"just one fourth [of interviewed African] farmers are using [fertilisers]..." 

previously every farmer had used fertilisers but "... the price of fertiliser was now out of reach"

"The 50 kg bag of diammonium phosphate costs around $25,

that is at least twice the world market price, 

[requiring] $50 to $100 per hectare a cost vastly beyond what the household can afford"

(Jeffrey Sachs)