I've read your last post with enormous interest Steve.
I have grave doubts about our over-use of nitrogenous fertilisers (and insecticides, fungicides etc) being 'safe' for our health.

And you're right about Africa (well, the West, which is all I have experience of) not using these chemicals due being unable to afford them. Animal manure (goats, sheep, cattle, donkeys) is used almost exclusively, and no insecticides, except on crops of cotton (according to my husband) way up in the North of his country.

The reason I'm very interested personally in all this is that my husband has started to be very ill with what we thought was sudden hay fever, and I have been wondering if it isn't actually a reaction to the crop- spraying which has been going on all around us during the past week. He never had any contact with these things as a young man in his own country, and could be severely allergic to something they've added to the 'brew' here lately.
There have been tractors pulling tankers of all sorts of chemicals going up and down the fields, and my poor husband has red eyes, can hardly breathe and feels very ill. I might persuade him to go to the doctor tomorrow.