Nitrogen Stewardship for Climate Smart Agriculture and Forestry - USDA-NRCS Strategies to Reduce Nitrous Oxide Emissions from Pastures and Cropland.

Nitrogen Stewardship is one of the ten U.S. Department of Agriculture’s (USDA) Building Blocks for Climate Smart Agriculture and Forestry.    Agriculture in the U.S. is a significant source of nitrous oxide (N₂O) emissions. This Greenhouse Gas (GHG) is over 250 times more potent than the same amount of carbon dioxide.  N₂O emissions from synthetic nitrogen fertilizers and organic sources represent a major source of GHG.  Cropland agriculture released approximately 136 million metric tons of carbon dioxide equivalent (MMTCO₂e) in direct N₂O emissions in 2013 and synthetic fertilizer and organic amendments account for more than 50 % of those emissions (72 MMTCO₂e).

The USDA building blocks goal for Nitrogen Stewardship is to reduce N₂O emissions by 7 MMTCO₂e annually by 2025. GHG emissions can be reduced substantially through improved nitrogen management and increased nitrogen use efficiency on crop and pasturelands.  N₂O emissions depend on many factors, but key factors are timing, source, placement, and quantity of nitrogen (both from organic and synthetic sources) applied.  Weather and soil health also influence nitrogen losses and the resulting efficiency with which it is taken up by crops.  In addition to reducing N₂O emissions, these practices can also significantly reduce nitrate leaching, improving local and regional water quality, and reduce on-farm input costs. The NRCS Conservation Practice Standard Nutrient Management (590) through the implementation of the 4Rs (right source, right rate, right time, and right place) is the primary practice used to reduce GHG emissions.  The 4Rs apply to not only the utilization of synthetic forms of nitrogen, but also the N₂O emissions from legumes, manure, compost, and other biosolids for crop production.