Asian Journal of Soil Science and Plant Nutrition

Declining soil organic matter and imbalanced fertiliser use threaten sustainable agricultural production in Bangladesh, where limited arable land demands efficient integrated nutrient management. This study assessed the effects of biochar, vermicompost, cowdung, and poultry manure, each combined with an Integrated Plant Nutrient System (IPNS)-based inorganic fertiliser dose, on chilli (Capsicum annuum L.) yield, soil carbon, and nutrient dynamics, compared with the recommended chemical fertiliser treatment. A field experiment was conducted during the 2018 rabi season at Shibalaya Upazila, Manikganj, using a randomised complete block design with five treatments and three replications. Soil samples collected every 30 days over five months were analysed for pH, organic carbon, and available nitrogen, phosphorus, potassium, and sulphur. Poultry manure produced the highest fresh (9.79 t ha⁻¹) and dry (2.85 t ha⁻¹) chilli yields, followed by cowdung and vermicompost, whereas biochar yielded the lowest among the organic amendments (7.83 and 2.41 t ha⁻¹, respectively). Biochar, however, was the only treatment to increase soil organic carbon, recording a 7.14% gain after five months, while organic carbon declined under all other treatments, most sharply under the recommended fertiliser (−14.30%) and more modestly under vermicompost, cowdung, and poultry manure (−9.64% to −10.71%). Soil pH and available nutrients increased initially before gradually declining, with biochar maintaining the greatest improvement in available sulphur. These findings indicate that poultry manure is the most effective amendment for enhancing short-term chilli productivity, whereas biochar shows greater potential for long-term soil carbon sequestration and soil fertility improvement, a trend observed within a single cropping season that warrants confirmation over successive seasons. The results have practical implications for integrated nutrient and soil-carbon management policy in Bangladesh and comparable smallholder farming systems.