The University of Sydney - Biogeochemistry Group

Dijkstra Laboratory 

Dijkstra Lab

Drought effects on soil carbon and nutrient cycling mediated by rhizosphere processes

Drought effects on soil carbon storage and nutrient cycling are examined in grassland and wheat cropping systems using innovative carbon and nitrogen isotope labelling techniques. This project will improve understanding of drought impacts on processes that occur at the interface between plant roots and soil that are vital for soil carbon storage and climate feedbacks, and sustainability of natural and agro-ecosystems.

Exploring beneficial genotype x environment x management interactions for crop yield: effects on soil health

Effects of wheat genotypes (G), environment (E, temperature and water stress), and management (M, crop rotation, fertilizer, and tillage) on soil health and key processes of carbon and nitrogen turnover are studied. Plant traits that affect belowground processes are seldom considered within breeding programs. However, better knowledge about belowground plant traits is desperately needed for sustainable agriculture. In this project the diversity of microbial components responsible for supplying nitrogen and mobilizing soil phosphorus to plants are characterised. The contribution of plant exudates from roots to stimulate nutrient cycling (rhizosphere priming) is also investigated.

Impacts of biochar on soil nitrogen and phosphorus dynamics

Effects of biochar on nutrient mineralisation, sorption/desorption are examined for biochars at different stages of oxidation. Biochar is a stable form of carbon, which could be used to enhance soil carbon. Biochar in soil is progressively more oxidised with time, and it is unclear how this aging process affects nutrient dynamics. In this project the effect of biochar aging on sorption and desorption of phosphorus are investigated, as well as nitrogen dynamics using 15N tracer techniques. The role of plants on nutrient dynamics is also investigated.

Effects of phosphorus availability on nitrogen mineralisation and loss

Effects of soil phosphorus availability on nitrogen dynamics are explored for a variety of soil types. Most nitrogen transformations in soil, including gross nitrogen mineralisation, nitrification, and denitrification are mediated by microbes. All of these microbes require phosphorus, but little is known how phosphorus availability affects these microbial processes. In this project the effect phosphorus availability on nitrogen transformations and loss (e.g., nitrous oxide emission) will be explored for soil types that differ in phosphorus and carbon content, pH and texture.

Effects of wildfires on temporal and spatial dynamics in soil carbon and nutrients

Effects of fire on soil carbon and nutrient dynamics, with soil depth and in time, are explored after wildfires in Victoria, Australia. In the summer of 2013 large forest wildfires occurred throughout Victoria. These intensive fires cause a pulse of carbon and nutrients in the soil, but little is known what their fate is after the fire. We follow soil carbon and nutrient dynamics after wildfire events in the Grampians National Park, and in Orbost State Forest, and examine how fast nutrient and different forms of organic carbon change through the soil profile.