基于高光谱图像的黄瓜叶片叶绿素含量分布检测

植物叶片叶绿素含量及分布是植物营养信息表达的重要指标。为了给大棚黄瓜营养元素的控制提供理论依据,该研究利用高光谱图像建立简单实用的光谱值和叶绿素含量关系的模型,从而实时、无损地检测叶片的叶绿素分布。选取黄瓜叶片的高光谱图像数据块中450~850 nm波段作为研究波段。选取8个具有代表性的植被指数,建立特征波长λ下相应的光谱反射值Rλ与黄瓜叶片叶绿素含量之间的关系模型。结果显示,基于最优指数(R695–705)-1-(R750–800)-1的模型可以很好地预测黄瓜叶片叶绿素的含量,校正集和预测集相关系数r分别为0.8410和0.8286,最小均方根误差RMSE分别为0.2045和0.2190 mg/g。最后根据最优模型预测叶片上任意位置叶绿素的含量,并通过伪彩手段描述叶绿素含量的分布。研究结果表明,利用高光谱图像技术分析黄瓜叶片叶绿素含量及其在叶面上的分布是可行的。另外,该研究确定的最优植被指数所包含的695~705和750~800 nm 2个波段可用于搭建更加简便实用的快速检测叶片叶绿素的便携式多光谱设备。     

不同施氮水平下温室番茄叶片反射光谱特征分析

利用便携式光谱辐射仪测定了温室番茄叶片的光谱反射率,研究了不同施氮水平下特定光谱指数与叶片氮含量、光合速率及产量的关系。结果表明,温室番茄叶片的光谱反射率在可见光波段随供氮水平的升高而降低,在近红外波段随供氮水平的升高而增加。随施氮水平的提高,绿峰的蓝移和红边的红移现象明显,而红谷反射率与光合速率之间的关系可用二次方程拟合,相关系数达0.805。番茄叶片氮含量的敏感光谱波段为580~695 nm,740~900 nm,由695 nm、770 nm两个波段构建的高光谱指数(RVI、NDVI)与叶片氮含量的相关性显著。而基于原始光谱数据对番茄产量的估测也可在温室中得到很好的运用,其中光谱指数RV(I710,680)、VARI700和产量的拟合方程最优。     

基于光谱特征参数的温室番茄叶片叶绿素含量预测

为了快速、准确估测温室番茄叶片叶绿素含量,提升作物精细管理水平,利用光谱分析技术研究了温室番茄不同生长阶段叶绿素含量和响应光谱的相关性,在幼苗营养生长阶段叶片叶绿素含量呈增长趋势,到移植50天前后达到最大值,在此期间反射光谱的红边会向红外方向（长波）偏移,同时绿峰向蓝光（短波）方向偏移,绿峰幅值减小。从结果期开始叶绿素含量呈下降趋势,而红边、绿峰及绿峰幅值向相反方向变化。为了定量分析叶绿素含量和叶片反射光谱间的关系,从自定义的68个光谱特征参数中提取了7个能反映叶绿素含量变化的最优参量,并使用逐步回归、岭回归、主成分分量回归和偏最小二乘回归消除了最优参量的多重共线性,建立了叶绿素含量预测模型,其中岭回归模型精度最佳,均方根误差（RMSE）为0.406,决定系数(R2)为0.839。     

番茄叶片叶绿素含量光谱估算模型

以番茄品种“金粉2号”为试验材料,在玻璃温室内设置3种土壤水分胁迫水平,以正常灌溉为对照,于2013年3—7月和8—12月两个生长季对番茄进行全生育期持续处理。采用便携式地物光谱仪测定各生育期番茄冠层的光谱反射率,同步测定叶片总叶绿素和叶绿素a含量,并基于3—7月数据计算常见高光谱植被指数,分别建立番茄叶片叶绿素总量和叶绿素a估算模型,用8一12月生长季的试验数据对模拟精度进行检验。结果表明：（1）水分胁迫对番茄叶片总叶绿素、叶绿素a含量和番茄冠层光谱反射率产生明显影响,水分胁迫越严重,叶绿素总量和叶绿素a含量均越低,番茄冠层光谱反射率也越低;（2）随着生育期的推进,番茄总叶绿素和叶绿素a含量均持续增加,而冠层光谱反射率在红光和蓝光波段的反射率逐渐减少;（3）4种估算模型中R670模型的决定系数（R。）最高,效果最佳（P〈0．01）,番茄叶片总叶绿素和叶绿素a最佳估算模型分别为：C_chl（a＋b）=44．83R670＋_670＋7.36,C_chl=39．92R_670＋5．12,均根方误差分别为0．45、0．42mg·g^-1,表明利用高光谱数据估算番茄叶片的叶绿素含量可行。     

基于数字图像分析监测不同氮肥处理下加工番茄生长状况的初步研究

利用数字相机获取田间加工番茄冠层影像,通过图像处理软件准确识别冠层和背景像素,分析了加工番茄不同施氮量下提取的地面覆盖度与生物学参数间的相关关系,其相关系数都达到0.96以上的极显著相关;分析了光谱参数--绿色深度指数（DGCI）与叶片叶绿素含量相关关系,二者表现出r=0.74以上的极显著直线相关。结果表明,利用地面覆盖度可在生长前期监控加工番茄生长量,预测生物学产量和叶面积系数;在果实膨大期预测吸氮量和经济产量。利用光谱参数DGCI可监测加工番茄叶片叶绿素含量。本结果可快速准确监测加工番茄生长发育,为加工番茄生产提供科学依据。     

冬枣氮素含量预测模型中特征波长选择方法的应用

为了提高近红外光谱法快速测定枣叶氮含量的准确性和鲁棒性。采用偏最小二乘法建立了冬枣叶片氮含量近红外光谱模型。模型的相关系数为0.799,均方根误差为0.055。整个光谱区域包含了许多与冬枣氮含量无关的光谱变量。冗余信息的存在降低了模型的预测性能。所以采用间隔偏最小二乘(IPLS)结合遗传算法和模拟退火算法来选择冬枣叶片氮含量的特征波长。用凯氏定氮法测定冬枣叶样品的氮含量。试验选用15棵枣树,每棵树5个叶片作为试验对象。用于光谱测量的仪器是ASD光谱仪,测试仪在350~2 500 nm波长范围内,光谱分辨率为1 nm。在数据采集前使用了白板进行校正(标准白板反射系数为1),每个样品测量了5次,取平均值作为样品的相对反射率。遗传算法结合间隔偏最小二乘法选取的4个特征波长为685,689,781,783 nm。根据这4个波长,建立了冬枣叶片氮含量近红外光谱模型。模型预测相关系数为0.9175,预测均方根误差为0.063。利用模拟退火算法,建立了7个波长的冬枣叶片氮含量的近红外光谱模型。模型的相关系数为0.9301,均方根误差为0.052。因此,近红外光谱结合光谱选择方法的特点,可以有效地提高模型的精度,使模型更实用。但光谱选择方法的特点并不普遍。基于单波长变量选择的模型更为敏感,更适用于均匀采样。基于波长间隔选择的模型抗干扰能力相对较强,但更适合于不均匀采样。因此,基于状态与模型相结合的特征选择可以更好地应用于模型。     

冬枣氮素含量预测模型中特征波长选择方法的应用（英文）

为了提高近红外光谱法快速测定枣叶氮含量的准确性和鲁棒性。采用偏最小二乘法建立了冬枣叶片氮含量近红外光谱模型。模型的相关系数为0.799,均方根误差为0.055。整个光谱区域包含了许多与冬枣氮含量无关的光谱变量。冗余信息的存在降低了模型的预测性能。所以采用间隔偏最小二乘(IPLS)结合遗传算法和模拟退火算法来选择冬枣叶片氮含量的特征波长。用凯氏定氮法测定冬枣叶样品的氮含量。试验选用15棵枣树,每棵树5个叶片作为试验对象。用于光谱测量的仪器是ASD光谱仪,测试仪在350~2 500 nm波长范围内,光谱分辨率为1 nm。在数据采集前使用了白板进行校正(标准白板反射系数为1),每个样品测量了5次,取平均值作为样品的相对反射率。遗传算法结合间隔偏最小二乘法选取的4个特征波长为685,689,781,783 nm。根据这4个波长,建立了冬枣叶片氮含量近红外光谱模型。模型预测相关系数为0.9175,预测均方根误差为0.063。利用模拟退火算法,建立了7个波长的冬枣叶片氮含量的近红外光谱模型。模型的相关系数为0.9301,均方根误差为0.052。因此,近红外光谱结合光谱选择方法的特点,可以有效地提高模型的精度,使模型更实用。但光谱选择方法的特点并不普遍。基于单波长变量选择的模型更为敏感,更适用于均匀采样。基于波长间隔选择的模型抗干扰能力相对较强,但更适合于不均匀采样。因此,基于状态与模型相结合的特征选择可以更好地应用于模型。     

基于叶片光谱透过特性的植物氮素测定

该文通过不同施氮水平下营养液栽培的水稻和黄瓜叶片在300～1100 nm的分光光谱透过率,与其叶绿素含量和含氮量的相关性分析,确定了560、650和720 nm作为特征波长,940 nm作为参比波长可用于植物营养的快速无损诊断。以上述波长的光谱透过率构建的21组光谱特征参数中,(T940-T560)/(T940+T560)、log(T940/T560)和log(T940/T650)与水稻和黄瓜叶片的叶绿素含量和含氮量的相关性较好,且经回归估测检验的相对误差均小于8%。因此,上述光谱特征参数可作为植物氮素营养指标用于植物叶片的叶绿素含量和含氮量的快速无损估测,从而为植物营养无损诊断提供技术支持。     

基于自然光照反射光谱的温室黄瓜叶片含氮量预测

利用便携式光谱辐射仪测量了自然光照条件下温室黄瓜叶片的光谱反射率,并计算了反射率光谱的一次微分光谱。反射率光谱以及一次微分光谱与叶片含氮量的相关分析表明,温室内光谱特性与叶片含氮量相关性最大的敏感波段分别是505～664 nm和685～722 nm。当利用原始光谱进行分析时,通过变量筛选得到了4个敏感波长,分别是568、596、640和664 nm。偏最小二乘回归分析(PLSR)以及归一化颜色指数(NDCI)分析都表明,建模时的相关系数R_C>0.800,模型验证时的相关系数R_V>0.700。对微分光谱进行的相关分析结果表明,利用单一敏感波长520 nm就可获得理想模型,建模时的相关系数为0.880,模型验证时的相关系数为0.787。对比原始光谱的PLSR模型与一阶微分光谱的一元线性回归模型可以得知,原始光谱以及一阶微分光谱都可用于温室内叶片含氮量的预测,而且一阶微分光谱在一些特殊的波长处具有更高的预测能力,这些模型将成为开发便携式作物长势诊断仪器的技术基础。     

基于多光谱图像技术的番茄营养素诊断模型

为了快速、准确估测番茄营养水平和生长状态,利用多光谱图像分析技术研究了温室番茄营养素含量和图像特征的相关性。在日光条件下采集了温室番茄叶片多光谱图像,并采用多尺度Retinex算法有效地解决了叶片平整度差异造成的图像质量退化问题。从颜色模型、比值植被指数和归一化差值植被指数出发,自定义了49个多光谱图像特征参数。结合相关性分析和系统聚类分析消除了多光谱图像特征参数的多重共线性,并提取了4个能反映叶绿素含量(SPAD指数)和全氮含量预测模型,其中SPAD指数模型的决定系数(R2)为0.8668,均方根误差(RMSE)为3.997;全氮模型的R2为0.7284,RMSE为0.5130。     

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.