Winds of Anger

[Achebe]

If you have the time and inclination would you help me understand the disconnect between the desert and an oasis 

The first bit is about the hot winds of anger turning a fertile patch of earth into a desert. Anger = hot, dessicating winds. Presumably, desert = your heart, or something along those lines.
So far so good.

Now you suddenly bring up a poisoned oasis. Hot winds don't poison an oasis. Deserts don't naturally have poisoned oases. What is the poisoned oasis representing? Nothing. At least, nothing that's apparent from the poem. Even if it did, let's say you put in a line like 'of the poisoned oasis of brotherly feeling', it would sound crappy. Because while there's a causal relationship between hot winds and a desert, however tenuous, there's none between either of the two, and a poisoned oasis. So even if you invested the image of a poisoned oasis with symbolic meaning, the causal relationship wouldn't work at the literal level.

You've got carried away with your desert metaphor.