Fertilizers: a higher yield with the perfect blend

Farmer cultivating her field.

Photo: Simon Scott

Legumes benefit from the application of phosphorus and other nutrients. However, there were no fertilizers that contain the optimum nutrient blend specifically for legumes. N2Africa helped to formulate legume-specific fertilizer blends in Ghana and Kenya which improved legume yields.

Grain legume growth and production are often limited by a lack of available phosphorus (P) in the soil. Legumes therefore need it to be added, for instance through the application of mineral fertilizer. While inoculants are relatively inexpensive (about USD 10 per ha), phosphate fertilizer tends to be four to five times more costly. The risk for farmers of investing in fertilizer is therefore relatively high.

Fertilizer blends

Moreover, some fields fail to respond to the fertilizer being applied, which makes the investment for farmers even more risky. In some cases this may be because other nutrients are the limiting factor: even though enough phosphorus is supplied, the legume may still not grow well because there is e.g. insufficient potassium or calcium too. And while legumes generally don’t need nitrogen (N) to be added because they can fix it from the air, the most commonly available fertilizer blends that contain phosphorus are nitrogen-phosphorus-potassium (NPK) and diammonium phosphate (DAP), both of which do contain N. Making chemical fertilizers containing nitrogen takes a lot of energy, so there would be an environmental benefit in omitting it where it is not needed.

Legume specific fertilizers help improve legume yields. Photo: Shutterstock

Legume-specific fertilizer blends were therefore not readily available in most of the countries where N2Africa operated. And even when appropriate fertilizers without nitrogen were available, such as single or triple superphosphate (SSP or TSP), they could often only be obtained on specific request.

While inoculants are relatively inexpensive, phosphate fertilizer tends to be four to five times more pricey

In some countries, N2Africa focused on improving the access to existing fertilizers (e.g. TSP and SSP in Uganda and Nigeria, Minjingu in Tanzania), because these fertilizers were considered effective enough in increasing legume yields. In other countries, emphasis was placed on formulating and disseminating legume-specific fertilizers because trials showed that additional nutrients would be required to improve legume yields. In Kenya and Ghana, N2Africa sought cooperation with commercial parties that were interested in blending these fertilizers.

Ghana: collaboration with YARA

In 2015, the N2Africa team in Ghana approached YARA, a fertilizer company, with the request to provide TSP fertilizer for field trials and demonstrations. The initial contact evolved into advanced collaboration evaluating new fertilizer blends for legumes.

Kenya: collaboration with MEA Limited

In Kenya, the legume fertilizer blend Sympal was developed. Sympal contains no mineral nitrogen, but offers a balanced supply of phosphorus, potassium, calcium, magnesium, sulphur and zinc.


  • Through partnering with companies N2Africa improved farmers' access to existing fertilizers.

  • N2Africa led to better formulation and dissemination of legume-specific fertilizers.

  • N2Africa cooperated with commercial parties who produced the new legume specific fertilizers blends and marketed them.

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