Seasonal changes in soil bacterial processes associated with C and N cycling in dairy pasture after application of compost and manure

Mr Ian Waite1, Dr Sasha Jenkins1, Dr Bede Mickan1,2, E/Prof Lynette Abbott1

1University Of Western Australia, South Perth, Australia, 2Richgro, Jandakot, Australia

We investigated use of manure and compost in restoration of dairy pasture via effects on soil bacterial community composition and functional diversity. Bacteria can influence both retention and loss of soil C and N during the degradation of organic matter. Bacterial communities in soil amended with manure or compost in a dairy farmer field experiment were characterized in winter and summer using community profiling of 16S rRNA genes. Inorganic fertilizer was applied with 2t/ha manure, or with compost applied at 3t/ha or 6t/ha. The dominant bacterial phyla were Proteobacteria, Actinobacteria, Acidobacteria, Bacteriodetes and Firmicutes and their relative abundance was influenced by organic amendment and application rate (for compost). The occurrence of C degrading functional genes and N functional genes were predicted using Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt). Putative PICRUSt gene counts associated with breakdown of hemicellulose, cellulose and chitin were highest for manure in winter. Predicted C genes and N gene abundance of amoB associated with nitrification was lowest in winter for soil treated with 6 t/ha compost. The complexity of soil bacterial community responses to manure and compost applied to this dairy pasture highlighted reduced potential for degradation of soil C and mineralization of N and retention of C and N in soils when 6t/ha compared to 3t/ha compost or manure were applied. Dairy soil management practices that influence soil bacterial contributions which enhance C sequestration and N retention in dairy soils will limit C and N losses via greenhouse gas emission and leaching.


Ian has been working in the Soil science discipline for over 20 years. His research has focused on the use of isotopic, chemical, biochemical and molecular approaches for analysing the link between microbial community structure and function in soils. Of particular interest is how microbial communities and the processes are impacted by soil amendments of organic matter including waste by-products.

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