Fertilizer has long been treated as a purely industrial product: mined minerals, chemical reactors, and massive global supply chains delivering nutrients to fields. But a new idea is beginning to take shape in agricultural science, and it sounds almost like science fiction. Instead of spreading chemicals across soil, farmers may increasingly rely on living organisms designed to feed crops from below. Engineered biofertilizers—microbes modified to help plants access nutrients more efficiently—represent one of the most intriguing shifts underway in modern agriculture.