Agro-environmental impacts, carbon sequestration and profit analysis of blended biochar pellet application in the paddy soil-water system

The application of biochar pellet blended with pig manure compost was investigated to estimate its agro-environmental impacts and to evaluate its soil carbon sequestration and profit analysis during rice cultivation. The experiment consisted of four different treatments such as control as pig manure compost only, pig manure compost pellet (PMCP), biochar pellet blended with biochar and pig manure compost (4: 6 ratios, BCP), and slow release fertilizer (SRF). The application of chemical fertilizer and pig manure compost in the whole treatment except the BCP were 90-45-57 kg ha⁻¹ (N-P-K) and 2600 kg ha⁻¹, respectively, based on the recommended rates for rice cultivation at National Institute of Agricultural Sciences (NIAS). The BCP and SRF were applied with N 90 kg ha⁻¹ basis only as basal application before transplanting. The pig manure compost, phosphorous and potassium were applied at basal application while nitrogen fertilizer was applied with three separations as basal and two additional applications. Results showed that concentrations of ammonium nitrogen (NH₄-N) and nitrate nitrogen (NO₃-N) in the BCP at an early stage of rice growth were lowest among the treatments, but their concentrations in the paddy water rapidly decreased at 21 days after transplanting. For paddy soil, NH₄-N concentration in the SRF was continuously high compared to the BCP until 20 days of rice cultivation. For paddy water, phosphate phosphorous (PO₄-P) concentrations in the BCP were three fold lower than the SRF at an early stage of rice growth. Similar pattern between potassium (K) concentrations in paddy water and potassium oxide (K₂O) contents in surface soil was also observed during rice cultivation where their concentrations decreased abruptly 41 days after transplanting. Carbon sequestration and mitigation of carbon dioxide equivalency (CO₂-eq.) emission in the BCP were higher at 1.65 tons ha⁻¹ and 6.06 tons ha⁻¹, respectively, than the control while result of its profit analysis was $145.59 (KAU, Korean Allowance Unit) per hectare during rice cultivation. The rice yield were not significantly different (p > 0.05) among all treatments.