Nairobi, Feb. 14 -- Just occasionally, we all do something so illogical and costly that it becomes a conundrum that seems unsolvable - in understanding why we do it.

A case in point is using fertiliser. The reality is that enriching our own soil is so easy, so cheap, and so much more effective than chemical fertiliser, that I, for one, cannot grasp why we don't just do it ourselves.

The secret, and apparently it is some kind of secret, despite creating some of the world's earliest flourishing civilisations thousands of years ago, is biochar.

It needs nothing except farm waste: old maize husks, stalks and leaves, dried chicken droppings are a good addition, but any leaves, branches or organic rubbish. And it requires only digging a tren...