Ms Katherine Polain1, Dr Oliver Knox1, Dr Nina Siebers3, Associate Professor Brian Wilson1,2
1Department of Agronomy and Soil Science, University Of New England, Armidale, Australia, 2Science Division, NSW Office of Environment and Heritage, University of New England, Armidale, Australia, 3Institute for Bio- and Geosciences (Agrosphere), Jülich Forschungszentrum, Jülich, Germany
The continuation of sustainable agricultural practice, despite climate change and an increasing human population, presents a global challenge requiring approaches that push beyond the boundaries of current research. One solution may reside within our soil microbial communities. Australian cotton (Gossypium hirsutum) is predominantly grown in vertosols, dynamic soils that can move nutrients from the soil surface into the sub-soil and from rhizosphere to bulk soil. Whilst cultivation of crop rotations may improve soil properties, the potential impact on microbial communities in response to this regime, remains unexplored.
Our work assessed and compared microbial activity (using respiration incubations) and biomass (via substrate induced respiration), in the top- (0-30 cm) and sub- (30-100 cm) soils of continuous cotton (CC) and cotton-maize (CM) rotations at three time points (pre-, in- and post-crop) for two growing seasons, sampling in the plant line, but not targeting the rhizosphere. In addition, we used a δ18OP-HCl stable isotope method to gauge the long-term impact of crop rotation on sub-soil microbial activity.
Our results highlight that, regardless of crop rotation, sub-soil microbial activity does not significantly (P = 0.11) differ from top-soil, with sub-soil microorganisms contributing 46% to the overall profile activity. Sub-soil microbial activity only differed (P = 0.03) when cotton was in-crop, resulting in a decrease in activity. Microbial biomass was different (P = 0.00) between both soil depth and crop rotation, with sub-soils contributing 37% to the profile’s microbial biomass. The long term implementation of rotations found CC system promoting microbial activity down the entire profile, in comparison to CM (P = 0.01) . Our work emphasises the importance of considering soils beyond the surface as a significant amount of activity and, to a lesser extent, biomass is occurring below 30 cm, with crop rotation and establishment significantly influencing microbial properties beyond the crop rhizosphere.
Katherine is in her final year as a UNE PhD candidate, investigating the role of soil microorganisms in sub-soil nutrient cycling under rotational cotton crops. Prior to her PhD studies, Katherine worked as a secondary science teacher in both New South Wales and the Northern Territory. Her honours was completed at Charles Darwin University, where she studied the role of microorganisms in the acceleration of acid mine drainage. In addition to her PhD studies, Katherine continues to engage with students and the wider community to promote science education and research, when she is not spending time with her young family!