"This is the kind of impact we would like to deliver to smallholder farmers across the African continent," says Joyce Kamande, one of 25 African entrepreneurs who spent six weeks at Oklahoma State University last year as part of the Mandela Washington Fellowship, a flagship programme of the U.S. government's Young African Leaders Initiative.

Kamande's passion for supporting small farmers grew from her own hard experiences growing up in a family struggling to survive on a landholding with limited space to grow crops and little access to soil amendments to increase productivity.

Efforts by African entrepreneurs such as Joyce Kamande to create fertilisers locally could make a significant difference on a continent where most farmers pay close to five times the global average price for fertilisers.

"Many smallholder farmers," Kamande points out, "use animal manure, which only gives micro-dosing and an unbalanced nutrient ratio to the degraded soil, or opt for cheap synthetic fertilisers that degrade and acidify the earth.

"Most small-scale farmers … don't know that they increase their yields from more robust, locally made, carbon-negative organic fertiliser made by farm waste from companies such as Safi Organics."