十水硫酸钠相变蓄冷保温箱保冷特性的试验研究

针对果蔬保鲜冷链物流中2~8℃的运输温区要求,为了保证运输中果蔬等农产品的品质,研发一种经济性较高,相变温度为6.4℃,相变潜热为141 J/g的硫酸钠水合盐体系,其成分为(75.5%Na2SO4·10H2O+3%硼砂+1.25%聚丙烯酸钠+16%NH4Cl+4%KCl+0.25%去离子水).相变材料封装于聚乙烯蓄冷板中,应用于发泡聚丙烯(expanded polypropylene)保温箱和真空绝热板(vacuum insulation panel)保温箱中,组成蓄冷式冷链运输装备.利用产品供应规范(good supply practice GSP)验证设备建立保温箱温度测试系统,得到箱内各点的升温曲线,通过平均保冷时间来评价保温箱的保冷效果,对比了保温箱载货与空载情况下箱内各点的温度变化.综合考虑保温箱内侧面布置、顶层布置等不同的摆放方式,聚丙烯发泡与真空绝热板不同保温箱体材质对保冷性能的影响.研究表明真空绝热板的保温效果优于发泡聚丙烯,可提高保冷时间13.31%;蓄冷剂在侧布形式下的保冷时间较侧布加顶布方式延长4.7%;在真空绝热板保温箱中分析了载货情况下的保冷性能较空载保冷时间减少0.77 h.研究结果为蓄冷保温箱在冷链物流中的进一步设计和优化提供支持,以及蓄冷技术在果蔬冷链物流中的应用提供参考.     

冷链专用蓄冷托盘设计与控温运输性能测试

目前蓄冷冷藏运输车普遍采用车体和蓄冷装置一体化设计,存在重心偏高、控温范围窄、蓄冷剂充注量与运输时间难以合理匹配等问题。基于此,该文设计并建造一款集标准托盘、蓄冷槽、蓄冷盒等装置于一体的冷链专用蓄冷托盘。蓄冷托盘适用于包括仓储、运输装备在内的全程冷链环境,该设备采用分体式设计,运用时利用夜间低谷电充冷,相变材料（Phase Change Material,PCM）种类和质量可根据运输货物实际情况灵活搭配。从而达到按需蓄冷、灵活控温、降低重心、节能降耗等多重目标。试验结果表明,使用水凝胶为PCM,质量为100、200、300 kg时,车厢控温时间可达1～3 d,基本满足中短途冷藏运输需要。同时,循环通风可将车内平均温度由9.3、6.9、6.7 ℃降至5.7、4.6、3.3 ℃。在车厢温度均匀性方面,无循环通风时,车厢温度场水平分层严重,截面间最高温差分别为2.8、2.8、3.2 ℃,截面内最大温差4.2、4.1、6.6 ℃;循环通风后,截面间和截面内最大温差分别降至0.4、0.4、0.5 ℃和0.8、0.9、0.7 ℃,降幅分别为85.7%、85.7%、84.4%和81.0%、78.0%、89.4%。与传统蓄冷冷藏车（300 kg PCM）相比,温度绝对不均匀度系数由2.5下降至1.2,下降52.0%;车厢重心高度由1.46 m下降至0.77 m,车厢重心下降47.3%。研究可为冷链节能低碳发展提供借鉴,为蓄冷冷藏运输装备拓展应用及优化设计提供参考。     

纳米复合相变蓄冷材料的制备及蓄冷特性分析

针对生鲜冷链物流领域冷藏运输温度要求,通过差示扫描量热仪（DifferentialScanning Calorimeter,DSC）对甘氨酸、山梨醇、甘露醇、氯化钾进行筛选,经优化后配置出主储能为0.6mol/L甘氨酸+0.1mol/L山梨醇（命名为TA2）,以此体系为基液添加纳米二氧化钛和纳米氧化铝,并添加高吸水性树脂（Super Absorbent Polymer,SAP）对防泄漏现象进行优化,探究添加纳米粒子后复合相变蓄冷材料的相变潜热和热循环稳定性。将该复合材料应用于自制保温箱,以水晶梨为试验对象进行了蓄冷箱保冷特性试验,对比蓄冷保温箱载货与空载情况下箱内各点的温度变化,综合考虑蓄冷保温箱内蓄冷剂侧面布置和顶层布置加侧面布置这两种摆放方式对保冷性能的影响。结果显示,添加质量分数为0.5%的纳米二氧化钛粒子可使基液的导热系数达到最大值,经优化的最终材料为TA2+0.5%TiO2 + 0.25%SAP,相变潜热为294.57 J/g,Onset温度为-5.8 ℃,经过200次循环试验,复合材料热性能稳定。蓄冷剂以侧布加顶布的摆放方式下的大部分箱内空间平均温度为1.9 ℃,可在0～5 ℃保持480 min,温度场更均匀,利于保持生鲜产品新鲜度。研究结果为相变材料在生鲜冷链物流中的研制及应用提供参考。     

基于CFD数值模拟的冷藏车节能组合方式比较

精确掌握温度控制是实现高质量食品冷链运输的关键,节能减排降低运输成本也是供应商所追求的目标。该文以短距离冷藏运输车为研究对象,以土豆为货物区试验材料,建立了求解冷藏车车厢温度场分布计算模型。模拟过程采用2种不同的风机制冷温度（0和3℃）,依据制冷机组功率和货物最佳冷藏温度,确定运输过程中打开和关闭制冷风机最佳间隔时间。模型以冷气出风口风速、冷气温度、车厢以及货物的初始温度、货物的物性参数为边界条件,采用计算流体力学（CFD）非稳态SST κ-ω计算模型,模拟开启风机和关闭风机不同阶段车厢内温度场的分布情况。结果表明在组合方式为制冷温度3℃,制冷时间和关闭制冷风机阶段都为10 min时比制冷温度为0,制冷时间15 min和关闭制冷风机为20 min时要节约3.6×105 J能耗。该研究为合理选择制冷风机温度和冷却时间最佳组合方式,以及实现节能减排降低运输成本提供了依据。     

架空炕与传统落地炕热性能对比试验

为了解架空炕与落地火炕升温特性、热效率等方面的特性,依据国家相关标准,对甘肃省临洮县传统落地火炕与2016年新推广的架空炕进行了热性能的对比试验,研究了炕面温度分布、炕面升温降温速率、排放烟气温度、炕温对室内温度的影响以及架空炕的节能减排等性能,研究结果表明:架空炕和落地火炕炕面平均升温速率分别为2.2和0.9℃/h;烟气热量能被架空炕充分地吸收利用,架空炕烟气排放平均温度较落地火炕烟气排放平均温度低36.1℃;架空炕和落地火炕的热效率分别为66.8%和37.1%,相比传统炕架空炕节柴率达到45%;有架空炕和落地火炕室内日平均温度分别为12.6和10.8℃,架空炕对室内有较好的增温效果;与落地火坑相比,架空炕有明显的节能减排效果,每铺架空炕每年节省945 kg薪柴,减排CO21 069.17 kg,减排SO20.45 kg,减排NOx 1.01 kg,减排PM107.4 kg,减排PM2.5为6.8 kg,架空炕的推广应用对中国农村节能减排具有重要意义。     

保温灯变功率供暖对哺乳仔猪环境调控及节能效果

为探究保温灯温度自动控制对哺乳仔猪温度调控和节能效果,选用可控硅作为控制器的控制电路主体,以PID(proportional, integral and derivative)算法的单片机对保温灯进行变功率温度控制。选择北方地区某猪场2个产房单元(23头母猪、25个250 W保温灯/单元),对照单元恒定功率供暖,试验单元保温灯温度自动控制供暖。结果表明,试验期间,产房内平均温度为20.7℃,试验单元与对照单元保温灯正下方距离地面0.3 m高处日平均温度在仔猪出生后第1周均为27.4℃,第2周分别为27.2和27.5℃,第3周分别为26.8和27.4℃。试验单元和对照单元保温灯正下方实体地板表面温度的平均值范围分别为29.5～31.0和31.0～30.6℃,漏缝地板表面温度的平均值均为22.9～23.0℃。哺乳仔猪21日龄断奶每批次可节能25.4%,试验条件下,保温灯温度自动控制2个冬季可回收设备成本。试验单元和对照单元保温灯正下方、侧下方实体地板和漏缝地板仔猪躺卧比例分别为40.7%～66.5%、14.4%～33.4%和0.9%～8.7%。结合地暖供暖,在无仔猪保温箱情况下,保温灯温度自动控制系统基本满足哺乳仔猪21日龄内温度需求,不仅节能,而且有利于减少仔猪死亡率并提高日增质量。     

温度降水等气候因子变化对中国玉米产量的影响

通过分析1981-2006年温度、降水、辐射各气象因子变化对中国玉米调查产量变化的影响,尝试剥离和评估各气象因子变化对中国玉米产量的影响。结果表明:1981-2006年玉米生育期内,中国绝大部分玉米种植区,日平均气温、日均最高温度、日均最低温度均表现为显著升高(全国尺度,平均每10年依次升高了0.39℃、0.37℃和0.40℃),日较差、降水和辐射则仅在部分地区表现出显著变化,且有增有减,因区域而表现不同。1981-2006年期间,中国玉米平均产量变化与生育期内平均温度变化,最高温度和最低温度变化之间,具有显著的线性负相关关系。部分地区的玉米产量变化还与日较差、辐射、降水变化存在显著线性相关关系。与基准年份1981年相比,米生育期内平均温度每上升1℃、日较差每下降1℃、辐射每下降10%和降雨总量每下降10%,对中国部分地区玉米产量影响显著。其中,生育期平均温度每上升1℃对玉米产量影响最大,相较其他因子而言,产量下降的区域(约25.1%)和变化幅度(平均约为-21.6%)都达到最大。1981-2006年,不同气候因子变化在各区域玉米产量的变化中作用有所差异,其中平均温度作为对产量影响的主导因子所占的区域比例最大(约为40%),其次是日较差(23%),而辐射和降水则比例相当,均接近20%。该研究为进一步开展气候变化对玉米产量的影响机制研究和政府部门进行气候变化条件下玉米产量预测、风险评估和制定相关应对措施提供参考。     

棉花铃重与花铃期热量条件关系

通过３个气候年挂牌观测和资料统计分析结果表明，棉花铃重与棉铃开花－叶絮期间热量条件关系密切，铃重与花铃期不同温度水平有效积温相关系数分别为ｒ１５℃＝０．７２，ｒ２０℃＝０．７１；铃重与花铃期平均温度相关系数ｒ＝０．５３；花铃期热量条件影响铃重的关键时期为开花后５～２０ｄ。剪无效花铃界日期为日平均气温稳定通过２５℃终日后５ｄ。     

二氧化碳制冷技术在农产品冷链物流保鲜中的应用研究进展

随着中国“双碳”政策措施的逐步落地，绿色环保的新型制冷技术成为发展重点。二氧化碳(CO₂/R744)作为无色、无味、无毒、不可燃的天然工质，具有热稳定性好、单位容积制冷量高、全球温室效应低的特点，是一种理想的传统制冷剂替代品。CO₂制冷技术逐步应用于农产品仓储物流、制冰、空调等领域，但当前中国农产品仓储物流过程普遍存在能耗高的突出问题，亟需研发绿色节能制冷技术。该文阐述了CO₂制冷原理与发展历程，并从制冷系统、制冷设备及相关配件的角度，深入分析了CO₂制冷技术与压缩机、换热器、节流装置等CO₂制冷设备的国内外研发情况；综述了CO₂制冷技术在农产品储存和运输环节中的应用进展，提出了亟待解决不同工况下CO₂制冷设备匹配度、低温环境下CO₂压缩效率与液化效率等技术难点；基于中国农产品冷链物流最先一公里和最后一公里断链的突出问题，建议加快研发适宜中国农产品冷链物流产业特点的CO₂移动式冷库和立体智能...     

移动式冷库性能及其冷却均匀性分析

针对果蔬冷链运输过程中采摘后的“最先一公里”的保鲜问题,该研究开发了一种移动式冷库。该设备用于田间果蔬预冷以及冷藏,以消除果蔬采摘后的田间热和呼吸热。对该设备冷库库板的导热热阻、机组制冷系数以及冷库内部的冷却均匀性进行了性能试验研究,并采用温度异质性系数和温度变异系数用以评价冷库内部的冷却均匀性。结果表明,冷库板的导热热阻为3.98 m²·℃/W,制冷一体机的制冷系数为2.07,具有较高的导热热阻以及制冷系数,有利于设备的节能运行;设备运行过程中冷库门侧左上角测点处具有较低的温度异质性系数为0.08 %,制冷机组侧右上角测点处具有较高的温度异质性系数为0.48 %,冷库整体的温度变异系数为0.034%,不论是温度异质性系数还是温度变异系数均低于0.5 %,可以认为该冷库具有较高的冷却均匀性,将有利于降低果蔬预冷过程的损腐率。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

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.     

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.     

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 from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

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.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.