Try walking 25 kilometres carrying a 50-kilogramme bag of fertiliser on your head, as farmers in Malawi do, and you might get a sharper appreciation of the difficulties in building agricultural supply chains in Africa.

It is hard to find a country that more embodies the struggles to improve African farming. Landlocked, crowded, one of the poorest countries on earth, Malawi’s 10m semi-subsistence smallholders coax harvests of corn from poor soils in family plots averaging just half a hectare.