In calcareous soils, the effects of biochar characteristics on maize growth are least understood. In a laboratory study, citrus peel biochar (CPB) and green waste biochar (GWB) were produced by slow pyrolysis at 300°C with 20 min residence time. Electrical conductivity, pH, ash, and nutrients i.e. N, P, K, Ca, Mg, S, Zn and Mn content in GWB were greater than CPB. Citrus peel biochar had wider C:N, C:P and C:S ratios than GWB. Efficacy of these biochars was tested for maize growth and nutrient uptake, and chemical properties of calcareous soil. Maize hybrid (Syngenta-6621) was grown in a greenhouse pot trial by using calcareous soil amended either with CPB or GWB at application rates of 0.0, 0.5, 1.0, 1.5 and 2.0% (w/w) along with NPK fertilizers. Our results revealed that increasing rates of CPB, effectively improved maize plant height; fresh and dry weight; chlorophyll content and photosynthetic rate; and N, P and K uptake. At varying GWB application rates, maize fresh and dry weight; and N and P uptake was improved. Regarding plant growth and nutrient uptake, the overall response of CPB was better than GWB. At 2.0% application rate, CPB resulted better fresh weight (19%), dry weight (24%), plant height (20%), N uptake (42%), P uptake (36%) and K uptake (30%), than from the treatment having same rate of GWB. Due to biochar addition, the highest percentage of N and P recovery (5.3 and 6.6%, respectively) was obtained at 2.0% CPB application rate, while the highest K recovery (9.8%) was obtained at CPB application rate of 0.5%. At 2.0% application rate, CPB decreased soil pH up to 7.96 and increased soil organic carbon up to 1.25%, and GWB increased soil electrical conductivity up to 1.45 dS m -1. Conclusively, CPB produced at 300°C pyrolysis temperature with 20 min residence time, could be effectively used at the rate of 2.0%, for improving maize growth and nutrient uptake, and chemical characteristics of calcareous soil.
