GCSE Science Revision: Physics 2 | Freesciencelessons
If the economy cannot grow forever then by how much can itgrow? Can it grow by enough to give everyone in the world today astandard of per capita resource use equal to that of the averageAmerican? That would turn out to be a factor of seven,*l a figurethat is neatly bracketed by the Brundtland Commission's call(Brundtland et al., 1987) for the expansion of the world economyby a factor of five to ten. The problem is that even expansion bya factor of four is impossible if Vitousek et al. (1986, pp.368-373) are correct in their calculation that the human economycurrently preempts one-fourth of the global net primary productof photosynthesis (NPP). We cannot go beyond 100 percent, and itis unlikely that we will increase NPP since the historicaltendency up to now is for economic growth to reduce globalphotosynthesis. Since land-based ecosystems are the morerelevant, and we preempt 40 percent of land-based NPP, even thefactor of four is an overestimate. Also, reaching 100 percent isunrealistic since we are incapable of bringing under direct humanmanagement all the species that make up the ecosystems upon whichwe depend. Furthermore it is ridiculous to urge the preservationof biodiversity without being willing to halt the economic growththat requires human takeover of places in the sun occupied byother species.
Science and metaphysics must work together to answer …
An old trick is to bury a nail in the substrate near the plant roots whereby the rusting nail will provide the necessary iron. I have seen this work well and despite some anecdotal answer at "Yahoo Answers", there is no scientific evidence that rust in small quantities such as a nail would provide will harm fish (it anything it will improve Redox balance with mineral Cations!!)
This said, I think newer methods such as balanced supplements are the way to go for added iron
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