海南地区菜豆和豇豆中植物生长调节剂残留和风险评估

为了评估海南地区菜豆和豇豆中植物生长调节剂的残留水平和潜在健康风险,本研究在海南地区5个豆类蔬菜种植基地,采集菜豆和豇豆样品共100份,利用液相色谱三重四极杆串联质谱仪(LC-MS/MS)对矮壮素、多效唑、烯效唑、复硝酚钠、氯吡脲、噻苯隆、脱落酸共7种植物生长调节剂进行检测分析,并结合急性膳食摄入风险(%ARf D)和慢性膳食摄入风险(%ADI)评估方法,对这两种蔬菜中所有检出的植物生长调节剂进行风险评估。在菜豆样品中共检出矮壮素、多效唑、脱落酸、复硝酚钠等4种植物生长调节剂,检出率为16%~100%,且残留最大值为0.02~1.2 mg/kg,其中矮壮素和复硝酚钠的残留量超过欧盟最高残留限量标准,脱落酸的残留量明显高于植物激素自身含量;矮壮素、多效唑、复硝酚钠、脱落酸4种植物生长调节剂的%ARf D评估结果分别为0.081%、 0.020%、 0.033%、 1.568%,其%ADI评估结果分别为0.394%、 0.067%、 3.11%、 0.020%。在豇豆样品中共检出3种植物生长调节剂,分别为多效唑、脱落酸、复硝酚钠,检出率为8.0%~100%,残留最大值为0.036~1.179 mg/kg,且脱落酸的残留量明显高于植物激素自身含量。%ARf D评估结果分别为0.034%、 0.025%、 1.130%,%ADI评估结果分别为0.088%、 0.224%、 0.017%。实验结果表明,虽然海南地区菜豆和豇豆中部分PGR农药超过国家或欧盟最高残留限量标准,存在超剂量使用的情况,但是所有检出的PGR农药膳食暴露风险极低,均在可控范围内,尚不存在食品安全风险。     

果蔬中植物生长调节剂残留量调查分析

通过调查常见果蔬中植物生长调节剂残留水平,分析果蔬种植生产中植物生长调节剂的使用情况,以及可能存在的风险因素。利用液质联用法检测市场上随机采集的果蔬样品12种植物生长调节剂残留,分析检出率,并与相关的最大残留限量规定比较。结果表明,检测的4种果蔬中均有植物生长调节剂残留,涉及4-氯苯氧乙酸、矮壮素和氯吡脲3种化合物,含量在0.007 10~0.670 mg·kg~(-1)。本次调查发现豆芽有违反国家相关规定使用4-氯苯氧乙酸的情况,葡萄中矮壮素残留水平高于日本肯定列表残留限量规定,存在一定的风险。     

施用氯吡脲和多效唑改良山药的品质

山药是重要的药食两用作物,其品质高低与其药用价值密切相关。本研究采用通用旋转组合设计植物生长调节剂氯吡脲和多效唑配施的13个组合,并结合SPSS13．0统计软件分析不同氯吡脲和多效唑组合喷施对山药品质的影响。结果表明,氯吡脲和多效唑单施或配施均能改善山药品质,配施效果更明显。在最适浓度范围,即氯吡脲为27～33mg／kg,多效唑为550～700mg/kg时,块茎干物质、蛋白质、淀粉及皂苷含量分别比对照提高7．02％、3．71％、4．87％和0．009％,可溶性糖含量稍有下降,为0．37％。本研究结果将为山药的优质栽培提供参考。     

茭白中矮壮素的残留与急性膳食摄入风险研究

采用超高效液相色谱-串联质谱法,研究了矮壮素在茭白、茭白植株中的残留分析及消解动态,并对我国不同人群的急性膳食摄入风险进行了评估。茭白、茭白植株样品采用乙腈提取,乙二胺-N-丙基吸附剂净化,电喷雾正离子反应监测模式监测。结果表明,在0.000 5～0.5 mg/L范围内,矮壮素的质量浓度与对应的峰面积呈良好的线性关系,相关系数大于0.998,方法检出限和定量限分别为0.000 1 mg/kg和0.005 mg/kg。在0.005、 0.05和0.5 mg/kg添加水平下,矮壮素在茭白植株和茭白中的平均回收率为82%～97%,相对标准偏差为3.2%～7.1%。所用方法灵敏度、准确度和精密度均符合检测要求。消解动态结果表明,矮壮素在茭白植株上的消解速率符合一级动力学方程,半衰期为2.7 d。根据急性膳食风险评估结果显示,采样间隔期为7、 14、 21d时茭白中矮壮素残留浓度对我国不同人群的急性膳食风险均在可接受范围内。     

蔬菜中植物生长调节剂残留的膳食摄入风险评估——以江浙地区为例

为明确蔬菜中植物生长调节剂残留的膳食暴露风险,2015年在江苏省和浙江省的生产基地和市场调研抽检了271份蔬菜样品,采用高效液相色谱-串联质谱法测定了20种常用植物生长调节剂的残留量。检测结果显示,蔬菜中植物生长调节剂残留的总体检出率为8.40%,检出值最高达2.1 mg/kg。对检出率相对较高(5%)的脱落酸、矮壮素、赤霉酸、多效唑、吲哚-3-乙酸和2,4-滴,采用点评估方法评估了不同人群的膳食摄入暴露风险。评估结果显示,在残留量的中间水平和蔬菜消费量的平均水平下(情景1),我国居民的暴露量为2.6×10~(-6)~2.8×10~(-4)mg/(kg bw),其中6岁以下儿童的暴露量为5.7×10~(-6)~6.3×10~(-4)mg/(kg bw);在最大残留水平和高消费水平下(情景2),我国居民的暴露量为3.4×10~(-4)~1.3×10~(-2)mg/(kg bw),其中6岁以下儿童的暴露量为4.6×10~(-4)~2.4×10~(-2)mg/(kg bw),暴露量均远小于各植物生长调节剂的每日允许摄入量(ADI)。结果表明,蔬菜中植物生长调节剂的膳食暴露风险极低,远未达到风险关注水平。植物生长调节剂在蔬菜生产中规范使用具有技术必要性和高安全性,建议加快推进其在各类蔬菜上的登记和限量标准制修订。     

荧光猝灭法检测猕猴桃中氯吡脲的净化剂配方优化研究

为了寻求检测猕猴桃中氯吡脲时样品预处理的净化剂配方最佳组合,以N-丙基乙二胺(PSA)、弗罗里硅土(Florisil)、烷基-硅胶(C₁₈)为净化剂,采用Design-Expert中的混料设计研究3种净化剂的不同组合对猕猴桃中杂质和氯吡脲的影响,建立净化率和保留率与净化剂配比的回归模型,优化最佳工艺参数。结果表明,建立的净化率和保留率的二次多项回归模型均显著(p <0.05),可用于净化剂对猕猴桃中氯吡脲影响的预测和分析;净化剂的最优配方为PSA (32%)、Florisil (25%)、 C₁₈(44%)。在该配方下,对含有不同浓度氯吡脲的猕猴桃提取液进行净化处理,净化率和保留率最低分别可达89.02%、 92.48%。该配方可用于猕猴桃样品的净化处理,对提高猕猴桃中氯吡脲残留量的检测水平具有重要意义。     

高效液相色谱-串联质谱同时测定有机肥料中9种抗生素药物残留

采用高效液相色谱-串联质谱法(HPLC-MS/MS),同时测定有机肥料中3类9种抗生素(土霉素、四环素、金霉素、强力霉素、青霉素G和普鲁卡因青霉素、磺胺嘧啶、磺胺二甲基嘧啶、磺胺噻唑)残留,对于有机肥料中抗生素残留的快速检测具有重要的意义。样品用Na2EDTA-Mc Ilvaine缓冲液超声振荡提取后,采用固相萃取小柱净化,高效液相色谱-串联质谱法检测,标准曲线外标法定量。采用多反应监测模式检测,除负离子扫描青霉素G外其他均用正离子扫描。方法在0.1、0.5、1.0 mg/kg添加水平下,样品平均回收率为63.1%~93.4%;相对标准偏差为1.7%~9.5%;四环素类药物的方法检出限均可达到0.05 mg/kg,磺胺类和青霉素类药物的检出限可达0.02 mg/kg。本方法简便、快速,重现性良好,可用于有机肥料样品中抗生素残留的快速确证检测。     

3种抑芽剂对马铃薯贮藏效果的影响

以马铃薯品种新大坪为试验材料,研究了氯苯胺灵粉剂、香芹酮粉利和1-萘乙酸甲酯粉剂对马铃薯贮藏效果的影响。综合其抑芽效果、失重率、呼吸强度以及品质的观测结果表明,3种抑芽剂对马铃薯的贮藏效果依次为氯苯胺灵粉剂 > 香芹酮粉剂 > 1-萘乙酸甲酯粉剂。与对照相比,3种抑芽剂处理均可将马铃薯休眠推迟70 d,使马铃薯贮藏150 d不发芽。香芹酮熏蒸粉剂剂量为0.6 mL/kg、1-萘乙酸甲酯粉剂剂量为100 mg/kg时贮藏效果最好,可取代氯苯胺灵粉剂,达到绿色安全的目的。     

缓/控释氮素肥料玉米苗期养分释放特点

采用盆栽试验．模拟田间生态环境．研究施用不同种缓／控释氮素肥料玉米苗期土壤尿素态氮、硝态氮、铵态氮和速效态氮含量，分析比较其在玉米苗期氮素养分释放特点。研究表明，在玉米苗期，施用醋酸酯淀粉包膜脲酶抑制剂nBPT涂层尿素肥料。土壤中尿素态氮和铵态氮的积累量最多．分别为21．72mg／kg和48．31mg／kg；醋酸酯淀粉包膜尿素肥料，硝态氮和速效氮含量最多．分别为102．90mg／kg和135．25mg／kg；丙烯酸树脂包膜脲酶抑制剂nBPT涂层尿素肥料，尿素自膜内迁移到土壤中的量较少，硝态氮和速效态氮含量最少。分别为53．74mg／kg和93．70mg／kg。包膜与脲酶抑制剂nBPT相结合的缓／控释肥料，对减少土壤石硝态氮的生成效果最为明显．明显优于其他缓／控释肥料．丙烯酸树脂包膜nBPT涂层尿素肥料控释效果最好。     

植物生长调节剂对甜高粱茎秆贮藏中糖分变化的影响

为降低甜高粱茎秆采后自然贮藏期内含糖量损失,掌握糖分损失与有关酶活性变化的关系,该文研究了采用植物生长调节剂处理甜高粱植株对其采后贮藏含糖量影响,以及有关酶活性的变化情况。结果表明,用适当种类和剂量的植物生长调节剂处理可以将甜高粱茎秆贮藏期延长到3～4个月,贮藏至112d,赤霉素(40mg/L)、马来酰肼钾盐(400mg/L)、萘乙酸钠(70mg/L)处理的茎秆干基含糖量分别为初始值的95%、92%和94%,均显著高于对照组。采用适当种类和剂量的植物生长调节剂对调节与甜高粱茎秆采后衰老及糖代谢有关酶的活性具有显著作用,这3种植物生长调节剂对甜高粱茎秆采后糖分损失的抑制与其调节有关酶活性有关。该项研究为解决大规模使用甜高粱茎秆制取燃料乙醇过程中的茎秆贮藏问题提供了参考。     

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.     

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,     

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.     

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.