Data on zero tillages affect on greenhouse gas emissions

The Australian Government has recommended that farmers move from cultivation-based dryland farming to reduced or zero tillage systems. The private benefits could include improvements in yields and a decrease in costs while the public benefits could include a reduction in greenhouse gas (GHG) emissions due to a diminution in the use of heavy machinery. The aim of this study is to estimate and compare total on-farm GHG emissions from conventional and zero tillage systems based on selected grain crop rotations in the Darling Downs region of Queensland, Australia. The value chain was identified, including all inputs, and emissions. In addition, studies of soil carbon sequestration and nitrous oxide emissions under the different cropping systems were reviewed. The value chain analysis revealed that the net effect on GHG emissions by switching to zero tillage is positive but relatively small. In addition though, the review of the sequestration studies suggests that there might be soil-based emissions that result from zero tillage that are being under-estimated. Therefore, zero tillage may not necessarily reduce overall GHG emissions. This could have major implication on current carbon credits offered from volunteer carbon markets for converting conventional tillage to reduced tillage system.

澳大利亚政府已建议农户摒弃基于传统耕作的旱地农业（dryland farming）模式，转而采用少耕或免耕耕作体系。该模式可为从业者带来私人收益：包括作物产量提升与生产成本降低；同时可产生公共收益：因重型机械使用量缩减而实现温室气体（Greenhouse Gas, GHG）排放削减。本研究旨在针对澳大利亚昆士兰州达令唐斯（Darling Downs）区域内的选定谷物轮作体系，评估并对比传统耕作与免耕耕作体系的农场内总温室气体排放量。研究已梳理出涵盖所有投入环节与排放环节的价值链条（value chain），此外还综述了不同种植体系下的土壤碳汇（carbon sequestration）与一氧化二氮（nitrous oxide）排放相关研究。价值链条分析结果显示，转向免耕耕作对温室气体排放的净效应为正向，但幅度相对有限。不过，针对碳汇相关研究的综述表明，免耕耕作可能引发此前被低估的土壤相关排放。由此可见，免耕未必能够全面降低温室气体总排放量。这一结论或将对当前自愿碳市场（volunteer carbon markets）中，针对将传统耕作转换为少耕体系的碳信用（carbon credits）政策产生重大影响。