北京市通州区果园土壤盐碱化特征

[目的] 探究京郊土地利用方式改变后土壤含盐量、盐分分布及碱化特征，为该区及类似地区土壤盐渍化改良利用和果树经济效益的提升提供科学依据。 [方法] 以北京市通州区原农田调整为果园(梨、樱桃、葡萄、苹果、桃)土壤为研究对象，测定土壤0-20 cm和20-40 cm深处全盐量、主要离子组成、pH值、电导率、碱化度等指标，利用描述性统计、相关性分析方法进行数据分析。 [结果] ①研究区土壤阳离子以Na⁺为主，阴离子以HCO^-₃为主，全盐含量0.83~5.39 g/kg，pH值 7.45~8.23，碱化度1.52%~12.77%，电导率0.1~2.37 mS/cm。 ②水平方向主要为中等强度变异，垂直方向无显著差异。 ③全盐量与电导率呈极显著的线性正相关关系(R²=0.864)。 [结论] 北京市通州区果园土壤盐分离子呈表聚积累，总体呈碱性，应及时采取相应措施提升土壤肥力，形成生态良性循环。     

民勤绿洲盐生草生境土壤盐分特征及离子组成

对民勤绿洲盐生草周围不同距离范围内的总体盐分状况、盐分离子组成及离子之间的相关性进行了研究。结果表明,盐生草具有一定的聚盐作用,在其周围形成了一定的"盐岛"效应。在距盐生草0-60 cm范围内,土壤剖面中的土壤盐渍化程度随土层的加深而加重,土壤阴离子主要有Cl^-和SO₄^2-,阳离子主要有Na⁺和Ca²⁺,土壤盐分主要是氯化钠、氯化钙、硫酸钠和硫酸钙,其次是氯化镁和硫酸镁。其中在盐生草周围0-40 cm范围内,垂直剖面0-20 cm土层土壤全盐含量为0.98~1.52 g/kg,属于非盐渍化土壤,20-40 cm土层土壤全盐含量达到了2.25~2.30 g/kg,属于轻度盐渍化土壤,40-60 cm土层土壤全盐含量达到了3.10~3.16 g/kg,属中度盐渍化;在距盐生草60 cm处,垂直剖面0-40 cm土层土壤全盐含量为0.83~1.86 g/kg,属非盐渍化,40-60 cm土层土壤全盐含量达到了2.43 g/kg,属轻度盐渍化。除HCO₃^-外,土壤盐分含量与各盐分离子之间均呈极显著正相关。     

基于光谱指数与机器学习算法的土壤电导率估算研究

土壤盐分是干旱区土壤盐渍化评价的重要指标。以新疆维吾尔自治区渭干河-库车河三角洲绿洲为例，基于土壤电导率 (Electrical conductivity，EC) 及可见光-近红外 (Visible and near infrared, VIS-NIR) 光谱数据，通过蒙特卡洛交叉验证 (Monte Carlo cross validation, MCCV) 确定364个有效样本。采用原始光谱 (Raw reflectance, R) 及其经过微分、吸光度 (Absorbance, Abs)、连续统去除 (Continuum removal, CR) 等6种预处理后的数据构建光谱指数。基于遴选出的21个最优指数，采用BP神经网络 (Back propagation neural network, BPNN)、支持向量机 (Support vector machine, SVM)、极限学习机 (Extreme learning machine, ELM) 三种算法对EC进行估算，并引入偏最小二乘回归 (Partial least squares regression, PLSR) 进行比较。结果表明：在基于R与6种光谱预处理数据构建的21个最优光谱指数之中，R_FD_RSI (R₁₉₁₃，R₂₁₄₂) 表现最佳 (r = 0.649) ；与PLSR相比，机器学习算法能够显著提高模型的估算精度，R²提高了34.55%。三种机器学习算法模型中，ELM表现最优 (R² = 0.884, RMSE = 3.071 mS?cm^-1, RPIQ = 2.535) 。本研究中所构建的光谱指数在兼顾遥感机理的同时能深度挖掘更多的隐含信息，并且基于机器学习算法的土壤EC估算模型精度显著提高，为干旱区土壤盐分定量估算提供了科学参考。     

基于Sentinel-2卫星数据的灌区农田土壤水盐协同反演

土壤含水量（soil water content, SWC）和土壤含盐量（soil salt content, SSC）是影响作物生长和农业生产力的重要因素。光学卫星图像已成为SWC和SSC估计的主要数据源。然而,在SWC或SSC变化较大地区,土壤水分和盐分会影响对方对光谱反射率的响应,使得SSC和SWC的反演精度较差。对此,该研究提出了一个半解析性的反射率模型—RVS模型,来模拟植被光谱反射率（R_v）对作物根区土壤含水量和含盐量的响应;并通过构建的RVS模型,对植被覆盖区域的土壤含水量和土壤含盐量进行同步监测。研究表明：RVS模型在反演研究区土壤含盐量和含水量时,精度较为可靠(水分：决定系数R²为0.63～0.74,均方根误差为0.017～0.028;盐分：决定系数R²为0.68～0.75,均方根误差为0.0525～0.0617)。在作物生长过程中,植被光谱反射率对深层土壤的含水量和含盐量的响应比对浅层土壤的含水量和含盐量的响应更加明显,而且随着作物的生长,影响光谱反射率的主导因素从土壤水分慢慢转向土壤盐分和水盐相互作用。该研究在一定程度上揭示了土壤水分、盐分、水盐交互作用对作物光谱反射率的干扰过程,实现土壤水分和盐分的同步监测,对实现区域尺度上土壤含盐量和含水量的精准监测具有一定的意义。     

北京山区典型植被类型土壤饱和导水率及其影响因素

研究典型植被类型的土壤饱和导水率(K_s)分布及其影响因素,可为北京山区植被建设提供有力借鉴,同时加深对于土壤水分运动的理解。选取北京山区最具代表性的4种植被类型,获取不同类型、不同层次的土壤饱和导水率,调查土壤理化性质与根系生物量、石砾体积,利用Pearson相关性分析、多元逐步回归、通径分析,明晰了北京山区典型植被类型下的土壤饱和导水率分布及其影响因素。结果表明:(1)土壤饱和导水率介于0.05~2.23 mm/min,属于高度变异,随土层向下不断减小,侧柏×灌木混交林、侧柏纯林与侧柏×五角枫混交林的土壤饱和导水率存在显著差异(p＜0.05)。土壤饱和导水率与土层深度之间的关系符合对数函数关系式y=±aln x+b,R²≥0.858。(2)相关性分析结果表明,土壤饱和导水率与容重、总孔隙度、毛管孔隙度、根系生物量、有机质含量均呈极显著相关关系(p＜0.01),与非毛管孔隙度、自然含水率呈显著相关关系(p＜0.05)。(3)逐步回归分析得Y=3.42X₂+0.78X₆-1.333,R²=0.862。进一步通径分析可知,根系生物量主要通过直接作用影响土壤饱和导水率,而总孔隙度通过间接作用影响土壤饱和导水率。可知,侧柏×灌木混交林的导水性能最佳,后续的植被建设应重点考虑侧柏×灌木混交林,以达到减少径流、涵养水源的目的。     

膜下滴灌棉田Dobson介电模型参数修改及水盐含量反演

新疆土壤盐渍化严重，亟需防治土壤盐渍化继续蔓延，水盐含量能直观表述盐渍化程度，所以反演土壤水盐含量对于土壤盐渍化的防治具有重要意义。以新疆典型的膜下滴灌棉田土壤为例，利用探地雷达250 MHz和1 000 MHz两个频率天线，通过共中心点法获取波速后转换为视在介电常数，结合野外实测数据，修正胡庆荣盐渍土介电模型参数，以修正后的胡庆荣盐渍土介电模型反演膜下滴灌棉田表层土（0~30 cm）的水盐含量，最终验证反演结果的适用性。结果表明：①通过修正胡庆荣介电模型中的参数，使该模型可以适用于膜下滴灌棉田土壤水盐含量的反演。参数A修正后的取值在0.74左右，参数ξ修正后的取值在0.14左右。②1 000 MHz频率天线反演的含水量优于250 MHz频率，且反演值与实际值具有较好的线性拟合关系，R²=0.948，RMSE为2.67 cm³/cm³。③探地雷达250 MHz和1 000 MHz频率天线的组合能够有效反演膜下滴灌棉田表层土的含盐量，反演值与实测值拟合程度较高，R²=0.835，RMSE为1.43 g/kg。探地雷达技术结合参数修正后的胡庆荣介电模型不仅提高了水盐含量的调查效率，还有利于绘制中尺度棉田土壤水盐含量分布图，为防治土壤盐渍化提供了理论数据支持。     

工程堆积体坡面不同植被格局的控蚀效果研究

为探明不同植被格局对工程堆积体陡坡坡面土壤侵蚀的影响,采用10,20,30 L/min 3种放水流量,对黄土区不同格局（裸坡、坡顶、坡中、坡底、条带）下的高陡边坡（32°,20 m×1 m）进行模拟放水试验,选取径流率、产沙率、减流效益、减沙效益等因子对堆积体坡面植被的控蚀效果进行分析。结果表明：3种放水流量下,条带、坡顶、坡中、坡底的平均径流率较裸坡分别减小57.33%,61.17%,41.62%,24.78%,平均产沙率较裸坡分别减小74.99%,61.10%,55.01%,46.43%,且径流率与产沙率的线性关系（R²=0.57~0.80,p<0.01）整体上弱于裸坡（R²=0.71,p<0.01）。不同植被格局中,条带及坡顶格局的减流效益分别是65.97%,60.52%,减沙效益分别为71.44%,57.22%,二者的控蚀效果远高于其他格局。产沙率与径流功率的线性相关性（R²=0.61~0.83,p<0.01）高于径流剪切力（R²=0.29~0.76,p<0.01）,径流功率能更好地反映堆积体坡面土壤侵蚀机制。     

黄淮麦区小麦籽粒锌含量差异原因与调控

小麦高产优质生产对保障我国粮食安全和人们营养健康有重要意义。通过实地调研和取样分析,研究了黄淮麦区276个田块的小麦籽粒锌含量与产量和产量构成、施肥和土壤养分、作物锌吸收利用等参数的关系。结果表明,黄淮麦区缺锌和非缺锌土壤的比例分别为42%和58%,两种土壤上的小麦籽粒锌含量分别介于16~52和17~58 mg·kg^-1,分别有7%和9%样本的籽粒锌达到推荐值40 mg·kg^-1。缺锌田块,籽粒锌含量与磷肥用量（r = -0.273,P < 0.01）、0~20 cm土壤有效磷（r= -0.283,P < 0.01）显著负相关,高低籽粒锌组的磷肥用量分别为73和137 kg·hm^-2,土壤有效磷分别为13和20 mg·kg^-1,有效锌分别为0.8和0.7 mg·kg^-1,但籽粒产量低于非缺锌土壤（7 204 和7 857 kg·hm^-2）。非缺锌田块,籽粒锌含量与磷肥用量显著负相关（r= -0.181,P < 0.05）,与0~20 cm（r= 0.236,P< 0.01）和20~40 cm（r= 0.183,P < 0.05）土壤有效锌显著正相关,高低锌组的磷肥用量分别为112和145 kg·hm^-2,0~20 cm的土壤有效磷分别为29和30 mg·kg^-1,有效锌分别为3.3和2.2 mg·kg^-1。因此,在缺锌土壤上,应首先解决土壤缺锌问题,将有效锌提升至临界值1.0 mg·kg^-1以上,非缺锌土壤有效锌保持在3.0 mg·kg^-1以上,同时适当减少磷肥用量和降低土壤有效磷水平,以减少磷对小麦锌吸收的负面影响,维持黄淮麦区小麦高产并改善籽粒锌营养。     

基于不同风蚀模型的区域土壤风蚀变化及影响因素研究——以内蒙古自治区为例

基于遥感数据、气象数据等,利用RWEQ模型和风蚀预报模型对内蒙古自治区2000—2017年土壤风蚀进行评估并分析其驱动因素。结果表明：（1） RWEQ模型（R²=0.85,P<0.01）和风蚀预报模型（R²=0.43,P<0.01）的预测值与¹³⁷Cs示踪技术风蚀的值具有较好的相关性,其中RWEQ模型预测精度更好。（2）时间上,RWEQ和风蚀预报模型模拟的结果均表明2000—2017年内蒙古自治区土壤风蚀呈下降的趋势,下降趋势分别为0.73,1.18 t/（hm²·a）,2个模型模拟的土壤风蚀模数在2011年均达到最低值。空间上,2000—2017年,2个模型的模拟结果均表明内蒙古自治区土壤风蚀以微度和轻度侵蚀为主,其中剧烈侵蚀在整个研究区的占比较小（RWEQ 1.79%,风蚀预报模型5.45%）,主要分布于北方风沙区的西南部。趋势上,89.74%（RWEQ）和72.05%（风蚀预报模型）的土壤风蚀模数呈下降趋势,其中显著降低的区域主要分布于北方风沙区的巴丹吉林沙漠和乌兰布和沙漠。（3）大风天数对土壤风蚀具有显著影响,随着大风天数的增多,土壤风蚀呈显著上升趋势,植被覆盖度和降水量的增长在一定程度上可抑制土壤风蚀的进程。     

黄土高原典型退耕草地植被特征对土壤入渗过程的影响

植被恢复过程可显著影响土壤入渗性能。通过选取黄土高原典型草地白羊草和铁杆蒿草地,设置不同种植密度（5,10,15,20,25,30株/m²）和采用人工模拟降雨试验（60 mm/h,60 min）,系统研究了草地植被特征对土壤入渗过程的影响。结果表明：（1）种植密度增加可显著延缓产流,不同种植密度下白羊草草地和铁杆蒿草地初始产流时间分别为0.76~5.74,0.87~2.08 s,且随盖度、根系生物量和有机质的增加呈幂函数增加（R²≥0.18,p<0.05）。（2）不同种植密度下白羊草草地的平均入渗速率、稳定入渗速率、入渗总量分别为0.47~0.82,0.46~0.82 mm/min和7.12~11.84 mm,铁杆蒿草地分别为0.38~0.67,0.35~0.60 mm/min和5.70~10.07 mm。当种植密度为20株/m²时,土壤入渗各参数均最大;平均入渗速率、稳定入渗速率、入渗量总量、入渗系数（K）随土壤有机质的提高呈幂函数增大（R²≥0.26,p<0.01）,衰减系数（α）随生物结皮盖度呈降低趋势（p>0.05）。（3）白羊草草地具有较高的根系生物量、生物结皮盖度和有机质含量,其初始产流时间、平均入渗速率、稳定入渗速率、入渗量总量及入渗系数（K）均不同程度高于铁杆蒿草地,衰减系数（α）低于铁杆蒿草地,土壤入渗性能较强。总体而言,对于典型退耕草地,土壤入渗总量（A）可表征为根系生物量密度（RMD）和土壤有机质（SOC）的拟合函数（A=2.77×RMD^0.149 SOC^0.614,R²=0.663,NSE=0.653）。研究结果可为黄土高原退耕草地生态水文过程和植被建设提供数据来源和理论依据。     

“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.