Decomposition, greenhouse gas emissions, and nitrogen release of rice straw and its derived biochar in paddy soil under anaerobic incubation
Saowalak Somboon, Sinthara Khenkhampha, Tanabhat-Sakorn Sukitprapanon, Phrueksa Lawongsa
Khon Kaen University, Soil Science and Environment, Thailand
Organic soil amendments like rice straw improve soil fertility through the decomposition process. However, the decomposition under anaerobic conditions results in CH4 production. Using pyrolysis to produce biochar may reduce CH4 production and subsequently affects nutrient availability such as nitrogen in soils. This research investigated the effects of the application of rice straw (RS, 10 t ha-1) and its derived biochar (BC, 3 t ha-1) on decomposition, greenhouse gas emissions, and nitrogen release in a 56-day anaerobic incubation experiment of submerged paddy soil. Our results showed that the RS treatment had the highest CO2 and CH4 emission rates, while the BC treatment had significantly lower emission rates, similar to the control. The CO2 emission rate of RS was higher than the BC and control from day 3, with the highest value at week 5 (352.6 g CO2 m-2 d-1). Meanwhile, the CO2 emission rate in BC increased after two weeks and was highest at week 6 (146.6 g CO2 m-2 d-1). Conversely, the CH4 emission rate of all treatments gradually increased after week 2. RS soil had the highest CH4 emission rate at week 5 (757.1 g CH4 m-2 d-1) and BC soil had the highest CH4 emission rate at week 4 (1.11 g CH4 m-2 d-1). Extractable NO3- content was higher in RS than in BC, while extractable NH4+ content was higher in BC than in RS. The highest contents of extractable NO3- and NH4+ in RS treatment were found in weeks 3 (4.7 mg kg-1) and 4 (165.0 mg kg-1), respectively. Meanwhile, the highest contents of extractable NO3- and NH4+ in BC treatment were found in weeks 4 (2.6 mg kg-1) and 5 (285.9 mg kg-1), respectively. Our findings indicated that transforming rice straw into biochar before soil application strongly reduces the decomposition and subsequently reduces CH4 and CO2 emissions from paddy soil. Furthermore, rice straw and biochar showed contrasting effects on NO3- and NH4+ availability that should be considered in fertilisation management.
Keywords: Methane emission, nitrogen, respiration, rice straw, rice straw-derived biochar, submerged soil
Contact Address: Saowalak Somboon, Khon Kaen University, Soil Science and Environment, 40002 Khon Kaen, Thailand, e-mail: parkaycogmail.com