My PhD research is focused on identifying the impacts that disturbances have on specific nitrogen cycling reactions in agroecosystems. Globally, only 50% of the N amended to soils is taken up by crops. Where does the other 50% go? Well, it could be transformed into gases and subsequently lost to the atmosphere, or it could be lost through runoff or leaching. Most gaseous species of N can have negative impacts on the environment, with the exception of N2.
Through my PhD I aim to expand on the cumulative knowledge of N-cycling in agroecosystems and to contribute to the understanding of how agricultural practices can support sustainability and decrease greenhouse gas emissions.
Through my PhD I aim to expand on the cumulative knowledge of N-cycling in agroecosystems and to contribute to the understanding of how agricultural practices can support sustainability and decrease greenhouse gas emissions.
Specific questions that we are addressing include:
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1. How do N-cycling reactions differ between long-term tillage practices?
For this objective, we are interested in determining how genes associated with specific N-cycling reactions including dissimilatory nitrate reduction to ammonium (DNRA) and non-denitrifier N2O reduction differ in moldboard plough, chisel/disk, and no-till plots. It is thought that systems that resemble more natural systems, which in this case would be no-till, will promote tighter N-cycling and less loss of N from the system. 2. How does N2O emission differ between the tillage practices? Higher N2O emissions from no-till soils have been observed from soils that were recently (up to 15 years) transitioned to no-till from a more conventional tillage practice. However, it is thought that over time, no-till should result in similar, or perhaps even lower, N2O emissions compared to tillages. 3. Are there differences in the abundance of these DNRA or non-denitrifier N2O reducers in the rhizospheres of different crops or during the growing season of cash crops? All plants exude a mix of carbon sources to the soil from the roots. These carbon sources can vary between plants and also differ across the growing season of plants. As such, it is expected that the abundance of DNRA and non-denitrifier N2O reducers will change in response to the A) crop and B) growth stage of the crop. |
4. How does harvesting impact N-cycling in alfalfa & orchard grass?
Alfalfa and orchard grass is considered a perennial mix and is often harvested multiple times throughout the growing season. Harvest results in the above ground biomass removal leaving behind a few centimeters of shoot. Once the stand accumulates enough growth another harvest will take place. This stress may be causing a release in exudates from the plant roots, thereby stimulating the growth of certain microorganisms. 5. Does termination time of alfalfa & orchard grass have an impact on A)N2O emissions and B) the quantity of specific N-cycling genes? To keep living roots in the ground over winter it is common to terminate alfalfa/grass systems in the spring before cash crop planting. However, waiting until spring to terminate the winter cover can cause practical issues for the farmer in the spring, especially if it is particularly wet or cold spring. As such, terminating in the fall may be a viable option in no-till systems that allow for the farmer to keep roots and shoots over winter. Determining if termination time effects N-cycling will be very informative for researchers and agricultural service providers. |
