Tropentag 2023, September 20 - 22, Berlin, Germany "Competing pathways for equitable food systems transformation: trade-offs and synergies."

Decomposition, greenhouse gas emissions, and nitrogen release of rice straw and its derived biochar in paddy soil under anaerobic incubation

Khon Kaen University, Soil Science and Environment, Thailand

Abstract

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