复合菌剂和NaOH预处理提高秸秆厌氧消化性能

为提高纤维素类原料厌氧消化性能,降低处理成本,该研究采用复合菌剂和2%、4%、6%、8%NaOH（以玉米秸秆干物质质量计）对以玉米秸秆为代表的纤维素类发酵原料进行预处理,研究不同预处理方式对纤维素等成分的含量、厌氧消化性能和生产成本的影响。试验结果表明,经复合菌剂和NaOH处理后,秸秆的木质素、纤维素和半纤维素总含量显著降低,产气量和产气效率提高,其中,添加6%NaOH的预处理方式效果最佳,复合菌剂次之,与未处理相比,单位干物质质量产气量从120.70 mL/g分别提高到374.30和334.76 mL/g,厌氧消化时间从大于30 d缩短到18和19 d。采用复合菌剂和2%、4%、6%、8%NaOH预处理生产沼气所需的可变成本分别为0.72、0.80、0.98、1.09和1.57元/m3。综合考虑产气效率和生产成本,复合菌剂预处理由于具有较低的处理成本、较高的产气效率和较短的消化时间更利于推广应用。     

氨化预处理对稻草厌氧消化产气性能影响

为了节省秸秆厌氧消化阶段另加N源调配营养的运行成本,同时又要保持良好产气效率。本试验选用氨化法对秸秆进行预处理,研究了不同浓度的氨对稻草厌氧消化产气性能的影响。以NH3·H2O为预处理药剂,按2%、4%、6%（相对于稻草的干质量）的NH3质量分数对稻草进行氨化,分别以50、65、80 g/L 3个不同负荷进行厌氧消化。结果表明：不同浓度的氨化预处理中,4%NH3氨化预处理效果最好。在65 g/L负荷率下,4%NH3预处理的消化70 d累积产气量为37?010 mL,消化产气量达总体积的90%（计T90）时产气量为33?920 mL,分别比未预处理稻草、2%和6%NH3预处理稻草T90时产气提高了38.3%、14.6%和8.2%,甲烷总产量分别提高了34.8%、15.1%和9.6%,比未预处理稻草同期（45 d）累积产气量以及甲烷总产量分别提高了60.8%和60.3%,产气周期提前10 d结束。消化后总固体（TS）、挥发性固体（VS）的减少量分别由41.6%和46.6%提高到了46.4%和58.6%,半纤维素和木质素质量分数分别由27.7%和6.9%减少到20.8%和5.2%,粗蛋白质量分数从4.0%提高到10.1%。本研究提供了一个有效地提高产气量的方法,研究结果将为大中型秸秆沼气工程提供设计依据。     

NaOH和H2O2预处理对玉米秸秆厌氧消化的影响

为提高秸秆厌氧消化的产气量及产气效率,采用NaOH和H2O2对玉米秸秆进行预处理,考察了不同浓度组合预处理对秸秆成分、厌氧消化性能的影响.试验结果表明,2％NaOH+3％H2O2预处理的处理效果最佳,与未经预处理的效果相比,总产气量提高了9.89％,消化时间缩短了14d,TS和VS降解率分别提高15.23％和17.85％.NaOH和H2O2联合试剂对秸秆进行预处理可以有效提高厌氧消化效率.     

太阳能蒸汽爆破和微波预处理对玉米秸秆产沼气的影响

为提高秸秆沼气工程效率,该文以玉米秸秆为原料,分别采用太阳能蒸汽爆破和微波辐射2种方法对其进行预处理,考察中温(35℃)条件下2种预处理方法的产沼气效果。试验结果表明:在接种量200g、发酵温度35℃、启动负荷22.6g/L(以总固体TS计)的试验条件下,2种方法均可破坏玉米秸秆原有刚性结构,使其易与厌氧微生物接触而被降解,其纤维素、半纤维素、木质素含量分别降低7.82%、50.56%、36.33%和20.13%、20.97%、54.03%;2种方法预处理后玉米秸秆沼气发酵TS(总固体)产气率分别达到239.89和281.45mL/g,VS(挥发性固体)产气率分别达到296.02和332.28mL/g,日均产气量分别达到320和334mL(分别高于对照15.11%和20.14%),同时料液滞留时间比对照分别减少42.11%和31.58%。该研究为秸秆预处理及提高秸秆沼气工程发酵效率提供了参考。     

香蕉秸秆与牲畜粪便固体联合厌氧发酵产沼气的特性

为了探讨香蕉秸秆与牲畜粪便的组合对固体厌氧发酵产沼气特性的影响,该文在20%的固体质量分数和中温(35±1)℃条件下,分别开展了不同质量分数的牛粪或猪粪与香蕉秸秆的联合厌氧发酵产气性能的比较研究。结果表明,与香蕉秸秆单独厌氧消化相比较,分别组合质量分数为75%的牛粪和猪粪,沼气累积产量可提高1.3～2.0倍。虽然组合猪粪或牛粪皆可改善底物厌氧消化产气性能,促进产气量的提高,但二者对改善底物的厌氧产气特性的影响不同,组合猪粪可以显著增强产气效率。对于猪粪与香蕉秸秆的组合底物,当猪粪的质量分数为50%时,甲烷产率和累积甲烷产量达到最高值,分别为191 mL/g和12.7 L,较牛粪与香蕉秸秆的组合底物分别提高了69%和92%。而沼气产率和累积沼气产量最高值出现在猪粪的质量分数为75%时,较牛粪与香蕉秸秆的组合底物分别提高了18%和32%,达到365 mL/g和23.9 L。此外,2种牲畜粪便的组合亦可显著增强底物中纤维素和半纤维素降解,它们的降解率相较于香蕉秸秆单独厌氧消化最高可提高1.2和3.6倍。该文研究结果可为香蕉秸秆和牲畜粪便固体厌氧产沼气工程提供参考。     

玉米秸秆储存方式对其与牛粪混合厌氧消化特性的影响

农作物秸秆是沼气生产的主要原料,但因其季节性收获特点,必须妥善储存才能为沼气全年生产提供高质量原料。该研究以玉米秸秆为原料,探索了储存方式(风干或青贮)对其厌氧消化产沼气性能的影响。首先研究比较风干秸秆和青贮秸秆的化学成分和结构特性,然后分别考查两种秸秆与牛粪在不同总固体混合比(total solids mixing ratios,TMR)条件下的产气特性。结果表明,玉米秸秆青贮后的纤维素等可消化纤维组分保存良好,风干秸秆的可溶性糖和水分损失殆尽。扫描电镜(scanning electron microscope,SEM)和X-衍射(X-ray differaction,XRD)结果显示,风干秸秆的木质纤维结构紧密,青贮秸秆表面则有很多裂缝和孔洞,木质纤维暴露,纤维素结晶度(0.42)低于风干秸秆(0.46)。厌氧消化结果表明,无论风干或青贮秸秆,当牛粪与秸秆TMR值为7∶3时,累积产气量、TS/VS产气量和TS/VS产甲烷量均高于其他4种比例,且青贮秸秆的产气性能优于风干秸秆。除1∶1比例外,其余TMR条件下青贮秸秆的累积甲烷产量均高于风干秸秆,当TMR值为7∶3时青贮秸秆的累积甲烷产量最高(1 816 mL)。秸秆青贮的储存方式不仅能良好保存化学组分和水分,还有利于提高沼气产量和品质,是适用于秸秆跨季节储存和预处理的一种可行方式。     

切割稻秸发酵产沼气性能影响因素优化

为了替代秸秆沼气湿式发酵的需进行粉碎预处理,探索切割颗粒秸秆的发酵工艺,简化工程操作流程,降低能耗。该文以稻秸为研究对象,研究发酵温度、发酵液浓度、稻秸粒度和堆沤时间对产气性能的影响,并进行试验验证。结果表明:温度与原料挥发性固体(volatile solid,VS)产气率的相关性显著(P0.01),最优组合为:40℃、堆沤2 d、粒度1 cm、总固体(total solid,TS)质量分数为8%,最优组合VS产气率为385.9 mL/g;40℃厌氧消化产沼气的速率快,各试验组前20 d累积产气量都达到总产气量的73%以上;正交试验中,40℃试验组均有发酵液温度高于水浴锅现象,以及生化培养箱验证试验组发酵液温度高于对照,2种现象说明水稻秸秆厌氧消化可能有少量放热。研究结果为秸秆沼气工程发酵工艺改进和运行提供参考。     

NaOH处理玉米秸秆厌氧生物气化试验研究

提出通过NaOH化学处理以改善玉米秸秆的可生物消化性能、提高玉米秸秆厌氧消化产气量的方法。NaOH添加量为玉米秸秆干物质的8%。对未处理和经NaOH处理的玉米秸秆进行了厌氧消化对比试验研究,厌氧消化负荷率为35,50,65和80 g/L。分析并比较了两者在不同负荷率下的日产气量、累积产气量、单位TS和VS产气量等。结果显示,与未处理玉米秸相比,NaOH处理过的玉米秸的干物质消化率和产气量明显提高,在35,50,65,80 g/L负荷率下,产气量分别提高了13.1%,39.8%,48.3%和47.8%,单位TS、VS的产气率分别提高了13.1%～48.3%、23%～61.3%;两种玉米秸分别在35和65 g/L负荷率下获得了最高单位TS产气量。NaOH化学处理使玉米秸细胞壁结构和化学成分发生了明显的变化,分别有53.2%、46.9%和66.6%的木质素、纤维素和半纤维素被分解,其中1/2～2/3被转化成了易被厌氧菌利用的可溶性物质,这是产气量提高的主要原因之一。研究结果对提高玉米秸的产气效率、实现大规模应用具有重要指导意义。     

不同预处理条件对棉秆厌氧发酵产沼气的影响

为探索合理的预处理方法以实现棉秆的高效厌氧发酵,研究了高温处理、NaOH处理与生物处理3种预处理方式对棉秆厌氧发酵产沼气的影响。经预处理的棉秆以8%的总固体质量分数,在常温（(23±2)℃）下进行沼气发酵试验。结果表明,经NaOH及生物预处理,棉秆的木质纤维结构破坏较明显,而高温预处理对棉秆的表观结构影响不大。3种预处理均能有效缩短发酵启动时间,并不同程度提高棉秆产沼气的能力,作用大小依次为：NaOH处理＞高温预处理＞生物预处理。其中以质量分数为4%的 NaOH对棉秆（含水率为60%）处理10 d的效果最佳,发酵61 d后的总产气量可达31 022.5 mL,日均产气量为508.57 mL/d,总固体产气率、挥发性固体产气率分别为193.89、216.30 mL/g,要远高于其他处理及对照,有效地提高了棉秆厌氧发酵的效率。     

玉米秸秆厌氧消化预处理方法及工艺优化

为提高玉米秸秆厌氧消化性能,该文采用碱液、酸液、沼液等方法对玉米秸秆进行预处理,比较不同预处理方式对秸秆成分、含量以及厌氧消化能力的影响。试验结果表明,经超声波辅助碱预处理后,秸秆的木质素和半纤维素总含量显著降低,产气量显著提高。基于Box-Behnken(BBK)试验设计,选择碱液预处理的固固比(Na OH/秸秆,下同)、预处理温度、预处理时间为试验因素,结合响应面分析法对碱液预处理条件进行响应面优化,结果表明,最佳玉米秸秆预处理条件为固固比22.4%,预处理温度37.9℃,预处理时间39.7 h,在此条件下还原糖产量的试验值为738.6 mg/g,沼气累积产量的试验值为661 m L/g,试验值与预测值误差不到0.5%,证明了响应面优化法的准确性和可行性。     

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.