Rotational woodlots and Ngitiri fallows have considerable amount of carbon storage and potential for soil fertility improvement though not well quantified. The objectives of this study were to develop allometric models for determination of above-ground carbon, quantify above and below-ground carbon, estimate soil organic carbon stocks and assess soil fertility status in rotational woodlots and Ngitiri in Meatu District, Tanzania. In each system, the experiment comprised 3 treatments, replicated 3 times in 8 and 10 year-old Acacia fallows. Ninety sample trees were measured for diameter at breast height (DBH) and height, and used in destructive sampling for development of allometric models. Several models were developed and the best fit model based on higher coefficient of determination (R 2 ) and low standard error was used to predict above-ground carbon for all tree components. Soil samples at 20 cm intervals were taken from 100 cm profile at each plot, standard routine soil analysis for organic carbon, nitrogen, phosphorus and potassium was done. The best fit models for A. tortilis and A. polyacantha were those which used DBH as predictor variable for different tree species. The highest total tree carbon storage under woodlots and Ngitiri was 22.0 ± 3.14 and 17.18 ± 2.13 t ha -1 respectively. In two years Ngitiri and woodlots captured between 6.4 to 9.16 and 1.41 to 5.02 t ha -1 respectively of above-ground carbon. Ngitiri and woodlots captured 91.3 and 60.7 t ha -1 of soil organic carbon respectively in two years. Total nitrogen, inorganic nitrogen and Olsen phoshorus was higher in woodlots than Ngitiri while potassium was low in woodlots than Ngitiri.The best fit models for predicting above-ground carbon in Acacia species are those which used DBH as predictor variables, though height may as well be used in some cases. Rotational woodlots and Ngitiri have the potential for carbon storage and soil fertility improvement. Though, Ngitiri can sequester more carbon than woodlots while woodlots have higher potential for soil fertility improvement. Therefore,iii it is recommended that Ngitiri be used for carbon sequestration while woodlots are appropriate for above-ground carbon storage and soil fertility improvement.