Fertilizers of the right amount and the right composition should be applied at the right time and the right place, given the crop and environmental conditions to maximize plant uptake and minimize environment losses (4R strategy). Quick tools to diagnose soil, fertilizer and plant properties are needed for fine-tuning fertilizer use. But quick tools are not easily found because properties can be measured in many different ways, and the relevance of the data will be crop- and environment-specific.