Dr. Eric Wilkman

The duration and frequency of seasonal drought is expected to increase across the world. These effects will be especially pronounced in dryland agricultural sites. Drought and rewetting events alter the soil nitrogen cycle, potentially modifying the sustainability of these agroecosystems. Plant-soil-nutrient cycling models, such as the widely used CENTURY model, define the roles of soil texture and precipitation on biogeochemical cycling and yet a mechanistic understanding of processes under different soil types and conditions and in response to the seasonality and intensity of drought and rewetting is still ill-defined. This project determines the temporal N2O and NO emission patterns in response to seasonal changes in soil N and water availability during and after droughts. We hypothesize that rewetting after in-season drought will cause greater N2O and NO emissions and this will be controlled by N availability. Rewetting after non-growing season drought will cause less emissions and will be controlled by C availability. We used 4 replicates of 3 separate soil types (sand, clay, and sandy-loam) transplanted from the North, Central, and Negev Regions of Israel. In half of the randomly allocated replicates, rainfall was manipulated with transparent rainout shelters. We found that there were significant differences in N oxide fluxes across soil types. Loess soils dominated emission patterns and while pulse emission losses were seen after rewetting, emissions decreased in the 2nd rewetting treatment. These findings are significant as mitigation of soil N emissions can only be accomplished by further understanding drought-climate feedbacks from precipitation induced fluxes.