The need for more uniform terms and measures of nitrogen use efficiency in agricultural production

A lthough nitrogen (N) is generally recognized as the most important nutrient required for productive agriculture, its widespread and luxurious use over many years has impaired soil, water, and air quality at local, regional, and global scales (Galloway et al. 2008; Sutton et al. 2013). To understand and evaluate various economic and environmental aspects of agricultural N use, different terms and calculations are used to describe how much applied N is incorporated into agricultural products and how much N may be lost to the environment. The terms “N balance” and “N surplus,” and different calculations of N use efficiency (NUE, the fractional amount of applied N incorporated into product N) are examined here to highlight how some of the conventional assumptions and calculations of N inputs and N outputs can lead to different conclusions about actual NUE (as obtained by the producers of crops and livestock), potential NUE (what is biologically feasible), and risks of environmental N loss. THE TERMS “NITROGEN BALANCE” AND “NITROGEN SURPLUS” The difference between N inputs (e.g., fertilizer N, kg ha−1) and N outputs (e.g., crop N, kg ha−1) is often referred to as either an N balance or an N surplus. While N balances of soil…