The extent and pathways of nitrogen loss in turfgrass systems: Age impacts

Highlights: • Total reactive N loss varied with turf age and showed a time delineated cup pattern. • Dissolved organic N (DON) leaching was a dominant pathway of N loss from turfs. • Proportional loss among reactive N species was affected by season and temperature. • Seasonal variations of C availability reacted to temperature to affect N loss pathways. Nitrogen loss from fertilized turf has been a concern for decades, with most research focused on inorganic (NO₃⁻) leaching. The present work examined both inorganic and organic N species in leachate and soil N₂O emissions from intact soil cores of a bermudagrass chronosequence (1, 15, 20, and 109 years old) collected in both winter and summer. Measurements of soil N₂O emissions were made daily for 3 weeks, while leachate was sampled once a week. Four treatments were established to examine the impacts of fertilization and temperature: no N, low N at 30 kg N ha⁻¹, and high N at 60 kg N ha⁻¹, plus a combination of high N and temperature (13 °C in winter or 33 °C in summer compared to the standard 23 °C). Total reactive N loss generally showed a "cup" pattern of turf age, being lowest for the 20 years old. Averaged across all intact soil cores sampled in winter and summer, organic N leaching accounted for 51% of total reactive N loss, followed by inorganic N leaching at 41% and N₂O-N efflux at 8%. Proportional loss among the fractions varied with grass age, season, and temperature and fertilization treatments. While high temperature enhanced total reactive N loss, it had little influence on the partitioning of loss among dissolved organic N, inorganic N and N₂O-N when C availability was expected to be high in summer due to rhizodeposition and root turnover. This effect of temperature was perhaps due to higher microbial turnover in response to increased C availability in summer. However when C availability was low in winter, warming might mainly affect microbial growth efficiency and therefore partitioning of N. This work provides a new insight into the interactive controls of warming and substrate availability on dissolved organic N loss from turfgrass systems.