2.1. Soil collection The soil used in the study was collected from an arable field located at the research farm (24.37 North latitude, 88.6 East longitude and 31-m elevation above the sea level) of the University of Rajshahi, Bangladesh. The soil was passed through a 4-mm sieve to eliminate coarse rock and plant material, thoroughly mixed to ensure uniformity and stored at 4 C before use (not more than 2 weeks). The unwanted materials such as dry roots, grasses, hard stones were removed from the soil. The soil was mixed thoroughly before starting incubation experiment. A sub-sample of about 0.5 kg was taken, air dried, passed through a 2-mm sieve and used for the determination of physical and chemical characteristics. Rice straw biochar preparation Rice straw was obtained from the research farm of the Department of Agronomy and Agricultural Extension, University of Rajshahi, Bangladesh. Oven dried rice straw was pyrolyzed using Muffle furnace (Gallonhop, England) as described by (Sanchez et al., 2009). In each cycle, 250 g of crushed rice straw was used for pyrolysis. Pyrex flask of 2 L capacity was used for this purpose. For the removal of vapors and gases from working area, a bended outlet composed of glass rod was used. To avoid the entry of oxygen in reaction chamber, high temperature resistant silicon grease was used to completely seal the junction of Pyrex flask and glass rod. The increase in muffle furnace temperature (per unit time) was adjusted at 8–9 C min1 . Twenty minutes’ residence time was maintained after attaining final temperatures (400 C) in reaction chamber of muffle furnace. After 20 min, muffle furnace was allowed to cool down to a temperature of 40–50 C. After cooling, the Pyrex flask was removed from the reaction chamber and rice straw biochar thus formed was collected. 2.3. Rice straw biochar characterization A physico-chemical characteristic of rice straw biochar is given in Table 2. The ash content was estimated by heating biochar samples in a muffle furnace using the method of (Slattery, Ridley, & Windsor 1991). Biochar samples were shaken in distilled water on mechanical shaker for 90 min in a 1:20 solid:solution ratio and electrical conductivity (EC) and pH of rice straw biochar were measured. The cation exchange capacity of rice straw biochar was estimated by modified ammonium acetate compulsory displacement method (Gaskin et al., 2008). The elemental analysis (P, K, Ca, Mg, Fe, Zn, Mn, and Cu) of rice straw biochar was done after wet digestion with nitric acid (HNO3)- perchloric acid (HClO4) (Jones Jr and Case, 1990). Calcium, Mg, and micronutrients (Fe, Zn, Mn, and Cu) were determined by atomic absorption spectrophotometer (AAnalyst 100, Perkin-Elmer, Norwalk, CT, USA). Phosphorus concentration was measured after developing yellow color by vanadate-molybdate method (Chapman & Pratt, 1962), on UV–visible spectrophotometer (UV-1201, Shimadzu, Kyoto, Japan). Potassium was determined on flame photometer (PFP7, Jenway, Staffordshire, UK). Nitrogen and carbon content in biochar were analyzed on Vario Micro CHNS-O Analyzer (Elementar Analysen systeme GmbH, Langenselbold, Germany). 2.4. Plants The Bangladesh Agricultural Research Institute (BARI) released wheat variety BARI Gom 28 was used as a testing plant. The pedigree/cross of BARI Gom 28 was CHIL/2STAR/4/BOW/CROW// BUC/PVN/3/2VEE#10 CMSS95Y00624S-0100Y-0200M-17Y-010M-5Y-0M. The accession number was BAW 1141. The BARI Gom 28 was released in the year of 2012 (Paroda et al., 2012). 2.5. Incubation experiment Sieved rice straw biochar (<0.5 cm) was mixed with soil (equivalent to 1000 g oven-dried weight) at a rate of 16.60 g rice straw biochar kg1 soil. The soil was thoroughly mixed with rice straw biochar in several plastic jars after application of rice straw biochar. The plastic jars were covered with plastic lids and a small hole was made to allow gas exchange and to maintain moisture loss, and then incubated at a constant temperature of 25 C and 70% relative humidity. Soil moisture was adjusted after every 2 days by weighing several plastic jars and adding the required amount of distilled water when the loss was >0.05 g. After every incubation interval, selected soil properties and nutrient status were estimated.