A growing imbalance between phosphorus and nitrogen-based fertilizer use throughout Africa might reduce crop yields for subsistence farmers by nearly 20% by 2050 relative to contemporary yields. A new study from the International Institute for Applied Systems Analysis (IIASA) documents the current underuse of phosphorus-based fertilizer throughout Africa, which results in 10% lower crop output than would be achieved by an ideal fertilizer balance. Because phosphorus must be mined, and reserves are limited, phosphorus-based fertilizers are more expensive than nitrogen-based fertilizers, and the gap in price will likely persist and expand. Consequently, poorer farmers increasingly will be forced to depend on nitrogen-based fertilizers, further exacerbating the current imbalance. Decreases in crop yields would further endanger the already tenuous food supplies needed to feed the rapidly growing African population. Thus, under conventional development projections, the problem of non-optimal fertilizer use would exacerbate hunger and malnutrition in Africa, a disquieting, but not inevitable scenario.