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82.
The yield gap of global grain production: A spatial analysis 总被引:4,自引:0,他引:4
Global grain production has increased dramatically during the past 50 years, mainly as a consequence of intensified land management and introduction of new technologies. For the future, a strong increase in grain demand is expected, which may be fulfilled by further agricultural intensification rather than expansion of agricultural area. Little is known, however, about the global potential for intensification and its constraints. In the presented study, we analyze to what extent the available spatially explicit global biophysical and land management-related data are able to explain the yield gap of global grain production. We combined an econometric approach with spatial analysis to explore the maximum attainable yield, yield gap, and efficiencies of wheat, maize, and rice production. Results show that the actual grain yield in some regions is already approximating its maximum possible yields while other regions show large yield gaps and therefore tentative larger potential for intensification. Differences in grain production efficiencies are significantly correlated with irrigation, accessibility, market influence, agricultural labor, and slope. Results of regional analysis show, however, that the individual contribution of these factors to explaining production efficiencies strongly varies between world-regions. 相似文献
83.
Rotifer community structure in fish‐farming systems associated with a Neotropical semiarid reservoir in north‐eastern Brazil
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Gilmar de Aguiar Arruda Leidiane Pereira Diniz Viviane Lúcia dos Santos Almeida Sigrid Neumann‐Leitão Mauro de Melo Júnior 《Aquaculture Research》2017,48(9):4910-4922
The study was conducted to assess the community structure of planktonic rotifers and their relation to the environmental impact of Nile tilapia, Oreochromis niloticus (Linaeus, 1758), aquaculture activities (ponds and net‐tanks), associated with a Neotropical semiarid reservoir in Brazil. Our hypothesis was that the ecological attributes of the rotifer community were different when considering the influence of fish aquaculture activities. We identified 28 species, with 10 species from the Brachionidae family. The average density and diversity index of rotifers were higher in reservoir stations, with mean values in the ponds approximately 50% lower than those of the reservoir. The microphagous species dominated during all the time, while the raptorial species were accidental in all studied environments. The ponds were represented by four significant indicator species: Brachionus caudatus, B. leydigi, Dicranophoroides caudatus and Testudinella patina and the reservoir by three: B. falcatus, B. havanaensis and Conochilus dossuarius. In general, nine species were significantly associated with some categories of environmental conditions, such as high or low turbidity and low values of conductivity and TDS. Four of the five best bioindicator species belonged to the microphagous genus Brachionus. B. havanaensis indicated five environmental conditions (IndVal > 93.1%), and it appeared to be a key species in this Neotropical semiarid reservoir influenced by aquaculture activities. The dominance of microphagous rotifers suggests a functional redundancy of species in the studied environments. We found that these systems and their management affected the planktonic rotifer community in this region of Brazil by increasing the species richness. 相似文献
84.
C Telbis U Neumann O Siegmann 《Zentralblatt für Veterin?rmedizin. Reihe B. Journal of veterinary medicine. Series B》1989,36(3):203-216
The recent review is based on recent literature on the epizootiology and on properties of avian paramyxoviruses in vivo and in vitro. Paramyxoviruses are classified according to their pathogenicity (especially serotype 1), in addition to serotyping by means of hemagglutination-inhibition tests and by monoclonal antibody binding assays. Also, neuraminidase-inhibition tests, double-immunodiffusion tests can be performed. Growth properties of the different paramyxovirus-serotypes are accessory techniques to classify paramyxoviruses parallel to the determination of the pathogenicity. Structural polypeptides can be demonstrated in polyacrylamide-electrophoresis, thus leading to a distinction of the different serotypes. 相似文献
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