Managing Reactive Nitrogen in Long Term Clean till and No till Organic Agroecosystems.

Organic agroecosystems have the potential to provide environmental services that promote soil conservation and health as well as reduce reactive nitrogen (N) that includes denitrification and ammonia volatilization. A 149 day N incubation was conducted under laboratory conditions to determine the effects of previous tillage management (clean/no till) and simulated freeze thaw events. Soil samples were collected from the Long Term Organic Tillage Study (LOTS) established in 2010 at the NDSU Dickenson Research and Extension Center. Treated soil samples were amended with ¹⁵N labelled urea or ¹⁵N labelled sugarbeet tops. Urea was added to determine if inorganic N cycles differently when applied to existing organic clean and no till systems. All soil samples including unamended control soils were maintained at 40, 60 and 80% of water filled pore space. The objective of this experiment is to monitor microbiologically driven processes that control N cycling: ammonification, nitrification and denitrification as well as to potentially link these processes with shifts in soil health. Results from the ongoing experiment verify that no significant ammonia volatilization occurred at 10°C, a temperature typical of Western ND where N amendments are routinely fall applied. Ammonium concentrations and nitrification in incubated soils amended with urea were significantly higher than those amended with sugarbeet irrespective of tillage management. A three way interaction, moisture by tillage by amendment, had a significant effect on the cumulative nitrous oxide (N₂O) and NO₃-N produced. We aim to identify the keystone microbial community members that control nitrification and denitrification during freeze thaw events. Gene expression (mRNA) and gene copy numbers of the amoA, nirS, nirK and nosZ genes will be measured via RT and qPCR prior to, during and after peaks in nitrification and denitrification rates. Our research will provide scientists, producers, industry and the public with information on the potential for no till organic farming systems to reduce GHG emissions and enhance soil health.