Assessing the Potential of Reactive N Loss during Transition from Dormancy to Growth in a Turfgrass Chronosequence.

Turfgrass systems account for roughly 35% of total urban lands in the United States. Growing concerns have been raised over N loss from turfgrass systems, but mainly focused on inorganic N leaching. Thus, a comprehensive evaluation is needed on N loss via multiple species and/or pathways.  Here, we examined both inorganic and organic N species in leachates and soil N₂O emissions from intact soil cores of a bermudagrass chronosequence (i.e., 1, 15, 37, and 109 years old) that were collected in winter. The measurements were made almost daily for soil N₂O emissions for 3 weeks, but once a week for N in leachates following water addition equivalent to 40mm precipitation. Four treatments were set up to further examine the impacts of temperature and N fertilizer,  including CK (no N, 23^oC), 30-N (30 kg N ha^-1, 23^oC), 60-N (60 kg N ha^-1, 23^oC), and 60-N-13 (60 kg N ha^-1, 13^oC). Compared to CK, 30-N and 60-N treatments increased total N in leachates by 203% and 411%, respectively, of which organic N accounted for 23-81%. Soil N₂O emissions were also increased by 165% and 316%, respectively, accounting for 2-25% of total N loss. However, compared to 60-N, 60-N-13 significantly reduced N₂O production by 69% and CO₂ emissions by 63% but increased N leaching by 16%, indicating that low temperature limited microbial activity. Our data demonstrated that organic N leaching and soil N₂O emission should not be overlooked as N loss pathways from turfgrass systems.