MITIGATING NITROGEN LOSSES IN SUSTAINABLE AGRICULTURE

Agriculture practices, particularly soil management (fertilizer and manure applications) account for 74% of the nitrous oxide (N2O) emitted in the USA. Nitrous oxide is a potent greenhouse gas, 300 times more effective than CO2. Nitrous oxide is produces mainly through a processes called denitrification, which convert nitrate nitrogen to nitrous oxide or N2 gas (atmospheric nitrogen). Denitrification occurs typically after large rain events when the soil stays saturated for several days at a time. Several countries around the world are beginning to create N2O emission factors for different agricultural management practices. An example of an emission factor would be to what degree does injecting manure versus broadcast applying it reduces or increases N2O emissions or what increase in N2O emissions do you observe when you apply (x) amount of nitrogen fertilizer above what the crop requires. These emission factors will be important in regulation and policy making and a similar requirements to quantify these emissions may occur in the USA in the near future. The most common way to measure N2O in the field is called the static chamber method. Here a chamber is placed in the field and left for 30 minutes and air sampled from within the chamber 4 times. The air is analyzed for N2O and the daily flux of N2O is calculated and eventually can be interpolated for the whole growing season, linking together regular samplings during the growing season. The concern with static chambers is that when you sample you don't know if you have missed a large emission event or if you measure large emissions you don't know if that is that is the highest part of the flux emission. This could lead to over or underestimation of N2O emission estimates. It is critical that we have measurements representative of field conditions for emission factor estimates, as well when these results are used in large climate change models. To address these concerns we are developing a method of continuous N2O measurements using automated chambers that sample the soil every 150 minutes rather than once or twice a week. We run the air into a trailer that has a N2O analyzer, which produces real-time results transmitted back to us at North Carolina State University. We are going to compare these results the static chamber method to determine if there is significant over or under estimation of emissions. In addition, we are going to develop a method of incorporating the continuous measurements into a static chamber study, this would only require only a limited number of auto-chambers. The chambers would be used to guide researchers on when the main N2O flux events is occurring and allow them to modify the static chamber calculations, making them more accurate to real world conditions.Using these newly developed methods we are going to evaluate different best management strategies used by farmers to mitigate nitrogen losses in the field. Anticipated evaluations will include comparing different organic amendment sources, legume cover crops and the use of enhanced efficiency nitrogen fertilizers. Enhanced efficiency fertilizers tend to slow the rate of nitrogen release into the soil either through physical barriers or modifying the nitrogen cycle. Slowing the release helps prevent nitrogen loss to the atmosphere through ammonia volatilization and could potentially reduce N2O emissions. In addition to the N2O measurements, we will measure ammonia volatilization and estimate nitrate leaching. By tracking the main nitrogen loss pathways as well was how much nitrogen is taken up by the plant we are able to create a nitrogen balance. This is used to determine nitrogen use efficiency. A higher nitrogen use efficiency means more of the nitrogen that is applied to being captured by the plant, rather than lost from the system. This is not only important economically to the farmer but also means the system is more sustainable from an air quality, greenhouse gas and water quality perspective.