Nitrogen Use Efficiency Helps Evaluate 4R Practices in Wheat
One of the principles of 4R Nutrient Stewardship is the inclusion of performance indicators, writes Steve Phillips, Director, North American Program, International Plant Nutrition Institute. Performance indicators are parameters that can be used to objectively evaluate outcomes from a specific set of management practices selected for a given cropping system. The performance indicators are chosen based on the sustainability goals for the production system. Nitrogen use efficiency (NUE) is a commonly used indicator to assess N management; however, it is important to note that NUE can be defined many different ways.
Estimating NUE on the farm can be as simple as measuring yield. One of the most basic methods for determining NUE is called Partial Factor Productivity (PFP), which is calculated as units of crop yield divided by units of nutrient applied. For example, applying N fertilizer at 90 lb/A to produce a 70 bu/A wheat crop would result in a PFP of approximately 47 units of grain per unit of applied N [i.e., (70 bu/A x 60 lb/bu) / 90 lb N applied/A]. Published literature suggests that a PFP of 40 to 80 is considered typical for cereals.
Another easy strategy for estimating NUE considers nutrient removal in the harvested portion of the crop. The ratio of nutrient removed to nutrient applied is called a Partial Nutrient Balance (PNB).
Using the above example and an N removal estimate of 1.15 lb N/bu for winter wheat(ipni.info/calculator), the PNB for this crop would be calculated as 0.93 [i.e., (70 bu/A x 1.2 lb N removed/bu) / 90 lb N applied/A]. A PNB equal to or very close to 1.0 suggests an efficient system, while values well below 1.0 might suggest the need for improved NUE. Conversely, a PNB much over 1.0 could suggest nutrient mining from the soil and a need for increased fertilizer application in the future.