玉米收获机割台振动特性及其主要影响因素分析

针对收获机械割台振动剧烈、故障率较高等问题,研究了割台动态振动特性及其影响规律。以4YZP-3XH-1型玉米联合收获机割台为研究对象,首先建立了割台机架有限元模型并计算其自由模态,研究了割台模态试验方法,利用特征实现算法识别其模态参数;其次,利用模态试验验证了有限元模型的准确性和可靠性,在此基础上,计算获取割台机架的约束模态;再次,利用时域和频域方法分析振动时域信号,获得怠速、运输和田间收获工况割台的振幅分布特征、主振方向和频率分布规律;最后,研究了割台振动的影响因素及其振动主频与模态参数之间的对应关系,指出了振动频率激起模态振型的规律。研究结果表明,割台机架第1阶试验模态频率为27.260 Hz,第2~10阶模态频率范围为34.311~126.035 Hz,模态振型以弯曲振型和扭转振型为主,割台主轴(28.77 Hz)、切碎刀(29.63 Hz)、还田机(43 Hz)等工作频率均落入其前10阶约束模态频率内;在怠速、运输和田间收获作业工况下,工作部件运行工况相较于仅发动机工作,2种模式下割台振幅相差1个数量级;引起割台振动的主要因素为:发动机的2阶发火频率(76.25 Hz),割台主轴、切碎刀、搅龙、拨禾链、还田机等工作部件的耦合振动,以及道路激励(1.5、2.5 Hz)。对比割台约束模态与振动频率,发动机2阶发火频率引起割台弯扭组合振型,道路激励引起整体振动,割台主轴(28.77 Hz)和切碎刀(29.63 Hz)振动频率激起割台机架的一阶弯曲振型,还田机(43 Hz)振动频率激起割台的扭转振型。研究结果可为收获机械割台模态试验与振动特性分析、对标设计和优化提供参考。     

秸秆还田残膜回收一体机振动特性分析与结构优化

该研究针对棉花秸秆还田残膜回收一体机振动剧烈、可靠性差等问题开展机具振动特性分析与结构优化。以接近激励源的部位确定机具主要振动测点,安装传感器与连接振动测试仪,获取空转和工作条件下机具振动信息,采用ANSYS Workbench中的Lanczos Method算法仿真求解机架模态频率和振型,建立机具振动力学模型,通过振动测试仪数据验证仿真模型的准确性,并提出机具结构优化方案。结果表明,仿真结果与实测振动数据有效值的相对误差为9.6%,秸秆粉碎装置与脱膜装置是造成整机振动剧烈的主要部件,田间收获工况下整机振动强度高于空载工况;实测振动频率36.13 Hz接近机架前两阶固有频率且处于外部激励频率范围内。采用正交试验对机架结构进行优化,得到最佳参数组合为侧板厚度12.0 mm,主连接梁管壁厚6 mm,副支撑梁宽度70 mm。优化后机架前两阶固有频率分别提升至50.700和53.322 Hz,避开了外部激励频率,振动测试结果表明,空载工况下,相比优化前主连接梁振动幅值降低48%,侧板振动幅值降低35%,田间收获工况下相比优化前脱膜装置轴承支座振动幅值降低47%。研究结果可为秸秆还田残膜回收联合作业机的振动特性分析与结构优化提供参考。     

联合收获机割台机架结构参数优化

为降低联合收获机正常工作时的共振,该文利用UG软件对沃得锐龙型稻麦联合收获机割台机架进行建模,求解出割台机架的模态频率和振型,并对割台机架进行模态试验验证及理论分析;在通过分析外部激振频率特点的基础上,使割台机架固有频率避开外部激振频率范围,并对机架进行结构优化与试验。试验结果表明:将割台机架横梁、弯梁厚度减少0.2 mm,底板、侧板厚度减少0.4 mm时,割台机架质量降低了14.02%,前4阶模态频率均避开了联合收获机各激励频率范围;将割台传动轴平衡配重块质量增加254.90 g,使得割台传动轴轴承座处沿联合收获机前进方向、上下方向位移振动幅值分别降低了25.70%和12.70%,并有效避免了割台共振的产生。该文的研究结果为降低联合收获机割台振动提供了设计依据。     

不同振动特性参数对杏树振动响应的影响

为研究振动时间、振动频率和振动激励点振幅等不同振动特性参数对杏树振动的影响,该文利用ANSYS软件对杏树进行了有限元建模分析;通过三因素三水平试验分析不同振动特性参数对杏树振动检测点的影响,利用Design Expert软件进行优化分析,并进行实验室验证试验。杏树自由模态振动响应分析表明最佳杏树振动采收响应频率范围为0～20 Hz;谐振动响应分析可知在最佳频率范围内,杏树振动激励点振幅为5、10和15 mm时,同一频率下,随着激励振幅的增大,相同位置加速度增大,但振动曲线整体变化规律和趋势一致。试验分析可知,各因素影响检测点1和2加速度的强弱顺序一致:激励点振幅振动频率振动时间;各因素影响检测点3加速度的强弱顺序为:振动时间激励点振幅振动频率;建立3个检测点的响应方程,由下至上3个检测点的回归方程决定系数分别为0.906 7、0.879 3和0.973 3;多目标参数优化结果为:振动时间7.207 s,振动频率15 Hz,激振点振幅10 mm,通过验证试验可知由下至上各检测点加速度为10.4g、10.2g和9.3 g,与优化值相近。该研究可为杏振动采收机械参数设计提供参考。     

4SY-2.9型油菜割晒机机架振动分析及改进

针对4SY-2.9型油菜割晒机因各部件运动产生的激振力随机不定而引起机架振幅大的问题,为降低割晒机工作时共振,对其机架进行建模,导入ANSYS Workbench中求解自由模态下机架的模态频率和振型,并通过模态试验与仿真分析结果对比验证有限元模型的准确性。通过分析机架外部激振频率特点和仿真结果,提出增加机架拱门结构的设计方案,开展拱门圆管厚度与安装位置仿真试验。优化后机架第1阶模态频率调整到15.339 Hz,避开了输送带弹齿和割刀激振力的激励频率范围,有效避免其共振产生。对优化后的机架模型进行有限元静力学分析,结果表明机架满足强度要求。割晒机在空载状态下,对安装机架拱门与未安装拱门纵梁最大变形点处采集加速度时域信号,并通过FFT频谱分析得到功率谱分析图,试验结果表明:测点最大峰值点X方向幅值降低了71.47%,Y方向幅值降低了70.60%,Z方向幅值降低了70.21%。田间试验表明:改进的油菜割晒机田间通过性好,作业效率高,能实现有序中间条铺,条铺宽度满足后续捡拾脱粒机作业幅宽;割晒的油菜平均铺放宽度为1 674 mm,割茬平均高度为330 mm,平均堆放高度为603 mm。优化后的油菜割晒机机架动态性能良好,作业质量满足后续工序作业要求。该研究可为同类宽幅机架的设计研究提供参考。     

基于时频和功率谱密度的移栽机振动特性测试与分析

针对移栽机机械受激励产生振动影响取苗、顶苗工作稳定性的问题,该研究以2ZTT-2型顶夹式气动蔬菜移栽机为研究对象,对移栽机的振动特性进行研究。采用时频分析和功率谱密度分析相结合的方法,得到信号能量在时间轴以及频率轴上的分布特征,并运用锤击法,研究了不同工况下各测点主要频率与该测点代表运动部件的前5阶固有频率之间的对应关系。试验结果表明:取苗摆动装置运动、苗盘横移是移栽机的主要振源,取苗机械手开合、顶苗机构伸缩是振动的次要原因。振动信号频率主要分布在低频频率(0～10 Hz)处,取苗摆动装置运动时加速度振动幅值为5.43 m/s2,整机运转时为1.71 m/s2,振幅下降了68.51%,并且移栽机取苗摆动装置运动所引起的主要振动频率(6.10 Hz)与对应测点处的第5阶固有频率(6.25 Hz)相近,发生了共振现象。研究结果可为移栽机振动特性分析、结构优化设计提供参考。     

基于模态的玉米收获机车架振动特性分析与优化

为研究玉米收获机车架振动特性及其优化方法,该文通过振动测试与模态分析方法,分析车架田间振动特性,并以提高1阶扭转频率为目标优化车架结构。首先,通过有限元建模及模态分析,提取车架固有频率与振型,其次,通过整机田间振动试验,获取车架4个测点处振幅统计特征及功率谱,分析其对车架振动特性的影响,最后,研究车架壁厚和刚度与固有频率的关系,以提高车架1阶扭转频率为目标优化车架。研究结果发现,测点振幅大小依次为:车架后桥上方、发动机横梁位置、发动机纵梁位置、车架前桥上方,其中车架后桥上方振幅已超过发动机振幅,发生共振;模态振型与田间振动试验对比发现,1阶扭转和2阶弯曲模态对车架振动影响较大,引起车架共振主频为9.79 Hz,接近1阶扭转共振频率;发现优化后车架1阶扭转振型位移由7.778下降到3.768,1阶弯曲振型位移由6.83下降到3.651,显著改善了车架振型,1阶扭振频率由15.9927提高到22.4595 Hz,提高车架1阶扭转频率。田间耐久试验表明优化后车架无故障时间由20提高到60 h。该研究可为农机装备的振动特性分析与减振设计提供参考。     

基于拉格朗日法的悬臂输送槽阻尼摆模型构建与验证

为准确分析联合收割机输送槽在作业时产生的不平衡摆动现象，该研究建立了基于液压缸支撑的联合收割机悬臂输送槽阻尼摆模型。首先对悬臂输送槽系统进行受力分析，并基于拉格朗日法建立其动力学微分方程。为进一步确定动力学微分方程中的参数，利用有限元法和模态分析法对液压缸刚度和阻尼进行参数标定；并进行田间试验获取输送槽所受外界激励。利用二次积分与快速傅里叶变换（fast fourier transform，FFT）处理田间试验采集到的加速度信号，得到悬臂输送槽振幅及振动的主频成分，为动力学微分方程的验证提供依据。最后求得悬臂输送槽角速度和摆角的表达式，将理论得到的初始状态下悬臂输送槽摆幅与田间试验实际摆幅进行对比。结果表明：稳定状态下，理论求解得到的同一水平位置两测点对应的摆幅分别约为0.0979、0.0957mm，与试验实际摆幅误差约为1.11%和4.30%，验证了该联合收割机悬臂输送槽阻尼摆模型的准确性。研究结果可为长江中下游地区水稻联合收割机悬臂输送槽结构优化提供理论依据。     

环模制粒机齿轮减速器动力学特性分析

环模制粒机的内部激励会引起整机振动,振动是导致环模与压辊使用寿命降低的主要原因。该研究针对环模制粒机振动大、关键部件使用寿命短等问题,以SZLH420型环模制粒机减速器为研究对象进行动力学分析与试验。首先基于累积势能法计算齿轮时变啮合刚度,建立斜齿轮传动动力学模型,采用解析法对传动系统进行模态分析和非线性动力学求解,求得最大振幅Y向(水平径向)为0.008 mm、Z向(轴向)为0.004 2 mm、转角为0.000 87°,并通过有限元仿真验证动力学模型和固有频率。最后进行主轴扭矩测试与斜齿轮振动加速度试验。结果表明,整机振动加速度频率与斜齿轮一致,故斜齿轮传动系统对整机振动具有重要影响,其主要振动频率在4.25、9.17、13.86、18.13、23.86、47.53 Hz附近;齿轮振动最大幅值Y向为0.006 mm、Z向为0.004 mm,与动态响应计算对应振幅最大差值不超0.002mm,验证了理论计算的准确性。研究结果可为环模制粒机性能的提高提供理论与试验依据。     

基于运行稳定性的离心泵导叶安装位置优化试验与分析

为提高导叶式离心泵的运行稳定性,探寻径向导叶相对隔舌的最佳安装位置,该文通过数值模拟确定了某型号单级单吸导叶式离心泵的3种典型导叶安装位置,并通过试验对3种安装位置下的外特性、压力脉动和振动特性进行了测试。对比分析了外特性曲线、压力脉动幅值和频域特性、振动幅值和频域特性。研究结果表明,蜗壳隔舌处于导叶出口流道中间位置时,离心泵水力性能最好,效率相对于其他2个位置最多提高2个百分点;测点在3个方向上的振动加速度幅值均处于较低水平,但是会增大蜗壳扩散段在大流量时的压力脉动幅值,最多高出2.25 k Pa。由于径向导叶的存在,2倍轴频和3倍轴频是压力脉动的主要激励频率;2倍轴频与6倍轴频是振动加速度的主要激励频率。蜗壳扩散段压力脉动幅值随着流量增加先减小后增大,在0.6倍工况达到最低值。导叶安装位置对压力脉动频域分布规律和振动加速度频谱特性的影响较小,相同工况下,测点的压力脉动频域分布规律和振动加速度频谱特性基本相同。因此,该研究为径向导叶的合理布置提供了参考。     

两种退耕还林模式对土壤微生物优势类群的影响

以两种退耕还林模式的桦木林地、苦竹林地和农耕地(对照)为对象,对各样地土壤微生物优势类群数量的季节性动态变化、垂直分布特征及其与土壤酶活性的相关性进行了研究。结果表明,土壤微生物的优势类群为微球菌属(Micrococcus)、芽孢杆菌属(Bacillus)、链霉菌属(Streptomyces)、游动放线菌属(Actinoplanes)、酵母菌(未定属)、木霉菌属(Trichoderma)这6类。两种退耕还林模式下土壤优势微生物类群数量存在差异,春、夏、秋三季均为苦竹林所占比例最大,冬季为桦木林最大。两种林地和农耕地土壤微生物优势类群数量季节性变化规律为微球菌和酵母菌在夏、冬季较大,春、秋季较少;芽孢杆菌在秋季最大,夏季最小;游动放线菌与木霉菌数量在四季中变化不大;链霉菌是夏季最高,冬季最少。各优势微生物类群数量的垂直分布特征表现为微球菌、游动放线菌、木霉菌随土壤层的加深其数量逐渐降低,芽孢杆菌、链霉菌数量则随土壤层的加深而逐渐增加,酵母菌随土壤层的加深其数量减少,但趋势不明显。两种林地对各优势微生物类群数量的根际效应为:链霉菌和木霉菌的R/S值大于1,酵母菌的R/S值小于1,微球菌和游动放线菌在桦木林的R/S值大于1而在苦竹林小于1。在优势微生物类群和土壤酶之间,微球菌与转化酶,芽孢杆菌与纤维素酶,木霉和游动放线菌与过氧化氢酶,酵母与脲酶呈显著正相关关系。     

太行山低山丘陵区不同植物群落物种多样性研究

 通过样地法对小浪底水库库区山地生态系统不同群落间的Shannon-Wiener指数(H′)、Simpson指数(D1)、Margalef物种丰富度(D2)、种间相遇概率(P)和Pielou均匀度指数(Jsw)等多样性指数进行研究,利用统计方法分析不同群落的物种多样性指数与其所处环境的关系。结果表明:1)物种多样性指数和丰富度指数与群落类型有密切关系,同一类型的群落中,多样性指数随演替时间表现出复杂的关系;2)土壤含水量对H′、P、Jsw、D1等呈极显著的正相关性,土壤厚度与H′、D1、P呈显著正相关性;多样性指数与坡度无相关性;土壤有机质、速效氮、速效磷等养分指标与多样性指数H′、D1有显著的正相关;3)多样性指数H′与乔木、灌木群落生物量表现为正相关关系,草本群落与D1相关性不显著;4)乔木林群落的恢复时间与Jsw、H′呈正相关关系,其余多样性指数(P、D1、D2)与恢复时间关系不显著(P>0.05);恢复时间每增加10a,群落物种数平均增加约6种;5)物种多样性指数H′与灌木的盖度和高度呈极显著正相关性;有些单优群落随高度增加和盖度提高,多样性指数反而表现出降低;6)草本植物群落的高度和盖度与物种丰富度指数D2与呈显著的负相关关系,与H′相关性不显著。     

Localisation of nitrate in the rhizosphere of biochar-amended soils

A wheat seedling rhizobox approach was used to differentiate between the rhizosphere and non-rhizosphere (bulk) soil amended with low and high rates of biochar (20 and 60 t ha⁻¹ vs. control). Nitrate (NO₃⁻) was added as the main nitrogen (N) source because emerging biochar research points to reduced NO₃⁻ loss through leaching and gaseous loss as nitrous oxide. The rhizosphere under the different treatments were distinct (P = 0.021), with greater soil-NO₃⁻ and biochar-NO₃⁻ contents in the high biochar treatment. Biochar addition increased wheat root length ratio (P = 0.053) and lowered root N uptake (P = 0.017), yet plant biomass and N content were similar between treatments. The results indicate localisation of NO₃⁻ within the rhizosphere of biochar-amended soils which has implications for NO₃⁻ loss and improved nitrogen use efficiency.     

水稻幼苗根系吸收NO3-对细胞膜电位的影响

利用玻璃微电极技术测定了扬稻6号(籼稻)幼苗根尖细胞在吸收不同NO3-浓度(0.01、0.02、0.1、0.2、0.5、1.0和2.0.mmol/L)过程中膜电位的变化。结果表明,1)水稻根系吸收NO3-引起膜的去极化,去极化到一定程度后出现复极化;有小部分水稻根表现为超极化。在0.01～1.0.mmol/L范围内,去极化大小随外界NO3-浓度的增加而增加,且差异显著(P0.05)。0.01.mmol/L.NO3-产生较小的去极化,平均为3.8.mV;0.5.mmol/L.NO3-产生了最大去极化,平均为40.2.mV;当外界NO3-浓度大于1.0.mmol/L时膜电位去极化大小呈下降趋势。根系吸收不同浓度的NO3-而使膜电位去极化的进程符合Michaelis-Menten动力学。2)复极化有部分复极化和完全复极化两种。超极化也有两种:一种是膜电位先超极化,后缓慢复极化;另一种是先出现一个小的去极化,然后是较大幅度的超极化。3)运输蛋白抑制剂PGO抑制了根系吸收NO3-而产生的膜电位的响应。4)对于经CaSO4溶液预培养的水稻来说,C2+主要引起膜电位超极化。     

Towards bioremediation of toxic unresolved complex mixtures of hydrocarbons: identification of bacteria capable of rapid degradation of alkyltetralins

Background, aim and scope  Unresolved complex mixtures (UCMs) of aromatic hydrocarbons are widespread, but often overlooked, environmental contaminants. Since UCMs are generally rather resistant to bacterial degradation, bioremediation of UCM-contaminated sites by bacteria is a challenging goal. Branched chain alkyltetralins are amongst the individual classes of components of aromatic UCMs which have been identified in hydrocarbon-contaminated sediments and a number of synthetic alkyltetralins have proved toxic in laboratory studies. Thus, alkyltetralins should perhaps be amongst the targets for UCM bioremediation strategies. The slow degradation of several alkyltetralins by a microbial consortium has been reported previously; however, the bacteria involved remain unidentified and no single strain capable of alkyltetralin biodegradation has been isolated. The present project therefore aimed to enrich and identify bacterial consortia and single strains of bacteria from a naturally hydrocarbon-contaminated site (Whitley Bay, UK), which were capable of the degradation of two synthetic alkyltetralins (6-cyclohexyltetralin (CHT) and 1-(3’-methylbutyl)-7-cyclohexyltetralin (MBCHT)). Materials and methods  Bacteria were enriched from sediment collected from Whitley Bay, UK by culturing with CHT and MBCHT for a period of 4 months. Biodegradation experiments were then established and degradation of model compounds monitored by gas chromatography–mass spectrometry. Internal standards allowed the generation of quantitative data. 16S rRNA gene clone libraries were constructed from individual enrichments to allow assessment of microbial community structure. Selective media containing MBCHT were used to isolate single bacterial strains. These strains were then tested in liquid culture for their ability to degrade MBCHT. Results  The consortia obtained through enrichment culture were able to degrade 87% of CHT and 76% of MBCHT after only 46 days compared with abiotic controls. The 16S ribosomal RNA gene clone libraries of these bacteria were dominated by sequences of Rhodococcus spp. Using selective media, a strain of Rhodococcus was then isolated that was also able to biodegrade 63% of MBCHT in only 21 days. Discussion  The present report describes the isolation of a single bacterial strain able to degrade the resistant MBCHT. Although significant losses of MBCHT were observed, putative metabolites were not detectable. Rhodococcus sp. have been reported previously to be able to biodegrade a range of hydrocarbon compounds. Recommendations and perspectives  Due to their environmental persistence and toxicity, aromatic UCMs require bioremediation. The culturing and identification of such bacteria capable of rapid degradation of alkyltetralins may be an important step toward the development of bioremediation strategies for sites contaminated with toxic UCMs.     

不同砧木对脐橙幼树生长和叶片养分含量变化的影响

以体细胞杂种红桔+枳和红桔+粗柠檬、有性杂种Troyer枳橙和Sweingel枳柚作砧木的脐橙2年生嫁接苗为试材,利用盆栽试验研究了不同砧木对苗木生长和叶片养分含量年动态变化的影响。结果表明,红桔+枳的生长势和花量明显地优于其它砧木,红桔+粗柠檬的生长和花量介于2种有性杂种之间;砧木基本上不影响叶片N、P、K、Mg和Mn含量年变化,但明显影响叶片Ca、Fe和Zn含量的年变化;在同一个生长期,不同砧木对叶片养分含量有明显的影响。此外本文还讨论了体细胞杂种砧木的利用价值。     

Oxidation of methane in the rhizosphere of rice plants

Oxidation of CH₄ in the rhizosphere of rice plants was quantified using (1) methyl fluoride, a specific inhibitor of CH₄ oxidation, and (2) measuring changes in plant-mediated CH₄ emission after incubation under air, N₂, or 40% O₂. No significant rhizospheric CH₄ oxidation was observed from rice plants in the ripening stage. CH₄ emission from rice plants 1 week before panicle initiation increased by 40% if CH₄ oxidation in the rhizosphere was blocked. The growth stage of the rice plant is an important factor determining the rhizospheric CH₄ oxidation. Fluctuation of rhizospheric CH₄ oxidation during the growing season may help to explain the observed seasonal CH₄ emission patterns in field studies. Measurements from four rice varieties showed that one variety, Pokkali, had higher rhizospheric CH₄ oxidation. This was probably because Pokkali was in an earlier growth stage than the other three varieties. Both in the early and in the late growth stages, incubation under N₂ caused a much stronger CH₄ flux than inhibition of CH₄ oxidation alone. Apparently, N₂ incubation not only blocked CH₄ oxidation but also stimulated methanogenesis in the rhizosphere. Incubation under a higher O₂ atmosphere (40% O₂) than ambient air decreased the CH₄ flux, suggesting that increasing the oxidation of the rice rhizosphere may help in reducing CH₄ fluxes from rice agriculture. The O₂ pressure in the rhizosphere is an important factor that reduces the plant-mediated CH₄ flux. However, inhibition of methanogenesis in the rhizosphere may contribute more to CH₄ flux reduction than rhizospheric CH₄ oxidation.     

Characterization of Intergeneric Hybrids of Saccharum using Molecular Markers

The potential use of RAPD markers in identifying genuine intergeneric hybrids of Saccharum was examined in 12 hybrids of Saccharum with Erianthus spp., Sorghum bicolor and Zea mays. In the three groups of hybrids examined, RAPD markers could precisely identify the true hybrids of Saccharum officinarum × Sorghum bicolor and Saccharum officinarum × Zea mays. Though Erianthus had a very distinct RAPD profile and as many as 107 Erianthus-specific bands were identified, a decisive profile that can identify all the hybrids could not be obtained. The strong molecular differentiation between S.officinarum and Erianthus was not adequately resolved in the RAPD profiles of their hybrid progenies which suggest that more refined molecular techniques will be required for the characterization of Saccharum–Erianthus hybrids.     

Distribution of inorganic phosphorus fractions in some soil profiles of Zagros forest of Iran

The aim of the present study was to evaluate the status of inorganic phosphorus (P) fractions in ten virgin soil profiles, and to study the relationships between P fractions and soil properties from Kohgyloyeh and Boir Ahmad province, Iran. The soils belonged to Alfisols, Entisols, Mollisols, and Inceptisols. Mean annual precipitation and temperature ranges were 450–850 mm and 12.2–22.4°C, respectively. Inorganic P was fractionated by sequential extraction with NaHCO₃, NH₄OAc, MgCl₂, NH₄F, NaOH, citrate-dithionite-bicarbonate (CBD), and H₂SO₄, which are referred to as NaHCO₃–P, NH₄OAc–P, MgCl₂–P, NH₄F–P, NaOH–P, CBD–P, and H₂SO₄–P, respectively. Generally, the NaHCO₃–P, NH₄OAc–P, MgCl₂–P, and NH₄F–P were higher in surface horizons, especially wherever there was higher annual precipitation. Results showed that H₂SO₄–P constituted the largest inorganic P fractions in all profiles. For all the soils studied the distribution of P fractions was similar to that of weakly weathered soils under arid and semi-arid regions which represent an early stage of development. Pedogenic P compounds were higher where weathering was higher, i.e., in surface horizons and at higher annual precipitation.     

Diversity of arbuscular mycorrhizal fungi in alkaline soils of hot sub humid eco-region of Middle Gangetic Plains of India

The aim of this study was to evaluate the diversity and distribution of arbuscular mycorrhizal (AM) fungi in the salt affected soils of Varanasi district. Saccharum munja Roxb. was predominate among all the vegetation and shown strong AM fungal colonisation. Soil characteristics revealed their neutral to alkali nature and habituated six genera and eight different species of AM fungi i.e. Acaulospora (1), Cetraspora (1), Entrophospora (1), Funneliformis (2- F. geosporum and F. mosseae), Glomus (1), Rhizolglomus (2- R. intraradices and R. fasciculatum) in the rhizosphere of native salt tolerant vegetation. Rhizolglomus fasciculatum was the most widely distributed species under strongly alkaline condition (52.96%) while Funneliformis mosseae was well distributed under slightly (22.99%) to moderately alkaline condition (35.78%). Soil alkalinity was observed to be detrimental for AMF but members of family Glomeraceae registered their presence more frequently (～65%) with higher spore density showing strong adaptation which might be helpful in restoration of moderately to strongly alkaline disturbed eco-region.