Simultaneous cropping of maize withGliricidiasepium and relay cropping of maize withSesbaniasesban are the twoagroforestrysystems for soil fertility improvement which fit well within the small land holdings in the densely populated southern part ofMalawi, in Sub Saharan Africa. These systems have been promoted because of their postulated beneficial effects,i.c. provision of firewood and timber, restoring soil fertility, minimizing erosion. Nevertheless, crop yields in the farmers' fields are still low, which is attributed to low nutrient use efficiency due to competition between the trees and the crop for belowground resources and due to lack of synchronization between nutrient release by added treepruningsand nutrient demand by the crop.This research was designed to understand the (1) patterns of decomposition, mineralization, immobilization andremineralizationof high quality treeprunings(Gliricidiasepium andSesbaniasesban ) and low quality crop residues (pigeonpealeaves,pigeonpearoots and maizestover); (2) interactions between low and high quality organic materials (3) distributions and densities of roots of trees and crops in simultaneous cropping systems; and (4) carbon sequestering and nutrient cycling legume tree-based systems. Time of application ofpruningswas important for the synchronization of N release to N demand by the crop. Fertilizer substitution values (relative to CAN) ofgliricidiapruningswere 0.66, 0.32 and 0.20 for applications in October, December and February, respectively.Splitapplications of treepruningsprolonged mineral N in the topsoil but did not increase maize N uptake and yield.Rates of decomposition followed the order:gliricidia>pigeonpealeaves >sesbania>stover>pigeonpearoots. The rates of mixtures were in between those of individual components. In both greenhouse and field, N uptake and yield of treatments with mixtures were lower than those with treepruningsbut higher than those with crop residues. Maizestoverimmobilized N andremineralizedit again after a few months. Maize had a higher root density in the ridge (0-30 cm) thangliricidia. The reverse was true for the subsoil, suggesting little competition betweengliricidiaand maize for belowground resources. Maize was a stronger competitor for belowground resources thanpigeonpea, because of the slow initial development ofpigeonpea.Thegliricidia-maize system sequestered large amounts of carbon in biomass and roots, and increase soil carbon levels significantly. It also improved the water holding capacity and water infiltration rate. The deep rooting of trees andpigeonpeasfacilitated the pumping of nutrients from the subsoil to the topsoil. However, because of the higher crop yield and nutrient withdrawal with the harvested crop in theAgroforestrysystems compared to sole maize, nutrient depletion was also higher. Hence, the tree-legumeAgroforestrysystems will be not sustainable on the longer term without external nutrient input.