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The extent and pathways of nitrogen loss in turfgrass systems: Age impacts
Citation:
Chen, H., T. Yang, Q. Xia, D. Bowman, D. Williams, Johnt Walker, AND W. Shi. The extent and pathways of nitrogen loss in turfgrass systems: Age impacts. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 637638:746-757, (2018). https://doi.org/10.1016/j.scitotenv.2018.05.053
Impact/Purpose:
Nitrogen is the most limiting nutrient for plant growth in terrestrial ecosystems and thus increase in N input often leads to increase in plant biomass and yields (Conant et al., 2013). Over the past 50 years, synthetic N application has increased by ~ 10 fold from ~ 12 Tg yr-1 in the 1960s to ~ 100 Tg yr-1 in the 2000s (Fields, 2004; Mulvaney et al., 2009; Tilman et al., 2001). Still, there is no sign that this trajectory will change in the future. Tilman et al. (2001) predicted that synthetic N application would reach 236 Tg yr-1 in 2050. It is undeniable that synthetic N application has helped support an increasing world population (Mulvaney et al., 2009; Tilman et al., 2001). However, not all N spread on land can be recovered in plant biomass and yields. On a worldwide scale, fertilizer N recovery efficiency (i.e., N in harvested plant biomass per N input) has remained < 50% (Bouwman et al., 2005; Conant et al., 2013), indicating that a sizable amount of N is drifting in the environment – soil, water, and air. Indeed, reactive N in the environment has increased steadily since the 1960s and its negative impacts on natural resources, human health, and ecosystem services are broadly recognized (Fields, 2004; Vitousek et al., 1997; WHRC, 2007). Society is aware that controlling N loss from an ecosystem is crucial for sustaining the environment, and yet questions about how to effectively accomplish this control remain.
Description:
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.
