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71.
Break crop benefits in temperate wheat production 总被引:4,自引:0,他引:4
John Kirkegaard Olaf Christen Joseph Krupinsky David Layzell 《Field Crops Research》2008,107(3):185-195
Changes in the sequence of crops grown on agricultural land are well known to enhance the yield of grain crops such as wheat. A survey of the literature gathered from around the world show mean yield benefits of up to 20% or more. Much is known about the principal mechanisms responsible for these benefits, including effects on disease control, improved nitrogen nutrition and water supply, although researchers continue to be challenged by inexplicable “rotation effects” that have yet to be documented or fully understood. This review summarizes our current understanding of the ‘better-known’ mechanisms of crop rotation, and discusses other mechanisms (e.g. changes in rhizosphere biology, allelopathy or soil structure) that may help to account fully for the rotation benefits that have been observed by agricultural producers for more than 2000 years. Where possible we emphasise new techniques employed to investigate these less well-understood aspects of the “rotation effect”. At the farm level, the inability to capitalize on the benefits of break crops may owe more to economics, the availability of suitable break crops and the complexity of the crop response. Computer-based decision support tools have been developed to assist growers to apply the information gathered from scientific studies, although efforts to integrate this information at whole-farm scales are embryonic. 相似文献
72.
This paper shows how the world wide web can facilitate the transformation of a trans‐national identity into a global, or pan‐national identity. Specific to the Philippines diaspora is the concept of tahanang, or home as a metaphor for a pan‐national Philippine identity. Not only does the web facilitate the spatial interactions of diasporic communities but it also fosters the representation of national identity. In the case of the Philippine diaspora we find that social networking, via the web, operates at and through a variety of spatial scales, including intra‐diasporic, inter‐diasporic, diaspora‐host, and diaspora‐homeland. 相似文献
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Effects of previous cropping on seed yield and yield components of oil-seed rape (Brassica napus L.)
Klaus Sieling Olaf Christen Bahadour Nemati Herbert Hanus 《European Journal of Agronomy》1997,6(3-4):215-223
Information about the effect of the preceding crop or crop combination on the seed yield of oil-seed rape is extremely scarce. Experiments were carried out in northwest Germany to investigate the effect of different preceding crops on the growth, seed yield and yield components of oil-seed rape. The two directly preceding crops, wheat and oil-seed rape, had only a negligible and non-significant effect on the seed yield of the following oil-seed rape crop. Oil-seed rape grown after wheat had more pods per plant, due to an increase in the number of pods on the higher category branches. In contrast, the seed yield and yield components were more affected by the cropping sequence, i.e. the crops 2 years before. Averaged over two experimental years, the greatest yields were observed in oil-seed rape following the sequence peas-wheat (694 g m−2), whereas the smallest seed yield occurred after 2 years of oil-seed rape cropping (371 g m−2). The differences in the seed yield were again associated with more pods per plant, which compensated for the lower number of plants m−2, whereas the number of seeds per pod and the mean seed weight were almost unaffected by the previous cropping. It was not possible to relate the described differences to the crop development, since differences in the biomass caused by the previous cropping were only significant at maturity. Oil-seed rape grown after 2 years of oil-seed rape had the highest ratings of stem canker (Leptosphaeria maculans) as well as verticillium wilt (Verticillium dahliae). But the general level of the diseases was low, and therefore other causes for the effects described must be considered. 相似文献
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Multielement isotope analysis of bovine muscle for determination of international geographical origin of meat 总被引:1,自引:0,他引:1
Osorio MT Moloney AP Schmidt O Monahan FJ 《Journal of agricultural and food chemistry》2011,59(7):3285-3294
Multielemental (C, N, H, S) stable isotope ratio analysis was used as an analytical tool to verify the geographical origin of beef from several European and non-European countries. Beef samples were collected from nine different countries, and the (13)C/(12)C, (15)N/(14)N, (2)H/(1)H, and (34)S/(32)S ratios of defatted beef were measured using isotope ratio mass spectrometry (IRMS). There were highly significant differences in the mean isotopic values of the beef from different countries. The results of discriminant analysis showed that the four isotope ratios were significant for the discrimination of geographical origin and that 84.9% of the samples were correctly assigned to the country of origin (82.2% when cross-validated). Beef was also classified according to geographical origin when additional information on different feeding regimens used in Ireland was included, with 85.0% of the samples correctly allocated and 82.9% cross-validated using the isotopic signatures. All of the Irish beef samples verifiable as pasture-fed beef were correctly classified and then cross-validated. 相似文献
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Axel Dinter Christian Oberwalder Patrick Kabouw Mike Coulson Gregor Ernst Thorsten Leicher Mark Miles Gabe Weyman Olaf Klein 《Journal of Soils and Sediments》2013,13(2):278-293