Link to Rice physiology(hey, it's an aquatic plant and there's a ton of research done

Mineral nutrition/nutritional deficiencies

Look at the uptake kinetics and graphes.
You'll note that large flat spot between deficiency and toxic excess that is the huge target that EI is based on, it's huge comparatively. Farmers can take advantage of this and often reduce fertilizered due to cost efficiency rather than a plant "need".


Regards,
Tom Barr