Nitrogen Management to Help Reduce Greenhouse Gas Emissions.

Fertilizer nitrogen (N) consumption is increasing in association with the growing food, fiber, and fuel demands of a growing global population.  Apparent recovery of fertilizer N by most cereal crops often ranges below 40 to 50%, but may be raised to the 60 to 70% range.  Losses of N from farm fields can contribute to direct and indirect emissions of nitrous oxide (N₂O), which has a global warming potential 296 times that of a unit mass of carbon dioxide (CO₂). Appropriate N management decisions, based on sound agronomic and environmental research, can improve crop production and help reduce greenhouse gas (GHG) emissions. Improved N management decisions can also increase the bio­mass production required to help restore and maintain soil organic carbon (SOC) levels, which are necessary for sustainable production. Ecological intensification of crop production, which includes implementing best management practices (BMPs) for fertilizer, is being increasingly recognized in the scientific community as a key means to reduce  GHG emissions; especially  per unit of crop or food production. Such intensified crop management helps to limit and prevent the conversion of natural areas to cropland and allows selective conversion of lands to forests for GHG mitigation. While emissions of N₂O are strongly influenced by site-specific and weather conditions, and the cropping system, they are also affected by appropriate fertilizer N source, rate, timing, and placement: part of 4R Nutrient Stewardship.  When 4R N stewardship is implemented in combination with appropriate conservation tillage and other cropping system practices, emissions of N₂O per unit of N applied may be reduced as much as 20 to 50%.  With an expanded global emphasis, farmers and their advisers are being asked to improve N management intensity to raise N use efficiency and effectiveness in their fields.