Fertilizer microdosing developed by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and is partners is helping farmers in drought-prone areas of sub-Saharan Africa increase agricultural productivity.

“We began with the realization that poorer farmers in drought-prone areas will not invest in fertilizer — or only in very small quantities,” recalls Steve J. Twomlow, ICRISAT global theme leader on agro-ecosystems and leader of the microdosing project in southern Africa. “The question was not what quantity of fertilizer would maximize yields, but rather how to maximize returns from a small investment in fertilizer.”

ICRISAT challenged an international workshop of scientists to determine by simulation how best to allocate two 50-kg bags of fertilizer on a small-scale farm. To the surprise of many, the largest gains were achieved by spreading the fertilizer broadly. ICRISAT worked with the Zimbabwean Department for Agricultural Research and Extension and several nongovernmental organizations (NGOs) to implement on-farm participatory trials in which farmers applied small quantities — just enough to fill a bottle cap — of ammonium nitrate. The results confirmed the simulation.

ICRISAT then challenged the donor and NGO community to promote these findings in their drought-recovery programs. In the 2003-2004 cropping year, 170,000 farmers each received a 25 kg bag of ammonium nitrate with advice on how to apply it on an acre (0.4 hectare) of grain. Almost every farmer achieved a significant yield gain, with most obtaining a 30-50 percent improvement. More than 40,000 tons of additional grain reduced the cost of food aid imports to Zimbabwe by more than US$8 million.

Following the success of this initiative, microdosing is being tested in Mozambique and South Africa, and fertilizer companies in Zimbabwe and South Africa have agreed to distribute smaller packs of fertilizer with advice on how best to apply it.

Meanwhile, ICRISAT scientists working much further north in the Sahel realized that, after decades of nutrient mining, improving the productivity of pearl millet and sorghum would require at least 100 kg of nitrogen-phosphorus-potassium (NPK) fertilizer per hectare, costing about $40.

“We could not recommend something that we were sure farmers would not be able to afford,” recalls Ramadjita Tabo, ICRISAT deputy director for West and Central Africa and regional coordinator of the Desert Margins Program. “Initially we used 6 grams of NPK per hill for a total of 60 kg per hectare. We then searched for a fertilizer with a higher concentration of phosphorus [the most limiting nutrient in sandy soil] and decided to use di-ammonium phosphate, requiring only 2 grams per plant and reducing total fertilizer use to 20 kg per hectare.”

West African farmers found a labor-saving method for microdosing. While one farmer goes about making holes, another follows with one vessel containing seed and another containing di-ammonium phosphate or NPK. He puts the seed and a 3-finger pinch (2 grams) of fertilizer into the hole and pushes the soil over the hole with his feet. This microdosing is supplemented with 1 gram of urea per plant 3 weeks after sowing. The result has been yield increases of 44-120 percent.