SUMMARYThe soil water storage, soil water content, available water content and soil water balance under various cover crop residue management practices in a Nitisol were evaluated in a field experiment at the Kabete Field Station, University of Nairobi. The effects of surface mulching, above and below ground biomass and roots only incorporated of (mucuna pruriens), Tanzanian sunnhemp (Crotalaria ochroleuca) and Vetch (Vicia benghalensis) cover crops, fertilizer and non fertilized plots on soil water balance were studied. Tomato (Lycopersicon esculentum) was used as the test crop. Since water content was close to field capacity, the drainage component at 100 cm soil depth was negligible and evapotranspiration was therefore derived from the change in soil moisture storage and precipitation. Residue management showed that above and below ground biomass incorporated optimized the partitioning of the water balance components, increasing moisture storage, leading to increased tomato yields and water use efficiency. Furthermore, vetch above and below ground biomass incorporated significantly improved the quantity and frequency of deep percolation. Soil fertilization (F) and non fertilization (NF) caused the most unfavourable partitioning of water balance, leading to the lowest yield and WUE. Tomato yields ranged from 4.1 in NF to 7.4 Mg ha-1 in Vetch treated plots. Vetch above and belowground biomass incorporated had significant (p ≤ 0.1) yields of 11.4 Mg ha-1 compared to all other residue management systems. Vetch residue treatment had the highest WUE (22.7 kg mm-1 ha-1) followed by mucuna treated plots (20.7 kg mm-1 ha-1) and both were significantly different (p ≤ 0.05) compared to the others irrespective of residue management practices.