Interspecific root/rhizosphere interactions affect phosphorus (P) uptake and the productivity of maize/faba bean and maize/wheat intercropping systems. The aim of these experiments was to determine whether manipulation of maize root growth could improve the productivity of the two intercropping systems. Two near isogenic maize hybrids (the larger-rooted T149 and smaller-rooted T222) were intercropped with faba bean and wheat, under conditions of high- and low-P availability. The larger-rooted T149 showed greater competitive ability than the smaller-rooted T222 in both maize/faba bean and maize/wheat intercropping systems. The higher competitive ability of T149 improved the productivity of the maize/faba bean intercropping system in P-sufficient conditions. In maize/wheat intercropping systems, root growth, shoot biomass, and P uptake of maize were inhibited by wheat, regardless of the P-supply. Compared with T222, the larger-rooted T149 suffered less in the intercropping systems. The total biomass of the maize/wheat intercropping system was higher for wheat/T149 than for wheat/T222 under low-P conditions. These data suggested that genetic improvement of maize root size could enhance maize growth and its ability to compete for P resources in maize/faba bean and maize/wheat intercropping systems. In addition, depending on the P availability, larger maize roots could increase the productivity of intercropping systems. Interspecific root / rhizosphere interactions affect phosphorus (P) uptake and the productivity of maize / faba bean and maize / wheat intercropping systems. The aim of these experiments was to determine whether manipulation of maize root growth could improve the productivity of the two intercropping systems. Two larger isogenic maize hybrids (the larger-rooted T149 and smaller-rooted T222) were intercropped with faba bean and wheat, under conditions of high- and low-P availability. The larger-rooted T149 showed greater competitiveness than the smaller-rooted T222 in both maize / faba bean and maize / wheat intercropping systems. The higher competitive ability of T149 improved the productivity of the maize / faba bean intercropping system in P-sufficient conditions. In maize / wheat intercropping systems, root growth, shoot biomass, Compared with T222, the larger-rooted T149 poor less in the intercropping systems. The t Total biomass of the maize / wheat intercropping system was higher for wheat / T149 than for wheat / T222 under low-P conditions. These data suggest that genetic improvement of maize root size could enhance maize growth and its ability to compete for P resources in maize / faba bean and maize / wheat intercropping systems. In addition, depending on the P availability, larger maize roots could increase the productivity of intercropping systems.