Like an obstinate cashew in the hands of a teenage nut-sheller, the problem of how to unleash the rich potential of Tanzanian agriculture is a tough one to crack.

Four in every five Tanzanians live in rural areas; most are subsistence farmers. Eighty-five per cent of cultivated land is still worked with hand-held tools, 10 per cent with animals and just 5 per cent with machines. For a decade, the sector’s growth has failed to match the overall expansion of the economy. Without a transformation in agriculture, Edward Lowassa, prime minister, admitted in a recent speech, there will be no escape from poverty.