Biochar and N-Fertilisation Effects on Greenhouse Gases Emissions and Productivity of Low Land Rice

Abstract

Paddy field is an important source of methane (CH4) and nitrous oxide (N2O) which causes global warming. Biochar has been reported to mitigate the emission of these gases. However, its efficacy under co-application with nitrogen (N) and zero tillage is largely unknown. We conducted a two-year study at AfricaRice researcher centre Bouake, Cote Divoire to investigate the potential of combined biochar and nitrogen fertiliser (N) application in mitigating N2O and CH4 emissions and improving low land rice yield and soil properties under no tillage. A completely randomized block design composed of 12 treatments and three replications were used. Treatments included: control (C1N2, tillage with hoe + 120 kgN/ha ), low biochar (B1, biochar at 3 t/ha ), high biochar (B2, biochar at 6 t/ha), activated biochar (BA, biochar at 3 t/ha + cow dung at 5 t/ha), medium N (N2, 120 kgN/ha), high N (N3, 180 kgN/ha), low biochar and low N (B1N1, biochar at 3 t/ha + 60 kgN/ha), low biochar and medium N (B1N2, biochar at 3 t/ha + 120 kgN/ha), low biochar and high N (B1N3, biochar at 3 t/ha + 180 kgN/ha), high biochar and low N (B2N1,biochar at 6 ton/ha + 60 kgN/ha ), high biochar and medium N (B2N2, biochar at 6 t/ha + 120 kgN/ha), high biochar and high N (B2N3, biochar at 6 t/ha + 180 kgN/ha). Findings indicated that rice straw biomass was most responsive to treatment application. C1N2 recorded highest cumulative CH4 emission (195.04 kg/ha) while lowest CH4 emission (98.15 kg/ha) was observed in BA. N application enhanced CH4 emission than biochar but biochar promoted N2O emissions. B2N2 produced highest N2O emission (4.14 kg/ha) while the lowest N2O emission (0. 48 kg/ha) occurred in B1. Activation of biochar with cow dung, BA did not trigger any major change in either CH4 or N2O emission compared to B1 but significantly decreased GWP and GHGI compared to C1N2. Relative to B2N2 and B2N3, GWP, GHGI and carbon sequestration were significantly decreased by B1. Increasing biochar increased carbon sequestration. More so, increasing N with or without biochar progressively increased rice yield whereas increasing biochar alone without N from B1 to B2 decreased rice yield. B2N3 and B2N2 both significantly promoted rice yield more than C1N2. In contrast, increasing biochar without N, from B1 to B2 increased rice harvest index similar to BA. Weak and positive correlations were found between rice morphological traits and GHG emissions as well as GHG emission and rice yield. Regardless of rates, neither the application of biochar with or without N nor the application of N with or without biochar significantly impacted soil properties. Co-application of N application with biochar decreased GHGs emissions, sequestered carbon and improved rice yield over the current farmer’s management practices. B2N3 is an adoption candidate by farmers due to its high rice yield potential and relative environmental friendliness.