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61.
A greenhouse experiment was conducted with Lolium perenne to determine whether ammonium (NH4+-N) fixation by clay minerals can increase the recovery of nitrogen following application of 15N labelled urea. A silty loam subsoil, Bt horizon from an Alfisol derived from loess, pH (CaCl2) 7.9, was chosen for the experiment. The NH4+-N fixation capacity was altered by varying the distribution of potassium (K) in the upper and lower soil layer. In the K0 treatment (control), the upper soil layer fertilized with urea was not supplied with K, whereas the lower soil layer was fertilized with 300 mg K kg?1 soil. In the K1?, K2? and K3 treatment the upper soil was supplied with 100-, 200- and 300 mg K kg?1 soil, respectively. The soil in the lower layer of the K3 treatment was not supplied with K. The recovery of 15N from applied urea (15N uptake of Lolium perenne plus residual soil 15Nt) was 86.1% in the K0 treatment and 75.2%, 69.1% and 69.6% in K1-, K2- and K3 treatments, respectively, showing that 15N losses were smallest in the K0 treatment. Two weeks after applying 15N labelled urea the amounts of nonexchangeable 15NH4+-N in the upper soil layer were significantly higher in the K0 treatment than in the treatments with K application. Apparently, NH4+-N fixation by clay minerals can reduce NH3 volatilization after urea fertilization, if the amount of exchangeable K is low. 相似文献
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In response to rapidly growing interest in precision farming, universities and others have developed numerous educational programs. Many of these events are multi-day conferences and workshops as these venues provide the time necessary for attendees to learn about the many technologies, analysis approaches, and management strategies that make up precision farming. The Washington State University Western Precision Agriculture Conference, the Assiniboine Community College Precision Agriculture Conference and the University of Nebraska–Lincoln Crop Modeling for Environment-Specific Management Workshop exemplify these types of educational programs. The Western Precision Agriculture Conference uses a traditional format where the audience primarily listens to presentations. The Assiniboine Community College Precision Agriculture Conference provides a mixture of presentations and hands-on sessions where attendees actually use precision farming tools or develop site-specific management plans. Finally, those who attend the University of Nebraska–Lincoln Crop Modeling for Environment-Specific Management Workshop complete exercises related to each topic and presentation. Because a conference or workshop brings many experts together for a short period of time, organizers of all three events have tried to capture conference content for later use in other educational programs. Their approaches to this include videotaping interviews of conference speakers and assembling software and data used during the conference on compact disk. Given the multidisciplinary nature of precision farming, conferences and workshops that utilize multiple expert presenters such as those discussed in this paper are among the best sources of precision farming education. 相似文献
64.
Sutton T Baumann U Hayes J Collins NC Shi BJ Schnurbusch T Hay A Mayo G Pallotta M Tester M Langridge P 《Science (New York, N.Y.)》2007,318(5855):1446-1449
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Like all species, humans have exercised their impulse to perpetuate and propagate themselves. In doing so, we have domesticated landscapes and ecosystems in ways that enhance our food supplies, reduce exposure to predators and natural dangers, and promote commerce. On average, the net benefits to humankind of domesticated nature have been positive. We have, of course, made mistakes, causing unforeseen changes in ecosystem attributes, while leaving few, if any, truly wild places on Earth. Going into the future, scientists can help humanity to domesticate nature more wisely by quantifying the tradeoffs among ecosystem services, such as how increasing the provision of one service may decrease ecosystem resilience and the provision of other services. 相似文献
66.
Periodic slow earthquakes from the Cascadia subduction zone 总被引:1,自引:0,他引:1
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White T 《Science (New York, N.Y.)》2003,299(5615):1994-1997
70.
In higher eukaryotes, the S phase and M phase of the cell cycle are triggered by different cyclin-dependent kinases (CDKs). For example, in frog egg extracts, Cdk1-cyclin B catalyzes entry into mitosis but cannot trigger DNA replication. Two hypotheses can explain this observation: Either Cdk1-cyclin B fails to recognize the key substrates of its S-phase-promoting counterparts, or its activity is somehow regulated to prevent it from activating DNA synthesis. Here, we show that Cdk1-cyclin B1 has cryptic S-phase-promoting abilities that can be unmasked by relocating it from the cytoplasm to the nucleus and moderately stimulating its activity. Subcellular localization of vertebrate CDKs and the control of their activity are thus critical factors for determining their specificity. 相似文献