Is this the thread you were thinking of?
http://hypography.com/forums/earth-s...ld-we-use.html
If so, your focus here seems to be on agriculture in desert/semi-desert conditions in africa.
Sahel - Wikipedia, the free encyclopedia
This helps narrow the focus of the thread some.
One problem pointed out in the wiki article is the poor soil of this area.
"Soils in the Sahel are mostly acidic (which results in aluminum toxicity to plants), and are very low in nitrogen and phosphate."
This can be compensated for by fertilizer and buffers (bicarbonates I think) to negate the acidity. I am not sure what to do about aluminum.
Google "acidic soils" and "food crops".
The other huge problem is the rainfall of the region. I do not know how deep one must drill a well in this area to hit a water table but here is one link that says between 10 m and 450m in Gambia:
Sourcebook of Alternative Technologies for Freshwater Augumentation in Africa
Google "water table depth" and "whateverCountryName"
The things you could research is how other regions irrigate their arid areas. Looking at the USA, you can see we have diverted rivers (colorado) to irriagate parts of california (there are problems with this also).
Google "drought resistant crops". Watch for crops whos temps fall within the specs of the country your researching. Keep in mind some crops do better in heat/full sun than others. Other crops have short growing seasons that may fall within the monsoon periods or close enough that you might be able to get multiple crops of (oats for example). Or Wheat right before the monsoon starts and a quick crop of oats right at the end.
*I am not saying either of these would work there, just examples of one type with a longer growing season (wheat) and one with a short growing season (oat).
A problem to solve would be Irrigation and evaporation and how to minimize this. So would energy to run pumps. You MIGHT be able to figure out how to use animals to run the pumps, depending on how deep the wells. Another part would be running this at night to minimize evaporation and stress on the animals and rotating teams of animals.