Nitrogen Stewardship: Balancing Crop Production Management and Environmental Protection

Population-driven increases in the consumption of food, fiber, and fuel, have resulted in increased global demands for fertilizer nitrogen (N) which exceeded 100 million tons (Mt) in 2007 and are expected to exceed 112 Mt by 2015. Cereal grain crop recovery of applied N often ranges below 50% in the season of application, leaving the remainder subject to soil retention or loss via different pathways: runoff, leaching, volatilization, and denitrification. Gaseous loss of N from soils as nitrous oxide usually represents only a small fraction of total potential N losses, but is important to society because it is one of the more potent greenhouse gases (GHGs). Improved fertilizer N management - based on the ‘4R’ best management practice (BMP) principles of the right N source, at the right rate, right time, and right place - helps enhance crop N use efficiency. Improved fertilizer N stewardship also minimizes residual soil nitrate-N (NO₃-N) and risks of groundwater contamination, and it helps reduce direct and indirect nitrous oxide emissions and impacts on climate change. Appropriate fertilizer N management stimulates crop biomass production necessary to help maintain and increase soil organic carbon (SOC), provided that crop residue is maintained on the soil surface through conservation or reduced tillage systems and soil disturbance is minimized. Maintenance and increase of SOC is usually possible only if crop productivity is maintained or increased. Risks of N loss from farms and fields varies among fertilizer N sources, and the rate, time, and place of application in different cropping systems, as well as with site- and weather-specific conditions. Through appropriate fertilizer N stewardship, apparent in-season crop N recovery may be increased by as much as 25% above current levels, and nitrous oxide emission reductions from 20 to 50% may be attainable in many field environments.  The International Plant Nutrition Institute has developed a preliminary GIS-based county and watershed-scale assessment of N and other major nutrient balances in the U.S. The potential for international adaptation of the GIS-based approach will be discussed as a means to help improve N use efficiency and effectiveness in crop production.