In the high rainfall zone of southern Australia, dryland crop yields are often constrained by naturally dense clay subsoils that are poorly structured, restrict the movement of air and water and impede root growth. A decade of research has shown that subsoil manuring – the incorporation of large volumes of nutrient-rich organic matter into the subsoil by deep ripping – can significantly improve these hostile subsoils and increase crop yields due to sustained changes in the soil physical, chemical and biological properties.
Although soil microbial communities are considered to be one of the key agents in this process there has been minimal research into their role in ameliorating subsoil constraints and increasing crop yields following subsoil manuring. This ongoing investigation aims to uncover the main microbiological processes involved in subsoil manuring and establish a relationship between soil microbial communities, soil physicochemical characteristics and crop performance. In order to do this, analysis of the structure and function of the soil microbial community is being paired with measurements of the organic amendment, soil and plant. This will enable us to understand the linkages between plant-soil-microbial factors after subsoil manuring and identify the key drivers of improved yields.
Bacterial and fungal communities in the subsoil have been found to change over time in response to subsoil manuring and are affected by a range of factors including soil pH, sodicity, plant roots and type of organic matter applied. Results suggest that the success of the subsoil manuring intervention depends on the stimulation of the native soil microbial community, and that amelioration leads to a shift in both soil properties and microbial communities to more closely resemble those found in the topsoil. A greater understanding of the role of soil microbiology in subsoil amelioration will allow for the exploitation of these processes for enhanced productivity and profitability of dryland agricultural production systems.