|The rapidly increasing global population, climate change and dwindling resources have made it very difficult to meet global food demand. To address the issue of food insecurity, sustainable intensification of agriculture (SIA) has been proposed. However, the consequences of poorly managed agricultural intensification can negatively affect the ecosystem. Biochar and compost application has been widely recommended as a highly promising soil fertility replenishment option to promote sustainable agriculture. In Kenya, only relatively recent few studies have been done to assess the effect of biochar applications on the quality of poor soils. This research is therefore, intended to investigate how biochar, applied alone or with compost could improve soil quality and increase maize yield in an acidic Ferralsol in Kamiti sub-catchment, Kiambu County of Kenya. Specifically, the study sort to 1) assess the effect of biochar, compost and their combined application on soil physical properties, 2) assess the effect of biochar, compost and their combined application on soil chemical properties and 3) determine the effect of biochar, compost and their combined application on maize growth and yield. To achieve the objectives, 6-month field trial was carried out on an acidic Ferralsol with high Al and Fe contents at the Kenyatta University Research Farm using the Randomized Complete Block Design (RCBD) comprising six treatments which included; control with no amendment (C), 20 t ha-1 Biochar (20B), 40 t ha-1 Biochar (40B), 20 t ha-1 Compost (20C), 40 t ha-1 Compost (40C) and 20 ha-1 Biochar + 20 ha-1 Compost (BC). During the study, data on plant height, stem diameter and leaf area were taken after every 2 weeks. Plant samples taken at the tasseling stage and soil samples taken at physical maturity stage of the maize, respectively, were dried, ground and sieves (< 2 mm) before being sent to the Soil Science laboratory of the Department of Soil Science / Soil Ecology, Ruhr University Bochum for analysis. Statistical analysis of data was done using SPSS (version 25) statistical software. The study showed that single or combined application of biochar and compost reduced soil bulk density. The reduction in bulk density followed the decreasing order BC<40B<40C<20B<20C and C. The incorporation of biochar and compost singly or in combination increased soil water holding capacity as well as aggregate stability by 56.7% (in 40B) and 71.5% (in 40C) respectively. Soil chemical properties including available phosphorus (P), electrical conductivity (EC), exchangeable K and Mg, and cation exchange capacity (CEC) were significantly increased in the amended soils than the unamended control. Plant growth parameters such as plant height, stem diameter and leaf area were increased by the application of the organic amendments with BC treatments recording the highest increases. Grain yield (GY) and hundred grain weight (HGW) were significantly improved relative to the control treatment for all organic amendment, with increases in grain yield between 12.2% (in 40B and 40C) and 22.8% (in BC). The results suggest that the application of biochar and compost can reduce soil bulk density, increase aggregate stability, water holding capacity, soil nutrient status and maize yield. The study concludes that biochar-compost-base soil management approach offer the potential for soil fertility improvement, and recommend it for adoption by farmers in Kamiti sub-catchment.