Emissions and Soil Organic Carbon in Calcareous Soils as Affected by Bone char and Phosphate Rock

Greenhouse gases (GHG), as anthropogenic emitted gases, causing global warming (Ricke and Caldeira, 2014) are among major environmental threats issued by scientists and policymakers on a daily timescale around the world. Carbon dioxide (CO 2 ) represents the major partner of GHG (Tietenberg and Lewis, 2018). Its emissions are increasing continuously because of the economic development and nowadays it reaches a critical level of growth (Ridzuan et al., 2020). Accordingly, it is necessary to reduce CO 2 emission in all productive sectors, whether agricultural or industrial. In the agricultural sector, organic residues are usually used to increase and sustain soil productivity (Getahun et al., 2020 and Schils et al., 2020), especially in low fertile soils (Elshony et al., 2020) and calcareous ones (Simpson and Simpson, 2017; Hye et al., 2019 and Motaghian et al., 2020). On the other hand, these amendments emit significant amounts of CO 2 upon their decomposition (Farid et al., 2018). Probably, such agricultural activities contribute to 30-35% of the global GHG emissions (Foley et al., 2011). Alternatively, the addition of pyroletic form of carbon to the soil, as a soil amendment, improves soil physical and chemical characteristics T STUDY aims to identify the role of bone char (BC) application to calcareous soils in reducing CO 2 emission and improving soil fertility compared to phosphate rock (PR). The bovine bone was subjected to anaerobic thermal decomposition (pyrolysis) for two hours at a temperature of 650 °C to produce bone char. A closed-system incubation experiments were conducted to follow the CO 2 emission from the soil treated with BC or PR by rates 1.25 and 2.5%. CO 2 emissions were tracked over 90 days at two different ambient temperatures (15+2 and 27+2C). Results of elemental composition of BC were similar to PR, but BC was characterized by the presence of organic carbon.The active surface groups of bone char are very similar to the phosphate rock groups, but the presence of organic matter resulted in the existence of C = C and O = C groups. Application of BC to soil increased phosphorus solubility and retention of CO 2 compared to phosphate rock (PR). Carbon dioxide (CO 2 ) immobilization was very high in high temperature (27+2C) reached 3274-3870 mg/kg soil compared to 101-242 mg/kg soil in low temperature (15+2 C) in BC-treated soils. BC application to the soil in winter increased the organic carbon from 1.1 to 1.52%, while the percentage dropped from 0.79 to 0.55 in high temperature, with increasing of the dissolved organic carbon form by 40-60 mg/kg soil.