Greenhouse Gas Emissions and Soil Inorganic N Under Dryland Winter Wheat Fallow Management Systems As Affected By Climatic Variability in Semi-Arid Great Plains.

Semi-arid Great Plains, the major wheat producing area of the US, is challenged by climatic variability. Greenhouse gases (GHGs) emissions from dryand wheat-fallow fields under conventional (CT), no-tillage (NT) and chemical free organic (CF) management systems were measured from May 2011 to July 2013 in southeaster Wyoming. The objective of the study was to determine the effect of long-term management systems on GHG emissions and soil nitrate (NO3) under varying precipitation years. Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were collected using closed vented chambers. The year 2011was a wet year (20% more precipitation than 30-yr average), whereas 2012and 2013(January to July: 39% below) were dry years that received 64% and 39% les precipitation, respectively. Consequently, water filled pore space was higher in the fallow phase than in the wheat phase in 2011 compared to the other two years. The CO2 emissions were greatest in 2011 while N2O emissions peaked during the first year of drought with the lowest emissions during the second year of drought. More residue supplies left on soil after 2011 cropping season and warm and dry conditions in 2012, enhanced microbial decomposition, causing more N2Oduring the following year. When averaged across all sampling dates, CO2 emissions were 14% and 19% and N2O emissions were 26% and 25% lower in NT than in CT and CF. respectively. Methane assimilation however, was 16% greater in CT and CF than in NT. NT was also more effective in soil NO3 accrual than CT and CF. In summary, all management systems may take longer than a year to recover and rebuild SOM but NT appears to be more effective in SOM protection during drought.