Soil microbial community structures and activities in relation to nitrogen cycling in two contrasting soils in Malawi – community responses to added carbon

Akane Chiba¹, Yoshitaka Uchida¹, Satoshi Ishii2, Patson Nalivata3, Keston Njira3

1 Graduate School of Agriculture, Hokkaido University, Kita9 Nishi9, Kita-ku, Sapporo, Hokkaido 0608589, Japan,,

2University of Minnesota, USA

3Lilongwe University of Agriculture and Natural Resources, Malawi


Fallowing is known as one of the conservative farm management techniques, which results in high crop yields and quality, potentially due to some changes in soil microbial structures and activities. However, few studies have investigated these changes in sub-Saharan Africa, where decreasing soil fertility is a serious issue. In this study, we examined the effects of different farm managements on the soil microbial community structures using soils sampled in Malawi, sub-Saharan Africa. Two sites located next to each other, within 100 m, were selected. One was the conservatively managed soil (maize after bean, followed by 1 year fallow) and another was the intensively farmed soil (maize after maize, continuous). Meanwhile, the addition of crop residues, including rice straw, is known as a technique to prevent the decrease of soil fertility. Thus, we performed incubation studies to investigate soil microbial responses of these soils to rice straw application. Changes in the bacterial diversities in these soils following the addition of rice straw were investigated with 16S rRNA gene approach on Miseq. Similar trends of nitrogen activities, such as the rapid decrease in soil NO3-N after rice straw application, were observed in the two soils. Bacterial community structural analyses suggested that the rapid increases in the ratios of Firmicutes and Betaproteobacteria to added carbon were different in the two soils. Future studies should focus more on functional genes to understand the gap between soil microbial activities and community.