Nitrogen (N) fertilizer management is a key determinant of grain cropping system productivity and sustainability. Broadly, our N fertility research measures crop response to N fertilizer in tandem with real-time measurements of plant-soil N status. We focus on measurement technologies and platforms that are farmer-accessible so that our research results are more immediately applicable to farm management. These include drone- and satellite-based multi-spectral images, hand-held sensors and simple in-field tests of soil and plant N concentrations. We combine these measurements with field trials quantifying the effect of N fertilizer rate/timing on grain yield and quality under a wide range of environmental conditions. Our work in wheat, barley and rice has improved the understanding of fertilizer timing effects on grain yield and protein, presented novel methods for translating site-specific, in-season measurements to fertilizer response probabilities, and elucidated the comparative utility of various reflectance technologies. In maize, we have illustrated how combined multispectral indices can differentiate between crop N and water stress. We have also improved and refined the methods for conducting soil nitrate quick tests and developed novel tools for translating in-field tests to fertilizer equivalents.