Nitrogen Cycle Complexity


Here at the Bruns lab we are interested in learning how the application of manure and other carbon sources impact specific reactions associated with the nitrogen cycle. We are also interested in identifying how past management history may influence the nitrogen cycle and greenhouse gas emissions.


Agriculture accounts for 75-80% of anthropogenic nitrous oxide (N2O) emissions in the U.S. Denitrification in fertilized soils and during animal waste handling results in about 60% and 30% of N2O emissions, respectively. This proposal aims to gain knowledge of how soils and manures can be managed to counteract denitrification and to promote a bacterial process known as nitrite ammonification, the end product of which (ammonium) is not lost directly to the atmosphere. We hypothesize that nitrite ammonification occurs to a significant extent in soils managed using no-till practices and labile carbon amendments, either with animal or green manures. Particularly in combination, these practices increase labile soil carbon content and improve soil water-holding capacity, and they are being adopted by farmers in response to more variable and extreme weather resulting from climate change. Innovative soil management, such as manure injection currently evaluated at Penn State's Sustainable Dairy Cropping Systems project, minimizes disturbance during carbon enrichment and needs to be assessed for its effect on denitrification and nitrite ammonification. Moreover, manure storage and handling practices favoring nitrite ammonification over denitrification need to be identified. Specific objectives of this proposal are to 1) measure bacterial groups and labile carbon substrates in manures from dairies of varying size and manure handling systems; 2) measure GHGs and temporal and spatial changes in nitrite ammonification and denitrification in no-till soils of the Sustainable Dairy Cropping Systems project; 3) conduct soil mesocosm studies to determine relationships between substrates, physicochemical conditions, microbial processes, and GHGs to understand conditions favoring nitrite ammonification over denitrification.

Conceptual model of N forms related to carbon pools in soil.


Below are some links to other reputable sources of information regarding climate change, the nitrogen cycle,  and agriculture: