1K-50型果园开沟机开沟部件功耗影响因素分析与试验

为探明1K-50型果园开沟机工作参数和双旋耕刀辊结构参数对作业功耗的影响规律,该文建立了分析开沟部件功耗的切土,运、抛土力学模型,得到了开沟部件功耗与整机工作参数、刀辊结构参数以及土壤力学性能之间的函数关系。搭建了基于土槽试验台的开沟部件功耗测试装置,模拟坚实度为950k Pa的葡萄园土壤环境,以刀辊转速、前进速度、开沟深度和刀辊型式为试验因素,进行单因素试验和多因素正交试验,测得旋耕刀辊在不同结构和工作参数下的功率消耗,得到影响开沟部件功率消耗的因素主次顺序为刀辊型式前进速度刀辊转速开沟深度,其功耗较优参数组合为采用D3型刀辊,刀辊转速为150 r/min,前进速度为0.06 m/s,开沟深度为0.15 m,测得此时开沟部件平均功耗值约为1.22 kW。将装置正交试验表中各因素值代入功耗解析式,利用MATLAB软件进行数值计算与分析,得到影响功率消耗因素的主次顺序与台架试验结果相同,求得功耗理论值与试验值的相对误差百分比最大为12.86%,最小为2.00%,验证了功耗理论模型具有较高的准确性。该研究可为机具改进和小型林果园开沟机的设计提供参考。     

鼹鼠趾仿生及表面热处理提高齿形开沟刀减阻耐磨性能

为提高农用开沟机械开沟刀的减阻耐磨性能,该文针对课题组前期研制的齿形开沟刀,利用仿生结构和不同表面热处理对原齿形开沟刀进行优化。以鼹鼠前爪第3趾为仿生对象,设计了仿生开沟刀。使用EDEM软件进行模拟仿真试验,通过分析齿形开沟刀和仿生开沟刀的开沟功耗,对比2种刀片的减阻性能;进行台架磨损试验,利用金相显微镜、显微硬度仪、摩擦磨损试验机分析5种表面热处理仿生开沟刀的耐磨性能。单齿仿真试验发现,仿生开沟刀刀齿的整体三维表面结构特征有利于减阻。仿真试验结果表明沟深为150、200、250、300和350 mm时,仿生开沟刀比齿形开沟刀的开沟功耗分别降低9.68%、10.44%、10.22%、10.70%和10.95%,仿生开沟刀的减阻性能更优。台架磨损试验结果表明,渗铬淬火高温回火(Ⅱ型刀)、渗碳淬火低温回火(Ⅲ型刀)、激光熔覆WC/Ni60A粉末合金(Ⅳ型刀)和氧乙炔火焰堆焊铸造WC焊条(Ⅴ型刀)比淬火中温回火(Ⅰ型刀)处理的仿生开沟刀的磨损质量分别降低14.17%、42.05%、66.98%和75.96%,Ⅰ、Ⅱ、Ⅲ、Ⅳ和Ⅴ型刀的耐磨性能依次提高,Ⅴ型刀最优。5种刀片组织结构、显微硬度和摩擦系数的分析结果表明,Ⅰ、Ⅱ和Ⅲ型刀的硬化层显微组织主要为淬火和回火马氏体,Ⅳ和Ⅴ型刀主要为WC硬质相,Ⅳ和Ⅴ型刀的组织结构更优;Ⅰ、Ⅱ、Ⅲ、Ⅳ和Ⅴ型刀的平均显微硬度为558、700、888、1 195和1 441 HV0.1;平均摩擦系数为0.67、0.57、0.26、0.25和0.22,Ⅴ型刀的显微硬度和摩擦系数最优,与台架磨损试验结果相一致。田间试验结果表明,优化后的Ⅲ型和Ⅴ型刀比原来齿形开沟刀的开沟功耗分别降低11.45%和5.41%,磨损质量分别降低28.26%和82.63%,仿生结构优化与表面热处理能够提高齿形开沟刀的减阻耐磨性能。该研究可为提高开沟刀减阻耐磨性能提供参考。     

圆盘式开沟机作业功耗仿真分析及试验验证

为探明土壤条件和工作参数对圆盘式开沟机作业功耗的影响规律,该文采用光滑粒子流体动力学方法构建了土壤-开沟刀盘的有限元模型,利用ANSYS软件中的显示动力模块LS-DYNA对开沟刀盘土壤切削过程进行仿真分析,得出开沟刀盘在土壤切削过程中功率消耗的变化规律。结合正交试验设计和数值模拟技术,研究土壤坚实度、刀盘转速和开沟深度对圆盘式开沟机作业功耗的影响规律,得出影响作业功耗的因素主次顺序是土壤坚实度开沟深度刀盘转速。采用多变量单目标优化方法,建立关于土壤坚实度、刀盘转速和开沟深度的作业功耗模型,利用Matlab软件对功耗模型进行求解,得出当土壤坚实度为120 N/cm~2,刀盘转速为225 r/min,开沟深度为405 mm时,作业功耗最小为32.4 k W。通过土槽试验对优化结果进行验证,结果表明:理论值与试验值的相对误差为5.68%,作业功耗模型和优化结果具有较高的准确性。该研究可为圆盘式开沟机选择节省功耗的参数组合提供参考。     

葡萄园反转双旋耕轮开沟机的研制

开沟施肥是葡萄园生产过程中的重要环节。传统的葡萄园开沟施肥通常是人工挖掘填埋,劳动强度大,工作效率低。为了提高开沟效率,通过对葡萄园环境及其开沟农艺要求的分析,设计制造了一种驱动型葡萄园小型开沟机,该机为旋耕刀以反转方式进行开沟工作,抛出的土由挡土导流板引导落在沟的两旁。对开沟机进行的性能试验结果表明:该开沟机2次作业开出的沟深可达500mm左右,沟宽超过200mm,且沟壁光滑、沟型整齐平直、沟中残留碎土少,满足葡萄园农艺要求;该机开沟部件碎土、抛土性能好,整机操作灵活,能适应葡萄园管理要求,也可用于其他果园、茶园、农田等开沟作业;该开沟机成本低,经济效益较好。     

油菜高速直播机开畦沟装置刀组优化与试验

针对长江中下游现有油菜机驱动型开畦沟装置高速（≥10 km/h）作业存在功耗较大、沟形不稳定的现实问题,该研究设计了一种刀体低阻触土面近似为螺旋桨叶面的类螺桨式开畦沟装置。基于运动学、动力学设计了由4组刀盘组成的类螺桨式刀组,确定了影响其作业功耗、作业质量的关键参数范围。基于EDEM软件开展了刀片刃型、螺距角及弯折角的单因素试验,结果表明：后磨刃耕阻最小,螺距角增大使刀片耕阻先减小后增大、抛土性能下降,弯折角增大使整体耕阻减小、抛土性能下降;1～4号刀盘的刃角结构为后磨刃,螺距角分别为7°、5°、4°、3°,折弯角分别为120°、120°、90°、90°时阻力较小,抛土性能较好。以螺距角、作业速度和刀盘转速为因子的Box-Behnken仿真试验,采用遗传算法对功耗和抛土性能进行多目标优化,结果表明：作业速度、刀盘转速、螺距角增大均使功耗上升,其中作业速度影响最大;作业速度降低、刀盘转速增高均使抛土效率提高;优化后1～4号刀盘对应的的螺距角分别为6.7°、4.7°、3.5°、2.5°;作业速度6、9、12 km/h时刀盘较优转速分别为540、620、810 r/min,优化刀组作业功耗低...     

Development of vineyard ditcher with reversal twin rotary tillage wheels

开沟施肥是葡萄园生产过程中的重要环节。传统的葡萄园开沟施肥通常是人工挖掘填埋,劳动强度大,工作效率低。为了提高开沟效率,通过对葡萄园环境及其开沟农艺要求的分析,设计制造了一种驱动型葡萄园小型开沟机,该机为旋耕刀以反转方式进行开沟工作,抛出的土由挡土导流板引导落在沟的两旁。对开沟机进行的性能试验结果表明：该开沟机2次作业开出的沟深可达500 mm左右,沟宽超过200 mm,且沟壁光滑、沟型整齐平直、沟中残留碎土少,满足葡萄园农艺要求;该机开沟部件碎土、抛土性能好,整机操作灵活,能适应葡萄园管理要求,也可用于其他果园、茶园、农田等开沟作业;该开沟机成本低,经济效益较好。     

犁旋组合式油菜播种开沟起垄装置设计

针对中国南方稻田土壤黏重、高含水率土壤使传统油菜开沟起垄机构作业后沟壁易垮塌影响垄沟排水和后期油菜生长,研制了犁旋组合式油菜播种开沟起垄装置。设计了犁体式成沟起垄部件的入土角、翼板角度和翼板长度等结构参数,优化了旋转式切土部件的旋耕弯刀、沟壁切土直刀的安装方式及其结构参数。在室内土槽进行了多因素二次正交旋转组合试验,结果表明:影响沟面宽稳定度、垄高稳定度的主次顺序为沟壁切土直刀的回转半径、翼板长度、翼板角度;影响回土率的主次顺序为翼板长度、翼板角度、沟壁切土直刀的回转半径。装置最优的工作参数组合为沟壁切土直刀的回转半径为351 mm,翼板长度为78 cm,翼板角度为41°。对最优工作参数组合进行试验验证,各评价指标试验结果与软件分析值的相对偏差均不超过1%。该研究可为油菜垄作高产栽培提供技术参考。     

基于颗粒放尺效应的逆旋开沟机刀辊功耗分析与试验

为探究粗粒化建模对逆旋开沟机刀辊功耗的影响,提高离散元法的计算效率,该研究以1K-50型开沟机开沟部件为对象,利用EDEM软件构建适于南方葡萄园土质环境的刀辊-土壤离散元模型,将仿真模型中的土壤颗粒分别放大2～5倍进行开沟仿真试验,对刀辊功耗、工作阻力及土壤运动状态进行分析。结果表明：在土壤颗粒直径为5 mm、刀辊转速132 r/min、前进速度0.06 m/s、开沟深度0.3 m工况下,刀辊稳定作业阶段的功耗、水平阻力及垂直阻力平均值分别为3.73 kW、923.85 N和148.30 N,仿真功耗相对实际功耗的误差为9.9%。开沟仿真过程中刀辊的功耗、工作阻力平均值及土壤运动状态随放尺比例的变化而变化,其中刀辊功耗与水平阻力平均值随放尺比例增大而减小,垂直阻力平均值随放尺比例先减小后增大再减小,且增大放尺比例使得土垡从刀片正切面的抛出时刻提前,抛出速度减小,土垡逐渐松散,壅土高度增加,但不改变正切面上各深度土层的土壤分布顺序。放尺比例为2～5时,仿真计算时间相较原尺状态减少99%,但仿真功耗相对实际功耗的误差超过32%,当放尺比例为1.2时,能够将功耗相对误差控制在11.1%,仿真时间为22.9 h,仿真数据量313.72 GB。研究结果可为农机领域离散元放尺计算及构建刀辊-土壤粗粒化模型提供一定参考。     

多功能集成式播种开沟器的设计与试验

针对播种作业时土壤扰动大、种床土壤紧实度不足、播种深度均匀性差等问题,设计了一种集开沟、回土、镇压一体化的多功能集成式播种开沟器,其滑刀、挡土板、镇压轮相互配合能够实现开出种沟,种子落至沟底,湿土回流沟内,镇压轮镇压种沟,种子与土壤紧密接触。通过土槽试验,以土壤扰动量、土壤紧实度为试验指标进行三元二次回归正交试验得到开沟器各参数最优组合为滑刀滑切角44.6°、挡土板倾角3.2°、弹簧形变量11.8 mm。在最优参数下与双圆盘播种开沟器、尖角式进行田间对比试验,多功能集成式播种开沟器播深变异系数比双圆盘开沟器播深变异系数低了32.4%,比尖角式开沟器低了25.2%;集成式开沟器作业后的土壤紧实度比双圆盘开沟器紧实度高38.6%,比尖角式开沟器紧实度高62.9%;多功能集成式播种开沟器作业产生的土壤扰动量比双圆盘开沟器降低16.3%,比尖角式开沟器降低36.5%,其回土量比双圆盘开沟器提高29.9%,比尖角式开沟器提高61.5%。试验结果表明该开沟器可以改善种床环境,增强土壤紧实度,提高播种深度均匀性,可为播种开沟器的设计提供参考。     

收获开沟埋草一体机双圆盘开沟机构设计与参数优化

为提高己研制的稻麦联合收获开沟埋草多功能一体机免耕播种时的开沟播种质量,设计双圆盘开沟机构与一体机相结合.为获取影响双圆盘开沟机构作业质量因素的最优参数,以机器前进速度、开沟器入土深度、开沟器排种管固定装置固定孔中心点至排种管出口中心点横向距离为试验因素,以种子入沟率、各行播种量稳定性变异系数、播种均匀性变异系数为试验指标,进行三因素五水平二次正交旋转组合试验.试验结果表明:各试验因素对于种子入沟率与各行播种量稳定性变异系数影响程度从大到小皆依次是:固定孔横向距离、开沟器入土深度、机器前进速度;各试验因素对于播种均匀性变异系数的影响程度从大到小依次是:机器前进速度、开沟器入土深度、固定孔横向距离.优化所得双圆盘开沟机构开沟播种作业最佳参数组合为机器前进速度为0.46 m/s;开沟器入土深度为3.25 cm;固定孔横向距离为16.16 mm,验证试验表明各指标试验结果与理论优化结果相对误差均小于4％,验证了所建模型与优化参数的合理性.     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO_2浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO_2浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO_2浓度水平(310μmol/mol和400μmol/mol),针对主要C_3作物水稻、小麦和大豆,研究"绿色革命"以来大气CO_2浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO_2浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Collection and preliminary evaluation of native turfgrass accessions in Italy

Despite a raising interest on turfs in Italy, all theavailable varieties of this kind in the Country are of foreign origin, and areoften poorly adapted to the prevailing climatic conditions. This prompted tobegin a collection activity of indigenous turfgrass species, with the ultimategoal of identifying promising materials for future breeding based on localgenetic resources. The collection was carried out in three areas of Italy, viz.the northern Po Plain, the coastal region of Liguria, and the island of Sardiniathat are characterised, respectively, by subcontinental, warm temperate, andtypical Mediterranean climate. Altogether, 141 sites were visited, yielding 226accessions belonging to eight species of potential interest for turfs:Poa pratensis, Poa trivialis,Festuca rubra, Festuca arundinacea,Lolium perenne, Agrostis stolonifera,Agrostis tenuis, and Cynodon dactylon,this last being a warm-season grass. Poa pratensis andCynodon dactylon were mostly collected in northern Italyand Sardinia, respectively, whereas Festuca arundinacea andLolium perenne were rather ubiquitous. The collection sitesranged from 0 to 1040 m asl, but sites over 750 m wereonly visited in the inner part of Sardinia. All the accessions, collected aswhole plants, were transplanted at Lodi, northern Italy, where they are beingevaluated. Their preliminary evaluation for traits of importance for turf use,such as sward colour and overall quality, highlighted the great variation andthe occurrence of interesting accessions in all species. Other characters wererecorded, bearing specific importance in individual species, and in all casespromising accessions were identified. The germplasm of Festucarubra, Festuca arundinacea, and Loliumperenne proved highly infected by endophytic (symbiotic) fungi of thegenus Neotyphodium.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Leaf position and genotype differences for mineral element concentrations in sorghum grown on tropical acid soil 1

Mineral element deficiencies and toxicities are common problems associated with sorghum [Sorghum bicolor (L.) Moench] production on acid soils. To better understand some of the mineral element problems and the analysis of plant tissue of sorghum plants grown on acid soils, four sorghum genotypes were grown on an acid Oxisol at Carimagua, Colombia limed with dolomite at 2 and 6 Mg ha^‐1.

Samples for mineral element analyses were obtained from leaves at different positions on the four genotypes. Concentrations of P and Mg were highest in the flag leaf (Leaf No. 1) and decreased as the position on the plant declined from the top of the plant for plants grown at 2 Mg lime ha^‐1. Similar decreases in P, Mg, K, and Zn concentrations occurred in plants grown with 6 Mg lime ha^‐1. Concentrations of Ca, S, Si, Mn, Fe, Cu, and Al increased as leaf position declined from the flag leaf for plants grown at 2 and 6 Mg lime ha^‐1. The higher lime supply enhanced Ca and reduced Mn and Fe concentrations in leaves. Differences in mineral element concentrations for the four genotypes used were fairly extensive. The elements to show the greatest range among genotypes were Al and Si and the elements to show the least range among genotypes were P, K, and S. Care should be used in collecting leaf samples for plant analysis and genotypic differences for accumulation of mineral elements should be considered in interpretation of results.