Low soil phosphorus availability is a primary constraint to crop growth in many low-input agroecosystems. The development of crop genotypes with root traits capable of increasing phosphorus acquisition may sustain soil fertility in such systems by increasing crop biomass, thereby reducing phosphorus loss via erosion.  Examples of this are provided from two recent studies, one in Costa Rica and one in Mozambique, in which common bean genotypes with root traits improving phosphorus acquisition reduced P loss through erosion. The phosphorus-extractive genotypes also had substantially greater biological nitrogen fixation and greater biomass production. These results indicate that phosphorus-extractive crop genotypes may sustain soil fertility better than conventional genotypes in low-input systems.