Effects of green manure application on soil microbial communities and activities in the decontaminated sandy soil paddy field in Fukushima, Japan

On March 11, 2011, Japan experienced an unprecedented earthquake off the Pacific coast of Tohoku, and suffered the direct and long-term effects of the earthquake and tsunami in the area. In Fukushima prefecture, agricultural land contaminated with radioactive Cesium from the Fukushima Daiichi Nuclear Power Plant. Therefore, surface soil were removed for deconamination, and low fertility sandy soil was covered. Organic matter input is necessary to increase soil organic matter and green manure application is an effective method to improve soil fertility in the paddy field. Soil microbes and enzyme activities are sensitively responded to organic matter addition, but their dynamics on the dressed field are not well investigated. In this study, we focused on changing the microbial community, diversity and enzyme activities along with the green manure decomposition process in the sandy soil dressed paddy field in Japan. The green manure of hairy vetch and oat were harvested and incorporated in May 2020 and their decomposition process as cellulose and hemicellulose contents were determined. Soil bacterial communities were analyzed using 16S amplicon sequencing. The green manure was rapidly decomposed within the first 13 days, and they did not remain 50 days after green manure incorporation. Soil microbial biomass carbon was higher in the M treatment after GM treatment, but was not significant between treatments after 50 days. Dehydrogenase and β-glucosidase activities changed during the harvesting period, but did not correlate with GM decomposition. Microbial diversity (OTU numbers and Shannon index) also changed with GM application, but they were not associated with GM decomposition. Soil prokaryotic communities and some bacteria ( Baciili and Chlorolfexi ) are significantly influenced by GM treatment. However, Clostrida was not affected by GM. Mixed green manure treatment showed significantly rapid hemicellulose decomposition than other treatments. In this process, Anaerolineae were negatively correlated with the decreasing of hemicellulose in this treatment. These results showed that GM treatment affected microbial communities, and their response was active during the decomposition process.