Effect of temperature and moisture on the degradation and sorption of florasulam and 5-hydroxyflorasulam in soil

The degradation rate and sorption characteristics of the triazolopyrimidine sulfonanilide herbicide florasulam and its principal degradation product 5-hydroxyflorasulam (5-OH-florasulam) were determined as a function of temperature and moisture in three different soils. The half-life for degradation of florasulam ranged from 1.0 to 8.5 days at 20-25 degrees C and from 6.4 to 85 days at 5 degrees C. The half-life for degradation of 5-OH-florasulam ranged from 8 to 36 days at 20-25 degrees C and from 43 to 78 days at 5 degrees C. The degradation rate of both compounds was strongly influenced by temperature, with activation energies ranging from 57 to 95 kJ/mol for florasulam and from 27 to 74 kJ/mol for 5-OH florasulam. Soil moisture content had negligible impact on the degradation rate. Apparent (nonequilibrium) sorption coefficients for florasulam and 5-OH-florasulam at 0 days after treatment (DAT) were 0.1-0.6 L/kg and increased linearly with time for both florasulam and 5-OH-florasulam (r(2) > 0.90) to levels as high as 12-23 L/kg. Heats of adsorption were calculated on one soil as a function of time. Heat of adsorption values for both florasulam and 5-OH-florasulam increased as incubation time increased and the amount of each compound decreased; values were near 0 kJ/mol initially and increased to a maximum of 91 and 66 kJ/mol for florasulam and 5-OH-florasulam, respectively.     

Land degradation and soil and water conservation in tropical highlands

Land degradation is not uniform, even in the same landscape, but nevertheless an overall consensus seems to grow on the fact that many areas are under way of rehabilitation. It is a debateable question whether the improving areas are improving because of interventions—or whether this has more to do with processes of innovation and adaptation. The international symposium ‘HighLand2006’ on land degradation and land rehabilitation, held in Mekelle (Ethiopia), from 21 to 25 September 2006, created a forum for those conducting research in East African Highlands as well as in similar regions around the globe to discuss findings. Tropical highlands (>1000 m a.s.l.) cover 4.5 million km² with an average population density of 33 inhabitants km⁻². Nearly all tropical highlands suffer from land degradation, especially medium to very high water erosion. Exchange of experiences during in-door sessions and excursions led to results which are condensed in this special issue. Studies presented tend to invalidate hypotheses on irreversibility of land degradation in tropical mountain areas. Circumstances are that in highly degraded environments, with high pressure on the land, no other alternatives are left open but to improve land husbandry; and that this is particularly successful in places where decision making processes at different levels in society give the highest priority to the implementation of soil and water conservation and other land rehabilitation, in situ and at catchment level.     

Simulation of tridecane degradation under different soil water contents

A mathematical model for the degradation of n-tridecane in a leached chernozem with different water contents was developed on the basis of budget ratios and the Mono kinetic equations. In the course of the verification, the model equations were simplified and solved numerically. The cases of uniform and step-wise initial pollutant distributions in a soil-filled co lumn were considered. The model was refined in accordance with the experimental data on the decrease in the tridecane concentration during three months. A statistically significant positive effect of the moisture and the uncontaminated upper soil layer on the rate of the tridecane decrease was shown. It was found that the degradation of the tridecane stopped and then recommenced again. The tridecane concentration in the soil at which its decrease almost stopped was determined. It was supposed that the hydrocarbon-oxidizing microorganisms, in the course of their life activity, excrete products that are accumulated and inhibit the degradation of the hydrocarbon. The parameters of the microbial activity in the soil were determined in a numerical experiment.     

Deforestation effects on soil degradation and rehabilitation in western Nigeria. IV. Hydrology and water quality

Hydrological and water-quality measurements were made on a 44·3 ha watershed under forest cover and following deforestation and conversion to an agricultural land-use. Under secondary tropical rainforest, water yield ranged from 2·2 per cent to 3·1 per cent of annual rainfall. Deforestation of 7 per cent of the watershed area increased water yield to 7·0 per cent of annual rainfall. Baseflow increased with deforestation, and increased progressively with time after deforestation. It was 5·1 per cent of annual rainfall in 1979, 15·1 per cent in 1980, 16·4 per cent in 1981 and 17·9 per cent in 1982. In comparison, surface flow was 4·5 per cent in 1979 and 6·2 per cent in 1980, but decreased to 2·3 per cent in 1981 and 2·4 per cent in 1982. Total water yield following deforestation and conversion to agricultural land-use ranged from 9·6 per cent to 21·3 per cent of the annual rainfall received. The dry season flow decreased with time as the dry season progressed, but increased over the years following deforestation. Surface runoff during the rainy season depended on ground cover and soil quality. The extent and severity of soil degradation affected the dynamics of surface flow. Because of actively growing crops, plant nutrient concentrations in surface runoff were low. Forested lysimeters had higher seepage losses than cropped lysimeters, and the water-use efficiency was 1·9–3·6 kg ha⁻¹ mm⁻¹ for cowpeas compared with 6·1–11·0 kg ha⁻¹ mm⁻¹ for maize. The delivery ratio was high immediately after deforestation and decreased to a steady value of about 3·2 per cent within 7 years. The data show five distinct phases of soil degradation in relation to generation of surface runoff. © 1997 John Wiley & Sons, Ltd.     

Effects of soil degradation and management practices on the surface water dynamics in the Talgua River Watershed in Honduras

When tropical forests are felled, subsequent land uses affect surface runoff, soil erosion, and soil compaction. In some cases, they can markedly change the hydrology of a region with disastrous effects on human life. The objective of this paper is to investigate the effect of rainfall on stream hydrology due to conversion of primary forests to agriculture. Near surface water dynamics were compared for three land uses on the steep hillsides in the Talgua River Watershed in Honduras: degraded grass‐covered field; traditional coffee plantation; and primary forest. Infiltration and surface runoff rates were measured using several methods. A clear difference was observed in hydraulic conductivity between the degraded and non‐degraded lands. The degraded grass‐covered hillslopes developed a surface restrictive layer with a low saturated hydraulic conductivity of 8 to 11 mm/hr, resulting in more frequent overland flow than traditional coffee plantation and primary forest. Soils under the latter two land‐use types maintained high infiltration capacities and readily conducted water vertically at rates of 109 and 840 mm/hr, respectively. Dye tests confirmed that the coffee plantation and primary forest both maintained well‐connected macropores through which water flowed readily. In contrast, macropores in the degraded soil profile were filled by fine soil particles. Soils in the degraded grass‐covered field also showed more compaction than soils in the coffee plantation. Copyright © 2004 John Wiley & Sons, Ltd.     

Influence of soil moisture on sorption and degradation of hexazinone and simazine in soil.

Sorption and degradation rates of hexazinone and simazine on soil were determined in a sandy loam soil incubated, during 44 days, at 25 degrees C with moisture contents ranging from 4% to 18%. Herbicide levels in soil solution were also measured, after extraction of this solution by a centrifugation method. All experiments were conducted with treated soil in plastic columns, and the results showed that this method is suitable for the simultaneous study of pesticide sorption and degradation in soil at different environmental conditions. In general, sorption of both herbicides was higher for aged herbicide residues compared to recently applied herbicides, and soil subjected to drying and rewetting cycles had the highest sorption values. K(f) values ranged from 0.5 to 1.2 for simazine and from 0.2 to 0.4 for hexazinone. Degradation rates increased with soil moisture content for both herbicides, and drying-rewetting of soil yielded degradation rates slower than that obtained at 10% soil moisture content. Hexazinone concentration in soil solution decreased with incubation time faster than simazine.     

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.     

水土保持的水环境效应研究

 非点源污染已成为我国很多湖库型水源地的主要污染源,给人们的生活和健康以及经济社会的可持续发展造成严重危害。水土保持措施是防治非点源污染,保护水源水质,保障饮水安全的重要手段。笔者界定了水土保持水环境效应的概念;将非点源污染的类型划分为农业型、水土流失型、农村生活型、城市径流型和降水降尘型;首次系统地揭示水土保持的水环境效应机制;定量分析小流域综合治理与区域综合治理水土保持的水环境效应。     

土壤食细菌线虫对菲降解的影响

以菲作为多环芳烃污染物的代表,通过室内培养试验研究了在菲降解菌恶臭假单胞菌存在与否的条件下,接种食细菌线虫对未灭菌土壤中菲去除的影响。析因设计包括4个处理:单独接种恶臭假单胞菌(B),单独接种食细菌线虫(N),同时接种食细菌线虫和恶臭假单胞菌(BN)以及未接种线虫和细菌的对照(CK);分别在培养后第0、5、14、28天进行破坏性采样,测定土壤中菲的残留量,食细菌线虫和恶臭假单胞菌的数量,土壤FDA(荧光素二乙酸酯)水解酶、过氧化氢酶的活性。结果显示,相比CK,在培养前期(0~14天),处理N提高土壤中菲的去除率;而在培养后期(14~28天),BN处理降解菲的优势逐渐显现出来。在培养结束(28天)时,各处理菲的去除率依次为BN(48.2%)B(45.1%)N(44.4%)CK(43.5%)。试验结果还表明,接种食细菌线虫能显著(p0.05)促进细菌以及土壤酶活性。总之,食细菌线虫和细菌的交互作用可能促进土壤中菲的降解。     

Tillage effects on soil degradation, soil resilience, soil quality, and sustainability

Soil degradation, decrease in soil's actual and potential productivity owing to land misuse, is a major threat to agricultural sustainability and environmental quality. The problem is particularly severe in the tropics and sub-tropics as a result of high demographic pressure, shortage of prime agricultural land, harsh environments, and resource poor farmers who presumably cannot afford science based recommended inputs. Tillage methods and soil surface management affect sustainable use of soil resources through their influence on soil stability, soil resilience, and soil quality. Soil stability refers to the susceptibility of soil to change under natural or anthropogenic perturbations. In comparison, soil resilience refers to soil's ability to restore its life support processes after being stressed. The term soil quality refers to the soil's capacity to perform its three principal functions e.g. economic productivity, environment regulation, and aesthetic and cultural values. There is a need to develop precise objective and quantitative indices of assessing these attributes of the soil. These indices can only be developed from the data obtained from well designed and properly implemented long-term soil management experiments conducted on major soils in principal ecoregions.     

手性异丙甲草胺在土壤中的选择性降解

Separation of chiral enantiomers and the dissipation of rac-metolachlor and S-metolachlor in soil were evaluated using achiral high-performance liquid chromatography （HPLC） and chiral gas chromatography （GC） methods. Under the experimental conditions the possible metabolite was considered to be N-（2-ethyl-6-methyl-phenyl）-2-hydroxy-acetamide. Because of the presence of two chiral elements （asymmetrically substituted carbon and chiral axis）, the baseline separation of metolachlor enantiomers was not achieved. S-metolachlor degraded faster in soil than rac-metolachlor. After a 42-day incubation, 73.4% of rac-metolachlor and 90.0% of S-metolachlor were degraded. However, due to the absence of biological processes the degradation process in sterilized soil showed no enantioselectivity. The results indicated that enantioselective degradations could greatly affect the environmental fate of metolachlor and should be considered when the environmental behavior of these compounds was assessed.     

Influence of soil depth on asulam adsorption and degradation

Asulam (methyl(4-aminobenzenesulphonyl)carbamate) is not adsorbed to any marked extent by the soils examined above the pH range 4.5–6.0. The adsorption which takes place is inversely correlated with pH. Comparatively higher amounts of asulam are retained by topsoil samples than by their respective subsoil samples. Asulam degradation is rapid in topsoils and slow in subsoils. The addition of yeast extract to the latter enhances degradation. The sensitivity of the analytical procedure is improved by extracting the Bratton-Marshall colour into n-butanol.     

土壤含水量、温度对Bt棉间苗叶、蕾Bt蛋白降解的影响

为了解土壤环境因子对Bt棉Bt蛋白降解的影响,为Bt棉生态风险性评价提供依据,室内采用ELISA法,研究了土壤不同含水量、温度影响下,Bt棉间苗叶、蕾Bt蛋白在土壤中的降解动态,并用指数模型对Bt蛋白降解动态进行拟合,估算了DT50和DT90。结果表明:不同含水量、温度条件下,Bt棉间苗叶和蕾Bt蛋白在取样第48 d,就降解了初始量的56.18%~93.26%,表明Bt蛋白前期在土壤中能快速降解,后期稳定下降。70%土壤持水量、35℃下Bt蛋白在前期降解最快,DT50(降解50%Bt蛋白所需时间)为12.29 d(间苗叶)和10.07d(蕾),DT90为41.06 d(间苗叶)和33.96 d(蕾)。适宜条件下,Bt蛋白在土壤中可被完全降解。土壤温度和含水量均会显著影响Bt蛋白在土壤中的降解。取样前期(32 d前)土壤温度和含水量对Bt蛋白降解有显著交互作用。温度是影响Bt蛋白降解的主要因子,同一含水量下,随温度升高,Bt蛋白降解速率加快。同一温度,100%土壤持水量条件下,Bt蛋白降解速率最慢,在较高温度(25℃和35℃),70%土壤持水量条件,Bt蛋白在前期(32 d或48 d前)降解速率显著快于50%土壤持水量条件。本研究表明,较高温度和适宜土壤含水量有利于Bt蛋白前期快速降解。     

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.     

Impact of soil degradation on crop production in Brazil

A conceptual model is proposed to facilitate understanding of the effects of soil and crop management practices on soil properties, yields, economics and political interference in production from heavy clay oxisols of the Brazilian developed regions. This model was developed for illustrative purposes, and was established by qualitative and quantitative analyses of data and observations on the rates of change of soil structure, the susceptibility of soils to this changes, and its effects on different cropping systems. Rates of production, technological aspects of production, production efficiency and profitability are compared. In general, the model is presented as a hypothetical function for characterizing and facilitating understanding of the impact of soil degradation on several aspects of crop production from oxisols in Brazil.     

土壤斥水性影响土壤水分运动研究进展

土壤斥水性广泛存在于各类土壤,是影响植物生长、土壤水分运动以及土壤侵蚀等水土过程的重要因素。该文阐述了土壤斥水性的基本概念,介绍了几种常用的斥水性强度测定方法及适用范围。在此基础上,论文对土壤斥水性如何影响土壤水力性质以及水分运动特征等研究现状作了全面评述,重点讨论了近年来该领域的研究热点,如土壤斥水性影响下的指流观测和理论模拟以及斥水性土壤蒸发过程等。最后,提出了相关研究中亟待解决的若干关键科学问题,主要包括确定土壤斥水性影响指流现象和蒸发过程的物理机制的揭示;考虑土壤斥水性参数的土壤水分运动数学模型的构建;以及对新模型的求解及对数值解的理论分析。由于土壤斥水性对土壤水分运动有重要的关联效应,相关问题的深入研究对进一步认识土壤水分运动的内在物理机制具有重要理论意义,也将为掌握和有效利用土壤斥水性提供实践指导。     

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.     

土壤含水率与土壤碱度对土壤抗剪强度的影响

土壤含水率和土壤碱度是表征土壤物理化学性质的两个重要参数。通过室内三轴不固结不排水试验,研究了土壤含水率和土壤碱度对土壤抗剪强度的影响。试验处理采用5种土壤碱度(土壤可交换钠百分比ESP=0、5、10、20、40)和4种土壤质量含水率(0.05、0.10、0.20以及饱和含水率0.34)水平。试验结果显示,土壤黏聚力随着土壤含水率的增加基本上呈先增大后减小之趋势;当土壤含水率在0.10附近时黏聚力达到其最大值。土壤内摩擦角随着土壤含水率的增加而线性减小。土壤碱度对土壤黏聚力的影响机理较为复杂,其影响效果随土壤含水率的增加而减小;但土壤碱度对土壤内摩擦角的影响较小。土壤碱度对土壤抗剪强度的影响程度明显地小于土壤含水率对其的影响程度。     

Effect of soil structure on soil water status

Although the need for research into soil structural features responsible for water loss from soil is recognised, the research has been hampered by the lack of suitable techniques for measuring in situ soil macrostructure. Therefore, in a field experiment, structural parameters obtained from eight differently tilled (loam) soils in winter and spring were correlated with gravimetric soil water content (at 5 and 10-cm depths) and evaporative water loss during daylight hours. Percentage of voids and aggregates of different sizes, mean aggregate size, mean void size and macroporosity percentage were all calculated from structural data obtained from sectioned blocks of soil that were impregnated with paraffin wax in the field.Significant negative correlations were observed between soil water content, and percentage of 4–8 and 8–16-nm voids, mean aggregate size and macroporosity percentage, especially in winter when there are long periods without precipitation. However, inverse relationships were detected between evaporative water loss during daylight hours on selected days and mean aggregate size, mean void size and macroporosity percentage. But evaporative water loss during daylight hours apparently did not influence water content of bare soil with coarse structure at the surface.     

Effect of reduced iron on the degradation of chlorinated hydrocarbons in contaminated soil and ground water: A review of publications

Chlorinated hydrocarbons are among the most hazardous organic pollutants. The traditional remediation technologies, i.e., pumping of contaminated soil- and groundwater and its purification appear to be costly and not very efficient as applied to these pollutants. In the last years, a cheaper method of destroying chlorine-replaced hydrocarbons has been used based on the construction of an artificial permeable barrier, where the process develops with the participation of in situ bacteria activated by zerovalent iron. The forced significant decrease in the redox potential (Eh) down to ?750 mV provides the concentration of electrons necessary for the reduction of chlorinated hydrocarbons. A rise in the pH drastically accelerates the dechlorination process. In addition to chlorine-organic compounds, ground water is often contaminated with heavy metals. The influence of the latter on the effect of zerovalent iron may be different: both accelerating its degradation (Cu) and inhibiting it (Cr). Most of the products of zerovalent iron corrosion, i.e., green rust, magnetite, ferrihydrite, hematite, and goethite, weaken the efficiency of the Fe⁰ barrier by mitigating the dechlorination and complicating the water filtration. However, pyrrhotite FeS, on the contrary, accelerates the dechlorination of chlorine hydrocarbons.