Dijkstra Laboratory 

The interactive effects of grazing (clipping), nitrogen and phosphorus addition on carbon and nutrient dynamics are examined in a grassland near the Centre for Carbon, Water and Food in Camden, NSW. This project will fill important knowledge gaps in managing grasslands for sustainable production.

This project will determine soil-plant combinations that have potential to maximise organic carbon sequestration in the soil. Mineral associated organic matter (MAOM) is the key element for the long-term preservation of soil organic matter (SOM). Crop/pasture plants supply different organic compounds in the soil through organic residues, root biomass and exudates. Microbial processing of plant organic compounds is highly variable, with labile compounds mineralised quickly and believed to stabilise SOM by forming MAOM. Our research will determine carbon use efficiency of plant organic compounds and assess the efficiency of organic compounds of plant and microbial origin to form MAOM with different soil minerals. This project will provide the first comprehensive examination of the relative roles of plant exudates in relation to soil mineralogy in determining SOM stabilisation.

This project will investigate how much carbon plants need to invest belowground in return for water and nutrients. By using economic principles of supply and demand the project quantifies carbon expenditure for water and nutrients in grasslands and crops under different climate and land management scenarios. Novel triple and quadruple isotope labelling techniques are used to explore the dependency of carbon investment on plant-microbial interactions and availability of belowground resources.

In this project microbial carbon use efficiencies of specific substrates are examined and to what degree they are controlled by soil properties, including pH, texture and various carbon fractions. The interaction between substrate type and microbial community (fungi vs. bacteria) on soil aggregation is also assessed. This project will provide understanding about the fate of plant inputs (litter, exudates) in soil. 

Soil pH has strong effects on mineralization and loss of nitrogen and phosphorus in soil, which can influence how efficient nitrogen and phosphorus fertilizers are taken up by agricultural crops. In this project soil pH effects on plant uptake, mineralization and loss of nitrogen and phosphorus are assessed and associated fertilizer use efficiency in cropping systems.