Nitrogen–climate interactions in US agriculture

Abstract

Agriculture in the United States (US) cycles large quantities of nitrogen (N) to produce food, fuel, and fiber and is a major source of excess reactive nitrogen (Nr) in the environment. Nitrogen lost from cropping systems and animal operations moves to waterways, groundwater, and the atmosphere. Changes in climate and climate variability may further affect the ability of agricultural systems to conserve N. The N that escapes affects climate directly through the emissions of nitrous oxide (N 2 O), and indirectly through the loss of nitrate (NO 3 -), nitrogen oxides (NO x ) and ammonia to downstream and downwind ecosystems that then emit some of the N received as N 2 O and NO x . Emissions of NO x lead to the formation of tropospheric ozone, a greenhouse gas that can also harm crops directly. There are many opportunities to mitigate the impact of agricultural N on climate and the impact of climate on agricultural N. Some are available today; many need further research; and all await effective incentives to become adopted. Research needs can be grouped into four major categories: (1) an improved understanding of agricultural N cycle responses to changing climate; (2) a systems-level understanding of important crop and animal systems sufficient to identify key interactions and feedbacks; (3) the further development and testing of quantitative models capable of predicting N-climate interactions with confidence across a wide variety of crop-soil-climate combinations; and (4) socioecological research to better understand the incentives necessary to achieve meaningful deployment of realistic solutions.

Patterns of new versus recycled primary production in the terrestrial biosphere

“…These numbers are especially significant when considered in light of human cropping systems where <50% of annual fertilized crop N demand is met via recycling (26). This highly efficient nutrient recycling via plant-soilmicrobe interactions represents a vital global ecosystem service.…”

Importance of non-CO2emissions in carbon management

“…Overlooking the multiple emissions drivers in this complex system when devising mitigation policy can lead to overly optimistic assumptions of how deeply CO 2 and other GHG emissions can feasibly be cut [97]. Taking a systemic, bottom-up scenario approach to interrogating future levels of N 2 O and CH 4 emissions reveals how, despite strong technological mitigation combined with changing patterns of consumption, a warming climate and growing population limit efforts to curb food system emissions.…”

Nitrogen and Phosphorus Recovery from Wastewater

“…Two percent of global reactive nitrogen introduced annually escapes as N 2 O and contributes to global warming and affects the ozone layer [9] and 12 % escapes as NO x and NH 3 , affecting the atmosphere in numerous ways [10]. Additionally, resulting climate change and nitrogen interactions may also affect agricultural productivity by exposing crops to elevated O 3 levels [11], flooding and extreme precipitation, drought, and heat. Moreover, phosphorus discharge, even in concentrations, as low as 0.02 mg/l can induce eutrophication of rivers and lakes, making them bogs that are unfit for navigation, fresh water supply, recreation, or agriculture [12,13].…”