添加微生物菌剂对牛粪高温堆肥腐熟的影响

通过向堆肥中添加微生物菌剂和腐熟堆肥研究了其对堆肥腐熟速度的影响。结果表明,添加菌剂和腐熟堆肥在堆制初期均能促进堆体快速升温,较对照提前1～4d到达高温阶段（>50℃）,且菌剂添加量越大,升温越快;与对照相比,添加600mg·kg^-1菌剂和50g·kg^-1腐熟堆肥使高温期（>50℃）延长了3～4d。堆制29d后,添加600 mg·kg^-1菌剂和50 g·kg^-1腐熟堆肥的处理均较好腐熟,种子发芽指数分别为92.1%和84.4%,其他处理则未达到腐熟。这表明向堆肥中接入一定量的菌剂和腐熟堆肥均可加快堆肥腐熟,缩短堆肥周期。     

不同微生物菌剂对番茄秸秆好氧堆肥中氮磷钾元素的转化规律的影响

以番茄秸秆为堆肥原料,添加鸡粪和玉米秸秆后调节含水量及C/N,添加3种微生物菌剂进行好氧堆肥,研究不同微生物菌剂作用下堆体氮、磷、钾元素的动态变化及其对堆肥品质的影响。结果表明,番茄秸秆堆肥经历了升温期、高温期和降温期,霉菌、放线菌和酵母菌混合菌剂(菌剂1)作用下堆体升温快,高温持续时间长,堆肥腐解25 d即达到腐熟,堆肥腐熟后发芽指数最高达115%。与对照相比,添加霉菌、放线菌和酵母菌混合菌剂可使堆体氮素损失率下降27.7%,有效磷增加126%,速效钾增加105%。因此,添加霉菌、放线菌和酵母菌混合菌剂可加快堆肥的腐熟进程,减少营养元素的损失,提高堆肥产品的品质。     

接种微生物菌剂对猪粪堆肥的效果研究

研究了接种微生物菌剂对猪粪堆肥的效果。结果表明,添加菌剂堆肥温度第4 d达到50℃,50℃以上持续时间达10 d,第25 d粪大肠菌群值减少到102个/g,种子发芽指数达89%,NH4 -N含量为64.9 mg/kg,C/N下降为18.6∶1,上述指标均达到腐熟要求;对照堆肥温度第7 d达到50℃,50℃以上持续时间为4 d,第25 d粪大肠菌群值为9.6×103个/g,NH4 -N含量为916 mg/kg,C/N为21.0∶1,种子发芽指数为46.5%,均未达到腐熟要求。说明接种微生物菌剂能明显加速堆肥的腐熟进程。     

加入外源菌剂后脱氢酶活性在农业废弃物静态高温堆腐过程的变化

在静态通气条件下,分别以养殖场鸡粪、猪粪、牛粪为材料,加入麦秸作为调节物质,研究了加入外援菌剂堆腐过程堆体脱氢酶活性变化及其与温度的关系。结果表明,添加微生物菌剂使得堆体温度迅速上升,整个堆肥过程中的堆体温度高于对照,在堆肥的第1～2 d进入高温期,且高温阶段持续时间延长为16～20 d;对照处理在堆腐的4～5 d后进入高温期,持续时间较短仅为7～8 d。3种物料脱氢酶活性大小相比较,加菌剂处理, 牛粪 [H+ 29.32 μL/(g·d)]鸡粪 [H+ 25.66 μL/(g·d) ]≈猪粪 [H+ 25.34 μL/(g·d)],脱氢酶高峰出现的时间以牛粪 (6 d) 鸡粪(12 d) 猪粪(14 d) 。CK处理均在堆肥后第10 d脱氢酶活性达到最高,3种物料的脱氢酶大小的顺序为牛粪 [H+ 24.62 μL/(g·d)] 鸡粪 [H+ 21.6 μL/(g·d)] 猪粪 [H+ 18.62 μL/(g·d)]。加菌剂处理在高温堆肥初期过高的温度不利于土壤微生物的活动,因此在温度大于60℃以上时,脱氢酶的活性与温度呈直线负相关,此后脱氢酶活性与温度成显著性直线正相关;对照处理升温较缓慢,酶活性和温度增长同步,整个堆腐期间的脱氢酶活性与温度成显著性直线正相关。     

微生物菌剂对油枯堆肥过程中理化性质的影响研究

以油枯为基本原料,采用好氧堆肥方式进行堆肥试验,研究了添加4种不同微生物菌剂的条件下,油枯-稻壳-甘蔗渣堆肥体系中pH、C/N、水溶性NO3--N、水溶性NH4＋-N中的动态变化规律及菌剂对高温堆肥腐熟进程的影响。结果表明,添加菌剂能有效缩短堆肥到达高温的时间,延长高温分解阶段,加快物料水溶性NH4＋-N和C/N降低,pH和水溶性NO3--N含量升高,加快了油枯堆肥腐熟化进程。添加VT菌剂的堆肥处理相比其他在堆肥15d后最先进入高温分解阶段,高温持续时间为10d,提早5d腐熟,水溶性NO3--N含量从71.41mg.kg-1增加到887.4mg.kg-1,C/N的降低有效促进了NH4＋-N向NO3--N的转化,加快了油枯堆肥化进程,有助于提高堆肥腐熟化程度,说明添加VT菌剂的堆肥腐熟效果相对显著。     

添加腐熟猪粪对猪粪好氧堆肥效果的影响

为明确添加腐熟猪粪对猪粪好氧堆肥启动期和高温期微生物数量及酶活性变化规律,探讨微生物影响堆肥温度的机制,揭示影响畜禽粪便堆肥持续高温的主要微生物,该研究比较了猪粪自然堆肥与添加腐熟猪粪(质量分数3%)堆肥过程中有机质降解及嗜温、嗜热微生物数量和脱氢酶、蛋白酶、纤维素酶活性变化特征。结果表明,24 h内添加腐熟猪粪堆肥温度比自然堆肥高出5℃,但高温期平均温度较自然堆肥低8℃,高温（＞50℃）期比自然堆肥短4 d。自然堆肥和添加腐熟猪粪堆肥嗜温菌数量先高后低,嗜热菌数量随着温度的升高而上升。添加腐熟猪粪堆肥升温期嗜温、嗜热细菌和纤维素降解菌增殖速度较快,且数量分别比自然堆肥高出12.2%、152.6%、60.3%。添加腐熟猪粪堆肥脱氢酶、纤维素酶活性高峰提前,并使蛋白酶活性增加4.9%。但高温期后,嗜热纤维素降解菌数量比自然堆肥少22.5%,纤维素酶活性及有机质损失率也分别比对照低25.8%、6.1%。以上结果表明,在猪粪高温好氧堆肥中添加腐熟猪粪可以加快堆肥初期升温速度,但由于高温期嗜热纤维素降解菌数量减少,纤维素酶活性降低,不能促进猪粪堆肥持续高温。该研究为猪粪堆肥菌剂的筛选及适宜的接种时间提供依据。     

不同微生物菌剂对鸡粪高温堆腐的影响

以鸡粪和玉米秸秆为原料,采用好氧堆肥的方式,研究添加三种不同微生物菌剂对鸡粪高温腐熟效果的影响,探索有益微生物菌剂在畜禽废弃物高温堆肥中的作用。分析了堆肥不同时期各处理的堆温、pH值、种子发芽指数、水溶性铵态氮、水溶性有机氮、全氮、有机碳的变化。结果表明,在添加玉米秸秆调节物料碳氮比(25/1)的情况下,添加本研究中所采用的微生物菌剂可以迅速降低物料对种子发芽指数的影响,使发芽指数在21 d内达到80%以上,较对照提高45.52%;对水溶性铵态氮的转化和水溶性有机氮的形成都有明显的促进作用,腐熟堆肥的氮素保持提高25.46%;明显提高堆肥初期发酵温度,使堆体在第2 d达到高温阶段,并持续7 d以上,最高温度比对照高4.8℃,满足堆肥无害化卫生要求,大大缩短堆腐周期。综合多项指标分析,接种菌剂M2对促进有机碳的分解、有机氮的形成和提高腐熟效率更为有利。     

不同禽畜粪便静态高温堆肥过程中蔗糖酶活性的变化

在静态通气条件下,以养殖场鸡粪、猪粪、牛粪为材料,小麦秸秆作为堆肥调节物质,分别研究了接种微生物菌剂（接种菌剂处理）和不加菌剂（对照处理）堆肥过程中蔗糖酶活性的变化特征及其与温度的关系。结果表明,接种菌剂处理与对照处理在堆肥过程中蔗糖酶活性的变化趋势基本一致,即在高温腐解期蔗糖酶活性持续较高,在低温腐殖化期蔗糖酶活性急剧下降,且维持较低水平。接种菌剂能明显地提高堆肥过程蔗糖酶的活性,酶活性峰值高且出现时间较对照早4～8d。供试的3种物料蔗糖酶活性差异不显著,接种菌剂处理鸡粪、猪粪和牛粪蔗糖酶活性的最高值分别为87．84、81．3和86．8mg·（g·d）^-1,对照处理分别为62．9、60．9和63．79mg·（g·d）^-1,但3种物料接种菌剂和对照处理酶活性峰值出现的时间不尽相同,鸡粪的两种处理相同,猪粪加菌剂比对照提早8d,牛粪加菌剂较对照早4d出现。整个堆肥过程中蔗糖酶活性与堆体温度变化关系密切,对照处理堆体温度与蔗糖酶活性的关系为一元二次方程,表现为高温腐解期为显著性直线负相关,低温腐殖化期为显著性直线正相关,而加菌剂处理堆体温度和蔗糖酶活性间为极显著直线正相关。     

氧化还原类酶活性在小麦秸秆静态高温堆肥过程中的变化

选取小麦秸秆为试验材料,采取发酵罐处理方法,在静态通气条件下研究了堆腐过程中堆体温度变化、氧化还原类酶活性变化、温度与酶活性变化的关系、不同酶活性之间的关系。结果表明：（1）添加微生物菌剂处理较不添加微生物菌剂处理（CK）升温快、温度高、高温持续时间长;添加微生物菌剂处理堆体温度第2d上升到50℃以上,第3d达最高温度67.1℃,50℃以上持续6d;CK堆肥第3d达到50℃,第4d达最高温度59.5℃,50℃以上持续5d。（2）过氧化氢酶活性初期较低,中期迅速升高,并维持在较高水平,堆肥第10d到堆肥结束,添加微生物菌剂处理的过氧化氢酶活性明显高于CK;添加菌剂处理多酚氧化酶活性在堆肥前期和后期高于CK,说明添加菌剂可加速木质素的降解及其产物的转化;添加菌剂处理的脱氢酶活性在堆肥中期显著高于CK;添加菌剂处理的过氧化物酶从堆肥第12d到堆肥结束活性均高于CK的过氧化物酶活性,表明添加微生物菌剂可促进物质的氧化。（3）脱氢酶活性和过氧化物酶活性在堆肥中期达到最高值,两者变化趋势相同;过氧化氢酶活性、脱氢酶活性、过氧化物酶活性在堆腐后期比较稳定,多酚氧化酶活性堆腐后期呈增长趋势。     

一种生物矿质复合材料对猪粪堆肥品质的影响

QE制剂是一种含有微生物和矿物质的新型复合材料。为研究该材料对畜禽粪便高温堆肥进程及品质的影响,设置无添加剂(CK)、添加常规微生物菌剂(BJ)、添加QE制剂(QE)共3组处理,并以猪粪为原料,立式密闭发酵塔(容量50t)为反应装置,进行了为期7d的堆肥实验。结果表明:QE组堆温于第3天达到最大值72.7℃,比CK、BJ组分别提前2d、5d,且55℃以上持续天数为4d,高于其它两组处理。QE制剂可以有效提高堆肥的养分含量,堆肥7d后总氮、总磷、总钾含量分别达到2.62%、3.04%、2.29%,比BJ组高16.25%、2.36%、4.09%,比CK组高29.00%、14.72%、16.84%。同时,添加QE制剂的堆肥品质符合国家《有机肥料》(NY525-2012)标准,且优于其它两组处理。此外,QE、BJ组堆肥7d的种子发芽率指数分别为93.33%、90.00%,堆体已完全腐熟,而CK组为31.67%,未腐熟。研究表明,QE制剂在畜禽粪便高温堆肥过程中具有促进升温、加强保温、减少氮素损失、提高养分含量、改善堆肥品质的作用。     

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.