埋深与形状对土中结构自由冻拔的影响     

邢爽  鈴木輝之  李曰兵  郝冬雪 《农业工程学报》2011,27(9):231-235

冻拔破坏是季节性冻土地区土中结构常见的破坏形式。为了探明季节性冻土地区土中结构冻拔位移与结构埋深、结构截面形状的关系,利用挤塑保温板加工成长度不等的圆柱体与长方体,埋置于室外冻胀土中,模拟土中结构,开展一个冻融周期的室外自由冻胀试验。观测气温、地温、冻深及土体、圆柱体、长方体的冻拔位移等参数,对比试件的冻胀位移,分析自由冻拔的影响因素。结果表明：当埋深小于临界埋深时,一个冻融周期后2种截面的残余冻胀位移均随埋深增加而快速增大,而当埋深大于临界埋深时,残余冻胀位移随埋深增加无明显变化;埋深相同的长方体与圆柱体的残余冻胀位移相对差均值为10%,考虑到试验过程中其它偶然因素的影响,截面形状对土中结构的自由冻拔无明显影响。  相似文献   

Multivariate analysis of soils: microbial biomass,metabolic activity,and bacterial‐community structure and their relationships with soil depth and type     

Antonio Gelsomino  Arianna Azzellino 《植物养料与土壤学杂志》2011,174(3):381-394

A multivariate statistical approach based on a large data set of abiotic and biotic variables was used to classify four contrasting‐land‐use soils. Soil samples were collected at increasing depth from a calcareous agricultural soil, a temperate upland grassland soil, a moderately acidic agricultural soil, and an acidic pine forest soil. Analytical investigations were carried out by using a combination of conventional physical, chemical, and biochemical methods coupled with denaturing gradient gel electrophoresis (DGGE) community fingerprinting of PCR‐amplified 16S rRNA gene‐coding fragments from soil‐extracted total‐community DNA. The data set of soil physical, chemical, and biochemical variables was reduced in dimensionality by means of a principal‐component‐analysis (PCA) procedure. Compositional shifts in soil bacterial‐community structure were analyzed through a clustering algorithm that allowed identifying six main bacterial‐community clusters. DGGE fingerprinting clusters were further analyzed by discriminant analysis (DA) using extracted PCA components as explanatory variables. Soil organic matter–related pools (TOC, TN) and functionally related active pools (microbial biomass C and N, K₂SO₄‐extractable C) significantly decreased with soil depth, and resulted statistically linked to one other and positively related to enzymatic activities (acid phosphatase, arylsulfatase, β‐glucosidase, dehydrogenase, hydrolysis of fluorescein diacetate) and silt content. Besides organic‐C gradients, pedogenetic‐driven physico‐chemical properties, and possibly soil thermal and moisture regimes seemed to play a key role in regulating size and energetic ecophysiological status of soil microbial communities. DGGE analysis showed that contrasting horizons were conducive to the dominance of particular bacterial ribotypes. DA revealed that the bacterial‐community structure was mainly influenced by organic matter–related variables (TOC, TN, CEC, C_flush, N_flush, Extr‐C), chemical properties such as pH, CaCO₃, and EC, together with textural properties. Results indicate that, beyond land use or plant cover, pedogenetic‐driven physico‐chemical conditions changing with soil type and depth are the key factors regulating microbial size and activity, and determining the genetic structure of bacterial community.  相似文献   

Effects of the seed weight and burial depth on the seed behavior of common ragweed (Ambrosia artemisiifolia)     

JEAN‐PHILIPPE GUILLEMIN  BRUNO CHAUVEL 《Weed Biology and Management》2011,11(4):217-223

Common ragweed (Ambrosia artemisiifolia L.) is one of the annual plants that were described recently as invasive weeds in Europe. This species is described as an invasive plant that produces seeds that are highly variable. Its production of variably sized seeds is regarded as promoting its spread in different environments. Experiments were carried out to determine the influence of the seed weight and temperature on germination and the influence of the seed weight and burial depth on seedling emergence. The seeds were divided into a number of classes of weight and the seed weight effect on germination was evaluated by Petri dish assays. In another experiment, the seeds were buried at different depths in a clay soil/sand mix to estimate the burial effect on germination and seedling emergence. The germination level of A. artemisiifolia was high overall, between 76.8% and 94.2%. The seed germination was modified by temperature but it was not influenced by the seed weight. The amounts of germination and seedling emergence were greater for the seeds on the soil surface and decreased with an increasing burial depth, from 2 to 8 cm. No germination or emergence was observed for the seeds that were buried at 10 and 12 cm. The lightest seeds were more sensitive to burial. A greater level of seedling emergence for those seeds that were placed near the soil surface could explain the success of this species in open habitats, where the probability of deeper burial is low. After high seed production, the management of A. artemisiifolia in fields could be partly achieved through soil tillage, burying seeds below 10 cm, and not carrying out deep soil tillage the following year.  相似文献   

医学文献的标引深度与知识创新     

万德芬 《农业环境科学学报》2005,(1)

浅意识标引、次浅意识标引和深意识标引可从不同层面揭示医学文献中的知识。通过这三种文献标引方式，经过标引的语句、结构、语义关系，将有效知识进行系统化组织，为形成新理论、技术和方法打下基础。

  相似文献   

南海北部陆架区海域鯵科鱼类的分布     

陈国宝  李永振 《上海海洋大学学报》2003,(2):146-151

1997年12月至1999年6月对南海北部陆架区海域进行了底拖网渔业资源调查。调查分春(4-6月)、夏(7-9月)、秋(10-12月)、冬(12-2月)4个季节,每个季节都进行全海域的大面积定点调查,共采获科鱼类31种,分隶属于11属。通过对渔获种类组成和渔获率在不同区域、不同季节、不同水深以及昼夜变化等的分析,结果表明,北部湾海区的渔获率最高,粤东海区最低,并由西往东呈逐渐递减的趋势;夏、冬季科鱼类的渔获率较高,而春、秋季较低;渔获率沿水深梯度的变化为≤100m水深海域沿水深的增加而增加,>100m水深海域随水深的增加而下降,以80～100m海域的渔获率相对较高;午夜的渔获率最低,14时最高。  相似文献   

拖拉机耕深自动监控系统的动态辨识     

鲍一丹  吴国桢  程文祥 《浙江大学学报(农业与生命科学版)》1995,(3)

以奔野－２５拖拉机液压悬挂系统为研究对象，通过对初步构成的耕深自动监控系统进行动态特性试验，用频率法建立了该控制系统的数学模型，找出系统动态性能不佳的原因，并提出改进设想，为农机电气自动控制系统的辨识提供一种有效方法。  相似文献   

Locating QTLs controlling constitutive root traits in the rice population IAC 165 × Co39   总被引：2，自引：2，他引：2  

B. Courtois  L. Shen  W. Petalcorin  S. Carandang  R. Mauleon  Z. Li 《Euphytica》2003,134(3):335-345

Drought is an important constraint to productivity in rainfed rice environments. Improvement in the various components of rice drought tolerance is now possible through the identification and manipulation of DNA markers linked with genes controlling these quantitative traits. A recombinant inbred line population was derived from the cross IAC165 × Co39. A molecular map was built that contained 182 RFLP and microsatellite markers. Segregation distortions were limited to a few chromosomal segments. Constitutive root traits, including maximum root length, root thickness and root dry weight in various layers, were measured on 125 lines in a greenhouse replicated experiment. QTL analysis was performed using composite interval mapping. Between 1and 4 main effect QTLs, which explained individually between 5.5 and 24.8% of the variability, were identified for each trait. The most important genomic regions, which carried QTLs for several traits, were found on chromosomes 1, 4, 9, 11 and 12.The QTL locations were in good agreement with previous studies on these traits, confirming the value of the QTLs in a different genetic background. Epistasis represented a non-negligible component of the observed variability for some of the traits but was not detected for others. These results add to the understanding of the genetic control of root morphology in rice, which is necessary to strengthen marker-aided selection programs to improve varieties for water-limited environments. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Assessment of Upland Rice Rooting Depth: Does the Herbicide Injection Technique Work?   总被引：1，自引：0，他引：1  

G. K Trebuil  B. Courtois  W. Herrera 《Journal of Agronomy and Crop Science》1996,177(2):85-93

Water stress is a major constraint to upland rice production. Plants with deep root systems are needed to increase water uptake. For varietal screening or for field diagnosis, breeders and agronomists need methods to monitor rice rooting depth. We assessed a simple, manual technique based on the injection of herbicide at a chosen soil depth using long needles mounted on a veterinary syringe. The time of appearance of herbicide phototoxicity symptoms in the leaves of four rice genotypes with contrasting rooting systems was monitored in the glasshouse and field -experiments. Three herbicides (atrazin, diuron and metribuzin) were tested. Metribuzin was selected as the reference herbicide as it consistently induced distinct leaf phototoxicity symptoms 4 days after its application, regardless of the genotype tested. Through the injection of metribuzin at different depths, significant differences in he number of plants affected by the herbicide were detected under field conditions between the extreme genotypes. The ranking of genotypes obtained in the glasshouse and field experiments was consistent with what is known about their respective rooting patterns. However, risks of herbicide leakage above the treated zone reduce the reliability of the technique and precautions were necessary- to avoid them. Following the precautions increased he time needed to treat one hill to about 5min, which limits the field of application of the manual technique. Moreover, metribuzin remained present at levels toxic to rice seedlings 7 months after being injected into the soil, in spite of its fast downward mobility and degradation rate. This long residual effect might cause environmental concern.  相似文献   

天津滨海园林绿化中土壤盐分的演变规律   总被引：4，自引：0，他引：4  

龙怀玉  张万钧  黄明勇 《北京林业大学学报》2000,22(5):45-48

在天津经济技术开发区 ,依据“允许深度”建立“浅密式”排盐设施并配以相应的管理后 ,连续 10a的观测数据表明 :土壤盐分的空间分布符合正态分布 ;1m土体内不同土层的含盐量及 1m土体的总含盐量随治理时间的延长按照指数规律平稳地减少 ,盐分的表聚性逐渐减弱 ,土壤盐分的空间变异性变小 ;同时 ,土壤盐分的主组成分由NaCl向Na2 SO4 转变 .土壤盐分的演变规律表明 :通过“浅密式”排盐系统 ,可在不到 5a的时间内 ,便在 97.5 %置信度的保证下 ,将开发区土壤的含盐量控制在 0 .2 %以下 ,基本上解除了土壤盐分对园林植物的危害  相似文献   

不同地类红壤坡面土壤有机质及氮素分布研究     

蒋薇  王克勤  郭玲梅  苏备 《广东农业科学》2014,41(15):61-65

选取我国云南地区抚仙湖流域典型流域尖山河小流域为试验区袁以不同土地利用类型的径流小区作为试验对象袁对径流小区内土壤不同土层有机质尧全氮和速效氮含量进行测定遥结果表明院在土地利用方式不同的红壤坡面上袁土壤有机质尧全氮和速效氮的含量均表现为坡下部﹥坡中部﹥坡上部曰土壤剖面有机质尧全氮和速效氮的含量均随着土层深度的增加而降低袁即0耀20 cm>20耀40 cm>40耀60 cm袁且随深度增加含量差距减小曰在坡耕地尧次生林尧人工林和灌草丛4 种土地利用类型中袁土壤有机质的含量表现为次生林>人工林>灌草丛>坡耕地袁土壤全氮的含量表现为灌草丛>坡耕地>人工林>次生林袁土壤速效氮的含量表现为坡耕地>次生林>灌草丛>人工林遥通过回归分析发现袁土壤有机质尧全氮和速效氮含量之间均具有显著的线性相关关系袁土壤有机质是表征土壤供氮能力的重要指标曰通过相关性分析得到土层深度与土壤有机质尧全氮和速效氮的含量之间均具有显著的负相关关系曰不同土地利用类型土壤有机质和全氮含量之间的换算系数不同袁表现为坡耕地>灌草丛>人工林>次生林遥  相似文献