农田土壤特性的空间变异性及分形特征

对24 m×24 m面积内的49个观测点进行了土壤含水量和坚实度的空间变异性研究.根据测定结果,用经典统计方法计算了均值、标准差、变异系数等统计特征值,认为该法不能定量的描述土壤特性的空间变异性.于是,用分形理论计算了含水量与坚实度的分形维数.结果表明,在一定范围内,土壤具有分形特征,分形维数可表示土壤特性在空间的不均一程度.     

绿洲区域土壤盐渍化主要参数的空间异质性分析

通过研究土壤盐渍化主要参数的空间异质性,反映绿洲不同程度盐渍化的空间分布.借助传统统计学、地统计学与野外实测数据相结合的方法,以渭库绿洲为例,分析土壤三个剖面层(0-10cm,10-30cm,30-50cm)盐渍化主要参数(电导率、含水量、含盐量、pH)的空间异质性.对研究区域各层土壤盐渍化的监测采样控制在95％置信水平、15％相对误差的可接受范围.研究表明:土壤盐分表聚强烈,呈现出东南高,西北低的盐渍化空间格局.土壤盐渍化严重威胁绿洲的生态安全,因此了解盐渍化空间分布,有利于土壤盐渍化的快速诊断,对进行合理的水资源灌溉利用,防治和改良土壤盐渍化具有科学指导意义.     

The effect of temperature and water content on the rate of decomposition of the herbicide linuron in soil

Rates of linuron breakdown were measured in soil held at the water-holding capacity (WHC), ½ WHC and WHC and at two temperatures, 4°C or 22°C. Breakdown rates were greater at the higher temperature and increased with water content. The energy of activation for the degradation was calculated. Comparison with published figures leads to the speculation that the initial step in degradation by microorganisms is different from that in chemical processes. Effet de la température et de la teneur en eau sur le taux de decomposition du linuron dans le sol Les taux de dégradation du linuron ont été mesurés dans un sol maintenu à sa capacité de rétention, à la moitié et au quart de cette capacité, ainsi quà deux températures 4°C ou 22°C. Les taux de dégradation furent plus grands à la tem-pérature la plus haute et augmentérent avec la teneur en eau. L'energie d'activation pour la dégradation a été calculée. La comparaison avec des chiffres publiés conduit à penser que la première étape de la dégradation par des microorganismes est differente de celle qui intervient dans le processus chimique. Abbau von Linuron im Boden in Abhangigkeit von Temperatur mid Wassergehalt Der Abbau von Linuron im Boden wurde bei 100%, 50% und 25% Wasserkapazitat und bei zwei Termperaturstufen (4°C und 22°C) untersucht. Die Abbauraten nahmen mit steigender Temperatur und steigendem Wassergehalt des Bodens zu. Die fur den Abbau erforderliche Aktivierungs-energie wurde errechnet. Ein Vergleich der Ergebnisse mit Literaturangaben fuhrt zu der Vermutung, daβ der erste durch Mikrooganismen verursachte Abbauschritt verschieden ist von dem bei rein chemischem Vorgang.     

Isolation and characterisation of a bacterial strain degrading the herbicide sulcotrione from an agricultural soil

BACKGROUND: The dissipation kinetics of the herbicide sulcotrione sprayed 4 times on a French soil was studied using a laboratory microcosm approach. An advanced cultivation‐based method was then used to isolate the bacteria responsible for biotransformation of sulcotrione. Chromatographic methods were employed as complementary tools to define its metabolic pathway. RESULTS: Soil microflora was able quickly to biotransform the herbicide (DT₅₀ ≈ 8 days). 2‐Chloro‐4‐mesylbenzoic acid, one of its main metabolites, was clearly detected. However, no accelerated biodegradation process was observed. Eight pure sulcotrione‐resistant strains were isolated, but only one (1OP) was capable of degrading this herbicide with a relatively high efficiency and to use it as a sole source of carbon and energy. In parallel, another sulcotrione‐resistant strain (1TRANS) was shown to be incapable of degrading the herbicide. Amplified ribosomal restriction analysis (ARDRA) and repetitive extragenic palendromic PCR genomic (REP‐PCR) fingerprinting of strains 1OP and 1TRANS gave indistinguishable profiles. CONCLUSION: Sequencing and aligning analysis of 16S rDNA genes of each pure strain revealed identical sequences and a close phylogenetic relationship (99% sequence identity) to Pseudomonas putida. Such physiological and genetic properties of 1OP to metabolise sulcotrione were probably governed by mobile genetic elements in the genome of the bacteria. Copyright © 2011 Society of Chemical Industry     

Spatial variability in the degradation rates of isoproturon and chlorotoluron in a clay soil

Thirty separate soil samples were taken from different locations at the Brimstone farm experimental site, Oxfordshire, UK. Incubations of isoproturon under standard conditions (15 °C; ?33 kPa soil water potential) indicated considerable variation in degradation rate in the soil, with the time to 50% loss (DT₅₀) varying from 6 to 30 days. These differences were confirmed in a second comparative experiment in which degradation rates were assessed in 11 samples of the same soil in two separate laboratories using an identical protocol. There was a significant negative linear relationship (r²= 0.746) between the DT₅₀ values and soil pH in this group of soils. In a third experiment, degradation rates of the related compound chlorotoluron were compared with those of isoproturon in 12 separate soil samples, six of which had been stored for several months, and six of which were freshly collected from the field. Degradation of both herbicides occurred more slowly in the stored samples than in the fresh samples but, in all of them, chlorotoluron degraded more slowly than isoproturon, and there was a highly significant linear relationship (r²=0.916) between the respective DT₅₀ values.     

Cold storage degradation of the herbicide metribuzin in field soil samples awaiting analysis

In conjunction with a study of herbicide degradation in the field, metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-l,2,4-triazin-5-one) was shown to be degraded at-37±5°C in soil samples awaiting analysis. Products of this degradation process include the known derivatives DADK (6-tert-butyl-2,3,4,5-tetrahydro-l,2,4-triazine-3,5-dione) and DK (4-amino-6-tert-butyl-2,3,4,5-tetrahydro-l,2,4-triazine-3,5-dione) and these products themselves have been shown to be degraded further under the same storage conditions. Loss of the herbicide can be approximated using half order kinetics with respect to metribuzin; however, loss of both previously identified metabolites is most rapid when metabolite concentrations are highest. Assuming half order kinetics, samples of Almasippi very fine sandy loam containing metribuzin (0.5 mg/kg) can be expected to lose 50% of the herbicide in 282 days at - 37°, a period which is short enough to affect residue analysis results significantly should samples be stored for extended lengths of time prior to analysis. Implied in these results is the desirability of immediate analysis following collection of samples; otherwise rates of loss during storage must be determined to allow adjustment of results to compensate for residue losses in samples awaiting analysis.     

玛纳斯河流域绿洲土壤养分空间变异特征与格局

运用经典统计学及地统计学的半变异函数定量研究了玛纳斯河流域绿洲表层土壤(0～10cm)中有机质、全氮、全钾和全磷4种养分含量的空间变异特征。结果表明:4种养分含量数据均服从正态分布,有机质、全氮和全磷的理论模型属于指数模型,全钾的则符合球状模型。全氮和全钾的空间自相关范围为24.18km和35.78km,空间结构上具有中等空间相关性,随机性因素引起的全氮和全钾的变异分别占48.93%和48.23%,是结构性因素(气候、母质、地形、土壤类型等)和随机因素(施肥、耕作措施、种植制度等)共同作用的结果;有机质和全磷的空间自相关范围为79.10km和82.63km,空间结构上具有强相关性,块金值与基台值之比分别为25.06%和20.00%,其空间变异主要由结构性因素引起的。在地理信息系统(GIS)支持下,通过Kriging插值研究了玛纳斯河流域绿洲土壤养分的空间水平分布规律并对土壤养分要素含量等级进行了评价。有机质、全氮和全钾具有南北部高,中间低,由南北向中心递减的趋势;有机质、全氮、全钾含量为较丰富以上等级面积分别占研究区的0%、97.91%、99.69%;全磷含量从中心往南递增,北部分布较均匀;全磷含量为较丰富以上等级的面积占研究区的10.62%。     

Effect of soil water content at the time of application on herbicide content in soil solution extracted in a pressure membrane apparatus

Wettable powder formulations of simazine, metribuzin and linuron and a suspension concentrate of simazine were sprayed on to soil particles which were either at a water content equivalent to pF 2·5 or air dry. Air dry samples were then wetted to pF 2·5 immediately or after 24 h. Soil solutions were removed using a pressure membrane apparatus at intervals up to 96 h after wetting. In each case the concentration in soil solutions expressed after 96 h following application to wet soil, or dry soil wetted immediately, were close to those predicted on the basis of Freundlich adsorption isotherm data obtained in slurry equilibrium conditions. There were, however, some differences after shorter periods. Concentrations were always lower in solutions obtained from air dry soil that was not wetted for 24 h. After 96 h simazine and metribuzin concentrations were about 50% of those obtained following application to wet soil, while that of linuron was about 25%. Differences of this size may be large enough to affect mass transfer phenomena and phytotoxicity. It seems likely that suspension of these herbicides sprayed in formulations on to wet soil dissolved in soil water at least as fast as would be predicted theoretically.     

Availability to plants of herbicide residues in soil. Part II: Data for use in vegetable crop rotations

The response of a variety of vegetable crops to fifteen herbicides was estimated in culture solution over concentration ranges chosen to correspond with those that might occur in soil solution. Examples are given to show how these results can be used, in conjunction with the method for estimating the available herbicide residues (in Part I), to decide which crops may safely be sown in soil containing a herbicide residue.     

Theoretical approach to the dynamics of the inoculum density of Verticillium dahliae in the soil: first test of a simple model

A mathematical equation was developed that describes the inoculum densities of microsclerotia of Verticillium dahliae in the soil over a long time span. The equation was based on measurable parameters and ecologically meaningful principles. In the model, the number of systemic infections of plant roots during crop growth was related to soil inoculum density. In turn, formation of microsclerotia in debris and reduction of the amount of crop growth were related to the number of systemic infections. Finally, a gradual release and mortality of microsclerotia in the soil were included to calculate subsequent inoculum densities in the soil.
Fitting the function to experimental data of potato cvs Element, Ostara, Mirka and Astarte, flax, pea, barley, sugar beet, onion and faba bean gave a very high correlation between observed and predicted soil inoculum densities. The clear differences in inoculum production among potato cultivars and other crops were expressed in quantitative terms. The highest inoculum density after incorporation of the debris of a susceptible crop was estimated to occur at 2.3 thermal time units of 3600 degree days (base 0°C). Ten per cent of the initial input of inoculum was still present after 4.5 thermal time units. The model was used to predict the dynamics of soil inoculum densities for V. dahliae under various cropping frequency schemes and performed satisfactorily.     

Field degradation of the herbicide metribuzin and its degradation products in a Manitoba sandy loam soil*

The degradation of the herbicide metribuzin (4-amino-6 r-butyl-3-(methylthio)-1, 2, 4-tnazin-5-(4H)one) applied at 1 and 2 kg/ha at times equivalent to pre-emergence (12 June), post-emergence (5 July), and pre-harvest (15 August), has been investigated in Almasippi very line sandy loam at Carman, Manitoba. Gas-liquid chromatographic analytical results showed that metribuzin degraded during the growing season, and that residue levels immediately prior to freeze-up (25 October) were in general less than 10% of applied metribuzin independent of application date, and were largely unchanged the following spring. The metabolites and photoproduct of metribuzin were present in maximum amounts near 13 July for the first two treatment dates, a time closely following maximum soil temperature readings, and these compounds in turn degraded almost completely by freeze-up. The following spring only very low levels were detected. Under the conditions described, metribuzin and its degradation products degraded to low levels and should not provide a carryover problem the next growing season.     

Availability to plants of herbicide residues in soil. Part I: A rapid method for estimating potentially available residues of herbicides

A simple extraction method with water is described which allows the quantitative determination, within 1 day of the residues of soil-applied herbicides which are potentially available to plants. The validity of this method has been examined with a growth test using Brassica rapa in soils containing residues of different ages.     

The use of cytochrome P450 genes to introduce herbicide tolerance in crops: a review

Mechanisms of herbicide resistance include (1) modified target site, (2) enhanced detoxification or delayed activation, and (3) alterations in the uptake, translocation, or compartmentalization of a herbicide. The first two mechanisms have mainly been identified in plants. Herbicide resistance genes were isolated for several herbicides of different modes of action. Genes that coded for herbicide target or detoxification enzymes were transferred into crop plants. The transgenic plants expressing these genes were tolerant of the active ingredients of herbicides. Before commercialization, the transgenic plants were tested in the field for risk assessment. In the case of crops with herbicide detoxification enzymes, including cytochrome-P450-species-metabolizing xenobiotics, the substrate specificity of the enzymes as well as the toxicological properties of the herbicide metabolites and the pattern of secondary metabolites in plants must be evaluated. © 1999 Society of Chemical Industry     

Evaluation of sampling methods and assessment of the sample size to estimate the weed seedbank in soil, taking into account spatial variability

As field sampling is time consuming, it is necessary to develop efficient sampling techniques to obtain accurate estimates of the weed seedbank in soil. The relative efficiency between sampling schemes depends on the spatial variability in weed seed density across agricultural fields. Spatial variability of the weed seed density was characterized by theoretical correlograms. A systematic sampling (square grill) scheme was considered and it was found that, taking into account spatial variability, this sampling scheme was more efficient than simple random sampling. As a result, the sample size can be reduced in comparison with that given in previous studies, where spatial correlation was ignored. The reduction depends on the correlation structure defined as a function of the ratio, τ, between the nugget effect and the sill of the variogram. The maximum reduction of the sample size, without loss of either precision or confidence level corresponds to the case where there is no nugget effect, τ = 0. The opposite extreme case, where the reduction is nil, corresponds to the case of a pure nugget effect τ = 1. The abaci based on given expressions are provided to determine the sample size in species whose spatial pattern can be fitted either to a Poisson or to a negative binomial distribution.     

Fate of glyphosate in soil and the possibility of leaching to ground and surface waters: a review

The very wide use of glyphosate to control weeds in agricultural, silvicultural and urban areas throughout the world requires that special attention be paid to its possible transport from terrestrial to aquatic environments. The aim of this review is to present and discuss the state of knowledge on sorption, degradation and leachability of glyphosate in soils. Difficulties of drawing clear and unambiguous conclusions because of strong soil dependency and limited conclusive investigations are pointed out. Nevertheless, the risk of ground and surface water pollution by glyphosate seems limited because of sorption onto variable-charge soil minerals, e.g. aluminium and iron oxides, and because of microbial degradation. Although sorption and degradation are affected by many factors that might be expected to affect glyphosate mobility in soils, glyphosate leaching seems mainly determined by soil structure and rainfall. Limited leaching has been observed in non-structured sandy soils, while subsurface leaching to drainage systems was observed in a structured soil with preferential flow in macropores, but only when high rainfall followed glyphosate application. Glyphosate in drainage water runs into surface waters but not necessarily to groundwater because it may be sorbed and degraded in deeper soil layers before reaching the groundwater. Although the transport of glyphosate from land to water environments seems very limited, knowledge about subsurface leaching and surface runoff of glyphosate as well as the importance of this transport as related to ground and surface water quality is scarce.     

Plant pathogen culture collections: it takes a village to preserve these resources vital to the advancement of agricultural security and plant pathology

ABSTRACT Plant pathogen culture collections are essential resources in our fight against plant disease and for connecting discoveries of the present with established knowledge of the past. However, available infrastructure in support of culture collections is in serious need of improvement, and we continually face the risk of losing many of these collections. As novel and reemerging plant pathogens threaten agriculture, their timely identification and monitoring depends on rapid access to cultures representing the known diversity of plant pathogens along with genotypic, phenotypic, and epidemiological data associated with them. Archiving such data in a format that can be easily accessed and searched is essential for rapid assessment of potential risk and can help track the change and movement of pathogens. The underexplored pathogen diversity in nature further underscores the importance of cataloguing pathogen cultures. Realizing the potential of pathogen genomics as a foundation for developing effective disease control also hinges on how effectively we use the sequenced isolate as a reference to understand the genetic and phenotypic diversity within a pathogen species. In this letter, we propose a number of measures for improving pathogen culture collections.     

Adsorption of systemic fungicides and a herbicide by some components of plant tissues,in relation to some physicochemical properties of the pesticides

Lignin, an important component of plant tissues, adsorbed five systemic fungicides and one herbicide (carbendazim, triadimefon, nuarimol, triarimol, fenarimol and fluometuron) more strongly than bovine serum albumin, cellulose, ethylcellulose or sodium polygalacturonate. Significant correlations were found between the extent of the adsorption of the pesticides on the lignins extracted from three different plant species, and the log Poet (Poet is the octan-1-ol/water partition coefficient) of the compounds. The more lipophilic fungicides triarimol and fenarimol (log Poet about 2.6) were adsorbed to the greatest extent. Fluometuron, triadimefon and nuarimol (log Poet about 2.0) were moderately adsorbed, whereas carbendazim with the lowest log Poet (1.34 at pH 5.0), was adsorbed more than expected from its Poet value. The anomaly of carbendazim is discussed; it is ascribed to it's partial protonation at pH 5.0, whereas the other pesticides were non-ionised.     

Foliar residues and toxicity to Aphis citricola of three systemic insecticides applied to the soil in a citrus grove

A study was made of the accumulation of aldicarb, ethiofencarb and dimethoate in citrus leaves and fruit; the toxicity of these insecticides to the spirea aphid (Aphis citricola Van der Goot) was also studied. The effectiveness of the treatments was affected mainly by the rate of accumulation of the toxicant in the leaves. At 18 g a.i. per tree, the greatest residues found in the leaves were 106, 12.2 and 1.3 μg 8^?1 fresh weight for aldicarb, ethiofencarb and dimethoate, respectively. The concentration in mature leaves was very similar to that in young leaves. The residue levels in the mature fruits were much lower than in the leaves. The main components of the residues in the leaves were aldicarb sulphoxide [2-methyl-2-(methylsulphinyl)- propionaldehyde O-methylcarbamoyloxime], dimethoate, omethoate and ethiofencarb sulphoxide [2-(ethylsulphinylmethyl)phenyl methylcarbamate]. A laboratory study with synthetic diets showed similar toxicity for all three insecticides, whereas in detached leaves, or when taken up by citrus trees, ethiofencarb was the least toxic to the aphids.