The efficiency in the use of nitrogen (N) and potassium (K) may be severely limited in soils with high rates of nutrient loss and that also tend to harden and restrict root growth. The choice of legume residues should take into account the nutrient supply and the need for soil improvement. We assessed the capacity of alley cropping systems to enhance root development, increase nutrient uptake and improve the use of N and K in maize. The experiment included six treatments with residues of four perennial Fabaceae: Clitoria + Gliricidia (C + G); Acacia + Gliricidia (A + G); Leucaena +Gliricidia (L + G); Leucaena + Clitoria (L + C); Leucaena + Acacia (L + A) and a control without legumes. We determined chemical and physical indicators, root length density (RLD) and an efficiency index. The results demonstrate the effects of amending soils with N and K with root growth constrained by hard‐setting. The application of combined residues improved the physical properties of hard‐setting soils and increased basic cations in the topsoil. A combination of residues with N and K fertilizer increased the maize yield. The relative efficiency and RLD in the L + A treatments were highest as a result of increased application through the residues containing N and K. The choice of residues for hard‐setting soils should take into account the supply of nutrients as well as the improvement of soil properties.