Carbonaceous Greenhouse Gases and Microbial Abundance in Paddy Soil under Combined Biochar and Rice Straw Amendment

Little is known about the carbonaceous greenhouse gases and soil microbial community linked to the combination of biochar (BC) and rice straw (RS) in paddy soils. The objectives of this research were to evaluate the effects of combining BC and RS on (1) CH4 and CO2 production from paddy soil, (2) archaeal and bacterial abundance, and (3) rice grain yield. The experiments consisted of a pot trial and an incubation trial, which had a completely randomized design. The experiments included five treatments with three replications: (a) the control (without BC, RS, and chemical fertilizer (CF)); (b) CF; (c) BC 12.50 t ha(-1); (d) RS 12.50 t ha(-1); and (e) combined BC 6.25 t ha(-1) + RS 6.25 t ha(-1) + CF. In the sole RS treatment, CH4 production (0.0347 mg m(-2) season(-1)) and the archaeal and bacterial abundance (5.81 x 10(8) and 4.94 x 10(10) copies g(-1) soil dry weight (DW)) were higher than outcomes in the sole BC treatment (i.e., 0.0233 mg m(-2) season(-1) for CH4 production, and 8.51 x 10(7) and 1.76 x 10(10) copies g(-1) soil DW for archaeal and bacterial abundance, respectively). CH4 production (0.0235 mg m(-2) season(-1)) decreased significantly in the combined BC + RS + CF treated soil compared to the soil treated with RS alone, indicating that BC lessened CH4 production via CH4 adsorption, methanogenic activity inhibition, and microbial CH4 oxidation through bacterial methanotrophs. However, the archaeal abundance (3.79-5.81 x 10(8) copies g(-1) soil DW) and bacterial abundance (4.94-5.82 x 10(10) copies g(-1) soil DW) in the combined BC+ RS + CF treated soil and the RS treated soil were found to increase relative to the treatments without RS. The increase was due to the easily decomposable RS and the volatile matter (VM) constituent of the BC. Nevertheless, the resultant CO2 production was relatively similar amongst the BC, RS, and BC + RS treated soils, which was indicative of several processes, e.g., the CO2 production and reduction that occurred simultaneously but in different directions. Moreover, the highest yield of rice grains was obtained from a combined BC + RS + CF treated soil and it was 53.47 g pot(-1) (8.48 t ha(-1)). Over time, the addition of BC to RS soil enhanced the archaeal and bacterial abundance, thereby improving yields and reducing CH4 emissions.