal CFUs in the 2–10 cm depth compared to the other soils The highest enzymatic activity was found in the 0–2 cm depth of soils with ryegrass compared to their respective soils without ryegrass. Ryegrass residues under NT maintained several hundred-fold greater CFUs than the respective underlying surface soils. Fluometuron degradation in soil and ryegrass residues proceeded through sequential demethylation and incorporation of residues into nonextractable components. The most rapid degradation was observed in surface (0 to 2 cm) soil from CT and NT–ryegrass plots. However, degradation occurred more rapidly in CT compared to NT soils in the 2 to 10 cm depth. Ryegrass cover crop systems, under NT or incorporated under CT, stimulated microbiological soil properties and promoted herbicide degradation in surface soils.     

适宜水分和养分提高土壤中磺酸二甲嘧啶降解率

医疗和养殖过程中抗生素的广泛使用导致了土壤环境中抗生素的污染。为了解进入农田土壤中抗生素的降解规律,该文以养殖业广泛使用的磺胺二甲嘧啶和2种不同养分水平的土壤为试验材料,采用盆栽方法研究了肥料种类(有机肥、NPK肥、N肥、PK肥等)、耕作强度(翻耕、免耕)、水分条件(长期干燥、长期湿润、干湿交替、长期潮湿)及种植作物(种植蔬菜、不种蔬菜)对土壤中磺胺二甲嘧啶降解的影响。结果表明,与不施肥处理比较,施用有机肥、NPK肥、N肥可促进土壤中磺胺二甲嘧啶在土壤中的降解,并以施用有机肥的效果最为明显;但施用PK肥对土壤中磺胺二甲嘧啶的降解影响不明显。翻耕可促进土壤中磺胺二甲嘧啶的降解,干湿交替、长期湿润比长期干燥和长期潮湿土壤环境下更有利于磺胺二甲嘧啶的降解。种植蔬菜比不种蔬菜土壤的磺胺二甲嘧啶的降解率高,根际土壤中磺胺二甲嘧啶的降解高于总体土壤。高养分土壤中磺胺二甲嘧啶的降解一般高于低养分土壤。分析认为,施肥、土壤养分水平、种植蔬菜对土壤中磺胺二甲嘧啶的降解的影响可能主要与这些因素改变了土壤微生物活性有关;翻耕可促进土壤中抗生素的光降解强度。研究认为,施肥、耕作和水分管理可以在一定程度上加速土壤中磺胺二甲嘧啶的降解。