Managing agricultural nitrogen loss to restore air and water quality in the United States
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Nitrogen (N) is an essential element for enhancing crop production. In 2017, the United States (US) applied 11% of the world’s synthetic N fertilizer, produced 6% of the world’s livestock manure, and received 10% of the world’s atmospheric N deposition from industrial and agricultural activities. However, anthropogenic N enrichment of agricultural systems degrade air quality through gaseous N loss into the atmosphere and water quality through N leaching along with water flows into the riverine system. In recent years, there observed an increase of reduced N deposition from US areas with intensive agriculture and an expansion of summer hypoxic areas in the Gulf of Mexico. To reduce the hypoxic zone to 5,000 km2, current annual total N loads should be reduced by 45% compared to the average level during 1980-1996. Thus, it is imperative to come up with an effective strategy to better manage agricultural N loss to restore the environment without significantly reducing crop yield. In order to study the modeled responses of N gain (crop yield) and N loss (nitrous oxide, ammonia, and N loading) to better N management practices from 1961 to 2018 in the US, we conducted a series of sensitivity simulation experiments using a Dynamic Land Ecosystem Model (DLEM) coupled with improved agricultural and aquatic modules. N inputs considered in DLEM simulations include biologically fixed N, synthetic N fertilizer, livestock manure, and atmospheric N deposition. Through these experiments, we can provide quantitative information on how to realize sustainable crop production.