I was going to post 'what is unclear' but now I see you
are not 'southern....'
In the south, land is often 'poor' being made up of clay
and other soils which don't absorb water. It is hard.
Around here, the land is hard red clay, which grows only
tobacco well. That an scrub pine trees. You can forget a
garden since it stops raining all summer. But if it does
rain, it rains every day, making sure your garden is ruined
from too much water and rot.
The land must also be fertilized. To raise crops, you
need fertilizer. The joke is that he says you need
fertilizer to raise an umbrella. He was being funny.
In the last line Williams simply states he is still alive
so it all must be all right.
It was a good comment about the land in North Carolina
and other parts of the south.