<Emphasis Type="Italic">Stenotrophomonas maltophilia</Emphasis>: a new potential biocontrol agent of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis>, causal agent of potato brown rot

Stenotrophomonas maltophilia was isolated from the rhizosphere of eggplant in the Nile Delta of Egypt, and its antagonistic potential against Ralstonia solanacearum race 3 biovar 2, the causal agent of potato brown rot, was in vitro evaluated on KB agar medium and in vivo on potato plants. In vitro, four isolates of S. maltophilia (PD3531, PD3532, PD3533, and PD3534) appeared antagonistic. The isolate (PD3533) was screened as the most promising antagonist for the in vivo tests. In the greenhouse, the antagonist was applied directly to soil or by bacterization of potato eyepieces. Stenotrophomonas maltophilia significantly suppressed potato brown rot in Egyptian clay soil but not in Dutch clay soil. Survival of a rifampicin and chloramphenicol-resistant S. maltophilia strain PD4560 was investigated in two pairs of clay soils, conventionally and organically managed, from Egypt and the Netherlands. The survival of S. maltophilia was significantly less in Dutch than in Egyptian soils, while the converse occurred for R. solanacearum. These results are in agreement with those obtained in the in vivo biocontrol tests. In conclusion, S. maltophilia may be useful for control of brown rot in the area where it was originally isolated, the Nile Delta in Egypt.     

天津蓟州独乐寺古建筑群昆虫多样性及关键害虫防治

对天津蓟州区独乐寺古建筑群昆虫多样性进行系统调查，并对危害建筑、设施、重要文物和古树的害虫进行了综合防治研究。结果表明，寺内发生的昆虫共计12目37科66种，其中有害昆虫5目10科17种。危害古建筑木质构件和泥塑雕像等文物的主要是花斑皮蠹(Trogoderma variabile)，危害古建筑室外木构件的主要为黑颚条蜂(Anthophora melanognatha)和黄胸木蜂(Xylocopa appendiculata)，黑颚条蜂及十二斑毛斑蜂(Melecta duodecimmaculata)也在壁画和泥塑上筑巢危害；危害古树的主要为白蜡脊虎天牛(Xylotrechus rufilius)等害虫。另外，山斑大头泥蜂(Philanthus triangulum)在山门等处掘土筑巢，造成的危害比较严重。在相关害虫发生期、危害部位和习性调查基础上，综合采用色板、黑光灯、糖醋液诱杀和药物喷洒、注杆、滴孔、药棉填塞、熏蒸等方法，对各类害虫进行了防治，取得良好效果。     

粘土路基施工技术

本文主要论述了路基填筑粘土不利因素以及粘土掺灰的机理特点，同时介绍了粘土处理在工程施工中的技术应用。     

Ecophysiological and genetic variation in seedling traits and in first-year field performance of eight <Emphasis Type="Italic">Acacia senegal</Emphasis> provenances in the Blue Nile,Sudan

The genetic variation in seed weight, seed number per kg and seedling traits was compared among eight Acacia senegal provenances originating from the clay plain (east) and sand plains (west) of the gum belt in Sudan. The main objective of this study was to identify germplasm sources of A. senegal that have a good seed germination capacity and seedling traits suitable for reforestation in the clay-soil part of the dryland gum belt in the Blue Nile region in Sudan. A specific objective was to tentatively explore the adaptive strategy of A. senegal populations. Seventeen-week-old seedlings were planted in the field at spacing of 3 m × 3 m, giving 100 trees per plot and replication; within a randomized complete block design with four replications. The experimental site was in the clay plain region. Seed variables showed significant differences. Clay plain provenances showed considerable variation in seed weight and seed number. They had the smallest seed weight but the highest seed number, while the sand (western) provenances had the largest seed weight but lowest seed number. Seedling branch number, root length, root to shoot ratio and shoot dry weight differed significantly among the provenances 12 weeks after germination. Clay provenances had the highest branch number and shoot dry weight but the shortest roots and lowest root to shoot ratio. This was interpreted as showing better adaptation to the site in these local provenances in comparison to those originating from the western sandy soil regions. High positive correlations were observed between seedling variables, such as root nodule and branch numbers; this could be used for early selection. The variation was greater between provenance groups than within them, suggesting that especially selection among groups would yield genetic gain.     

黏土颗粒表面分维模型的构建及其应用

构建了黏土颗粒物表面分维数学模型,并以高精度数字光学显微系统为基础,测算了部分黏土样品的颗粒表面分维,结果验证了表面分维数学模型的合理性,形成了一套简约的黏土颗粒表面分维分析方法。     

Relations Between Net Nitrogen Mineralization and Soil Characteristics Within an Arable Field

Within-field variations in plant-available soil nitrogen (N) are likely to be affected by differences in soil characteristics. To study this, a 3- year field investigation was conducted during 1998-2000 on a 15 ha arable field in Sweden with considerable within-field soil texture variability. In 34 plots soil N uptake by crops, net nitrogen mineralization (Nm) during the growing season and soil mineral N in spring and shortly after harvest were determined. Beside these parameters, topography, soil organic matter content (SOM), clay content, pH(H 2 O) and grain yield were recorded. The variations in Nm were considerably large both within the field and between years. The within-field variation in Nm could partly be explained by the variation in SOM and clay content (adjusted coefficient of determination = 0.23, P <0.001). The pattern in Nm differed between years, partly because of seasonal variations in soil moisture. For these reasons, the pattern of Nm is difficult to predict without seasonal adjustments.     

土壤细颗粒对有机质的保护能力研究

本文主要综述了土壤细颗粒(<20μm或<50μm)对土壤有机质的保护能力,详细阐述了土壤储存细颗粒态有机质的能力模型及其意义,探讨了影响土壤细颗粒对有机质的保护能力的主要因素。     

蒸发条件下粘土层对土壤水和溶质运移影响的模拟

以土壤水和溶质运移的动力学原理为基础 ,采用数值模拟方法 ,研究了在浅层地下水和蒸发条件下含有粘土层土壤的水和Cl-的运移状况 ,重点探讨了两种粘土的层位和层厚对水和Cl-运移影响的差别及原因。研究结果表明 ,粘土层对土壤的水和溶质运移影响的程度 ,与层状土壤中该粘土及其组合土壤的水力学性质有关。本文模拟的重粘土 (简称Y粘土 )与轻壤土所组成的层状土壤 ,其基本情况为 ,随粘土层层位的升高和层厚加大 ,土壤水分蒸发和地下水补给速率降低 ,Cl-积累减少。而轻粘土 (简称R粘土 )与轻壤土所组成的层状土壤 ,由于它们的导水率曲线在压力水头h约 - 10 0 0cm处相交 ,当h低于此值时 ,R粘土的导水率就大于轻壤土的。因此 ,蒸发、补给速率和Cl-积累强度出现以顶位最高 ,甚至高于均质轻壤土 ,其次为底位 ,最低为中部层位的现象。在蒸发条件下Cl-在剖面中的积聚部位主要是土表。粘土层的存在 ,起到了阻滞作用 ,而阻滞程度则与该粘土水力学性质、层位、厚度和地下水埋深有关     

Role of wheel tracks in runoff generation and erosion under vegetable production on a clay loam soil at Pukekohe, New Zealand

The effects of wheel traffic on soil surface hydraulic properties, and consequent effects on erosion, following planting of vegetable crops in beds have not been widely studied. This paper describes two trials to quantify how wheel tracks influence infiltration and erosion rates, and assesses the value of cultivating wheel tracks for reducing erosion. The trials were carried out under natural rainfall, on Dystric Nitosols with clay loam texture and strong, stable structure. Net rates of erosion from onion (Allium cepa L.) beds with cultivated or uncultivated inter-bed wheel tracks were measured with erosion pins and repeat topographic surveys of sediment trapped in silt fences. Infiltration rates in onion beds, cultivated and uncultivated wheel tracks, and changes in infiltration rates through winter, spring, and summer, were measured using the double-ring, ponded-water method.

Differences in erosion rate were only measured in the second trial in which erosion rate from the uncultivated treatment was 21 Mg ha⁻¹, compared to 1 Mg ha⁻¹ for the cultivated treatment. Erosion occurred through mobilisation of soil along the edge and base of the wheel tracks, with no evidence of erosion of the onion beds. Most of the eroded soil comprised soil aggregates, with 75% between 0.25 and 4 mm in diameter, suggesting soil was transported in runoff along the wheel tracks as stable aggregates. Uncultivated wheel tracks had very low infiltration rates compared to onion beds and cultivated wheel tracks. The differences in infiltration rates between cultivated and uncultivated wheel tracks were consistent in both trials, with minor differences due to rainfall patterns and the implements used to cultivate wheel tracks. There were clear trends in infiltration rates through time, with rates in the uncultivated wheel tracks increasing during the growing season from 1.4×10⁻⁷ to 2.1×10⁻⁵ ms⁻¹ and in onion beds from 1.1×10⁻⁴ to 2.5×10⁻⁴ ms⁻¹, while rates in the cultivated wheel tracks decreased from 1.7×10⁻² to 2.4×10⁻³ ms⁻¹. The major increase of infiltration rate in uncultivated wheel tracks occurred after October when the soil surface began to dry out, and frequent wetting and drying cycles caused the compacted surface soil to crack. Most erosion occurred in the winter/early spring period when storm frequency and rainfall intensity was highest, and infiltration rates in the uncultivated wheel tracks lowest. Cultivating wheel tracks is a simple and effective practice to increase infiltration of rainfall and reduce erosion rates on clay-rich, strongly structured soils.     

土壤透气性及粘土颗粒比表面积与粘土颗粒粒度分布分形维数关系

采用数字显微系统测定了部分华南地区土壤中粘土颗粒粒径分布分形维数值,提出了土壤中粘土颗粒群粒度分布分形维数的几何法计算模型,并就这种分形维数与土壤比表面积和土壤透气性等性质的相互关系作了初步探讨。结果表明,采用数字显微系统测定的粘土颗粒粒径分布分形维数值介于2.2708到2.9483之间,与常规方法测定结果吻合;含砂较多的土壤样品,BET比表面积和Blaine透气时间随粒度分布分形维数值增大而减小;含粘粒较多的土壤样品,BET比表面积和Blaine透气时间同随粒度分布分形维数值增大而增大。