In 1st part of question you have asked enriching soil with micro-nutrient fertilizer, Actually which very expensive as well as difficult to do (#Not Possible) There are numerous of micro- organism which can be used for soil micronutrient enrichment.
There are variety of bacteria, including Azomonas species, Azotobacter species, and others.
Micro- Biology is branch of Biology which deals with all these matters.
Regarding adding micronutrient in Plants, spraying is best and efficient method.
If for soil micro- nutrient if you will go with liquid it will be a bad choice, since it will evaporate fast, but solid along with sand can be much more beneficial. ( I am adding again, it is for soil, for plant liquid spraying is good)
Objections and suggestions are invited.
1st part of the question ie. micro nutrients can be used mostly by thespray.
2nd part liquid formulation works efficiently becoz it can be absorbed by leaves quickly and starts working, than solid formulations. and one more thing in most of the cases micronutrients are applied in plants when they are deficient in the soil so applied in form of liquid form.
By using drip irrigation (Fertigation) spraying by using knapsack sprayer is also useful but take appropriate amount of liquid fertilizer