Precision Nitrogen Management: Past, Present and Future

R. Khosla, Y. Miao, E. Phillippi, and L. Longchamps.

Nitrogen is the primary limiting nutrient in agricultural production.  Managing N fertilizer input has been a preeminent focus of scientists and farmers since at least the 19^th century.  Over the last 50 years researchers and growers have developed robust methodologies to model and manage N uptake by crops to feed the ever-growing global population.  However, mis-management of N is common and has resulted in low N use efficiency and serious environmental problems. In order to address this challenge, it is necessary to examine the ways in which we have come to manage N fertilizer.   This review will elucidate the history of modern N fertilizer management and examine the current and future directions of precision N management.  Modern N fertilizer management began by using crop and soil based models to determine uniform rates of N fertilizer application.  Researchers developed these optimization models with treatments that applied varying rates of N fertilizer that were then replicated across a field.  Typically, soil and crop based models incorporate a yield goal estimate combined with an estimate of N present in the soil from sampling to determine the rate of N to be applied uniformly.  However, these models do not account for the inherent spatial variability present in soil across a field or the variability of N uptake by the crop.  This resulted in application rates that are not agronomically optimal and potentially damaging to the environment. More recently, methods and management techniques have been developed that better characterize the variability of N uptake by crops using sensing technologies.  Soil and crop parameters are estimated non-destructively using leaf sensors, proximal active canopy sensors, low altitude unmanned aerial vehicle (UAV)-based remote sensing, aerial and satellite remote sensing technologies to diagnose crop N status and determine in-season N application rates.  Even with the precise measurements and modelling capability that remote sensing offer, there is still significant and necessary room for improvement in global nitrogen use efficiency.  The future of N fertilizer management will rely on site-specific modeling that incorporates both soil and crop models with remote sensing.  In addition, genetic engineering may allow us to transform the rhizosphere microbiome and plant physiology in ways with profound impact on the bioavailability of plant available N for crops.  Knowledge gaps and research needs will be discussed.       

Keywords: Nitrogen use efficiency, Precision nitrogen management, crop sensing, crop growth modeling, sustainable development