间歇灌与农艺措施结合节水高产机理研究

针对阻碍农田水利用效率的关键因素及提高水利用效率的途径,采取把间歇灌灌溉技术、覆盖秸秆技术、化控、密植等农水措施溶于一体,取得了显著的节水增产效益和具有较强的可操作性。小麦、夏玉米产量分别为5250kg/hm²和8250kg/hm²,水分利用效率达1.61kg/m³和2.42kg/m³,平均为2.01kg/m³的较高水平。并对其节水高产机理作了探讨。     

种下分层施用有机肥和化肥对花生产质量的影响

采用花生营养分层调控-起垄-播种一体机,通过研究花生种下分层施用有机肥与化肥对花生生长发育、养分积累、产量和品质、土壤理化性状的影响,旨在为砂姜黑土区夏花生微域土壤调理、高效施肥提供科学依据。结果表明,与有机肥和化肥撒施相比,种下施肥能改善花生农艺性状、提高经济性状,改善土壤理化性状,增加花生养分积累量,油酸含量平均增加1.94个百分点,产量平均增加554.0 kg/hm²,增产11.2%,其中,花生种下5和8 cm分层施用有机肥600 kg/hm²和化肥600 kg/hm²产量最高,为5759.4 kg/hm²。花生种下5和8 cm分层施用有机肥和化肥的产量比种下5 cm同层施用有机肥和化肥的产量平均增加175.7 kg/hm²,平均增产3.3%,油酸含量平均增加0.89个百分点。化肥减施25%时,花生种下施用有机肥和化肥比有机肥和化肥撒施产量平均增加258.1～419.4 kg/hm²,平均增产5.2%～8.5%,油酸含量平均增加0.75～1.71个百分点,其中花生种下5和8 cm分层施用有机肥和化肥的增产提质效果最好。总之,花生种下5和8 cm分层施用有机肥600 kg/hm²和化肥450 kg/hm²,与撒施有机肥600 kg/hm²和化肥600 kg/hm²相比,化肥减施25%,花生增产419.4 kg/hm²,增产8.5%,能实现有机肥和化肥协同增效,达到化肥减施和大面积均衡增产的目的,应在夏花生主产区推广应用。     

不同有机物料投入下黄河故道土壤有机碳积累特征的研究

【目的】黄河故道潮土区土壤有机质含量低、结构差是限制当地作物优质高产的重要问题,通过连续施用不同有机物料,探究不同有机物料投入下,黄河故道区典型土壤的有机质积累特征,为该区土壤的快速固碳提供理论依据和参考方案。【方法】试验共设置7个处理：单施NPK肥作为对照(CK),其他处理在单施NPK肥的基础上增施有机肥6000 kg/hm_² (M1)、有机肥12000 kg/hm_² (M2)、树枝菌渣6000 kg/hm_² (B1)、树枝菌渣12000 kg/hm_² (B2)、秸秆菌渣6000 kg/hm_² (S1)、秸秆菌渣12000 kg/hm_² (S2), 采用随机区组设计。【结果】与CK相比,外源有机物料施入会显著增加玉米产量和有机质含量,增幅范围分别为21.7%～58.3%和37.4%～70.1%,产量的增加直接导致进入土壤的秸秆残渣及根茬碳相应增加38.9 kg/hm_²～76.9 kg/hm_²,致使 B2处理增产保肥效果最佳。就有机物料种类而言,用量为12000 kg/hm_²的树枝菌渣对土壤活性有机质的提升幅度最大,比相同用量的有机肥和秸秆菌渣高26.2%和57.0%,秸秆菌渣的碳库管理指数最高,但与树枝菌渣相比无显著差异。树枝菌渣由于碳氮比高,在土壤中分解慢,相同用量下,矿化消耗的碳量低于秸秆菌渣和有机肥,单位碳投入下的呼吸量比秸秆菌渣和有机肥低42.3%和29.3%。【结论】用量为12000 kg/hm_²的树枝菌渣由于碳投入量大,矿化消耗少,对黄河故道潮土有机质提升效果最好,玉米增产最明显。     

秸秆覆盖量对不同容重黑土坡耕地水土流失的影响

[目的] 研究免耕背景下土壤容重和秸秆覆盖对东北黑土坡耕地水土流失的影响,为东北黑土区保护性耕作技术的改良和推广提供理论依据。[方法] 通过模拟传统翻耕和免耕条件下的土壤容重（1.2,1.3 g/cm³）,结合不同秸秆覆盖量（0,328,656,984 g/m²）开展人工降雨试验,对比不同方式下黑土的初始产流时间、产流速率、径流量以及土壤流失量。[结果] ①土壤容重的增加显著缩短了初始产流时间并增加了水土流失量。同一秸秆覆盖量条件下,与容重为1.2 g/cm³时相比,1.3 g/cm³容重时的土壤初始产流时间缩短了13.1%～49.9%,径流量增加了0.4%～90.4%,土壤流失量增加了24.6%～302.8%;②与无秸秆覆盖相比,秸秆覆盖下的土壤初始产流时间延长了1.2～2.9倍,径流量减少了3.1%～38.9%,土壤流失量减少了34.0%～97.9%,且秸秆覆盖的保土效果与秸秆覆盖量呈极显著正相关关系（p<0.01,r=0.862）;秸秆覆盖量为656 g/m²时达到最佳的水土保持效果;③土壤容重的增加会加剧黑土水土流失,但秸秆覆盖显著降低了黑土水土流失,综合对比发现土壤容重为1.3 g/cm³时采取秸秆覆盖,平均减少了10.7%的径流量和74.2%的土壤流失量。[结论] 为有效防治水土流失,建议东北黑土区免耕时应注意结合秸秆覆盖措施,且秸秆覆盖量保持在656 g/m²以上为宜。     

兼顾产量和氮肥利用效率的间作体系小麦最适施氮量分析

探究小麦蚕豆间作体系下的小麦最适氮肥施用量,建立作物产量和氮肥利用效率协同提高的间作体系氮肥管理策略。通过2年的田间定位试验,在N 0、90、180、270 kg/hm² 4个小麦施氮水平下,研究了小麦蚕豆间作体系的产量效应、氮肥利用效率、兼顾产量与氮肥利用效率的小麦最适施氮量和推荐阈值,探讨了间作提高小麦产量和氮肥利用效率的关键土壤因子效应。结果表明,在4个施氮水平下,与单作小麦相比,间作小麦产量平均增加22.12%,产量可持续性指数平均增加3.68%,土地当量比平均为1.13,氮肥表观利用率平均增加18.44%,氮肥农学利用率平均增加9.64%,氮肥偏生产力平均增加21.14%。回归分析结果表明,小麦间作最高产量施氮量较单作平均减少3.28%,增产18.76%。以小麦相对产量的85%～90%作为氮肥施用量的推荐范围,小麦单作氮肥推荐阈值为101～128 kg/hm²,间作小麦氮肥推荐阈值为90～117 kg/hm²,小麦间作较单作施氮量减少9.40%～12.22%,小麦产量增加18.20%。综合小麦产量和氮肥利用效率的关系,单作小麦最适施氮量为133 kg/hm²,间作小麦最适施氮量为106 kg/hm²时可兼顾提高小麦产量和氮肥利用效率,保证小麦增产及氮肥减施增效。结构方程分析表明小麦间作中硝态氮是提高氮肥利用效率的关键土壤因子。     

太行山前平原冬小麦综合节水技术效应分析

在河北省鹿泉市南铜冶村试区实施了工程、农艺等综合节水技术,冬小麦全生育期浇2次水,使小麦产量达7500kg／hm²,水分利用效率达18kg／hm².mm。若种植节水品种、实施秸秆覆盖节水措施,冬小麦水分利用效率可达24．3kg／hm²·mm,为太行山前平原实施节水农业提供了科学依据。     

河西灌区绿肥对春小麦化学氮肥的替代及增产潜力初探

针对河西灌区春小麦连作普遍、对化肥依赖过高等问题，探讨麦后复种绿肥对下茬小麦的影响，以期为试区建立基于复种绿肥的化肥减量小麦生产技术提供理论依据。2018～2019年，在河西绿洲灌区设置田间试验，研究了4种绿肥翻压量(0、15000、30000、45000 kg/hm²)、2个施氮水平(0、180 kg/hm²)下的小麦干物质累积及产量构成、绿肥替代化肥的短期潜力。结果表明，种植翻压绿肥第一年，绿肥还田15000、30000和45000 kg/hm²可分别替代化学氮肥11.3%、18.5%和36.5%。施氮180 kg/hm²配合30000 kg/hm²绿肥还田、不施氮配合45000 kg/hm²绿肥还田2个处理的籽粒产量差异不显著，分别较施氮不复种绿肥增产18.4%和15.7%，收获指数分别增加13.0%和12.6%，穗数分别增加13.8%和14.1%，穗粒数分别增加26.8%和15.9%。施氮180 kg/hm²配合30000 kg/hm²绿肥还田的干物质累积量和累积速率明显高于其他处理。通径分析表明，绿肥化肥配施主要通过提高有效穗数，进一步提高穗粒数和千粒重，从而提高产量，说明施氮180 kg/hm²配合绿肥还田30000 kg/hm²处理通过优化小麦有效穗数、穗粒数和千粒重对产量产生了调控作用。综上所述，施氮180 kg/hm²配合绿肥还田30000 kg/hm²是河西灌区小麦增产的可行措施。     

秸秆腐解与养分释放特征对腐熟剂用量的响应

农业生产系统存在秸秆养分释放与作物生长需求匹配程度低等问题,拟通过腐熟剂用量调节还田小麦秸秆腐解及养分释放率,使之与作物生长需求相吻合,进而提升夏玉米产量。以人元腐熟剂为供试腐熟剂,小麦秸秆为供试秸秆,郑单958 为供试玉米品种。采用完全随机区组试验设计,设置4 种腐熟剂施用量:30 kg/hm²(T1)、45 kg/hm²(T2)、60 kg/hm²(T3)、75 kg/hm²(T4),以不施腐熟剂为对照(CK)。测定秸秆腐解率、养分释放率、夏玉米关键生育期的株高、茎粗、生物量和作物产量,通过回归分析探究秸秆养分阶段性释放如何调控夏玉米生长及籽粒产量形成。腐熟剂用量为45 kg/hm² 时,秸秆最终腐解率可达69.28%。腐熟剂用量对不同养分释放的调控效果不同,其中,氮和有机碳的释放率呈线性变化,磷和钾的释放率呈阶段性变化。腐熟剂施用对抽雄期(VT)各养分释放率均有显著的促进效应。三叶期(V3)较CK 而言,T2 和T4 处理氮、磷释放率增幅分别达到203.67%、187.05% 和17.72%、45.24%; 抽雄期,T3 处理秸秆钾、有机碳释放率较CK 分别增加5.33% 和22.42%; 生理成熟期(R6),T2 处理的氮、磷、钾释放率分别较CK 增加了2.55%、17.87%、3.78%,T1 处理的有机碳释放率较CK、T3 处理分别增加3.64% 和4.61%。此外,腐熟剂施用后,夏玉米株高和茎粗均显著增加。成熟期,T2 处理单株生物量可达320.0 g,较CK 增幅17.19%。最终,T2 处理玉米产量显著提升,达11.6 t/hm²。腐熟剂施用显著影响麦秆腐解率,施用45 ～ 60 kg/hm² 腐熟剂后夏玉米花前小麦秸秆的养分释放率显著提升,在夏玉米生长关键期提供更多养分,最终显著提升了夏玉米籽粒产量。     

安徽省全椒县立体复合种植模式及配套技术

安徽省全椒县实施油菜=西瓜-水稻、西瓜=棉花-冬菜、蔬菜-水稻-蔬菜、冬菜-棉花=蔬菜、小麦=西瓜=大豆、马铃薯=西瓜=棉花、西瓜=玉米-水稻等多种立体复合种植模式及其配套栽培技术,1997年各类面积达1.33万hm²,其中5600hm²田粮食单产达 7500kg/hm²,产值达3万元/hm²,分别比传统种植模式(油菜-水稻,麦-稻)增长12.4%和24%,取得明显的社会、经济和生态效益。     

寿阳试验区玉米地农田水分平衡及其覆盖调控试验

寿阳地区春玉米缺水时期主要在播种-拔节期和拔节-孕穗期,分别缺水约36.3mm和120mm,占总缺水量的23.2%和76.8%,造成玉米产量大幅度下降。该文根据山西寿阳试验区土壤-作物水分供需平衡规律,进行农田覆盖微环境农田水分调控试验。结果表明,农田覆盖可有效地抑制土壤水分的无效损耗,农田水分调控效应非常显著。地膜覆盖的抑蒸保墒效应可使0～150cm土层的土壤储水量增加10.3～45.0mm,增产玉米1488kg/hm²,水分利用效率提高20.2%;秸秆覆盖的微集水保墒效应可使0～200cm土层的储水量较不覆盖的增加30.7～78.4mm,每公顷玉米产量增加2235.1kg,降水利用效率提高45.5%     

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.