1. B
2. C
3. D
4. C
5. C (not yet covered in class, but
see #16 below if you cannot reason it out)
6. E
7. C
8. A
9. C
10. C
11. B
12. cation-exchange
capacity represents the number of "sites" (spots) to which cations can attach on the surface of minerals. It is much
higher for some clay minerals than others. This number tells us how many
nutrient cations might be available to provide
nutrition to plant when the adsorbed cations are
taken up by plant roots.
13. This will not be on quiz- we
will get to this Monday or Wed.
14. The “Green Revolution” began in
the early to mid-1900s, and has greatly increased agricultural production in
the face of rising population (and even diminishing cropland) by:
mechanization, pesticides, herbicides, irrigation, new crop strains (breeding
and now genetic engineering), fertilizers. In the
1950s, the green revolution was applied to the farming in the tropics. The
billion dollar question is whether it can be successfully sustained and adopted
by poorer and developing countries, many of which are in tropical locations
(because of cost of fertilizers and pesticides, soil degradation, continued
loss of farmland, loss of water for irrigation, and loss of genetic
variability/variety). Even in developed countries, available land for
agriculture is declining.
15. The “missing sink” problem
(maybe better called the “unidentified sink(s)” problem)=> about 6 GtC are going into atmosphere from fossil fuels per year +
another 1-1.5 GtC from land-use change (largely
Amazon deforestation) =7-7.5 GtC total; HOWEVER, we
can only account for sinks for this excess carbon of about 3.3 GtC in the atmosphere (about 50-60% of the fossil-fuel
carbon release) +2.2 GtC in oceans by inorganic
dissolution=5.5GtC. So where is the rest of
the carbon (1.5-2 GtC)
going, ie, what is the "missing sink"?
There must be natural "sinks" for CO2 that have taken it up (for
example biological uptake in oceans, reforestation at temperate latitudes, regrowth of deforested tropical forests, uptake by mature
tropical forests as found by Phillips); a large amount of research money and
effort is going to identifying and understanding those sinks.
16. Erosion would be low in the
naturally forested landscape before 1900. The conversion to farm would increase
erosion, as agricultural processes commonly leave bare plowed fields for some
part of the year, which invites high rates of erosion. With abandonment, natural
vegation would begin to re-invade the farm and the
land would be covered all year round, thereby reducing erosion. As the land was
converted to city, erosion rates would likely be very high when the land was
first cleared for construction, but after the construction phase was over, the
erosion late would be very low as much of the original soil area becomes
covered by buildings and roads.