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

Authors: Powell, Joseph

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2015
Publication Date: 7/1/2015
Publication URL: http://handle.nal.usda.gov/10113/62855
Citation: Powell, J.M. 2015. The need for more uniform terms and measures of nitrogen use efficiency in agricultural production. Journal of Soil and Water Conservation. 70(4):67A-69A.

Interpretive Summary: The widespread and luxurious use of fertilizer and other nitrogen (N) inputs in agricultural production can impair water and air quality at local, regional and global scales. The terms N balance and N surplus, and different calculations of nitrogen use efficiency (NUE, the amount of applied N incorporated into product N) can lead to very different assessments of N use and N loss. More standard determinations of N inputs (e.g., feed N, fertilizer N, manure N) and N outputs (e.g., milk, forages, grain) would lead to a better understanding of differences in actual NUE (as obtained by producers of crops and livestock) and potential NUE (what is biologically-feasible). The information in this opinion piece can be used by dairy nutrition consultants, agronomic advisers, and producers to establish NUE benchmarks, realistic NUE targets, and approaches to achieve those targets.

Technical Abstract: Nitrogen (N) is recognized as the most important nutrient required for productive agriculture, yet its widespread and luxurious use can impair water and air quality at local, regional and global scales. To address the economic and environmental aspects of agricultural N use, various terms and calculations are used to describe how much applied N is incorporated into agricultural products, and how much may be lost to the environment. Differential use of the terms N balance and N surplus, and different calculations of N use efficiency (NUE, the amount of applied N incorporated into product N) highlight how conventional assumptions related to N inputs and N outputs may lead to different conclusions about actual NUE (as obtained by producers), potential NUE (what is biologically-feasible) and true risks of environmental N loss. The term ‘N surplus’ does not consider that all biological components (e.g., crops/pastures, livestock) of agricultural production systems have inherent inefficiencies in N use, such that N inputs always need to exceed N output (N incorporation into a product). Likewise, different calculations of NUE lead to large differences in estimates of how much applied N is actually incorporated into agricultural products and how much may be lost to the environment. More standard determinations of NUE for various N inputs (e.g., feed N, fertilizer N, manure N) and outputs (e.g., milk, forages, grain) could lead to a better understanding of differences in actual NUE and potential NUE, which can be used to establish NUE benchmarks, realistic NUE targets and approaches to achieve those targets. Calculations and interpretations of N input and N output relationships need to consider N requirements to achieve desired economic production levels and environmental targets, which should necessarily consider biologically-feasible N conversion efficiencies.