The acidic soil used in this study was collected from cropland of Rangamati, (22°39′1.8′′ N, 92°8′42.2′′ E). The sample was taken from the topsoil (0-10 cm), air-dried, and ground to pass a 2-mm sieve. The soil pH was 4.81 as determined in a 1:2.5 soil to water suspension; the soil organic matter was 15.22 g kg-1, CEC of the initial soil sample was 9.76 cmol(+) kg-1, K+, Na+, Ca2+ and Mg2+ were 0.61, 0.68, 5.00, and 1.7 cmol(+) kg-1, respectively. The residues of rice, wheat, maize, mustard, chickpea and groundnut were collected from BARI experimental plot. These residues were air-dried at room temperature and make small pieces then placed in biochar making device (made in Soil Science Division, BARI) and pyrolyzed under oxygen-limited conditions. The pyrolysis temperature was raised to the selected value of 700°C at a rate of approximately 20°C per minute and held constant for 1 h, then the biochar was allowed to cool to room temperature and ground to pass a 1-mm sieve. There were three replicates for each crop residue during the biochar-generating process. The residues and biochar were each thoroughly mixed and allowed to equilibrate for 1 h. The pH was then measured using a pH meter with a combination electrode. The pH of the residues and biochar were measured in deionized water at 1:5 (w/w) to water. Total N was determined by the modified Kjeldahl method. All cations (K+, Na+, Ca2+ and Mg2+) were extracted with 1.0 M ammonium acetate (pH 7.0) and readings were taken by AAS. They were sum up together to get the whole cation level. K, Cu, Fe, Mn and Zn were determined by NaHCO3 extraction followed by AAS reading. Boron was determined by the CaCl2 extraction method. Phosphorus was determined by Bray and Kurtz method while S by a turbidimetric method with BaCl2. Air-dried soil samples of 250 g were placed in plastic cups, and each crop residue or biochar was added at 10 g kg-1 (1%). The soil and crop residue or biochar were mixed thoroughly and then wetted with deionized water to 70% of the field water holding capacity of the soil. All cups were covered with plastic film, and a small hole was made to allow gaseous exchange but to minimize moisture loss, and then incubated at a constant 25°C. The cups were weighed every 3 days, with water added to maintain a constant moisture content throughout the experiment. The soils were sub-sampled after 1, 3, 6, 10, 20, 30, 40, 50 and 60 days to determine the soil pH. There were three replicates for each treatment with the controls having no incorporated crop residues or biochar. After 60 days of incubation, the soil samples were removed from the cups, air-dried, and ground to pass a 0.3-mm sieve. After incubation, soil exchangeable H+ and Al3+ were extracted with 1.0 M KCl and then titrated by 0.25 M NaOH to pH 7.0. The CEC of the soil samples was measured by the ammonium acetate compulsory displacement method. Exchangeable base cations were extracted with 1.0 M ammonium acetate (pH 7.0). Ca2+ and Mg2+ were measured with AAS, and K+ and Na+ with flame photometry. The soil NH4+–N and NO3−–N were extracted by 2.0 M KCl using 1:5 soil to the solution, and then were determined by the continuous flow analytical system (Skalar San++, The Netherlands). The same treatments with the incubation experiment were used in the pot trial. The experiment was carried out in a natural condition glasshouse. Air-dried soil samples of 5.5 kg were mixed with the amendments and then placed into ceramic pots. Nitrogenous fertilizer (Urea), phosphatic fertilizer (TSP) and potassic fertilizer (MoP) was added before seeded in amounts equivalent to N-255, P-50 and K-120 kg ha-1. After the preparation of pots, three maize seeds were sown in each pot. After 60 days, the whole maize plants were harvested by removing them from the individual pots. The plants were washed with distil water, oven-dried at 70ºC to constant weight before weighing the dry matter production. The plant materials were fine-ground and then acid digestion was carried out to measure the N, P, K, Ca and Mg contents with the methods mentioned above. Nutrient uptake (g kg-1) was calculated from the plant elemental analyses and the dry matter weight. After harvest of plants, soil samples were collected and ground to pass 0.3 mm sieve. Soil pH was measured in a 1:2.5 solid to water suspension. SPSS 15.0 (SPSS, Inc., Chicago, IL, USA) was used for the statistical analysis of data. A one-way analysis of variance was undertaken for each time interval of the incubations to determine significant differences between treatments. The significant effects for various treatments were detected using a t- test.