Reaction pathways of the diketonitrile degradate of isoxaflutole with hypochlorite in water

Isoxaflutole (IXF; Balance) belongs to a new class of isoxazole herbicides. Isoxaflutole has a very short half-life in soil and rapidly degrades to a stable and phytotoxic degradate, diketonitrile (DKN). DKN was previously discovered to rapidly react with hypochlorite (OCl-) in tap water, yielding the benzoic acid (BA) degradate as a major product, but the complete reaction pathway and mechanism have not been elucidated. Thus, the objectives of this work were to (1) determine the stoichiometry of the reaction between DKN and OCl-; (2) identify products in addition to BA; and (3) propose a complete pathway and reaction mechanism for oxidation of DKN by OCl-. Stoichiometry of the reaction showed a molar ratio of OCl-/DKN of 2. In addition, two previously uncharacterized chlorinated intermediates were identified under conditions in which OCl- was the limiting reactant. The proposed chemical structure of a chlorinated benzoyl intermediate was inferred from a series of HPLC/MS and HPLC/MS/MS experiments and the use of mass spectral simulation software. A chlorinated ketone intermediate was also identified using ion trap GC/MS. Two additional end products were also identified: cyclopropanecarboxylic acid (CPCA) and dichloroacetonitrile (DCAN). On the basis of the reaction stoichiometry, the structure of the chlorinated intermediates, and the identification of the products, two reaction pathways are proposed. Both pathways involve a two-step nucleophilic attack and oxidation of the diketone structure of DKN, leading to formation of BA, DCAN, and CPCA.     

Cleavage of the diketonitrile derivative of the herbicide isoxaflutole by extracellular fungal oxidases

Isoxaflutole is a herbicide activated in soils and plants to its diketonitrile derivative, the active herbicide principle. The diketonitrile derivative undergoes cleavage to the inactive benzoic acid analogue. In this paper, it is established that an oxidative mechanism implicating two successive reactions in the presence of dimethyldioxirane can chemically initiate the cleavage of the diketonitrile. It is also shown that two white rot strains, Phanerochaete chrysosporium and Trametes versicolor, are able to convert the diketonitrile to the acid when cultured in liquid media. This main metabolite amounts to 24.6 and 15.1% of initial herbicide content after 12-15 days of culture. Another polar metabolite represents <3.7% of the parent compound amount during the same period. Oxidative enzymes produced by the fungi show a time course similar to that of diketonitrile degradation. Purified laccase (EC 1. 10.3.2), in the presence of 2 mM 2, 2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) acting as a redox mediator at pH 3 supports the reaction with rates of 0.3-0.4 nmol h(-)(1) unit(-)(1).     

Processes affecting the dissipation of the herbicide isoxaflutole and its diketonitrile metabolite in agricultural soils under field conditions

Two-year field dissipation studies were conducted in three soil types in Minnesota to examine the processes affecting the dissipation of the herbicide isoxaflutole and its phytotoxic diketonitrile metabolite (DKN) under relatively cool, wet soil conditions. Plots of cuphea were treated with isoxaflutole and potassium bromide, a nonsorbed, nondegraded tracer. Replicate soil cores were collected six times during the growing season to a depth of 1 m, and the bromide or herbicide concentration was measured in each of five depth increments. The dissipation half-life (DT50) of isoxaflutole + DKN was 8-18 days in each soil. Bromide and herbicide concentrations were low at depths >40 cm throughout the study, and herbicide concentrations in soil 100 days after application were usually undetectable. Simulation modeling using Hydrus-1D for the loam soil suggested that plant uptake was an important mechanism of dissipation.     

Effects of moisture,temperature, and biological activity on the degradation of isoxaflutole in soil

The effects of several environmental factors on the dissipation, transformation, and mineralization of isoxaflutole were investigated in laboratory incubations. In the soil, isoxaflutole hydrolyzed to a diketonitrile derivative, which is the active form of the herbicide. The diketonitrile was then metabolized to an inactive benzoic acid derivative and later into two unknown products, which were found only in small quantities. Degradation of isoxaflutole was faster in soil maintained at -100 or -1500 kPa compared to that in air-dry soil. At 25 degrees C, the half-lives for isoxaflutole were 9.6, 2.4, and 1.5 days in air-dry, -1500 kPa, and -100 kPa moisture regimes, respectively. A simple Arrhenius expression described the response of isoxaflutole transformation (mineralization and transformation) to temperature in the range of 5 to 35 degrees C. An activation energy value (E(a)) of 67 kJ/mol for isoxaflutole suggested the transformation of the herbicide to the diketonitrile derivative was primarily a chemical reaction. Moreover, biological activity had little effect on the hydrolysis of isoxaflutole, with half-lives of 1.8 and 1.4 days in sterile and nonsterile soil, respectively. However, the transformation of diketonitrile to benzoic acid and the production of the unknown products were greatly reduced in the sterile soil, suggesting one or more biologically mediated processes.     

蔬菜种植年限对土壤磷素吸附解吸特性的影响

为揭示不同种植年限土壤磷的固定和释放机制,通过土壤磷的等温吸附、解吸试验研究种植年限分别为3～5年、15～20年、25～30年的黄棕壤0～5cm和5～20cm土层磷的吸附、解吸特性。结果表明:土壤磷的等温吸附曲线、吸附量-解吸量曲线分别与Langmuir方程(R2为0.8728～0.8436)、二次函数方程拟合良好(R2为0.9545～0.9970);随蔬菜种植年限延长,表层土壤磷最大吸附量(Qm)、磷最大缓冲容量(MBC)明显降低,而土壤磷吸附饱和度(DPS)和解吸率明显提高;种植年限15～20年、25～30年土壤磷的解吸率明显高于3～5年土壤。对表征土壤磷素吸附、解吸特性的主要因子如MBC及DPS等作相关分析发现,无定形铁铝含量的变化是影响土壤磷吸附解吸特性的主要因素。     

Fate of isoxaflutole in soil under controlled conditions

Isoxaflutole (IFT, 5-cyclopropyl-1,2-oxazol-4yl-alpha,alpha,alpha-trifluoro-2-mesyl-p-tolyl ketone) is a new pre-emergence proherbicide used in maize and sugarcane. Its two main derivatives are a diketonitrile derivative, 2-cyano-3-cyclopropyl-1-(2-methanesulfonyl-4-trifluoromethylphenyl)propane-1,3-dione, called DKN, and a benzoic acid derivative, 2-methanesulfonyl-4-trifluoromethylbenzoic acid, called BA. Few data are available of the factors influencing the degradation of IFT in soil, and the purpose of the present work was to determine the relative importance of, and factors affecting, the degradation of IFT in soil. Experiments were conducted on five soils with distinct physicochemical characteristics, at different temperatures and moisture contents in biotic and abiotic conditions. The isomerization of IFT to DKN is rapid, increasing with higher moisture contents and higher temperatures. It depends strongly on pH and is governed by chemical processes. The degradation of DKN to BA appeared to be essentially due to the biological activity of the soil.     

密集型农业下塑料膜温室中不同土地利用方式对土壤磷素吸附-解吸特性的影响

With rapid urbanization and economic growth, Chinese traditional rice-legume production is increasingly replaced by vegetable and horticultural flower production, which could affect soil properties. This study was conducted near Kunming City, Yunnan Province, Southwest China to investigate how soil phosphorus(P) sorption and desorption processes respond to land use changes and to relate P sorption and desorption parameters to soil properties. Soil samples(0–20, 20–40, 40–60, 60–80 and 80–100 cm) were collected from five sites representing four land use types: rice-legume production in a two-crop, one-year rotation(Rice), vegetable production in open fields(Vegetable), recent( 3 years) conversion from open fields to plastic-film greenhouse vegetable and flower production at two sites(VFCS1and VFCS2), and longer-term( 10 years) plastic-film greenhouse vegetable and flower production(VFCL). The changes in land use affected soil pH, electrical conductivity, available N and P and organic carbon content in topsoil and subsoil. In turn, these changes of soil properties influenced soil P sorption capacity. The P sorption maximum(Smax) was affected by land use types, soil sampling depth and their interactions(P 0.0001). For surface soil, Smax was in the order of Rice(1 380 mg kg-1) VFCL(1 154 mg kg-1) VFCS2(897 mg kg-1) VFCS1(845 mg kg-1) Vegetable(747 mg kg-1). The lowest Smax generally occurred at the surface(except for Rice at 80–100 cm) and increased with depth. The amount of P desorbed during the 8 successive extractions was in the range 23%–44% of sorbed P, and was not affected by land use types or sampling depths. The decreases in Smax suggested that soil P sorption capacity decreased when rice-legume production converted to more intensive vegetation and flower production and caution should be exercised when applying P fertilizer to minimize potential leaching and runoff P loss to the environment.     

Raw or incubated olive-mill wastes and its biotransformed products as agricultural soil amendments-effect on sorption-desorption of triazine herbicides

Raw olive-mill waste and soil amendments obtained from their traditional composting or vermicomposting were added, at rates equivalent to 200 Mg ha-1, to a calcareous silty clay loam soil in a laboratory test, in order to improve its fertility and physicochemical characteristics. In particular, the effects on the sorption-desorption processes of four triazine herbicides have been examined. We found that comparatively hydrophobic herbicides terbuthylazine and prometryn increased their retention on amended soil whereas the more polar herbicides simazine and cyanazine were less affected. Soil application of olive cake, without transformation, resulted in the highest herbicide retention. Its relatively high content in aliphatic fractions and lipids could explain the increased herbicide retention through hydrophobic bonding and herbicide diffusion favored by poorly condensed macromolecular structures. On the other hand, the condensed aromatic structure of the compost and vermicompost from olive cake could hinder diffusion processes, resulting in lower herbicide sorption. In fact, the progressive humification in soil of olive-mill solid waste led to a decrease of sorption capacity, which suggested important changes in organic matter quality and interactions during the mineralization process. When soil amended with vermicompost was incubated for different periods of time, the enhanced herbicide sorption capacity persisted for 2 months. Pesticide desorption was reduced by the addition of fresh amendments but was enhanced during the transformation process of amendments in soil. Our results indicate the potential of soil amendments based on olive-mill wastes in the controlled, selective release of triazine herbicides, which varies depending on the maturity achieved by their biological transformation.     

氮对土壤中氯氰菊酯及其降解产物3-苯氧基苯甲酸降解的影响

Increasing use of pyrethroid insecticides has resulted in concerns regarding potential effects on human health and ecosystems. Cypermethrin and its metabolite 3-phenoxybenzoic acid （PBA） have exerted adverse biological impacts on the environment; therefore, it is critically important to develop different methods to enhance their degradation. In this study, incubation experiments were conducted using samples of an Aquic Inceptisol supplied with nitrogen （N） in the form of NH4NO3 at different levels to investigate the effect of nitrogen on the degradation of cypermethrin and PBA in soil. The results indicated that appropriate N application can promote the degradation of cypermethrin and PBA in soil. The maximum degradation rates were 80.0% for cypermethrin after 14 days of incubation in the treatment with N at a rate of 122.1 kg ha^-1 and 41.0% for PBA after 60 days of incubation in the treatment with N at a rate of 182.7 kg ha^-1. The corresponding rates in the treatments without nitrogen were 62.7% for cypermethrin and 27.8% for PBA. However, oversupplying N significantly reduced degradation of these compounds. Enhancement of degradation could be explained by the stimulation of microbial activity after the addition of N. In particular, dehydrogenase activities in the soil generally increased with the addition of N, except in the soil where N was applied at the highest level. The lower degradation rate measured in the treatment with an oversupply of N may be attributed to the microbial metabolism shifts induced by high N.     

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.     

Effect of spherosome on degradation of tetrachloroethylene in soil

The fate of spherosome on the degradation of tetrachloroethylene in soil was investigated for 38 days. The time needed to become the half value of the initial concentration is 8 days for the case with spherosome and 15 days for the case without spherosome. The time needed for complete degradation is 25 days for the case with spherosome and 38 days for the case without spherosome. The degradation of tetrachloroethylene appeared to be essentially due to the biological activity of the soil. Spherosome should enhance the rate of tetrachloroethylene destruction.     

Effect of cryogel on soil properties

Samples from the A1 and A1A2 horizons of sandy loamy gray forest soil containing 3.1% organic matter have been mixed with a 5% solution of polyvinyl alcohol (PVA) at a ratio of 7 : 1 under laboratory conditions. The samples were frozen at ?20°C in a refrigerator; after a freezing-thawing cycle, the evaporation of water from their surface, their thermal conductivity coefficient, their elasticity modulus, and other properties were studied. It has been experimentally found that the thermal conductivity coefficient of cryostructured soil is lower than that of common soil by 25%. It has been shown that the cryostructured soil retains water for a longer time and that the water evaporation rate from its surface is significantly lower compared to the control soil. Cryogel has no negative effect on the catalase activity of soil; it changes the physical properties of soils and positively affects the population of indigenous soil microflora and the growth of the sown plants.     

Effect of Roundup Ultra on atrazine degradation in soil

Tank mixing pesticides and the use of pre-packaged mixtures have become common agricultural practices. However, pesticide degradation in multi-pesticide systems is rarely evaluated. The objective of this laboratory study was to determine the effect of Roundup Ultra on atrazine degradation in soil. Based on a 2-mm glyphosate-soil interaction depth, the isopropylamine salt of glyphosate was added to Aatrex-amended and non-amended soil at rates of 0, 1 (43 mg ai kg ^-1), 2, 3, 4, and 5×. Treatments were incubated for 4, 8, 12, 16, 20, 24, 28, and 32 days. Atrazine degradation was significantly different among treatments at 8 days. In the 0× treatment (Aatrex only), 87% of the atrazine was degraded. During the same 8-day period, atrazine degradation in the 1, 2, 3, 4, and 5× treatments was 77%, 69%, 60%, 61%, and 52%, respectively. Atrazine degradation approached 97% for all treatments after 12 days and statistical differences were no longer observed. Atrazine degradation was inversely correlated with Roundup Ultra rate and microbial activity at 8 ( r ²=0.97) and 12 days ( r ²=0.92). These results indicate that Roundup Ultra stimulated microbial activity while simultaneously inhibiting atrazine degradation.     

Influence of soil physicochemical and biological properties on the degradation and adsorption of the nematicide fosthiazate

The degradation and adsorption of the organophosphorus nematicide fosthiazate were investigated in nine soils with various physicochemical and biological characteristics. Fosthiazate was more persistent in acidic soils (pH <6), with half-life (t1/2) values ranging from 53.3 to 57.7 days, compared to soils with higher pH (pH >7), with t1/2 ranging from 14.1 to 20.7 days. Application of antibacterial and antifungal antibiotics to soil samples resulted in a significant inhibition of fosthiazate degradation only in two of the three acidic soils. In contrast, soil autoclaving resulted in doubling the t1/2 of fosthiazate in all studied soils, suggesting that both microbial and abiotic processes contribute to fosthiazate degradation. Statistical analysis indicated a significant negative correlation (P < 0.01) between soil pH and t1/2. Fosthiazate was generally weakly adsorbed with Freundlich adsorption coefficient (Kf) values ranging from 1.23 to 2.74 mL/g. Fosthiazate concentration was strongly correlated with soil organic matter content with higher Kf values in soils with higher organic matter content (P < 0.01). The mean t1/2 and Kf values derived from the laboratory studies were used to parametrize the FOCUS groundwater (GW) models PRZM, PELMO, PEARL, and MACRO for nematicide application in potato and tomato crops. Predicted environmental concentrations produced by the models PEARL and MACRO suggested a potential risk for GW in several scenarios, unlike PELMO and PRZM, which predicted low risk for GW. These findings suggest that the environmental fate of fosthiazate is strongly influenced by soil characteristics and that this nematicide should be used with care in acidic, light soils with low organic matter content.     

污泥及其混合堆肥对番茄土壤性质和N_2O排放的影响

目前关于污泥及其生物质堆肥的土地利用过程中土壤性质变化和温室气体排放数据十分缺乏,难以满足农田土壤氮素保存和温室气体减排的需求。该研究通过在番茄种植过程中添加800 kg/hm2新鲜污泥(S-H)、400 kg/hm2新鲜污泥(S-L)、800 kg/hm2秸秆堆肥(VM-S)和800 kg/hm2猪粪堆肥(VM-M),开展土壤性质、无机氮形态、作物生长以及N2O排放特征的研究。结果表明:堆肥处理显著增加了土壤电导率(electric conductivity,EC)(P0.05),其中猪粪堆肥时土壤EC值最大。添加污泥和堆肥都使土壤p H值显著上升(P0.05),最终趋于中性,且VM-M对土壤酸化的抑制效果略优于VM-S。污泥和堆肥处理时土壤NO3--N浓度显著高于对照,且各处理组NO3--N浓度均随时间逐渐下降,NO3--N主要被番茄吸收,部分NO3--N从土壤上层淋溶至下层;NH4+大多数被氧化为NO3-,部分NH4+被植物吸收。在施入的无机氮量相等情况下,VM-M、VM-S、S-H处理组中番茄地上部分生物量分别为1 515、1 383、1 103 g/株,株高分别为56.8、54.5、51.3 cm,对番茄生长的促进效果为VM-MVM-SS-H,而S-H比S-L多施入的氮肥对番茄生长并未起到明显促进作用(P0.05)。与对照相比,污泥或生物质堆肥都显著提高了土壤N2O的排放(P0.05),各处理组N2O的排放均集中于施肥后的前20天,且土壤N2O的排放通量大小顺序为S-L(0.76 kg/(hm2·a))VM-M(0.95 kg/(hm2·a))VM-S(1.19 kg/(hm2·a))S-H(1.71 kg/(hm2·a))。因此,在进行污泥及其生物质堆肥的土地利用时,应考虑有机肥的种类及其施用量,以在提高作物产量的同时改善土壤并减少温室气体排放,在进行污泥的农田利用时可先将污泥与畜禽粪堆肥。     

Effect of different wood pretreatments on the sorption-desorption of linuron and metalaxyl by woods

The sorption-desorption of two different pesticides, linuron and metalaxyl, by woods was studied. Sorbent/solution ratio and sorption kinetics were also determined. Untreated wood and water, NaOH, HCl, and octadecyltrimethylammonium bromide (ODTMA) treated pine (softwood) and oak (hardwood) were used as sorbents. Linuron and metalaxyl were sorbed by untreated woods up to 80 and 40%, respectively, in a short time when the sorbent/solution ratio of 1:10 was used. Sorption of pesticides was significantly higher by pine, having higher lignin content, than by oak. Freundlich sorption constants (K(f)) were 96.2 and 74.4 (linuron) and 8.28 and 4.95 (metalaxyl) for untreated pine and oak woods and increased 1.04-2.35-fold (linuron) and 1.33-2.17-fold (metalaxyl) when woods were treated. The sorption was higher by HCl- and ODTMA-treated woods. Additionally, Freundlich desorption constants also indicated greater sorption irreversibility of both pesticides for treated woods than for untreated woods. The results revealed wood residues as a promising, low-cost, and environmentally friendly material to immobilize pesticides in soils, preventing water contamination. Wood treatments aimed at removing soluble wood extracts or at modifying wood chemical structure could increase their sorption capacity.     

An isotopic exchange method for the characterization of the irreversibility of pesticide sorption-desorption in soil

An isotopic exchange method is presented that characterizes the irreversibility of pesticide sorption-desorption by soil observed in batch equilibration experiments. The isotopic exchange of (12)C- and (14)C-labeled triadimefon [(1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1, 2,4-triazol-1-yl)-2-butanone] and imidacloprid-guanidine [1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-1H-imidazol-2-amine] in Hanford sandy loam soil indicated that these systems can be described by a two-compartment model in which about 90% of sorption occurs on reversible, easily desorbable sites, whereas 10% of the sorbed molecules are irreversibly sorbed on soil and do not participate in the sorption-desorption equilibrium. This model closely predicted the hysteresis observed in the desorption isotherms from batch equilibration experiments. The isotopic exchange of triadimefon and imidacloprid-guanidine in Drummer silty clay loam soil indicated that there was a fraction of the sorbed (14)C-labeled pesticide that was resistant to desorption, which increased as pesticide concentration decreased and was higher for triadimefon than for imidacloprid-guanidine. In contrast, the batch equilibration method resulted in ill-defined desorption isotherms for the Drummer soil, which made accurate desorption characterization problematic.     

Structural transition in the humic matrix of soil gels and its effect on the soil properties

The analysis of drying-wetting cycles in soils has shown that the existence of the humic matrix of soil gels and, hence, the soil structure is ensured by hydrophilic bonds in dry soils and hydrophobic bonds in wet soils. This suggests that the structural transition from one mechanism controlling the stability of the soil gels and the existence of the soil structure to another mechanism occurs in the humic matrix of soil gels in a specific range of water content. The experimental results have confirmed the effect of the structural transition on the water stability of the soil structure, the pH_water, the hydrophilicity of the soil particle surface, and the structural-mechanical properties of the soils.     

氟磺胺草醚对大豆根际土壤微生物和酶活性的影响及其在根际的降解

【目的】 本研究旨在探讨不同浓度氟磺胺草醚在大豆根际土壤中的微生态效应,及其在根际土壤中的降解动态,为进一步研究除草剂的残留污染提供科学依据。 【方法】 以中黄13号大豆为材料,采用根箱进行了模拟栽培试验。设施用氟磺胺草醚3.75 mg/kg (低)、7.5 mg/kg (中)、18.75 mg/kg (高) 3个水平,以不添加氟磺胺草醚处理为对照,调查了大豆根际土壤细菌、真菌、放线菌数量,分析了根际土壤中过氧化氢酶、磷酸酶、脲酶、蔗糖酶4种酶活性,以及氟磺胺草醚在大豆根际土壤中的降解规律。 【结果】 低浓度氟磺胺草醚处理的大豆根际土壤细菌数量显著低于对照根际土壤 (P < 0.05),高浓度氟磺胺草醚处理在28 d时显著高于对照 ( P < 0.05);中浓度氟磺胺草醚处理与对照没有显著性差异。不同浓度氟磺胺草醚处理的大豆根际土壤真菌和放线菌数量与对照差异不显著。氟磺胺草醚处理的大豆根际土壤过氧化氢酶活性与对照没有显著差异;磷酸酶活性在取样初期略有降低;低浓度氟磺胺草醚处理的土壤脲酶活性显著降低,中浓度和高浓度处理对脲酶活性表现为先刺激后抑制;高浓度氟磺胺草醚处理的蔗糖酶活性在42 d和56 d时显著低于对照。高浓度氟磺胺草醚降解速率明显高于低浓度和中浓度,并且在试验初期降解迅速;3种浓度氟磺胺草醚在大豆根际土壤中的降解均符合一级动力学方程,降解半衰期由低浓度到高浓度逐渐变短。 【结论】 3种浓度氟磺胺草醚总体上降低大豆根际土壤中细菌的数量,而对大豆根际土壤真菌和放线菌的数量均没有显著影响。氟磺胺草醚对大豆根际土壤过氧化氢酶活性没有显著影响,在短期内对磷酸酶活性有一定程度的抑制作用,低浓度氟磺胺草醚可以显著降低大豆根际土壤脲酶活性,而高浓度氟磺胺草醚在试验后期可以显著抑制大豆根际土壤蔗糖酶活性。大豆根际土壤中氟磺胺草醚初始浓度越高,降解速率越快,半衰期越短。      

Effect of peroxidation on soil electrochemical properties

Treatment with hydrogen peroxide to destroy the organic matter shifts the surface charge towards positive values. This is in agreement with the suggestion that per oxidation produces artefacts in the soil residues, since metals released from organic matter precipitate as hydroxide coating and produce positively charged surfaces. In the presence of 0.1 M sodium pyrophosphate, treatment with hydrogen peroxide always shifts the surface charge towards negative values, notwithstanding the removal of the electronegative organic components. It is suggested that the bulk of electropositive iron and aluminium oxides in soil are associated with the organic matter and removed by the treatment, so that permanent negative charges of clay minerals dominate in soil residue.