In considering how best to improve poor agricultural soils in parts of Africa and improve crop productivity (Nature 483, 525–527; 2012), micro-dosing would be a practical and inexpensive way to balance soil nutrients.

Developing countries tend routinely to use fertilizers containing only nitrogen, but a balanced supply of nutrients is essential for a crop to flourish. Urea application doubled in Africa during 1975–2005, causing an increase in the ratio of applied nitrogen to phosphorus and potassium (see go.nature.com/eanpxq). Although urea is cheap and its use is tempting to poor farmers in need of a rapid return on investment, it selectively depletes soil phosphorus, potassium and micronutrients. Ultimately, this imbalance will render the nitrogen ineffective.

Micro-dosing soil with small quantities of correctly proportioned 'NPK' fertilizer would significantly increase crop yields for smallholder farmers who are unable to afford large-scale applications. This simple technique involves dispensing measured amounts of the fertilizer using a bottle cap, for example, into planting holes during sowing. The returns will more than justify the small investment.