Shallow autumn tillage does not reduce CH₄ emission from an Andisol paddy field in Morioka, a cold region in Japan

Abstract

　To mitigate CH₄ emission from paddy fields, accelerating the decomposition of the incorporated rice straw during the fallow season would be a practical strategy. Various ways to accelerate the straw decomposition rate have been proposed, but their effectiveness in cold regions has not been confirmed. In this study, the use of shallow autumn tillage to incorporate straw in the soil and its potential to mitigate CH₄ emission during the following rice growing season were evaluated in an Andisol paddy field in Morioka, a cold region in Japan. A japonica rice cultivar, ‘Akitakomachi’, was planted and grown from 2012 to 2014 under consistent conditions, but with two autumn tillage and straw incorporation treatments: conventional (15 cm) and shallow (7 cm). CH₄ fluxes from the plots were measured using a closed-chamber method throughout the 3 years. Overall, CH₄ emission did not differ between the conventional and shallow tillage plots in this study. However, CH₄ emission differed greatly among the years, especially during early rice growth stages, and the differences were related to the temperatures but not the soil moisture content during the previous fallow season. Simulation of water contents during the fallow period suggested that the percolation rate was sufficiently high to create more aerobic soil conditions during the fallow season in both the conventional and the shallow autumn tillage treatments. These results suggest that the soil water was neither so high nor so low that it retarded rice straw decomposition in the fallow season. The results suggest that shallow autumn tillage will not necessarily reduce CH₄ emission during the following growing season in an Andisol rice paddy in a cold region in Japan.