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1.
模拟植被地表覆盖率和粗糙度对坡面流水动力特性的影响 总被引：2，自引：2，他引：0
为研究刚性植被覆盖与地表粗糙共同作用下的坡面流水动力特性,在室内开展定床水槽冲刷试验,研究陡坡(15°)条件下10组流量(0.33~1.95m~3/h)、5种覆盖率(0,0.5%,1.0%,1.5%,2.0%)、4种不同地表粗糙度(0.01,0.18,0.25,0.38mm)的坡面流流速、流型流态、阻力系数等变化特性。结果表明:(1)水流流速变动范围为0.06~0.59m/s,流速与植被覆盖率和地表粗糙度呈负相关关系(r-0.90),当植被覆盖率增加,流速随流量增加的增幅降低;流速校正系数与植被覆盖率呈正相关关系(r0.75),而与地表粗糙度呈负相关关系(r-0.84);(2)所有试验条件下雷诺数处于153~910之间,流态主要集中于过渡区和虚拟层流区,流型多数处于急流区,随植被覆盖率和地表粗糙度的增加,弗劳德数逐渐小于1,具有向缓流区延伸的趋势;(3)坡面流总阻力系数与雷诺数呈幂函数关系,与地表粗糙度和植被覆盖率呈正相关关系(r0.81);(4)阻力影响指数结果显示,当流量小于1.05m~3/h时,地表粗糙度在影响总阻力过程中占主导地位,反之,植被覆盖率占主导地位;通过t检验,坡面流总阻力与颗粒阻力和形态阻力线性叠加结果差异性显著(p0.05),表明当存在颗粒阻力及形态阻力时,坡面流总阻力并不能使用线性叠加原理。 相似文献
2.
[目的]揭示含沙量对高陡边坡水动力学特性的影响,为高陡边坡土壤侵蚀机理模型精度的提升提供理论支撑。[方法]设定3个含沙梯度(0,4%,8%)和3个放水梯度(12,16,20 L/min),在36°坡面进行野外径流冲刷试验。[结果]随着放水流量的增大,平均流速随着含沙量增加而减小的趋势较小,雷诺数Re随着含沙量增加而减小的趋势较明显;当放水流量为16,20 L/min时,随着含沙量的增加,坡面流态均由紊流向过渡流发展;弗汝德数Fr随着含沙量的增加而增大,且均大于1,坡面径流流态属于急流。阻力系数f与雷诺数Re呈极显著幂函数关系(p<0.01),随着含沙量的增加,雷诺数Re对阻力系数f的影响逐渐减弱。含沙量与平均流速、雷诺数、阻力系数、水流剪切力和水流功率呈极显著负相关关系(p<0.01),相关系数绝对值大小顺序为R(Re)>R(ω)>R(τ)>R(ν)>R(f),雷诺数Re是描述水动力学参数与含沙量关系的最佳参数,含沙量与弗汝德数Fr关系不显著,与雷诺数、水流功率、水流剪切力以及流速间的关系可用二元线性函数表示。[结论]含沙量对高陡边坡水动力学特性具有... 相似文献
3.
刚性植被空间配置模式对坡面流水动力学特性的影响 总被引：6，自引：2，他引：4
通过室内人工模拟不可入渗光滑下垫面径流冲刷试验,讨论了5种刚性植被空间配置模式(行状、品字状、上部密集型、下部密集型、随机型及裸坡对照)的坡面水动力学特性。试验共在10组流量(0.2,0.3,0.4,…,1.1L/s)下冲刷,结果表明:植被的配置对坡面流水动力学参数影响显著。各刚性植被对坡面流流速抑制最大的是品字状的配置(平均流速0.689m/s),效果最差的是下部密集型的配置(平均流速0.568m/s)。坡面流阻力最大的是品字状配置(f=1.181)。各种配置类型下坡面流流态为过渡流-紊流态,配置模式不同对雷诺数影响远远小于流量对雷诺数影响。各配置模式下水深与流量的关系呈显著线性正相关(R20.99),流速随流量的变化关系为对数增加(R20.9),雷诺数与流量呈线性增加(R20.98),弗汝德数随流量的增加呈对数减少的趋势(R20.88)。 相似文献
4.
为揭示冻融作用对坡面土壤水蚀的影响,探究春季解冻期坡面土壤的水蚀动力参数动态响应时空演化过程,采用2个坡度(10°,15°)、4个流量(4.5,6.5,8.5,10.5L/min)和4个起始解冻深度(2,5,10,15cm),进行野外径流冲刷试验,系统地分析冻融坡面水蚀动力参数雷诺数、弗劳德数、流速、水流剪切力、水流功率和单位水流功率在不同起始解冻深度、不同流量和不同坡度条件下的时空演化过程。结果表明:冻融坡面水蚀动力参数雷诺数、流速、水流剪切力和水流功率随流量的增加呈增加趋势;水流剪切力、水流功率与单位水流功率随坡度增加而增大;水流剪切力和水流功率随起始解冻深度的加深而增大;雷诺数、弗劳德数、流速和单位水流功率随起始解冻深度的变化趋势不明显,其起始解冻深度为5cm时,水蚀动力参数随时间变化最为剧烈;建立了冻融坡面水蚀动力参数雷诺数(R~2=0.728)、水流剪切力(R~2=0.644)、水流功率(R~2=0.721)、流速(R~2=0.533)和单位水流功率(R~2=0.553)的幂函数预测方程。 相似文献
5.
人工模拟降雨条件下紫色土坡面流水动力学参数特征 总被引：4，自引：2，他引：4
采用人工模拟降雨法,在3.0m长、1.0m宽的可变坡土槽上,通过4个不同坡度(5°,10°,15°,20°)、5个不同雨强(0.6mm/min,1.1mm/min,1.6mm/min,2.12mm/min,2.54mm/min)的组合实验,对降雨条件下紫色土坡面流水动力参数特征进行了研究。结果表明,在实验的坡度和雨强范围内,紫色土坡面流平均雷诺数Re变化于104.9～1571.7之间,在一定雨强和坡度条件下,坡面流雷诺数Re随实验时间延长而逐渐增大,这主要与坡面形态受降雨侵蚀发生改变后坡面流流态由层流向紊流转变有关;坡面流弗罗德数Fr在各种雨强和坡度条件下都小于1,属缓流状态;坡面流阻力系数f与雷诺数Re无明显关系,但其与佛罗德数Fr之间呈显著的指数关系;曼宁糙率系数n与雷诺数Re之间为幂函数关系,但其与佛罗德数Fr无明显关系。 相似文献
6.
为探究芥菜浸提液对豇豆种子发芽和连作下豇豆早期幼苗生长影响的生理机制,在盆栽条件下,研究不同浓度(0、10、20、40 g·L-1)的芥菜浸提液对豇豆种子萌发及5年连作条件下豇豆幼苗生长指标、根系形态指标、叶片保护酶活性和土壤性质的影响。结果表明,高浓度(40 g·L-1)芥菜浸提液对种子萌发和胚根生长有强烈的抑制作用,其中发芽率、活力指数、胚根长度和数量分别显著降低85.70%、82.66%、36.15%和46.54%;而低浓度(10 g·L-1)芥菜浸提液对种子胚根生长有显著的促进作用,其中胚根长度和数量分别显著提高44.84%和80.82%。豇豆连作土壤浇灌芥菜水浸提液可不同程度地增加豇豆幼苗株高、茎粗、干质量、鲜质量和壮苗指数,在低浓度处理下豇豆生长指标分别显著增加60.33%、12.24%、85.87%、77.31%和50.82%;此外,豇豆幼苗根长度、根系表面积、根体积、根尖数等根系指标也均有不同程度地增加,其中以低浓度浸提液处理下的豇豆幼苗综合指标最好。芥菜浸提液处理还能促进幼苗叶片过氧化氢(H2O2)含量升高、以及抗氧化酶活性的提升,其中H2O2含量,过氧化氢酶(CAT)、超氧化物歧化酶(SOD)和脱氢抗坏血酸还原酶(DHAR)活性均随着芥菜浸提液浓度的增加而降低,过氧化物酶(POD)活性则相反,而谷胱甘肽还原酶(GR)活性未表现出明显的规律;芥菜浸提液还可以提高土壤pH值,降低土壤电导率,以及提高土壤酶活性,其中蔗糖酶和酸性磷酸酶活性随着芥菜浸提液浓度的增加而升高。综上所述,不同浓度芥菜浸提液对豇豆种子萌发起着低促高抑的作用,芥菜与豇豆之间存在明显的化感作用;芥菜浸提液可通过提高豇豆幼苗的抗氧化酶活性和改善豇豆根系环境,促进豇豆幼苗生长,缓解连作障碍对豇豆幼苗的危害,从而提高豇豆幼苗的抗逆能力。本研究结果为缓解豇豆连作障碍提供了新的途径。 相似文献
7.
为研究电磁场对换热表面析晶污垢的抑垢情况,该研究以电磁水处理动态试验台为依托通过一系列变工况的试验,获取了不同磁场强度、流速和入口温度下碳酸钙污垢热阻热阻曲线,又通过电磁场、流场及温度场之间的正交分析得出了各因素对析晶污垢生长的具体影响。结果表明,试验磁感应强度范围内污垢热阻随磁感应强度的增大呈减小趋势;不加磁场湍流状态下,流速越大污垢热阻越小;磁场与流速共同作用可以强化阻垢效果。随着入口温度的增加,热阻渐近值先增大后减小,在入口温度为30℃时出现极大值;电磁场处理产生的热阻减小的效果要大于入口温度增加引起的热阻增加的效果。通过正交分析,得出了影响污垢生长的主次因素由强到弱依次为磁感应强度、流速、入口温度。同时计算出了该试验台在试验工况下的最优运行工况,在入口温度30℃,流速0.4m/s,磁感应强度20 mT情况下抑垢效果最好。研究结果可为工业循环水除垢抑垢提供一定的参考。 相似文献
8.
不同覆盖度和雨强条件下崩积体坡面侵蚀的动力学特征 总被引：1，自引：1，他引：0
基于崩岗崩积体易侵蚀的特性,通过室内人工模拟降雨试验,研究30°坡度条件下,不同秸秆覆盖度(0,25%,50%,75%,100%)和雨强(60,90,120mm/h)组合坡面侵蚀的水动力学参数特征。结果表明:(1)不同条件下,雷诺数变化范围在462.86~750.19Re之间,雨强对雷诺数的影响达到极显著水平,覆盖度对雷诺数的影响不显著;弗罗德数的变化范围在0.06~0.64Fr之间,水流的流型为缓流,覆盖度对弗罗德数的影响达到极显著水平,雨强对弗罗德数的影响不显著;阻力系数的变化范围在9.65~1 018.19f之间。(2)覆盖度对坡面流流速的影响达到极显著水平,坡面流流速随着覆盖度的增加而减小;覆盖度对水深的影响达到显著水平,坡面径流深随着覆盖度的增大而增加;阻力系数与雨强和覆盖度之间无明显关系。(3)覆盖度与单位水流功率之间呈极显著的指数函数关系,与水流剪切力和断面单位能量之间呈显著的指数函数关系;雨强对流速、水深和阻力系数的影响都不显著。 相似文献
9.
鱼游泳能力对体长的响应及其在鱼道设计中的应用 总被引：4，自引：4，他引：0
为了探讨鱼类体长对游泳能力的影响并为鱼道水流的设计提供参考,该研究在封闭水槽中使用"递增流速法"测试了海南省某水利枢纽鱼道目标对象的游泳能力,并用Origin软件进行了数据统计分析,得到了试验鱼感应流速、临界游泳速度和爆发游泳速度的直线回归方程和Kaplan-Meier曲线。结果表明:1)随着试验鱼体长增大,相对感应流速、临界游泳速度和爆发游泳速度(体长/s)均减小,体长和鱼类速度的相关关系可用直线方程表示,且数据经过对数变换后的直线方程拟合效果比未经过对数变换的拟合效果更好,其中R2由0.664～0.725提高至0.907～0.933。2)根据鱼道设计规范、导则及文献,结合本工程目标过鱼对象的感应流速、临界游泳速度和爆发游泳速度(m/s),建议本工程鱼道进口诱鱼流速控制在0.35～0.47 m/s,池室流速控制在0.21～0.59 m/s,竖缝流速控制在0.57～0.74 m/s,出口断面至下一个池室之间的流速控制在0.21～0.50 m/s。鱼类体长对相对游泳速度(体长/s)产生了负面影响,鱼类游泳速度及其变化规律可对鱼道水流设计值提供参考。 相似文献
10.
为了研究间作体系下地表特性对土壤侵蚀的影响,采用人工降雨法分析了玉米马铃薯间作及起垄在不同降雨强度(40,80 mm/h)下的水力学参数的变化特征。结果表明:(1)同一降雨强度下玉米马铃薯间作的阻力系数高于玉米单作处理,雷诺数、弗劳德数和径流流速低于单作玉米处理(P0.05)。7月初80 mm/h降雨强度下玉米马铃薯间作和玉米单作的阻力系数分别为0.41～0.53和0.09～0.10;径流流速分别为0.11～0.12,0.19～0.21 m/s。玉米马铃薯间作的径流流速和阻力系数与马铃薯单作差异不显著(P0.05)。(2)同一降雨强度下间作高垄的阻力系数最高,径流流速、雷诺数和弗劳德数最低。40 mm/h降雨强度下间作高垄、间作低垄、玉米高垄的径流流速分别比玉米低垄分别减少35.71%,35.71%和14.29%。间作条件下起垄能增加坡面流阻力,降低雷诺数和弗劳德数,进而减缓坡面径流流速,这对于坡耕地土壤侵蚀的防治以及农业的可持续发展具有重要的指导意义。 相似文献
11.
Earthworms are target organisms both for scientists studying the biological component of soils and for farmers concerned with monitoring the quality of their soils. Different expellants are used to extract earthworms from the soil but differences in chemical properties and efficiency between commercial mustard and allyl isothiocyanate (AITC) solutions remain unknown. The objectives of this study were to compare (i) the concentration of irritating product (allyl isothiocyanate AITC) in two expellant solutions (diluted mustard or AITC solution) and (ii) their efficiency in extracting earthworms from the soil.AITC concentration was analyzed according to a new method, based on AITC solvent extraction and HPLC quantification, in one commercial mustard brand to assess its variability within and between batches of jars. According to mustard spiking with AITC standard solution, extraction recovery was estimated as 98 ± 2%. Earthworm field data were collected in spring 2012 in 22 cultivated fields located in east Île-de-France, comparing pure AITC to commercial mustard solutions. Species diversity, abundance and biomass of earthworms per plot were measured.We showed that AITC concentration in commercial mustard varied according to the use by date but not according to the batch. We thus recommend using the freshest mustard available from the same batch. Moreover, AITC solution was found to be about four times more concentrated in AITC than the commercial mustard solution. Despite this result, no significant differences were found in the efficiency of commercial mustard or AITC solutions to bring earthworms to the soil surface in terms of abundance, biomass or diversity. We thus discuss the advantage and drawbacks of using both expellants in the field. 相似文献
12.
榨菜(Brassica juncea)和紫甘蓝(Brassica oleracea)种间周缘嵌合体光合特性研究 总被引：2，自引：0，他引：2
对榨菜和紫甘蓝种间嫁接嵌合体的光合作用、叶绿素荧光、叶绿素含量、Rubisco的活性以及Rubisco酶大亚基和小亚基基因的转录水平等进行了测定分析。研究发现,种间周缘嵌合体TCC(茎尖分生组织细胞层LI-LII-LIII=TCC,T代表榨菜,C代表紫甘蓝;)的净光合速率为18.09μmol CO2·m-2·s-1,与亲本榨菜相当,但比亲本紫甘蓝高出24.8%。嵌合体的气孔导度和胞间CO2浓度显著高于2个亲本。叶绿素荧光参数中光系统II的实际电子传递量子效率(ФPSⅡ)和光化学猝灭系数(qP)在榨菜中最高,而嵌合体和紫甘蓝的这2个参数基本一致。对叶绿素含量测定后发现,嵌合体的叶绿素a、b及总含量与榨菜比较接近,比紫甘蓝高97%。TCC嵌合体Rubisco酶的初始活性和总活性处于榨菜(最高)和紫甘蓝(最低)之间,为1.76和3.75μmol CO2·g-1·min-1。而TCC嵌合体的Rubisco酶大亚基和小亚基基因的mRNA转录丰度与榨菜和紫甘蓝相比明显增高。以上结果说明,与TCC嵌合体光合机构的层源亲本——紫甘蓝相比,其叶绿素含量升高、Rubisco酶的活性以及其大小亚基基因的转录水平的增强可能是导致其净光合速率提高的原因。可见,TCC嵌合体的异源表皮(来自榨菜)对改善其内部光合组织(来自紫甘蓝)的光合能力有很大的促进作用。 相似文献
13.
Ping Fang Fa-Bo Chen Qi-Lun Yao Ke-Cheng Yang Guang-Fan Zhou Yong-Hong Fan Zhao-Rong Zhang Jin-Juan Shen Hong Zhang 《Genetic Resources and Crop Evolution》2013,60(1):129-143
In the present study, analyses of SSR molecular markers were performed to investigate the genetic diversity of 133 tuber mustard cultivars. Eighty-one pairs of SSR primers from a total of 600 in Brassica produced stable amplified bands. In addition, 810 bands were detected among the cultivars, and 724 of those were polymorphic (89.38 %). The average number of bands per locus was 10.0 with a range from 5 to 16. Shannon’s information index for each SSR locus varied from 0.52 to 3.72, with an average of 2.74. The coefficients of genetic similarity in the SSR marker patterns among the 133 cultivars ranged from 0.77 to 0.91, with an average of 0.85. The cluster analysis showed that the cultivars could be classified into six clusters when the genetic similarity was 0.83, with 90.23 % of the cultivars included in Clusters 5 and 6. Principal component analysis was carried based on the SSR data. The results showed that the first three principal components could explain the genetic variation with 85.47, 0.67, and 0.61 %, and the 133 cultivars could be divided into six clusters according to the nearest phylogenetic relationship. It was indicated that the similarity was high and the genetic diversity was narrow among the 133 mustard tuber cultivars. 360 individuals from 24 cultivars were analyzed to reveal the genetic structure and genetic diversity within cultivars. A total of 925 alleles were detected in the 24 cultivars. Estimates of the mean number of alleles ‘A’, the effective allelic number ‘Ae’, the observed heterozygosity ‘Ho’, and expected heterozygosity ‘He’ were 6.0, 3.6, 0.64, and 0.37, respectively. An obvious genetic deviation from Hardy–Weinberg expectation was observed both among and within cultivars and a considerable genetic variation was revealed within rather than among cultivars. It is necessary to broaden the genetic basis of the breeding germplasm in tuber mustard. Based on their geographical distributions, the tuber mustard cultivars in this study can be divided into up-Yangtze river, mid-Yangtze river, and down-Yangtze river groups. Genetic diversity was highest in mid-Yangtze river group, followed by up-Yangtze river group, and then down-Yangtze river group. It was presumed that the origin center or genetic diversity center of tuber mustard was mid-Yangtze river, and the crop was transmitted along the Yangtze river in both directions. 相似文献
14.
The magnetic-poly(divinylbenzene-1-vinylimidazole) [m-poly(DVB-VIM)] microbeads (average diameter 53-212?μm) were synthesized and characterized; their use as adsorbent in removal of Cr(VI) ions from aqueous solutions was investigated. The m-poly(DVB-VIM) microbeads were prepared by copolymerizing of divinylbenzene (DVB) with 1-vinylimidazole (VIM). The m-poly(DVB-VIM) microbeads were characterized by N(2) adsorption/desorption isotherms, ESR, elemental analysis, scanning electron microscope (SEM) and swelling studies. At fixed solid/solution ratio the various factors affecting adsorption of Cr(VI) ions from aqueous solutions such as pH, initial concentration, contact time and temperature were analyzed. Langmuir, Freundlich and Dubinin-Radushkvich isotherms were used as the model adsorption equilibrium data. Langmuir isotherm model was the most adequate. The pseudo-first-order, pseudo-second-order, Ritch-second-order and intraparticle diffusion models were used to describe the adsorption kinetics. The apparent activation energy was found to be 5.024?kJ?mol(-1), which is characteristic of a chemically controlled reaction. The experimental data fitted to pseudo-second-order kinetic. The study of temperature effect was quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy and entropy changes. The thermodynamic parameters obtained indicated the endothermic nature of adsorption of Cr(VI) ions. Morever, after the use in adsorption, the m-poly(DVB-VIM) microbeads with paramagnetic property were separeted via the applied magnetic force. The magnetic beads could be desorbed up to about 97% by treating with 1.0?M NaOH. These features make the m-poly(DVB-VIM) microbeads a potential candidate for support of Cr(VI) ions removal under magnetic field. 相似文献
15.
根迹土壤根诱导的化学变化对植物吸收重金属的影响 总被引：4，自引：0，他引：4
It is increasingly recognized that metal bioavailability is a better indicator of the potential for phytoremediation than the total metal concentration in soils; therefore, an understanding of the inffuence of phytoremediation plants on metal dynamics at the soil-root interface is increasingly vital for the successful implementation of this remediation technique. In this study, we investigated the heavy metal and soil solution chemical changes at field moisture, after growth of either Indian mustard (Brassica juncea) or sunffower (Helianthus annuus L.), in long-term contaminated soils and the subsequent metal uptake by the selected plants. In addition, the fractions of free metal ions in soil solution were determined using the Donnan membrane technique. After plant growth soil solution pH increased by 0.2-1.4 units and dissolved organic carbon (DOC) increased by 1-99 mg L-1 in all soils examined. Soluble Cd and Zn decreased after Indian mustard growth in all soils examined, and this was attributed to increases in soil solution pH (by 0.9 units) after plant growth. Concentrations of soluble Cu and Pb decreased in acidic soils but increased in alkaline soils. This discrepancy was likely due to a competitive effect between plant-induced pH and DOC changes on the magnitude of metal solubility. The fractions of free Cd and Zn ranged from 7.2% to 32% and 6.4% to 73%, respectively, and they generally decreased as pH and DOC increased after plant growth. Metal uptake by plants was dependant on the soil solution metal concentration, which was governed by changes in pH and DOC induced by plant exudates, rather than on the total metal concentrations. Although plant uptake also varied with metal and soil types, overall soluble metal concentrations in the rhizosphere were mainly inffuenced by root-induced changes in pH and DOC which subsequently affected the metal uptake by plants. 相似文献
16.
咸淡水交替灌溉下土壤盐分再分布规律的室内实验研究 总被引：5，自引：1，他引：4
咸水灌溉是解决目前淡水资源短缺的重要途径。为寻求合理的咸水农田灌溉方法,进行了不同矿化度和不同灌水模式的室内土柱咸淡水交替灌溉模拟试验,分析了咸淡水交替灌溉条件下土壤溶液电导率(EC)值和钠吸附比(SAR)的变化规律。结果表明：两种灌水模式下,灌水结束时土壤溶液EC值在22.5 cm处达到最高,且4 g/L>2 g/L,且与试验初期相比,土壤溶液EC值明显提高,土柱整体积盐明显。灌水模式对土壤溶液EC值的影响大于矿化度;两种灌水模式不同矿化度处理的SAR值变化规律基本一致。 相似文献
17.
Salsabil Marzougui Gerhard Sch?fer Lotfi Dridi 《Water, air, and soil pollution》2012,223(9):5817-5840
This study focuses on a detailed analysis of the errors introduced by two quasi-analytical approaches based on either Fick??s first law or a combination of Fick??s and Darcy??s laws to evaluate the vapour flux of chlorinated solvents from a source zone located in the unsaturated zone towards the atmosphere. A coupled one-dimensional numerical flow and transport model was developed and applied to three case studies characterised by different water content profiles in the vadose zone and under different levels of maximum dense nonaqueous-phase liquid vapour concentrations and vapour pressure conditions of the source zone. The steady-state concentration and pressure profiles obtained were then used in the two quasi-analytical approaches to estimate the flux towards the atmosphere. When mass fluxes due to density-driven advection become dominant and the vertical advective mass fluxes are increased due to strong pressure gradients in the soil air, the error was observed to increase when using the pure diffusion approach in the quantification of the surface flux calculated by the numerical model with increasing dimensionless Rayleigh numbers. Without taking into account the advective transport in the approach, the relative error calculated with only Fick??s law overestimates the real vapour flux when density-driven advection is dominant and underestimates it when pressure-gradient-driven advection dominates. The more advanced advective?Cdiffusive quasi-analytical approach fits reasonably well with the numerically obtained mass fluxes except near soil layer discontinuities, where the evaluation of both the concentration gradient and pressure gradient in the porous media as well as the determination of the average effective diffusion coefficients are rendered more difficult. 相似文献
18.
Rachhpal-Singh & Nye's model of ammonia volatilization is further expanded to account for the effects of transient-state water evaporation when the soil surface dries significantly. Full details are given of the derivation and numerical solution of equations describing transient-state water movement, and the diffusion and convection in soil of urea and its hydrolysis products, and of acid generated by ammonia volatilization. For the wide range of soil hydraulic properties considered, the effects of a dry soil layer on the rate of volatilization supplement the effects of increased convective supply of NH+4 and HCO?3 ions to the soil surface. The dry layer results in increased gaseous NH3 diffusion through the soil, and thereby increases the flux of NH3 across the soil surface and the neutralization of H+ ions generated by volatilization. 相似文献
19.
《Communications in Soil Science and Plant Analysis》2012,43(11):1367-1376
Abstract Ion diffusion through the soil matrix is dependent upon both the physical and chemical properties of the soil. Cation (K, Na, Ca and Mg) diffusion coefficients De, were determined for seven Indiana soils by using the ion diffuison flux to a hydrogen resin paper technique. Volumetric moisture, clay content exchange and solution phase ionic concentrations, buffer capacity and organic C content were variously related to the determined De values. The larger the diffusion coefficient of K, Ca, and Mg, the lower the clay content, and exchange capacity of soils, and the higher the concentration of these cations in the solution phase. From the present study, it was concluded that the De of these cations was affected by one or more soil physical and chemical property which must be considered if De is to be used to estimate supply rate of these ions to growing roots in soil systems. 相似文献
20.
L. C. Dickey M. F. Dallmer E. R. Radewonuk N. Parris M. Kurantz J. C. Craig 《Cereal Chemistry》1998,75(4):443-448
Corn particles were extracted in an agitated vessel with a 4:1 mass ratio of 70% ethanol to corn for periods of 1–6 hr at ambient temperature. The extract solution was filtered and centrifuged to remove suspended particles after extraction and then diluted to 40% ethanol to precipitate extracted solute. Measurements of the mass of suspended particles separated by centrifugation indicate that mixing the corn particles with the ethanol dissolves and weakens the protein between cells and between starch granules within cells near the particles' surface. Under the conditions of this study, corn particles release starch granules more rapidly than the protein bodies dissolve, as indicated by analysis of the centrifuged particles. The diffusion coefficient for ethanol solution in corn was estimated and compared with a coefficent derived from a fit of the trend in the rate of release of fine particles from the milled corn. The diffusion coefficient of pure zein in a stagnant 70% ethanol solution was estimated from the measurement of weight loss by a ball of zein. Analysis of the ambient temperature protein extraction rate indicates that 2-mm particles exhibit more convective mass transfer than 20-μm particles. 相似文献