CAROLINE WAMBUI IN a change from the droughts and floods that often plague his tomato plantation in central Kenya, David Kariuki's latest harvest has been more bountiful than he could have hoped - and yet, he is not sure he can afford his children's school fees. A stretch of favourable weather has led to a bumper crop for Kariuki, 34, and other farmers in Kirinyaga County, whose numbers have swelled as workers made jobless by the coronavirus pandemic turned to farming to make ends meet. With the market flush with fresh produce, buyers are offering only a fraction of the…