Temporal variation in Lake Balaton and its fish populations   总被引：4，自引：1，他引：3  

P. Bíró 《Ecology of Freshwater Fish》1997,6(4):196-216

Abstract— Dramatic changes have occurred in Lake Balaton in the last 40–45 years. Variations in water quality have resulted in a decrease in fish and invertebrate diversity. Fish assemblages have changed in response to human-induced eutrophication, environmental perturbations, introduction of exotic fish species, over-fishing and species-habitat interactions. Fish biomass and productivity first increased during the early 1970s with enhanced primary production, then decreased with the reduction of exploitation since the late 1970s and induced intra- and interspecific competition. Previous stable populations began to oscillate, and the majority of stocks became fragile by the mid-1980s. Extinction of native fish and invasion of new alien species alternate. Alien species have transformed the food webs, causing long-lasting ecological changes. Reduced and non-selective exploitation has resulted in higher fish density and lower production rates. Recent studies have revealed differences in the carrying capacity of fish between the littoral zone and the open water areas.  相似文献   

The place of Sanga cattle in dairy production in Uganda     

Grimaud P  Mpairwe D  Chalimbaud J  Messad S  Faye B 《Tropical animal health and production》2007,39(3):217-227

A survey was carried out on milk production and reproductive performance of dairy cattle: 24 farms, with a total of 900 animals and distributed in four agro-ecological zones, were visited every 15 days over 18 months. Cows were fed on natural pastures as the only source of feed, and animal performance was dependent on the season and exhibited a dramatic drop in dry spells. Numeric productivity indices integrating productive performance for settler’s, multipurpose, crop–livestock integrated and modern farms were 0.56, 0.74, 0.69 and 0.63, respectively. Milk productivity was higher on modern farms (6.7 L/cow per day) than in the other systems, and higher with Holstein-Friesian cows (7.7 L/cow per day) than with indigenous cattle (1.8 L/cow per day) or crossbred animals (3.7 L/cow per day). This paper speculates on the opportunity to improve the genetic potential of indigenous cattle, concomitantly with the efforts to adapt exotic cattle to a mountainous equatorial environment.  相似文献   

Recultivation of Agricultural Land Impaired by Construction of a Hydropower Plant on the Sava River,Slovenia     

Vesna Zupanc  Gerhard Kammerer  Helena Gr man  Igor &#x;antavec  Rozalija Cveji&#x;  Marina Pintar 《Land Degradation \u0026amp; Development》2016,27(2):406-415

Hydropower plants on the lower river Sava, Slovenia, were developed without sealing the underground upstream. As a consequence, without the countermeasures of elevating and recultivating, the agricultural land on the river banks would be inundated because of the water‐table increase of the river. To remedy this, the fields were elevated and recultivated. The goal of this study was to assess soil quality and production potential after land raising and recultivation and to answer the question whether it is possible to recover soil quality and crop yield after large‐scale mass manipulation, such as land raising. After recultivation and after the second year of land reuse for the two cultures grass–clover mixture and corn on two sites, Middle Pijavsko and Lower Pijavsko, soil physical and chemical characteristics and crop yields were evaluated. Mixing of topsoil with the second horizon during removal and during backfill with filling material resulted in uneven soil fertility, plant growth and decreased yield. Driving on the refilled second layer with heavy machinery caused soil compaction in the Middle Pijavsko in spite of favourable soil texture (loam, 38·7% sand). On the areas with very high sand content (over 55%) and low clay content (10%), soil compaction was not as severe or persistent. Recultivation measures restored the agricultural land almost to the production potential prior to powerplant construction. Immediate intensive land use (corn) showed less favourable effect on soil characteristics. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

水稻籼爪交和粳爪交杂种优势的研究Ⅰ.杂种农艺性状的表现   总被引：8，自引：0，他引：8  

肖国樱  袁隆平  唐俐  邓晓湘  罗闰良 《作物学报》2003,29(2):169-174

研究了籼爪交和粳爪交杂种在长沙、三亚两地农艺性状和干物质产量的表现. 由引进爪哇稻品种所配的籼/爪和粳/爪交杂种F1代表现为植株高大, 生长茂盛, 具有强大的干物质产量优势. 绝对干物质产量(单株穗期干重)为: 籼爪杂种＞粳爪杂种＞对照(籼籼交杂种), 干物质生产率(单株日干物质产量)为: 籼爪杂种＞粳爪杂种＞对照. 供试籼  相似文献   

Study of the Technology for Improving Grain Production Capacity of Shaanxi     

张正新  李思训  武世信 《中国农学通报》2005,21(4):383-383

确保粮食安全是当前和今后一个时期内农村经济工作中的重要任务之一。农业资源不足、生态环境恶化、农民生产积极性不高、农业科技体系建设滞后等问题是制约粮食生产发展的主要因素。加速科技创新、加快成果转化、建立稳定的生产基地和大力发展牧草产业是提高陕西粮食生产能力的主要科技对策。  相似文献   

山东省粮食生产与化肥施用状况研究   总被引：8，自引：0，他引：8  

宋海燕  叶优良  曲日涛 《中国农学通报》2005,21(9):380-384

对山东省建国以来的粮食作物产量与施肥状况进行了探讨,结果表明:建国以来,山东省粮食产量和化肥用量都在逐步增加,化肥与粮食单产之间呈显著正相关,但20世纪90年代粮食产量呈现下降的趋势,而化肥用量仍然增加,化肥的增产效率逐年降低;同时作为山东省主要粮食作物的小麦、玉米的产量呈现与粮食相同的趋势,通过对山东省几个地区的调查结果来看,小麦、玉米施肥量处于较高水平,且地区间施肥量、氮磷钾肥的施用比例以及化肥在两种作物上的分配比例差异较大。  相似文献   

“Ch型”谷子显性核不育的遗传及其应用研究（Setaria italica）   总被引：2，自引：1，他引：2  

胡洪凯  石艳华  王朝斌  赵虎臣 《作物学报》1993,19(3):208-217

通过对“Ch型”谷子显性核不育的遗传研究,证实“Ch型”的不育性与“澳大利亚谷”的细胞质无关,其育性是受两对显性连锁基因Ms-和Rf-上位互作控制的。其中Ms是显性不育基因,Rf是显性上位基因,当二者共同存在时,显性上位基因能抑制显性不育基因的表达,从而使不育表现可育。这种由杂交而来,并能找到“恢复系”的显性核不  相似文献   

Variation for plant characters and for performance of softwood cuttings of Rosa canina ‘Inermis’ seedlings     

D. P. De Vries  Lidwien A. M. Dubois 《Euphytica》1987,36(2):407-412

Summary Thirty, one-season-old Rosa canina Inermis seedlings (8–12 mm in diameter) were grown in the greenhouse. After 5 months, single-node softwood cuttings were made of each plant. Analysis of variance demonstrated marked differences between the internode length, number of leaflets per leaf and the leaf area of the original seedling, and between the time of axillary bud-break, axillary sprout length and weight of adventitious roots of their 23-day-old cuttings. Clonal root weight of cuttings was highly significantly correlated with: number of leaflets per leaf (r=–0.65), leaf area (r=+0.65), and days to axillary bud-break (r=+0.62). The origin of heterogeneity among Inermis seedling rootstocks, its probable effect on the flower production of cut roses and its possible use in the selection for clonal rootstocks are discussed.  相似文献   

Production of Haploid Sugar Beet (Beta vulgaris L.) by Culturing Unpollinated Ovules   总被引：4，自引：0，他引：4  

H. Lux    L. Herrmann  Claudia  Wetzel 《Plant Breeding》1990,104(3):177-183

The culture of unpollinated ovules is shown to be a suitable system for the production of haploid sugar beet (Beta vulgaris L.). The yield of haploids depended upon the genotype and varied between 0 and 13 % with a mean of 1.0 %. Haploid plants could be produced from approximately 50 % of all genotypes examined. The majority of the haploids isolated (about 90%) maintained the haploid genome level during the in vitro culture and propagation; 10% of the haploid clones showed a spontaneous doubling to the diploid genome level.  相似文献   

Inheritance of characters determining growth and development of tomato (Lycopersicon esculentum Mill.) under low energy conditions     

M. Nieuwhof  G. Pet  Frida Garretsen 《Euphytica》1987,36(1):205-213

Summary Diallel crosses were made between 15 tomato genotypes with varying performance under a low energy regime. It appeared that differences between genotypes for 11 vegetative and generative plant characters are determined mainly by additive genetic variation. For breeding cultivars adapted to low energy conditions, crossing genotypes with a high GCA for weight of trusses and fruits (WTF) and genotypes with a high GCA for weight of vegetative plant parts (WVP) seems most promising. Complications may arise from the negative correlation between GCA values for WTF and WVP, and the strong positive correlation between GCA values for fruit number and WTF, causing small fruits.  相似文献